geometry of ripples and dunes a kinematic theory for lower regime bedform shape is presented and examined in the light of extensive bedform data observed in large prototype channels depending upon the extent of bedform maturity the theory predicts uniquely defined nondimensional shapes for upstream faces these shapes are borne reasonably well by the observed data in spite of large variation in bedform size the length of upstream face relative to the wavelength is randomly distributed with most probable value of 0 614 which is close to the value 0 667 predicted by the theory for mature ripples and dunes

towards a formal description of foraminiferal assemblage formation in shallow water environments qualitative and quantitative concepts the use of foraminifera in palaeoenvironmental reconstructions e g sea level may be complicated by processes such as infaunal test production taphonomic degradation and bioturbation which act to modify contemporary analogue surface assemblages during and subsequent to burial understanding the palaeoenvironmental significance of these processes is limited by the absence of a clear theoretical description of the mechanics of foraminiferal assemblage formation a conceptual framework is proposed which describes assemblage formation in terms of the balance of test inputs and losses within a volume of sediment undergoing burial through the upper sedimentary zones of test production taphonomic processes and bioturbation a corresponding mathematical model is described and shown to explain empirical dead test distributions in terms of empirically defined standing crops sedimentation and mixing rates together with model estimates of standing crop turnover and or taphonomic decay rates this approach provides a quantitative basis for understanding assemblage formation and for comparing assemblage forming processes between species environments and study sites rates of standing crop turnover and taphonomic loss are identified as the primary unknowns in the study of foraminiferal assemblage formation these multiple unknowns make interpretations of cored data ambiguous emphasising the need for a detailed and coherent framework of theory and assumptions for understanding the mechanics assemblage formation if interpretations are to be clear and conclusive

a review on natural and human induced geohazards and impacts in karst karst environments are characterized by distinctive landforms related to dissolution and a dominant subsurface drainage the direct connection between the surface and the underlying high permeability aquifers makes karst aquifers extremely vulnerable to pollution a high percentage of the world population depends on these water resources moreover karst terrains frequently underlain by cavernous carbonate and or evaporite rocks may be affected by severe ground instability problems impacts and hazards associated with karst are rapidly increasing as development expands upon these areas without proper planning taking into account the peculiarities of these environments this has led to an escalation of karst related environmental and engineering problems such as sinkholes floods involving highly transmissive aquifers and landslides developed on rocks weakened by karstification the environmental fragility of karst settings together with their endemic hazardous processes have received an increasing attention from the scientific community in the last decades concurrently the interest of planners and decision makers on a safe and sustainable management of karst lands is also growing this work reviews the main natural and human induced hazards characteristic of karst environments with specific focus on sinkholes floods and slope movements and summarizes the main outcomes reached by karst scientists regarding the assessment of environmental impacts and their mitigation

subsidence rings and fracture pattern around dolines in carbonate platforms implications for evolution and petrophysical properties of collapse structures abstract this work focuses on the study of collapse dolines which are the most expressive collapse structures in carbonate rocks and their relations with preexisting and syn collapse fractures the study area has two fracture sets that were formed before folding early n s e w and late ne sw nw se striking sets which concentrate most of the dissolution in the region and allow the formation of the dolines we define subsidence rings as the circular and ellipsoidal concentric zones around collapse structures which are subjected to subsidence due to major collapses and represent locations where new fractures are formed in these subsidence rings the downfaulted topography plunges towards the doline center and reaches more than 10 m in relation to unaffected areas away from dolines the topographic data indicate that the mean radius of the combined rings is twice the radius of the collapse which corresponds to the closed depression due to failure and downfall of blocks the subsidence process enlarges links preexisting fractures and forms a new set of semicircular concentric opening mode fractures here named collapse fractures increases in the apertures and densities of these fractures occur towards the dolines which increases fracture porosity around collapse structures fractures are reactivated as normal faults close to the main collapse at the doline edge this increase in fracture intensity could represent an indicator of permo porous quality improvement in these areas further this fracturing increases structural instability raising the risk of accidents in areas built on soluble carbonate rocks since the affected area may be much larger than previously predicted subsidence rings around collapse dolines could merge with other rings from neighboring collapse structures and potentially increase porosity and permeability as well as linking areas in carbonate reservoirs

length of flow separation over dunes dimensional analysis was used to define the length of the flow saparation for the case of two dimensional uniform flow over dunes which was expressed in terms of bed form geometry and the sand size of the bed material experiments were conducted in a rectangular flume using artificial dunes and a flow visualization method to measure the flow separation length when dunes are flat length of the flow separation is affected by the sand grain roughness when dunes are steep the length of the flow separation is due mainly to the bed form geometry and is relatively constant the reverse rectangular steps can be considered as dunes of infinite length and the length of the flow separation for such steps will always be greater than that obtained for dunes of finite length

palaeoecology of boreal invertebrate faunas from the upper jurassic of central east greenland abstract the upper jurassic of milne land greenland is a transgressive regressive sequence ranging from offshore shallow sandbar complexes in the late oxfordian to outer shelf muds in the kimmeridgian and early to middle volgian within the middle volgian rapid shoreline progradation led to deposition of inner shelf silts and nearshore sands within this envirobmental framework 22 benthic macroinvertebrate associations and several assemblages occur they are dominated by suspension feeding bivalves less commonly by brachiopods or detritus feeding serpulid polychaetes despite frequently low rates of sedimentation and plenty of suitable substrates surprisingly few shells are bored or encrusted which may reflect biogeographic factors although some inter and intraspecific interactions are recorded the associations are thought to have been largely controlled by environmental parameters low diversity associations are related to low oxygen conditions at the sea floor or unstable shifting substrates but in some cases may have been due to biotic interactions levels with reduced rates of sedimentation and glauconite formation are characterized by epifaunal associations those with higher rates of sedimentation by infaunal or semi infaunal associations the temporal and spatial distribution pattern of the benthic invertebrate fauna is fairly complex due to the interplay of several biotic and abiotic factors the absence of strong environmental gradients in outer shelf areas and diagenetic overprint selectivity removing low density faunas among bivalves species replacement through time was in most cases ecological

preservation of mollusca in copano bay texas the long term record abstract the stratigraphic taphonomic and biologic records from two cores in copano bay texas were analyzed to determine 1 whether variations in shell content with depth were caused by variations in carbonate preservation carbonate production or sedimentation rate and 2 the extent to which characteristics of fossil assemblages such as species composition numerical abundance biomass and trophic and habitat structure identified similar or different trends below the top few cm of the sedimentary column variations in carbonate content with depth could be attributed to variations in carbonate production most biological attributes varied similarly with depth and hence time on both long 100 yr and short 10 yr temporal scales these variations could not be explained by any taphonomic process sediment reworking and burial or sedimentation rate despite a vigorous taphonomic milieu to obtain the shell content of copano bay sediments requires the preservation of nearly all carbonate produced preservation of a large fraction of the shell carbonate added requires the preservation of most of the relatively large shelled biota large species and adults which retain important evidence of changes in the community s history in this area the results reemphasize the importance of large individuals and biomass in paleontologic reconstruction and suggest that changes in community productivity which in paleontologic usage must be carbonate productivity are preserved in the fossil record

structure of upper cretaceous chalk benthic communities southwestern arkansas abstract paleoecological investigation of chalk facies in the saratoga and annona formations includes paleoenvironmental analysis as well as examination of benthic macro invertebrate faunas the saratoga sandy chalk facies was deposited in a middle shelf environment 25 50 m depth while the annona chalk marly chalk facies was deposited in a outer shelf environment 75 125 m depth each facies is characterized by a distinct community of benthic macro invertebrate fossils dominated in occurence by epifaunal suspension feeding bivalves and deposit feeding echinoids however sandy chalk also contains moderately common infaunal suspension feeding bivalves and gastropods and rare infaunal deposit feeding bivalves while chalk markly contains only rare infaunal bivalves and no reported gastropods differences in composition within and between the two communities apparently reflect original distribution of shelled taxa trace fossil preservation indicates that substrates in both facies were thixotropic functional analysis demonstrates that many taxa show adaptations for living on soft substrates differences in diversity within each facies may be owing to non uniformity of substrate softness because many suspension feeders were unable to cope with the softest substrates and are therefore sparse in rocks apparently representing these substrates variations in substrate softness may have been caused by differing rates of bioturbation presence of infaunal suspension feeding bivalves in the saratoga but relative lack in the annona may be primarily a manifestation of softer annona substrates caused by generally finer grain size of annona sediments several studies of chalk faunas have concluded that sparseness of originally aragonitic fossils was caused by secondary sea floor dissolution or diagenetic processes results of this study demonstrate that primary organism sediment interactions could have also played a significant role in causing the general lack of originally aragonitic fossils in upper cretaceous chalks

identifying the boundaries of sinkholes and subsidence areas via trenching and establishing setback distances abstract one of the most effective mitigation strategies in sinkhole areas is the exclusion of sinkholes and their vicinity to construction the application of this preventive measure requires precise mapping of the boundaries of the areas affected by subsidence and the establishment of adequate setback distances which is an important policy issue with significant economic implications through the investigation of several buried sinkholes in the mantled evaporite karst of the ebro valley by trenching this work illustrates that the actual extent of the subsidence areas may be much larger than that inferred from surface mapping and geophysical surveys the objective and accurate subsurface information acquired from trenches on the outer edge of the deformed ground revealed sinkhole radii 2 3 times larger than initially estimated increasing one order of magnitude the sinkhole area trenches can therefore help to reduce mapping uncertainties and the size of setbacks moreover the trenching technique in combination with geochronological data and retrodeformation analyses provides critical information on the subsidence phenomena and the characteristics of the sinkholes relevant to hazard assessment since recommended setback distances found in the existing literature are highly variable and rather arbitrary we include a discussion here on the main factors that should be considered when defining setback zones for sinkholes

can shallow and deep water chemoautotrophic and heterotrophic communities be discriminated in the fossil record abstract the recognition of marine chemoautotrophic paleocommunities has added a new dimension to the interpretation of the fossil record we compared the death assemblages formed by chemoautotrophic and heterotrophic molluscan faunas of the continental slope with their counterparts in shallow water and with a fossil chemoautotrophic analogue from the tepee buttes of the pierre shale cretaceous to determine whether differences between them could be ascribed to differences in community structure or taphonomy evaluation of guild and tier structure and size frequency distribution using abundance and energy flow paleoproduction and paleoingestion suggests that differences between inshore and offshore recent heterotrophic assemblages reflect autecologic differences in the living communities forming them rather than differences in preservation in contrast the degree of similarity between chemoautotrophic assemblages is a function of their taphonomic and autecologic history the differences observed amongst recent chemoautotrophic assemblages issue from changes in the abundance and preservability of the small heterotrophic fauna relatively poorly preserved offshore and the presence of a large heterotrophic fauna essentially restricted to shallow water taphonomic removal of the small heterotrophs and juveniles of larger species and the autecologic absence of large heterotrophs could produce an assemblage equivalent to that of the cretaceous tepee buttes from any one of the recent inshore or continental slope chemoautotrophic assemblages our analysis indicates that shelf communities represent the shallowest communities likely to be identified as fossil cold seep faunas farther inshore community attributes normally used to distinguish chemoautotrophic and heterotrophic faunas are no longer discriminative nearshore communities may have included a dominant chemoautotrophic guild but recognition would rely solely on the identification of known chemoautotrophic taxa community trophic structure has classically been evaluated on the basis of numerical abundance and species composition comparing these chemoautotrophic and heterotrophic assemblages demonstrates the importance of evaluating community structure on criteria that more clearly document the way energy flowed through the community namely paleoproduction and paleoingestion many of the unique structural attributes of these assemblages only became obvious using these measures

glauberite halite association of the zaragoza gypsum formation lower miocene ebro basin ne spain glauberite is the most common mineral in the ancient sodium sulphate deposits in the mediterranean region although its origin primary or diagenetic continues to be a matter of debate a number of glauberite deposits of oligocene miocene age in spain display facies characteristics of sedimentologic significance in particular those in which a glauberite halite association is predominant in this context a log study of four boreholes in the zaragoza gypsum formation lower miocene ebro basin ne spain was carried out two glauberite halite lithofacies associations a and b are distinguished association a is composed of bedded cloudy halite and minor amounts of massive and clastic glauberite association b is made up of laminated to thin bedded clear macrocrystalline massive clastic and contorted lithofacies of glauberite and small amounts of bedded cloudy halite transparent glauberite cemented by clear halite as well as normal graded and reverse graded glauberite textures are common this type of transparent glauberite is interpreted as a primary subaqueous precipitate gypsum thenardite or mirabilite are absent in the two associations the depositional environment is interpreted as a shallow perennial saline lake system in which chloride brines association a and sulphate chloride brines association b are developed the geochemical study of halite crystals bromine contents and fluid inclusion compositions demonstrates that conditions for co precipitation of halite and glauberite or for precipitation of na sulphates mirabilite thenardite were never fulfilled in the saline lake system

palaeoenvironmental significance of storm coquinas in a lower cretaceous coastal lagoonal succession vectis formation isle of wight southern england thin bioclastic limestone beds coquinas in the vectis formation wealden group lower cretaceous of the isle of wight southern england exhibit a range of biofabrics and internal stratigraphies these features are attributed to both simple and complex storm deposition of allochthonous biogenic and siliciclastic materials in coastal lagoons and on adjacent mudflats these modes of deposition facilitated preservation of dinosaur trackways desiccation cracks shallow tier trace fossils and in situ bivalve colonies through rapid burial the coquinas thus preserve a record of surficial muds commonly lost through reworking the principal components of the coquinas comprise dispersed elements from within the argillaceous background facies some of these beds are laterally traceable for up to 27 km providing the foundations for a high resolution event stratigraphic framework

sinkhole monitoring and early warning an experimental and successful gb insar application abstract sinkholes represent a natural risk that may hit catastrophically without clearly detectible precursors however they are often overlooked by people and administrators therefore sinkhole monitoring and associated early warnings constitute important research topics but currently only a few papers about sinkhole prediction can be found in this paper an experience of sinkhole monitoring and early warning with gb insar is described the latter is a highly precise instrument that is able to produce displacement maps with metric spatial resolution the described activities were carried out on elba island central italy where karstified limestone set off the occurrence of nine sinkholes since 2008 all within less than 3000 m2 causing major damage to an important road and many indirect losses in 1 year of monitoring two deforming areas were detected and the point where a sinkhole was about to propagate to the street level was predicted thus permitting the preventive closure of the road the deformation area was larger than the hole generated by the sinkhole thus showing a subsidence that continued for a prolonged time even after the cavity was filled up the occurrence of a 1 5 m wide sinkhole undetected by the gb insar also showed the lower detection limit of the instrument

molluscan death assemblages on the amazon shelf implication for physical and biological controls on benthic populations the amazon continental shelf is an example of an environment impacted by frequent and intense physical disturbance with regions of high sedimentation rates cycles of extensive sediment erosion and deposition result in periods of sediment remobilization and instability in the seabed and cause marked seasonal and spatial variations in the transport of water column organisms and benthic infauna in this study the molluscan death assemblages on the amazon shelf are examined in an effort to understand how this physical regime is reflected in death assemblages as well as to provide insight into biological controls on mortality inner shelf regions of 20 m water depth comprise 50 of the total shelf area that extends to 100 m and have no relict shell beds or randomly dispersed shells although a few living shell bearing species are occasionally present extensive death assemblages are found deeper than 40 m bivalves were most numerous on the shelf although gastropods dominate at the stations with the most extensive shell assemblages the incidence of boring varied between 3 general groups of stations from 5 12 and 30 and tended to be similar for gastropods and bivalves evidence for significant exposure time on the sediment surface alternating with periods of burial was found fewer than one third of all specimens reached adult size suggesting settlement in a marginal habitat in general the most abundant taxa in the living community were also dominant in death assemblages the most abundant relict bivalve crassinella lunulata however which reached densities of 5578 m 2 were never found alive on the shelf this species along with old reworked fragments of coral and bryozoans indicate onshore transport from south of the shelf or from the outer shelf where relict coraline deposits are exposed followed by deposition and downward mixing of shells into the deposit in spite of the overwhelming influence of the physical regime the incidence of boring is comparable to other environments suggesting significant biological control of benthic populations

stability charts for predicting sinkholes in weakly cemented sand over karst limestone forty nine physical models of sinkhole development were constructed and tested using a geotechnical centrifuge to replicate full scale sinkhole development in the small models the soil profile studied was weakly cemented sand overlying cavities in karst limestone with uncemented sand over the cemented sand layer in half the models in configurations with no uncemented soil overburden the parameters critical to predicting failure were the unit weight of the cemented sand c the thickness of the cemented sand overlying the karst cavity hc the true cohesion of the weakly cemented sand c and the diameter of the underlying karst cavity d brittle collapse of the cemented soil into the underlying cavity took one of two forms depending on geometry when hc d was less than or equal to 0 25 the plug of soil that fell into the cavity penetrated through the full thickness of the cemented layer leaving an open hole when hc d was greater than or equal to 0 31 the plug of soil that fell into the cavity did not penetrate through the full thickness of the cemented layer but left behind a stable arch a dimensionless stability chart was developed based on model results relating chc c and hc d at failure that chart can be used to predict the onset of failure extrapolating to configurations and soil cementation strengths not specifically tested in this research a study was also made of the influence of uncemented sand overburden on hastening sinkhole development for configurations with ratios of hc d less than or equal to 0 25 the thickness of the uncemented overburden was varied at the brink of sinkhole development there was significant arching within the uncemented sand and the influence of the overburden on hastening sinkhole failure was much less than the full geostatic overburden the maximum uncemented overburden pressure bearing down on the breakthrough plug never exceeded the weight of a cone of sand of diameter d and height 1 25d where d equals the diameter of the top of that inclined plug

investigation of a large collapse sinkhole affecting a multi storey building by means of geophysics and the trenching technique zaragoza city ne spain an active sinkhole around 100 m long has been investigated in the city of zaragoza ne spain subsidence activity on this depression including the sudden occurrence of a collapse sinkhole 5 m across led to the abandonment of a factory in the 1990s at the present time a building with 100 flats and shallow pad foundations partially built on the sinkhole is affected by rapid differential settlement the development of the sinkhole results from the karstification of the halite and glauberite bearing bedrock and the sagging and collapse of the overlying bedrock and alluvium more than 30 m thick gpr and electrical resistivity profiles have provided information on the distribution and geometry of the subsidence structure the application of the trenching technique and geochronological methods ams and osl dating has allowed us to infer objective and practical data on the sinkhole including 1 limits of the subsidence structure 2 subsidence mechanisms 3 cumulative subsidence 408 cm 4 subsidence rates on specific failure planes 1 8 cm year 5 episodic displacement regime of some fault planes the available information indicates that the progressive deformation recorded in the building will continue and might be punctuated by events of more rapid displacement this work illustrates the practicality of the trenching technique for the study of sinkholes in mantled karst areas

taphonomic implications of shell surface textures in bahia la choya northern gulf of california abstract the author collected shell samples of the bivalve chione from the extensive tidal flat system of bahia la choya northern gulf of california and examined their surfaces under the binocular and scanning electron microscopes samples were collected from environments ranging in degree of tidal exposure energy level and substrate inner tidal flats sandy outer flats rocky outer flats tidal channel estero channel salt marsh beach spit and subtidal surfaces were compared with those of shells experimentally subjected to bioerosion dissolution and abrasion in all more than 1100 shells were examined and described bioerosion by microborers is by far the dominant process attacking shell material in bahia la choya microbored textures dominated shell surfaces from all sedimentary environments with the exception of the beach where abrasion dominated chemical dissolution is important only in the fine grained salt marsh and inner flat environments many shells show composite textures which reflect the concurrent action of more than one taphonomic agent shells from the salt marsh for example frequently show the effects of both microboring and dissolution overprinted textures can document transport among environments

ocean quahogs arctica islandica and atlantic surfclams spisula solidissima on the mid atlantic bight continental shelf and georges bank the death assemblage as a recorder of climate change and the reorganization of the continental shelf benthos abstract the degree to which evidence of range shifts in shelf biomass dominants atlantic surfclams and ocean quahogs as a function of climate change is examined by comparing the dissimilarity in distribution of the living community and the record of habitation ensconced in the death assemblage comparison of the distribution of live animals and dead shells reveals for both species that live animals are rarely found where dead shells were not collected but dead shells were collected at a substantively larger number of sites than where live animals were found the geographic footprint resolved by the dead shells was much broader than that of live animals extensive spatially coherent regions exist inshore and offshore of the present day habitat of occupation where evidence of previous occupation exists sites where ocean quahog shells were found without live ocean quahogs included a portion of the continental shelf inshore of the present day habitable range an area only habitable under colder climatic conditions than observed today surfclam shells were found offshore of the present day habitable region in deeper water additional warming of bottom waters offshore would be necessary for surfclams to occupy the region now occupied solely by dead shells the death assemblage shows that these biomass dominants have repositioned themselves across the continental shelf during the past and this repositioning certainly is driven by changes in bottom water temperature moreover the distribution of surfclam shells indicates that the death assemblage may provide a possible window into the future as movement of the present day population is towards these deeper water previously occupied regions overall the death assemblage may provide an important source of information on range shifts sparing the need to carry out extensive and frequent benthic surveys and may permit reconstruction of ongoing shifts in community composition as a product of climate change when adequate survey data are not available

carbonate dissolution in nearshore terrigenous muds the role of physical and biological reworking because shallow marine sediments generally underlie waters which are saturated with respect to arago nite and calcite physical chemical dissolution of carbonate in these environments is sometimes discounted the present investigation as well as others before it show such an assumption to be unwarranted in this case study of terrigenous mud deposits from long island sound u s a demonstrates extensive dissolution of molluscan shell debris near the sediment water interface net buildup of carbonate varies significantly between different regions of the sound despite fairly uniform production of shell debris and similar total sedimentation rates aside from this apparent discrepancy between rate of supply and net carbonate sedimentation evidence for carbonate dissolution comes from the pitting of shells elevated ca levels in pore water and calculated undersaturation of pore waters with respect to carbonate minerals models of pore water distributions and carbonate supply imply dissolution ra

fish otoliths in superficial sediments of the mediterranean sea abstract otoliths represent a significant biogenic carbonate component in marine sediments that may provide valuable information for paleoenvironmental and biogeographic reconstructions in spite of their importance relatively little is still known about the taxonomic composition abundance and early taphonomic characteristics of recent otolith death assemblages which would add to their value to interpret situations in the geological record here we present data on the distribution of fish otoliths from bottom sediments collected in the central mediterranean sea ranging in depth from 51 to 3300 m the preservation of otoliths ranges from fresh semi translucent white specimens to dull coloured dark ones although whitish specimens are predominant across all the samples this diversity in lustre and colour and at times texture reflects the degree of early taphonomic processes undergone by these aragonitic bodies post mortem under submarine conditions never being exposed to diagenetic processes on land in general a correlation with depth is observed with best preservation observed in otoliths sampled at depths

generation of the benthic foraminiferal assemblage theory and preliminary data abstract the production of benthic foraminiferal communities is filtered through taphonomic mainly destructive processes within the sediments to generate the fossil assemblage both the production and the taphonomy depend on bottom water oxygen content and flux of organic carbon to the seabed an examination of the relationships of processes generating the fossil assemblage to oxygen and organic carbon supply is made using pore water geochemical measurements to estimate carbon flux for locations in the gulf of mexico and the central california margin the locations are plotted in a three dimensional field with bottom water oxygen content organic carbon flux and sediment depth as the axes then the response of foraminiferal standing stock taphonomic processes and the developing fossil assemblage to the field is investigated variation in the vertical stratification of foraminiferal standing stock and test production species stratification taphonomic process intensity and stratification and sediment bioturbation lead to marked differences in the way the fossil assemblage is generated across the oxygen content organic carbon flux field the result is that the oxygen carbon flux field has a significant impact on the fossil assemblage through the interaction of biological and biogeochemical processes in the sediments a model of this interaction is investigated to show how its elements change across the oxygen carbon flux field and how these affect the generation of the fossil assemblage

marine molluscs and late quaternary environmental studies with particular reference to the late glacial period in northwest europe a review abstract although it is now commonly thought that temperature is a minor factor in limiting the distribution of marine invertebrates particularly on a local scale there is evidence to suggest that some boreal molluscs particularly those which occur in similar environments on both sides of the north atlantic are valuable as oceanic temperature indicators this applies particularly to planktotrophic species whose northern limits of distribution are apparently controlled by summer surface temperature the oceanography of the eastern north atlantic is briefly considered in relation to zoogeographic subdivisions based on temperature and it is concluded that the latter are fairly crude and apply only to shelf seas most glaciomarine molluscan faunas are not specific to that environment an exception being that dominated by the bivalve portlandia arctica the role of marine molluscs in palaeoenvironmental research at the local level for the 13 11 ka bp period is illustrated by a site at inchinnan scotland it is concluded that a shell bed at this locality consists partly of a little modified life assemblage and partly of shells which have been gently reworked under conditions of generally rapid deposition during the same time interval the changing composition of molluscan faunas on the nw european seaboard suggests that a weak drift of north atlantic water replaced polar water at or a little later than 13 ka bp off scotland and a few hundred years later off northern norway evidence for relatively warm intervals early and late in the 13 11 ka bp period has been found particulary on the scottish coast and to a lesser extent more generally the later warm interval may be related to the southward movement of the polar front at the beginning of the younger dryas the value of the bivalve shell itself in the determination of temperature seasonality and calendar years is briefly discussed

review on sinkhole monitoring and performance of remediation measures by high precision leveling and terrestrial laser scanner in the salt karst of the ebro valley spain abstract the need to apply sinkhole remediation and monitoring programs is increasing concurrently with the rising engineering impacts of sinkholes in many regions however there is a significant gap in the scientific literature regarding the assessment of the performance of remedial works through subsidence monitoring monitoring techniques have experienced significant advances in the last few years thanks to the advent of new technologies this work presents a review of sinkhole monitoring methods and discusses some practical considerations about their capabilities and limitations it also documents a monitoring program high precision leveling and terrestrial laser scanner and the concurrent remedial works cement based and polyurethane grouting carried out in a highly active sinkhole that affects a flood control dike and the adjacent village of alcala ne spain the subsidence activity in the sinkhole is characterised by progressive sagging and the development of catastrophic nested collapses monitoring data reveal subsidence expansion and acceleration in the sector of the dike treated by polyurethane grouting above the main cavities in contrast subsequent cement based grouting of the large cavities significantly reduced subsidence rates displacement data also indicate substantial subsidence enhancement following flood recession and the associated water table drop buoyancy loss this case study illustrates that high precision leveling and terrestrial laser scanning are adequate complementary methods for monitoring specific sinkholes characterised by very high accuracy and detailed spatial resolution respectively

the rate of taphonomic loss in modern benthic habitats how much of the potentially preservable community is preserved abstract the post mortem fate of shells added by natural mortality to modern death assemblages was studied to determine the importance of taphonomic loss during the initial stages of the formation of a fossil assemblage individuals are added to the living community in pulses usually by larval settlement these input pulses usually are followed by discrete input pulses into the death assemblage the decay of these discrete input pulses in the death assemblage can be used to measure the rate of taphonomic loss as expressed by the half life of a pulse for instance if a species has a half life of 125 days and the input pulse begins with 500 individuals then the number of shells remaining after one half life 125 days is 250 shells at two sites on the texas coast the longest half lives did not exceed one year for any of the 13 species which produced input pulses during the study period little net addition to the death assemblage could be detected in spite of the transitory addition of hundreds of shells as input pulses these rapid decay rates show that death assemblages do not accumulate at the rate at which organisms die some species such as the infaunal bivalve tagelus plebeius did not decay measurably we predict that decay rates drop substantially with depth in the sediment so that individuals which die at depth or are rapidly reworked below the sediment surface have a greater chance of preservation the final composition of death assemblages is probably little related to the actual numerical input from the potentially preservable component of the living community

gypsum karstification in the middle miocene fatha formation mosul area northern iraq abstract karstified middle miocene sediments are widely exposed in northern iraq particularly in the area surrounding the city of mosul the unit is dominated by gypsum and exposed in thirteen anticlinal structures within the investigated area of about 1600 square kilometers synclines though containing the same sequence are not karstified due to a quaternary cover karst features were located from air photos over 4000 were recorded the smallest detectable being two meters in diameter the majority are sinkholes dolines developed in gypsum and manifested in the overlying collapsing limestone they are singular in lines or clusters shafts and karren are fewer in number and are usually developed in uncovered gypsum sinkholes are visibly located along fractures and at fracture intersections over gently inclined limestone beds overlying the gypsum two karst systems were identified an active and recent system characteristic of all the anticlinal structures and an older pleistocene fossil karst system characteristic of alan ishkaft albu saif and hammam structures the fossil karst system is preserved on remnant elevated old land surfaces and produces characteristic tight undulations in the limestone due to collapse inwards in sinkholes and elongated tunnels formed along a series of sinkholes the fracture study of anticlinal structures reveals that the mean fracture density per area ranges between 4 and 8 km km 2 and shows a unimodal character for most of the structures however the distribution of karst in relation to fractures is bimodal for at least half of the structures with mean values ranging from 4 5 to 11 km km 2 the fractures in the anticlines are thought to have formed due to folding but some are associated with major lineaments cross cutting the structures which is reflected in the bimodality and the crude unimodal fracture karst distribution karst features are related to the general fracture pattern but are more localized in densely fractured areas karst areas were also found to correlate with lower slope gradient and lower drainage density

a temporal and spatial study of mudflat erosion and deposition sediment elevations were measured on an intertidal mudflat in maine to determine the temporal and spatial changes in sediment volume the winter and spring months were times of greatest sediment change with erosion in winter months followed by rapid accretion in the spring in some months erosion and deposition took place during the same time interval but on different parts of the mudflat the data suggest that areas of erosion quickly become sites of accretion indicating that an equilibrium surface level is being maintained mudflats may strongly influence the adjacent estuary by acting as sediment banks that can periodically lend sediments to the particulate pool offshore we conclude that mudflats should not be thought of as steady accretionary environments but rather as more variable environments that respond to seasonal changes

taphofacies models for upper cretaceous ammonoids from the kotanbetsu area northwestern hokkaido japan abstract the taphonomic attributes of ammonoid shells in the upper cretaceous of the kotanbetsu area northwestern hokkaido japan are elucidated with reference to sedimentary facies the major attributes are 1 fragmentation rate and fragment separation rate 2 patterns of ammonoid size distribution and mean size 3 shell concentration within calcareous concretions 4 the occurrence of heteromorphic ammonoids and 5 the total number of individuals and species diversity these attributes are classified into four taphofacies analysis of which has lead to the following insights the fragmentation rate and fragment separation rate increase toward shallower environments thus these indices would chiefly reflect the energy level and the frequency of reworking events shells are so abundantly concentrated in storm dominated shelf environments that shell concentrations would be formed by storm and following reworking events the total number of individuals and the diversity differ among the four taphofacies these indices are the largest in the uppermost part of outer shelf these tendencies are inferred to complexly reflect environmental conditions such as energy levels frequency of reworking events and sea level changes

is there a reliable taphonomic clock in the temperate north atlantic an example from a north sea population of the mollusc arctica islandica abstract two hundred and seventy seven shells of the long lived bivalve mollusc arctica islandica collected from the fladen ground northern north sea were radiocarbon dated and their taphonomic condition assessed in order to determine whether taphonomic condition might provide a reliable indication of time since the death of the animal with nine stations from across the fladen ground sampled some strong geographic biases in 14c ages were apparent with living and modern post bomb pulse material found in the northern part of the fladen ground while older material first half of the last millennium and early holocene lateglacial was concentrated in the central and western sites samples from the south and east fladen ground were sparse and were dominated by material from the second half of the last millennium this south north distribution is interpreted as the result of environmental change over millennial time scales in the north sea causing a gradual northward shift of living a islandica populations and is not thought to be related to post mortem transport of shells to the south and east taphonomic condition assessed using discriminant analysis and principal component analysis of five characteristics amount of remaining periostracum presence and condition of the ligament extent of erosion at the shell margin amount of bioerosion and condition of the inner shell layer appeared to be a generally unreliable indicator of time since the death of the animal based on these five taphonomic characteristics discriminant analysis placed 81 1 of post bomb shells 39 6 of shells from the period 0 500 yr bp 68 0 of shells from the period 500 1000 yr bp and 20 0 of shells from the early holocene lateglacial group into the correct radiocarbon age grouping providing no support for the idea that this method can be used to triage shells for chronology construction as an alternative to radiometric dating

taphonomy and depositional dynamics of devonian shell rich mudstones abstract fossil preservation e g articulation of multi element skeletons provides important insights into depositional dynamics detailed taphonomic analysis of marine mudstones and associated shell beds from the middle devonian of western new york indicates that these beds record primarily episodic sediment deposition of short duration we propose a storm winnowing mud blanketing model to explain the variety of shell and mudstone beds observed and to explain apparent onshore offshore gradients of shell bed characteristics shell beds themselves appear to have accumulated during relatively long spans of time ranging up to perhaps thousands of years most are internally complex and exhibit evidence for multiple events of burial and exhumation by winnowing shell accumulation facilitated colonization of the seafloor by hard substrate encrusting organisms these contributed to increasingly complex communities that were ultimately destroyed and permanently blanketed by thick mud layers the sparsely fossiliferous mudstones which compose up to 85 of the hamilton stratigraphic section mainly record very abrupt inputs of sediment in some instances taphonomy of enclosed fossils indicates deposition of layers up to several centimeters thick prior to compaction within hours to a few days in turn some sequences of shell and mudstone beds were deposited within the life span of single colonial organisms and thus also record only relatively short spans of time overall this reinforces our conclusions that most time in mudstone sequences must be represented by discontinuities at sharp surfaces or thin condensed beds that bound more or less continuous bundles of shell and mudstone beds again these often subtle discontinuities can be recognized on the basis of taphonomic criteria many complex shell beds as well as simple shell beds can be traced along depositional strike for tens of kilometers condensed shell beds only a few centimeters thick can commonly be correlated for 100 to 200 km along and across depositional strike the correlatable nature of shell beds apparently reflects the temporal contrast between these beds and enclosing muds on a regional scale shell beds represent integrated accumulations that were deposited over spans of tens to thousands of years conversely the mud layers that blanketed and terminated shell bed accumulations may represent very rapid depositional events spanning hours to days which are locally isochronous thus the study of taphonomy of shell beds reveals a good deal of detail about their depositional history these studies imply that the stratigraphic record is even more episodic and discotinuous than commonly recognized episodic deposition implies that while the stratigraphic record of epeiric seas may be adequate for examining details of community succession and paleontology it probably can not generally be used for microevolutionary studies other than examination of patterns of stasis

les depots coquilliers faluns holocenes de baie comeau cote nord de l estuaire du saint laurent quebec extensive shell beds were found in the valley of riviere aux anglais near baie comeau along the north shore of lower st lawrence river those particular accumulations more or less well stratified and ranging from 2 to 15 m thick represent the top parts of unconsolidated formations of the goldthwait sea between 10 4 and 9 6 ka bp about 10 mounds have been discovered up to now their sizes vary but reach 50 103 m2 most overlie fine stratified sediments such as fine sand silt and clay they consist mainly of shell remains which sometimes represent up to 90 95 of the volume we can find various species of cirripeds 3 gastropods 7 brachiopods 1 echinoderms 1 and mostly pelecypods 11 including a large percentage of unbroken shells stratigraphic evidence suggests that these are natural formations faluns formed in a marine environment by sedimentation inside a seashore of ria type where the sea currents and waves played a prominant role in the concentration of shell remains the q

large depressions thickened terraces and gravitational deformation in the ebro river valley zaragoza area ne spain evidence of glauberite and halite interstratal karstification abstract in the studied reach of the ebro valley the terrace and pediment sediments deposited over glauberite and halite bearing evaporites show local thickenings 50 m recording dissolution induced synsedimentary subsidence recent data on the lithostratigraphy of the evaporite sequence allow relating the alluvium thickenings with either halite or glauberite dissolution the alluvium filled dissolution basin underlying the youngest terraces t8 t11 is ascribed to halite karstification the top of a halite unit approximately 75 m thick is situated 40 15 m below the valley bottom the thickenings of terrace t1 t7 and pediment sediments are attributed to interstratal glauberite karstification 1 coincidence between the elevation range of the terraces and that of the glauberite rich unit glauberite beds reach 30 and 100 m in single bed and cumulative thickness respectively 2 the exposed bedrock underlying thickened alluvium shows abundant subsidence features indicative of interstratal karstification the most common structure corresponds to hectometer scale sag basins with superimposed collapses in the central sector of each basin the subsided bedrock is frequently transformed into dissolution collapse breccias showing a complete textural gradation from crackle packbreccias to chaotic floatbreccias and karstic residues 3 paleokarst exposures show evidence of karstification confined to specific beds made up of secondary gypsum after precursory glauberite partly dissolved and partly replaced despite the magnitude of the subsidence recorded by the thickened alluvium and unlike nearby tributaries the terraces show a continuous and parallel arrangement indicating that the fluvial system was able to counterbalance subsidence by aggradation a number of kilometer size flat bottom depressions have been developed in the valley margin typically next to and inset into thickened terrace and pediment deposits the subsidence structures exposed in artificial excavations excavated in the bottom of some depressions and the correlation between the altitudinal distribution of these basins and that of the glauberite rich unit reveal that subsidence related to interstratal glauberite karstification is the main process involved in their genesis this research ascribes for the first time the thickenings and deformation of specific terrace levels and pediment levels and the development of large karstic depressions to interstratal karstification of exceptionally thick glauberite units

convective transport within stable river sediments local pressure variations of the order of 100 1000 n m2 can be observed between the upstream and downstream faces of the typically triangular shaped dunelike sediment structures that form at the sediment water interface of rivers laboratory experiments were conducted examining the influence of this localized pressure variation on contaminant transport processes within the sediment numerical modeling of the in bed flow via boundary element methods was also undertaken in order to predict convective transport under typical field conditions the laboratory experiments and numerical simulation of the in bed flow in several rivers verified that the pressure distribution observed on the sediment surface and the resulting interstitial fluid convection can control transport of chemically inert nonsorbed contaminants in stable sediments in bed peclet numbers were of the order of 100 1000 indicating the negligible influence of diffusion under the conditions examined

sinkholes pit craters and small calderas analog models of depletion induced collapse analyzed by computed x ray microtomography volumetric depletion of a subsurface body commonly results in the collapse of overburden and the formation of enclosed topographic depressions such depressions are termed sinkholes in karst terrains and pit craters or collapse calderas in volcanic terrains this paper reports the first use of computed x ray microtomography mu ct to image analog models of small scale similar to 2 km diameter high cohesion overburden collapse induced by depletion of a near cylindrical stock like body time lapse radiography enabled quantitative monitoring of the evolution of collapse structure velocity and volume moreover mu ct scanning enabled nondestructive visualization of the final collapse volumes and fault geometries in three dimensions the results illustrate two end member scenarios 1 near continuous collapse into the depleting body and 2 near instantaneous collapse into a subsurface cavity formed above the depleting body even within near continuously collapsing columns subsidence rates vary spatially and temporally with incremental accelerations the highest subsidence rates occur before and immediately after a surface depression is formed in both scenarios the collapsing overburden column undergoes a marked volumetric expansion such that the volume of subsurface depletion substantially exceeds that of the resulting topographic depression in the karst context this effect is termed bulking and our results indicate that it may occur not only at the onset of collapse but also during progressive subsidence in the volcanic context bulking of magma reservoir overburden rock may at least partially explain why the volume of magma erupted commonly exceeds that of the surface depression

reconstructing the internal structure and long term evolution of hazardous sinkholes combining trenching electrical resistivity imaging eri and ground penetrating radar gpr abstract the approaches aimed at characterising specific damaging sinkholes have received limited attention compared with other ground instability phenomena e g landslides moreover the practicality of the trenching technique in combination with numerical dating and retro deformation analysis for sinkhole site investigations has been barely explored this work illustrates the advantages of combining geomorphic mapping electrical resistivity imaging eri ground penetrating radar gpr and trenching for sinkhole characterisation and shows how the trenching technique contributes to fill significant gaps that neither geomorphic nor geophysical methods can address two large sinkholes 200 m long related to the interstratal karstification of evaporites and generated by contrasting subsidence mechanisms sagging collapse were investigated in the fluvia valley ne spain although gpr data may provide high resolution information on subsidence related stratigraphic and structural features at shallow depth the profiles acquired in the investigated sites with 100 mhz shielded and 40 mhz unshielded antennae provided limited insight into the internal geometry of the sinkholes due to reduced signal penetration related to the presence of conductive clayey material the eri sections satisfactorily imaged the general geometry of the sagging and collapse subsidence structures up to depths higher than 100 m and clearly captured the basal contact of the low resistivity sinkhole fill in the sections with adequate layout and resolution the trenches despite their limited depth ca 5 m allowed us to obtain valuable objective information on several key aspects of the subsidence phenomenon 1 mechanisms deformation style and kinematics progressive versus episodic 2 limits of ground deformation 3 temporal evolution expansion versus contraction 4 chronology and timing of most recent deformation phase 5 rates of subsidence and sedimentation and 6 the role played by subsidence in the development of lacustrine environments and the associated sedimentation patterns

use of gpr method for prediction of sinkholes formation along the dead sea shores israel abstract it seems the highly saline conditions of the dead sea ds coast line are not favorable for the use of ground penetrating radar gpr method for detection of underground caverns before sinkhole formation short time prediction the location of the formed caverns within the salt layer significantly more than the penetration depth of the electromagnetic waves combined with the saline ds brine groundwater covering the salt layer from above characterized by low electrical resistivity makes the application of electromagnetic waves ew impossible however our experience has shown that gpr technique in its 2d and 3d modifications can be a very efficient tool to predict sinkhole susceptibility case histories of gpr studies in the mineral beach and nahal david sites are presented the gpr study has shown that the method is effective in both urban sites and at most of sites of human activities of the dead sea coast dwellings routes agricultural areas etc but it fails in areas composed of saline mud in the subsurface some areas lower than 400 m elevation the fan areas are composed of sandy gravel sediments and the penetrating depth of the electromagnetic waves varies but is usually limited to the first meters up to 8 10 m maximum to 13 15 m but in any case not deeper than the water table depending on the dielectric constant which as a rule is 4 25 in areas covered by dead sea mud penetration depth is limited to the first meter due to the low electrical resistivity of the sediments models of sinkhole formation and principles of cavity detection in the ds area are discussed to understand the fundamentals of gpr use for the prediction of sinkhole susceptibility

shape and dimensions of stationary dunes in rivers the shape and dimensions length height of sand dunes in rivers are calculated by use of the measured bed shear stress distribution downstream a rearward facing step the transport of sediment is split up into bed load and suspended load which makes it possible to explain the transition to plane bed the model can predict flow resistance curves in alluvial streams

the application of gpr and eri in combination with exposure logging and retrodeformation analysis to characterize sinkholes and reconstruct their impact on fluvial sedimentation this work illustrates the practicality of investigating sinkholes integrating data gathered by ground penetrating radar gpr electrical resistivity imaging eri and trenching or direct logging of the subsidence affected sediments in combination with retrodeformation analysis this mutidisciplinary approach has been tested in a large paleosinkhole developed during the deposition of a quaternary terrace on salt bearing evaporites the subsidence structure exposed in an artificial excavation is located next to puilatos a village that was abandoned in the 1970s due to severe subsidence damage detailed logging of the exposure revealed that the subsidence structure corresponds to an asymmetric sagging and collapse paleosinkhole with no clear evidence of recent activity the sedimentological and structural relationships together with the retrodeformation analysis indicate that synsedimentary subsidence controlled channel location the development of a palustrine environment and local changes in the channel pattern gpr profiles were acquired using an array of systems with different antenna frequencies including some recently developed shielded antennas with improved vertical resolution and penetration depth although radargrams imaged the faulted sagging structure and provided valuable data on fault throw they did not satisfactorily image the complex architecture of the fluvial deposit eri showed lower resolution but higher penetration depth when compared to gpr roughly capturing the subsidence structure and yielding information on the thickness of the high resistivity alluvium and the nature of the underlying low resistivity karstic residue developed on top of the halite bearing evaporitic bedrock data comparison allows the assessment of the advantages and limitations of these complementary techniques highly useful for site specific sinkhole risk management this article is protected by copyright all rights reserved

evaluation of geochemical and hydrogeological processes by geochemical modeling in an area affected by evaporite karstification the ebro valley in the outskirts of zaragoza ne spain is severely affected by evaporite karstification leading to multiple problems related to subsidence and sinkhole formation in this work a combination of inverse mixing mass balance and forward reaction path geochemical calculations is applied for the quantification of the main karstification processes and seasonal variations in this area the obtained results prove the suitability of the applied methodology for the characterization of similar problems in other areas with scarce geological and hydrogeological information the hydrogeology and hydrochemistry of the system can be mainly attributed to the mixing of variable proportions of concentrated groundwater from the evaporitic aquifer and more dilute water from the overlying alluvial aquifer the existence of a good connection between these aquifers is supported by 1 the fast changes in the hydrochemistry of the karst aquifer related to recharge by irrigation and 2 the deduced input of evaporitic groundwater in the alluvial materials the evolution in some parts of the alluvial evaporitic aquifer system is clearly dominated by the seasonal variations in the recharge by dilute irrigation waters up to 95 of water volume in some sinkhole ponds whereas other points seem to be clearly determined by the hydrochemistry of the concentrated evaporitic aquifer groundwater up to 50 of the water volume in some springs the following reactions previous or superimposed to mixing processes explain the observed hydrochemistry in the studied area dissolution of halite naci gypsum caso4 2h 2 o anhydrite caso4 and dolomite camg co3 2 co2 b input and degassing and calcite caco3 dissolution precipitation the modeling results suggest the existence of a large spatial variability in the composition of the evaporitic groundwater mainly caused by large differences in the availability of halite in contact with the groundwater active subsidence associated with halite dissolution is expected to continue in the study area together with the episodic increase of gypsum dissolution associated with the input of dilute irrigation waters c 2015 elsevier b v all rights reserved

ecology of four infaunal bivalve species in the recent intertidal zone shikoku japan abstract spatial and density distributions mode of occurrence and size frequency histograms in living populations and death assemblages were analyzed quantitatively for four infaunal bivalve species on the intertidal flat of the coastal area of northwestern shikoku japan the results show that the mode of preservation of empty shells in the early process of fossilization differs greatly from species to species and or area to area the degree of taphonomic loss is low in deep burrowing species inhabiting muddy substrates and the spatial and density distributions and size frequency data of living populations are well preserved in the articulated empty shell assemblages in contrast dispersion of empty shells outside the habitat occurs frequently in the shallow infauna within coarser substrates this work suggests that articulated fossil shell assemblages of deep burrowing bivalves are probably autochtonous at the population level and that they may be most useful for detailed palaeoecological and palaeoenvironmental analyses

actual extension of sinkholes considerations about geophysical geomorphological and field inspection techniques in urban planning projects in the ebro basin ne spain abstract aerial photographs historical cartographies and field inspection are useful tools in urban planning design on mantled karst because they permit a wide time interval to be analyzed in the case of zaragoza city several works have confirmed the interest of these approaches in configuring the urban planning code and therefore represent a promising technique nevertheless some caveats should be taken into account when using this kind of information a detailed analysis is presented comparing in a case study from the surroundings of zaragoza geomorphological historical analysis and field inspection with geophysical data field inspection in a noncultivated area permits the constraint of the presence of karst indicators below the geomorphological resolution of aerial photographs and shows results consistent with geophysical surveys the studied case shows an inner zone coinciding with the sinkhole mapped from aerial photographs that correlates with changes in the position of the substratum and changes in thickness of alluvial sediments the integrated analysis permits us to define an external subsidence ring around the geomorphological sinkhole whose surface is twice the size of the inner zone this outer ring is indicated by geometrical changes in gpr profiles increases of thickness of the conductive shallower unit toward the collapse and small collapses on marginal cracks these results support the higher extension of karst hazards linked to sinkholes with respect to their geomorphological expression and the needed detailed analysis to constrain the real sinkhole size or the use of security radii surrounding this surficial evidence when geomorphological data is used for the hazard analyses or the urban planning at karstic zones

a genetic classification of sinkholes illustrated from evaporite paleokarst exposures in spain this contribution analyses the processes involved in the generation of sinkholes from the study of paleokarst features exposed in four spanish tertiary basins bedrock strata are subhorizontal evaporites and in three of the basins they include halite and glauberite in the subsurface our studies suggest that formation of dolines in these areas results from a wider range of subsidence processes than those included in the most recently published sinkhole classifications a new genetic classification of sinkholes applicable to both carbonate and evaporite karst areas is thus proposed with the exception of solution dolines it defines the main sinkhole types by use of two terms that refer to the material affected by downward gravitational movements cover bedrock or caprock and the main type of process involved collapse suffosion or sagging sinkholes that result from the combination of several subsidence processes and affect more than one type of material are described by combinations of the different terms with the dominant material or process followed by the secondary one e g bedrock sagging and collapse sinkhole the mechanism of collapse includes any brittle gravitational deformation of cover and bedrock material such as upward stoping of cavities by roof failure development of well defined failure planes and rock brecciation suffosion is the downward migration of cover deposits through dissolutional conduits accompanied with ductile settling sagging is the ductile flexure of sediments caused by differential corrosional lowering of the rockhead or interstratal karstification of the soluble bedrock the paleokarsts we analysed suggest that the sagging mechanism not included in previous genetic classifications plays an important role in the generation of sinkholes in evaporites moreover collapse processes are more significant in extent and rate in areas underlain by evaporites than in carbonate karst primarily due to the greater solubility of the evaporites and the lower mechanical strength and ductile rheology of gypsum and salt rocks

characterizing and monitoring a high risk sinkhole in an urban area underlain by salt through non invasive methods detailed mapping high precision leveling and gpr abstract two critical aspects for assessing the hazard and managing the risk associated with active sinkholes in developed areas are the precise mapping of the areas affected by ground instability and the quantitative characterization of the ground displacement kinematic style spatial temporal patterns rates however sinkhole site investigations typically provide a static picture of the instability phenomena and the performance of remediation measures is rarely evaluated using time series of displacement this work illustrates the practicality of a non invasive approach combining detailed mapping ground penetrating radar gpr and high precision leveling for the characterization at different time scales of the ground deformation associated with an active sinkhole in an urban area the selected highly active sagging and collapse sinkhole affects four multi storey buildings in zaragoza city spain involving direct losses higher than 15 meuro gpr data provided information on the internal structure of the sinkhole and the subsidence mechanisms the boundaries of the ground deformation zone established with the gpr data and especially high precision leveling indicate a sinkhole area two times larger than that previously proposed on the basis of airborne imagery and surface deformation features length from 100 m to 130 m the leveling profiles reveal an inner rapidly subsiding zone with vertical displacement rates as high as 3 cm yr an outer slow settlement ring and a marginal uplifting bulge with vertical displacement rates that reach 0 6 cm yr this phenomenon of marginal bulging is probably a relatively common process in sagging sinkholes which may have gone unnoticed since its identification requires the use of geodetic methods with utmost accuracy such as high precision leveling monitoring data indicate that ongoing salt dissolution significantly contributes to the active subsidence and reveal the high impact on the subsidence of water pumping from the evaporitic aquifer and the limited efficiency of a shallow compaction grouting program performed above cavities and karstification zones

sinkhole structure imaging in covered karst terrain 1 ground penetrating radar gpr and resistivity techniques have been widely used to map the locations of sinkholes in covered karst terrain to determine whether a sinkhole is a likely preferential conduit for groundwater flow however requires higher resolution imaging than that used in conventional sinkhole mapping surveys field observations combined with simulated surveys for a 15 m diameter 3 m deep sinkhole in west central florida are used to assess the resolution of gpr and resistivity surveys targeting the semiconfining unit that floors the sinkhole depression 2d resistivity surveys clearly show the central depression as well as resistivity contrasts between the cover sediments within and outside of the sinkhole but are inadequate for resolving breaches in the semiconfining unit or underlying conduits a 3d gpr survey resolves vertical structure on the order of tens of centimeters within the semiconfining unit as well as indicators of conduits that extend several meters beneath the central depression 3d gpr thus holds promise for imaging hydrologically significant features of sinkholes

subsidence mechanisms and sedimentation in alluvial sinkholes inferred from trenching and ground penetrating radar gpr implications for subsidence and flooding hazard assessment abstract sinkholes function as small sediment traps that may host valuable stratigraphic records for paleoenvironmental reconstructions and hazard assessments e g subsidence floods hurricanes tsunamis tephra fall out the sedimentological features and completeness of such archives are influenced by the sedimentation and subsidence patterns and rates however karst depressions are frequently treated as static basins unaffected by settlement this work illustrates the practicality of integrated studies combining trenching numerical dating and shallow geophysical techniques gpr for characterizing the subsurface subsidence structure associated with sinkholes and reconstructing their deformational and sedimentary history the approach is applied in two collapse sinkholes located in contrasting geomorphic settings relict terrace and floodplain related to deep seated interstratal karstification of evaporites the analysis of the sinkholes particularly the trenching technique provides practical information for assessing the associated subsidence hazard including the presence of larger cavities at depth the kinematic regime episodic versus progressive evidence of catastrophic displacement fluidization structures and the magnitude and timing of collapse events especially the most recent one the sinkhole located in the floodplain offers the opportunity of analyzing the possibilities and limitations of subsidence sinkholes as recorders of past floods in alluvial environments this depression shows a largely incomplete record attributable to the high frequency of flood events compared to that of the collapse events which create the accommodation space for sediment deposition these limitations could be partially overcome by selecting old sinkholes situated in low terraces and or affected by rapid subsidence

long term accumulation of carbonate shells reflects a 100 fold drop in loss rate shells in modern seabeds can be thousands of years old far older than would be extrapolated from the rapid rates of shell loss detected in short term experiments an extensive shelldating program on the southern california usa shelf permits rigorous modeling of the dynamics of shell loss in the mixed layer discriminating the key rates of carbonate disintegration and sequestration for the first time we find that bivalve shells experience an initially high disintegration rate l 1 decadal half lives but shift abruptly within the first 500 yr postmortem to a 100 fold lower disintegration rate l 2 millennial half lives at sequestration rate t burial and or diagenetic stabilization this drop permits accrual of a long tail of very old shells even when sequestration is very slow and allows only a minority 1 of all shells to survive the first phase these high rates of disintegration and low rates of sequestration are consistent with independent measures of high carbonate loss and slow sedimentation on this shelf our two phase model thus reveals significant spatial and temporal partitioning of car bonate loss rates within the mixed layer and shows how shell age frequency distributions can yield rigorous and realistic estimates of carbonate recycling on geological time scales

the muddy bottom of lake pannon a challenge for dreissenid settlement late miocene bivalvia abstract the late miocene dreissenids of lake pannon a long existing eastern central european lake bear witness to two very different modes of life which allowed these bivalves to successfully settle in what appears to be an inhospitable environment one guild is restricted to the genera mytilopsis conrad 1858 and sinucongeria lorenthey 1894 these representatives are extreme r strategists which tend to produce temporal boom and bust populations during time windows of improved ecological conditions these opportunities are interpreted here to correlate with cyclic shifts in the epilimnion hypolimnion relation and the corresponding oxygenation of bottom waters events which are probably triggered by low frequency orbital forcing the second guild is composed solely of congeria partsch 1836 the paradox of the proliferation of a single species characterised by extreme size and weight in a muddy oxygen deficient lake environment avoided by nearly all other molluscs points to a hidden mechanism not accessible to other species we tentatively link this mechanism with chemosymbiosis functional morphology in interplay with a highly sulphidic over saturated interstitial water support an interpretation of the large congeria subglobosa as a successful h2s pump model

the sedimentology stratigraphy and preservation of intertidal deposits in the minas basin system bay of fundy abstract intertidal sediments of the minas basin a macrotidal estuary at the head of the bay of fundy can be subdivided into six major facies tidal marsh beach mudflat sandflat channel lag and sandbar each is characterized by its grain size distributions sedimentary structures and biological communities these sedimentary facies occur in three types of high to low tide zonation depending on the local sediment source and wave and current energy the holocene stratigraphy presently preserved in the upper intertidal zone of minas basin consists of a relatively thin on the average less than 1 2 m wedge of sediment overlying bedrock only in a few sheltered locations where deposits accumulate to several meters is the marine transgressive stratigraphy well represented the hypothetical progradational or marine regressive stratigraphy of upper intertidal sediments would probably resemble from top to bottom the high to low tide sequence of facies occurring today on sheltered tidal flats lebensspuren would provide the most reliable representation of the ecology of intertidal sediments in minas basin they are useful in delineating communities as well as being sensitive indicators of sediment deposition microfauna are too easily transported or reworked field data from relict intertidal deposits dated 2300 3400 yr b p indicate calcareous organism hard parts would probably provide a biased fossilized record indirect evidence is discussed which suggest in situ dissolution of shells in certain intertidal sediments

taphofacies models for epeiric sea environments middle paleozoic examples abstract skeletonized organic remains display various modes of occurrence which may be used to better understand the sedimentary dynamics of strata within which they occur aspects of skeleton biostratinomy and early diagenesis are distributed nonrandomly within the stratigraphic record and therefore are useful in discriminating taphonomic facies for purposes of taphonomic comparisons skeletonized marine taxa are reduced to five generally defined types massive arborescent univalved bivalved and multielement different skeletal types display different attributes which reflect specific responses to physical chemical and or biological processes the taphonomic properties of disarticulation reorientation and sorting fragmentation corrosion and abrasion skeletal dissolution and early diagenesis display patterns which are predictable with respect to a variety of inter related physico chemical parameters these can be quantified through indices which evaluate relative frequencies of occurrence sedimentary events alter the temporal and spatial homogeneity of processes which generate background taphofacies and superimpose event related properties thereby generating composite taphofacies such events produce taphonomic signature which in themselves correspond to specific environmental conditions i e water depth and event intensity indeed background and event related processes interact to generate complex but nonetheless diagnostic facies attributes useful in reconstructing paleoenvironments the comparison of standard indices among beds should allow the recognition of stratigraphic patterns and facilitate the diagnosis of systematic gradients among taphonomic properties deductively derived taphofacies models corroborated by empirical data from paleozoic strata illustrate the distribution of taphonomic properties with respect to environmental energy turbulence background sedimentation rate and sediment oxygenation these parameters also indirectly influence other less obvious factors including bioturbation and sediment chemistry trends in the distribution of taphonomic properties taphonomic gradients permit us to map otherwise unrecognized trends in these environmental parameters across a hypothetical onshore offshore transect within a generalized epeiric sea setting taphofacies models provide the quantifiable basis by which evolution of taphofacies may be gauged and then related to biotic and abiotic phenomena moreover taphofacies models evaluate the preservability of skeletal remains in different environmental settings and therefore provide information important in paleoecological studies

lower flow regime bedforms rational classification a classification of lower flow regime bedforms is proposed based upon consideration of the effect of water flow on the shape and size of bedforms which is more rational than other systems presently in use it is suggested that a more quantitative system of bedform classification may lead to a better understanding of the occurrence and behaviour of bedforms the assumptions on which the proposed classification is based are shown to agree with published data relating bedform characteristics to mean flow depth and velocity the proposed classification offers a rational explanation for several hitherto puzzling aspects of bedform behaviour in laboratory and field situations since much presently available data is unsuited to testing these proposals further extensive experimental work on bedforms is required

a review of the ecological and taphonomic controls on foraminiferal assemblage development in intertidal environments intertidal foraminifera from surface sediments are commonly used as a high resolution indicator of sea level change the integrity of this approach is based upon the assumption that surface assemblages are similar in composition to their buried fossil counterparts this assumption may in some cases be inappropriate due to subsurface or infaunal production and taphonomic alteration here we review the current understanding of foraminiferal production and taphonomic loss in intertidal environments and examine the extent to which these processes can affect the development of foraminiferal assemblages in intertidal environments as a sediment layer undergoes burial dead tests are added at a rate proportionate to the standing crop at that depth as a consequence test accumulation within the layer is proportionate to the depth integrated standing crop depending on the nature of its vertical living distribution the upper 1 cm of sediment may therefore not adequately characterise a given species total input instead a comparison of each species contribution to the entire depth integrated living community may offer a better a priori estimate of relative input to the sediment column this provides an improved base line for identifying true taphonomic trends downcore the potential for infauna to create discrepancies between surface and subsurface assemblages may be minimised however where 1 reproduction is concentrated near to the sediment surface transforming an apparent infaunal standing crop into an effective epifaunal production 2 the living fauna is composed similarly at all depths of production and or 3 intense bioturbation homogenises the upper sediment layers the likely decline in the intensity of taphonomic processes with depth may mean that the foraminiferal production from different depths may not experience taphonomic processes uniformly consequently in addition to their possible gradual enrichment due to subsurface production infaunal species may be preferentially preserved by virtue of their production closer to the base of the taphonomically active zone additionally homogenisation of the sediment column by reworking may mix temporally and perhaps environmentally distinct faunas affecting the stratigraphic integrity of the sediment deposit the most important taphonomic processes in intertidal environments are those associated with early diagenesis while the organic cements of agglutinated taxa may be directly oxidised the associated changes in the saturation state of porewaters with respect to calcium carbonate may affect calcareous species the type of diagenetic reaction operating within the sediment provides a quantitative control on agglutinated test degradation but a largely qualitative control on calcareous preservation in addition calcareous test preservation is dependent upon the rate with which organic matter is supplied while agglutinated test preservation is independent of organic matter concentrations although the specific morphological pathways of test degradation for calcareous species are well understood the stages under which agglutinated tests are lost are less clear the combined but varying influences of production infaunal and species composition taphonomic processes and bioturbation may create complex pathways in the transition from live to dead to fossil assemblages understanding the extent to which infauna taphonomic loss and sediment reworking affect assemblage development in different intertidal environments is essential in order to interpret the fossil record

sinkholes in the salt bearing evaporite karst of the ebro river valley upstream of zaragoza city ne spain geomorphological mapping and analysis as a basis for risk management abstract a detailed sinkhole map has been produced in a stretch of the ebro valley 40 8 km2 including the western sector of zaragoza city ne spain during the last few decades around 70 of the original sinkhole area has been filled with anthropogenic sediments causing the disappearance of 137 ha of wetlands the interstratal karstification of salts halite and glauberite and a wnw ese trending joint set have played a major control in the development of sinkholes three morphometric types of sinkholes have been differentiated each attributed to a specific subsidence mechanism inferred from the paleosinkholes exposed in the surrounding of zaragoza city sagging of bedrock and cover collapse of bedrock and cover and collapse of cover material related to the downward migration of particles through dissolutional conduits each type of sinkhole is characterised by a distinctive behaviour in terms of controlling factors spatio temporal distribution and kinematics and consequently the proposed differentiation may have a practical utility the vast majority of the subsidence damage identified in the area occurs within the boundaries of pre existing sinkholes identifiable in old aerial photographs and topographical maps this fact demonstrates that the application of preventive planning strategies based on detailed geomorphological maps would have allowed avoidance of most of the large financial losses caused by subsidence in the area of the order of hundreds of thousands of euros per year

rapid subsidence in damaging sinkholes measurement by high precision leveling and the role of salt dissolution abstract investigations dealing with subsidence monitoring in active sinkholes are very scarce especially when compared with other ground instability phenomena like landslides this is largely related to the catastrophic behaviour that typifies most sinkholes in carbonate karst areas active subsidence in five sinkholes up to ca 500 m across has been quantitatively characterised by means of high precision differential leveling the sinkholes occur on poorly indurated alluvium underlain by salt bearing evaporites and cause severe damage on various human structures the leveling data have provided accurate information on multiple features of the subsidence phenomena with practical implications 1 precise location of the vaguely defined edges of the subsidence zones and their spatial relationships with surveyed surface deformation features 2 spatial deformation patterns and relative contribution of subsidence mechanisms sagging versus collapse 3 accurate subsidence rates and their spatial variability with maximum and mean vertical displacement rates ranging from 1 0 to 11 8 cm yr and 1 9 to 26 1 cm yr respectively 4 identification of sinkholes that experience continuous subsidence at constant rates or with significant temporal changes and 5 rates of volumetric surface changes as an approximation to rates of dissolution induced volumetric depletion in the subsurface reaching as much as 10 900 m3 yr in the largest sinkhole the high subsidence rates as well as the annual volumetric changes are attributed to rapid dissolution of high solubility salts

dead shell assemblages faithfully record living molluscan assemblages at one tree reef abstract reef associated sediments accumulate over time recording the history of biological communities the agreement between live and dead assemblages has been extensively studied because discrepancies between the two can reveal taphonomic bias anthropogenic impact and or a decrease in temporal resolution of dead assemblages to centennial scales i e time averaging given the potential of sedimentary assemblages to provide temporal perspectives on the history of modern communities assessments of live dead agreement in reef mollusk assemblage composition are necessary and timely for understanding rapid environmental change one tree reef otr southern great barrier reef australia has had very little direct anthropogenic influence over the past four decades making it a good system for focusing on taphonomic patterns live n 1335 and dead n 6919 molluscan assemblages were collected from three shallow 6 m carbonate soft sediment lagoons diversity and evenness metrics indicated no significant difference between the live and dead assemblages and dead assemblage rank order abundance explains 82 of that of the live assemblage differences in composition were largely due to sample size the low probability of sampling rare species and to a lesser degree differences in skeletal durability taphonomic factors were responsible for less than 20 of the differences in species composition between live and dead shell assemblages the live molluscan assemblage sampled was similar to the live assemblage sampled 30 years ago given that time averaging is approximately 19 years in the otr lagoon we conclude that the composition of the living assemblage has remained largely unchanged for the last 30 years these findings indicate that dead assemblages preserved in shallow fully carbonate environments primarily reflect the composition of the original source communities making them useful to identify recent changes in coral reef areas where anthropogenic impacts are present

effects of early sea floor processes on the taphonomy of temperate shelf skeletal carbonate deposits abstract cool water shelf carbonates differ from tropical carbonates in their sources modes and rates of deposition geochemistry and diagenesis inorganic precipitation marine cementation and sediment accumulation rates are absent or slow in cool waters so that temperate carbonates remain longer at or near the sea bed early sea floor processes occurring between biogenic calcification and ultimate deposition thus take on an important role and there is the potential for considerable taphonomic loss of skeletal information into the fossilised record of cool water carbonate deposits the physical breakdown processes of dissociation breakage and abrasion are mediated mainly by hydraulic regime and are always destructive impact damage reduces the size of grains removes structure and therefore information and ultimately may transform skeletal material into anonymous particles abrasion is highly selective amongst and within taxa their skeletal form and structure strongly influencing resistance to mechanical breakdown dissolution and precipitation are the end members of a two way chemical equilibrium operating in sea water in cool waters inorganic precipitation is rare there is conflicting opinion about the importance of diagenetic dissolution of carbonate skeletons on the temperate sea floor but test maceration and early loss of aragonite in particular are reported dissolution may relate to undersaturated acidic pore waters generated locally by a combination of microbial metabolisation of organic matter strong bioturbation and oxidation of solid phase sulphides immediately beneath the sea floor in otherwise very slowly accumulating skeletal deposits laboratory experiments demonstrate that surface to volume ratio and skeletal mineralogy are both important in determining skeletal resistance to dissolution biological processes on the sea floor include encrustation and bioerosion encrustation a constructive process may be periodic or seasonal and can be reversed it produces both information and material bioerosion in contrast is destructive and permanent in temperate areas bioerosion may destroy even very large shells during their long residence at the sea floor on the order of hundreds to thousands of years overall processes on the temperate sea floor may combine to destroy more carbonate than they produce and the preservation potential of temperate shelf carbonate into the rock record may be significantly affected where preservation does occur in such a destructive regime the effects of early sea floor processes will be key determinants of the deposit resulting in a taphofacies characteristic of temperate shelf carbonate sediments

taphonomic tiering experimental field taphonomy of molluscs and foraminifera above and below the sediment water interface abstract a review and synthesis of field based taphonomic experiments using molluscs and foraminiferans in marine systems reveal differing patterns of hardpart accumulation and destruction for these two major groups of fossil organisms for benthic molluscs most destruction appears to occur at the sediment water interface in siliciclastic settings mollusc preservation is suggested to be high once the shell is buried below the taphonomically active zone although this observation has not been experimentally addressed foraminiferal preservation however depends on microhabitat biogeochemical conditions within the sediments and test composition the taphonomically active zone for foraminiferans appears to be the upper 10 cm in most depositional settings from shallow to deep sea the preservation of tests or shells however has not been examined below the sediment water interface using field based experiments pore water geochemistry and associated microbial processes may be the most important factors in which to examine subsurface taphonomy the term taphonomic tiering is applied to variations in taphonomic activity within the sediments that differentially affect hard parts in essence the subsurface region where hardparts are presumed to be preserved is one of the new frontiers in experimental field taphonomy

taphonomy on the continental shelf and slope two year trends gulf of mexico and bahamas abstract the shelf and slope experimental taphonomy initiative was established to measure taphonomic rates in a range of continental shelf and slope environments of deposition eods over a multiyear period we deployed experiments on the forereef slope off lee stocking island bahamas and on the continental shelf and slope of the gulf of mexico for 2 yr in 18 distinctive eods at depths from 15 to 530 m overall most shells deployed at most sites had relatively minor changes in shell condition most eods generated relatively similar taphonomic signatures a few sites did produce taphonomic signatures clearly distinguishable from the central group and these sites were characterized by one or more of the following high rates of oxidation of reduced compounds presence in the photic zone and significant burial and exhumation events thus unique taphonomic signatures are created by unique combinations of environmental conditions that include variables associated with regional gradients such as depth and light and variables associated with edaphic processes such as the seepage of brine or petroleum or the resuspension and redeposition of sediment most sites however showed similar taphonomic signatures despite the variety of eod characteristics present suggesting that insufficient time had elapsed over 2 yr to generate a more diverse array of taphonomic signatures discoloration and dissolution were by far the dominant processes over the 2 yr deployment period periostracum breakdown loss of shell weight and chipping and breakage was less noticeable eods were chosen based on the expectation that the process of burial and the influence of depth and sediment type should play the greatest roles in determining between eod differences in taphonomic signature eod specific edaphic factors often overrode the influence of geographic scale environmental gradients taphonomic alteration was greater on hardgrounds and in brine exposed sites than on terrigenous muds dissolution was less effective at sites where burial was greatest discoloration occurred most rapidly at shallower sites and on hardgrounds water depth was less influential in determining taphonomic signature than burial state or sediment type the limited influence of water depth is likely due to the presence of shallow sites that for one reason or another were protected from certain taphonomic processes and deeper sites that were characterized by unusually strong taphonomic signals

sinkhole investigation in an urban area by trenching in combination with gpr ert and high precision leveling mantled evaporite karst of zaragoza city ne spain abstract sinkhole risks are becoming particularly severe in urban areas that lack careful planning and where karst depressions are frequently filled and developed these built up areas are the most challenging for sinkhole investigation they are the ones that require the highest priority and the application of novel approaches aimed at reducing the epistemic uncertainties associated with hazard assessments this work illustrates the strengths of the rarely used trenching technique for the investigation of sinkholes in mantled karst areas the approach has been tested on a buried sinkhole in the evaporite karst of zaragoza city analysing and comparing data gathered by trenching ground penetrating radar gpr using shielded and unshielded antennas with different frequencies electrical resistivity tomography ert and high precision leveling the sinkhole is located beneath a street and has led to the demolition of buildings creating a risk situation that requires careful assessment and management trenching provided the largest amount of objective data required for hazard assessment 1 precise location of the sinkhole edges 2 internal structure cumulative displacement subsidence mechanisms and their contribution the trench exposed an asymmetric structure with a minimum vertical displacement of 6 2 m comprising a complex collapse with different generations of faults and two marginal zones affected by gentle inward tilting collapse faulting accommodates at least 70 of the subsidence 3 age of the sinkhole and average subsidence rate the sinkhole was initiated sometime before or within 337 435 cal yr ad indicating a long term subsidence rate of ca 3 7 4 2 mm yr 4 kinematic style characterised by episodic collapse events as supported by leveling data the retrodeformation analysis together with geochronological data indicates four collapse events with a recurrence of around 400 years and suggests enhanced activity since ca 1950 ad the performance of gpr was highly variable depending mainly on the type of antenna and the timing of data acquisition the best quality data were obtained with shielded antennas and during relatively drier conditions the rather poor performance of ert commonly an adequate method for resolving subsidence structures at depth is attributed to the complex structure of the collapse sinkhole with spatially dense and abrupt resistivity changes in resistivity this case study strongly substantiates the implementation of the relatively inexpensive and highly objective trenching technique in sinkhole investigations