shelf to basin temperate skeletal carbonate sediments three kings plateau new zealand abstract three kings plateau is 10 000 km2 in area less than 500 m deep and includes the mainland shelf and submarine ridges and banks centered on three kings islands 34 s off northernmost new zealand the plateau receives little input of terrigenous sediment and lies in a zone of active nutrient upwelling and vigorous wind wave and tidal current activity as a consequence surficial sediments on and about the margins of the plateau are dominantly pure skeletal carbonate sands and gravels which lack mud to depths of 1500 to 3000 m plateau top sediments include a bryozoan calcareous red algal barnacle lithofacies on coarse and rocky substrates and a bivalve bryozoan lithofacies associated with particulate bottoms plateau edge sediments include a bryozoan ahermatypic co al serpulid lithofacies in areas of rugged topography and a bivalve gastropod lithofacies on sandy substrates both grading down slope into a planktic foraminiferal lithofacies by 1500 to 3000 m depth depending on locality the carbonates are dominated by a high mg calcite and or low mg calcite mineralogy with only subordinate aragonite active skeletal production is presently restricted to only about 10 percent of the plateau area principally in regions of rough sea floor topography on submarine cliff faces on bank tops and in in shore portions of the mainland shelf about these areas modern carbonates occur down to depths of 50 to 200 m below which the sediments are mainly relict and include rare glauconite redeposition of plateau derived skeletal carbonates into surrounding basins was especially active during the last glacial low sea level s it is inferred that this is the ultimate fate of the bulk of the shallow marine sediment and that the plateau top itself preserves only a thin laterally discontinuous mixed age and highly condensed sequence of quaternary temperate skeletal carbonates

discrete element modeling of progressive failure in a wide coal roadway from water rich roofs abstract progressive failure of roadway roofs is a common failure mechanism in underground coal mines especially when water rich roofs are in close proximity to the roadway in this case study at a chinese coal mine the udec voronoi method was used to investigate the process of progressive roof failure in a wide coal roadway from water rich roofs in the numerical scheme the studied domain was partitioned into polygonal blocks bonded through contacts with pre defined dimensions the parameters of polygons and contacts in the voronoi program were calibrated to rock mass properties obtained through laboratory tests based upon laboratory tests and previous research findings a time dependent strength degradation process from water absorption was assumed and implemented in the numerical modeling next the progressive failure of a roadway from water rich roofs was analyzed in detail the numerical results agreed well with field measurements and observations this method was demonstrated to reproduce the real phenomenon of roof failure in all of its complexity the numerical results revealed that the progressive failure mechanism was characterized by an initial fracturing of the roof due to strength degradation which was followed by significant dilation as fractures grew the large span of the roadway further contributed to the roof failure process the results also clearly showed that shear cracks were predominant in the roof and played a major role in the behavior of the roadway roof additionally support and excavation schemes that affect roof stability were observed

an investigation of the relationship between uniaxial compressive strength and degradation for selected rock types abstract the relationship between uniaxial compressive strength and degradation was investigated for selected rock types by using regression analyses to determine whether degradation was a useful predictor of compressive strength in addition the effects of aggregate particle size number of hammer blows during the degradation test engineering index properties petrographic characteristics and water saturation on the compressive strength degradation relationship were evaluated the results show that strong inverse relationships exist between compressive strength and degradation measured on a 9 5 4 75 mm size aggregate for sandstones and igneous metamorphic rocks but that no significant relationship exists for limestones dolomites the results also indicate a strong positive correlation between degradation and l a abrasion loss and can be used to establish a limit of allowable degradation for practical applications engineering index properties do not significantly affect the relationship between compressive strength and degradation but petrographic characteristics are important in explaining the strength and degradation behavior of the rocks studied water saturation decreases compressive strength and increases degradation to varying degrees

rhodolith assemblages from the lower tortonian carbonate ramp of menorca spain environmental and paleoclimatic implications abstract lower tortonian distally steepened carbonate ramp of menorca mostly consists of foramol and rhodalgal facies deposited in inner middle ramp ramp slope and outer ramp settings red algae are abundant from the middle ramp to the lower part of the slope and their taxonomic assemblages are clearly related to the bathymetric position melobesioids percentage increases basinward passing from 55 8 in the middle ramp to 97 in the toe of slope mastophoroids are more abundant in the middle ramp 43 1 and decrease toward deeper paleoenvironments 1 2 lithophylloids and sporolithaceans appear as accessory components from the middle ramp to slope settings the percentage of melobesioids and mastophoroids observed in the middle ramp suggest that growth of the rhodoliths started in a water depth below 10 20 m the deepest occurrence of the rhodoliths is in the ramp slope environment where the dominance of melobesioids and the low percentage of shallower water subfamily suggests a water depth range of 70 to 100 m shape and structure of rhodoliths are indicative of high energy conditions in all ramp settings and they do not reflect a decrease in hydrodynamic energy related to water depth increase these conditions are related to the presence of unidirectional currents that produced cross bedded grainstones existing in the middle ramp ramp slope and at the toe of the ramp slope settings the high percentage of mastophoroids in the shallowest environments and the presence of lithoporella and sporolithon in the coralline assemblages suggests that carbonate production took place in tropical waters

investigation of the excavation damaged zone around deep tbm tunnel using a voronoi element based explicit numerical manifold method abstract a voronoi element based explicit numerical manifold method is adopted to investigate the evolution process and failure characteristics of the excavation damaged zone around a deeply buried tbm tunnel an explicit time integration scheme of numerical manifold method is adopted as the numerical platform based on which a voronoi polygon assemblage is generated to approximate the blocky structure of the surrounding rock mass resulting from discrete fracture networks a new mathematical mesh generation method is developed to better adapt to the voronoi polygons and an excavation algorithm including both in situ stress equilibrium and tbm excavation modelling techniques is proposed to capture the mechanical response of the tbm tunnelling process with the newly developed ve enmm approach the progressive failure process of the surrounding rock mass in a headrace tunnel of yindajihuang project is simulated and the formation mechanism of the excavation damaged zone is explored simulation results show that a large extent of excavation damaged zone is easily formed in the highly fractured rock mass due to the high in situ stress in deep grounds besides relatively large convergence displacements are predicted around the tunnel surface leading to a high risk of tbm shield jamming as in the practical situation however the development of damaged zone is effectively restrained and the convergence displacements are well controlled by an early installation of the tunnel lining segments thus preventing the occurance of tbm shield jamming additional simulations are conducted to study the effects of the lateral in situ stress ratio on the excavation damaged zone it is inferred that the increase of lateral stress ratio facilitates the fracturing of the surrounding rock mass which results in a larger extent of the damaged zone and more severe squeezing deformation compared with those under lower lateral stresses

effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading a grain based universal distinct element code model was developed to generate a deformable polygonal grain like structure to simulate the microstructure of brittle rock it takes into account grain scale heterogeneity including microgeometric heterogeneity grain scale elastic heterogeneity and microcontact heterogeneity the microgeometric heterogeneity can be used to match the grain size distribution of the rock the discrete element approach is able to simulate the microheterogeneity caused by elastic variation and contact stiffness anisotropy the modeling approach was evaluated using lac du bonnet granite and a aspo diorite the microheterogeneity played an important role in controlling both the micromechanical behavior and the macroscopic response when subjected to uniaxial compression loading the crack initiation stress was found to be controlled primarily by the microscale geometric heterogeneity while the microcontact heterogeneity controlled the strength characteristics the effect of heterogeneity on the distribution and evolution of tensile stresses and associated extension cracks was also examined

the fate of foramol temperate type carbonate platforms abstract on rimmed shelves of bahamian type characterized by chlorozoan associations and typical of tropical seas carbonate production keeps pace with normal sea level rise except when rapid rise or drastic environmental changes occurs on the other hand open temperate carbonate shelves are characterized by low carbonate production of the foramol association molluscs benthic foraminifera bryozoans coralline algae etc and generally show seaward relict sediments because carbonate production cannot keep pace with normal rate of sea level change several examples of recent drowning foramol carbonate platforms e g large areas of the mediterranean sea eastern northeastern yucatan shelf as well as analogous ancient drowned foramol type carbonate platforms e g early to middle miocene of the southern apennines miami terrace may support the idea that the drowning of many ancient carbonate platforms has been favoured by their biogenic foramol sensu lato constitution because of their typically low rate of growth foramol carbonate platforms are fated to be drowned even if the sea level rise is one with which the normal growth of chlorozoan platforms can keep pace similar conditions may also occur in tropical areas where variations in environmental conditions such as the presence of cold waters changes in salinity and increased nutrients preclude the development of chlorozoan associations

nearshore temperate carbonate depositional systems lower tortonian agua amarga basin southern spain implications for carbonate sequence stratigraphy abstract the bryozoan rich lower tortonian carbonates of the agua amarga basin in southern spain province of almeria provide an example of sediments formed in a nearshore non tropical depositional setting based on data derived from logging of sections and from field mapping these lower tortonian carbonates form a depositional sequence which is subdivided into several depositional systems a lowstand systems tract which consists of volcaniclastic fan deltas and washover deposits formed on the leeward side of a basement shoal which delimited the basin towards the south a transgressive systems tract which is characterised by a landward encroachment of deposits is represented by submarine bars and dune deposits a highstand systems tract consists of progradational beach deposits owing to strong reworking and re distribution of the particles by currents and waves microfacies differentiation of the deposits in poor these tortonian non tropical carbonates display a style of deposition similar to siliciclastics suggesting that sequence stratigraphic concepts derived from tropical carbonates do not apply to non tropical carbonates

carbonate lithofacies as paleolatitude indicators problems and limitations abstract detailed study of miocene carbonates in the mediterranean region and their analogues on modern carbonate shelves in the mediterranean sea brazil and other areas reveals at least three major types of carbonate platform lithofacies in addition to the classic tropical coral reef chlorozoan lithofacies a chloralgal lithofacies similar to the chlorozoan but without hermatypic corals b rhodalgal lithofacies characterized by abundant encrusting coralline algae and c molechfor lithofacies consisting of benthic foraminifers molluscs echinoids bryozoans and barnacles these carbonate lithofacies present complex distribution patterns seemingly related primarily to latitude and depth that control water temperature although other factors e g water circulation river discharge suspended sediment controlling water salinity and temperature nutrient content light penetration etc also play important roles chloralgal and rhodalgal lithofacies can be considered two transitional terms between the two end members the chlorozoan lithofacies which characterizes shallow tropical shelves and the molechfor lithofacies which characterizes colder and or deeper areas detailed textural and sequential analysis are required for satisfactory interpretation of these lithofacies in ancient rocks

numerical observations of the failure of a laminated and jointed roof and the effective of different support schemes a case study roof failure related to laminated and jointed rock masses has been recognized as a major cause of fatalities in underground coal mines this paper presents numerical simulations of the failure of a laminated and jointed roof using the discrete element method while focusing on the initiation and propagation of and the interactions between microcracks and macroscopic fractures and the development of the associated damage stress and deformation in the laminated and jointed roof numerical modeling shows that the behaviors of bedding planes and vertical joints governed the progressive failure of the laminated and jointed roof microseismic activity corresponding to the development of microcracks in the roof intensified before major roof displacements and subsided in the later stages such activity could serve as a precursor of roof fall events the effectiveness of various support elements rock bolts metal meshes and anchor cables on the roof stability was numerically evaluated rock bolts and or anchor cables produced a banded compressive stress in the laminated roof restricting the separation of bedding planes rock bridges in the bolted roof suppressed the formation of macroscopic fractures and significantly reduced the interactions between fractures the roof skin support with a metal mesh provided confinement to the fractured roof thereby preventing fragmented rocks from falling and restricting progressive spalling between bolts the numerical simulations presented in this paper can be helpful for understanding the likely failure mechanisms of laminated and jointed roofs and for finding potential solutions

multi approach back analysis of a roof bed collapse in a mining room excavated in stratified rock roof bed deformation mechanics is a complex topic in mining practice there are a number of empirical analytical and numerical techniques that can be used to analyze and design underground excavations in stratified rock masses each has particular drawbacks however so the use of just one approach in order to obtain consistent and economic designs is not practical to deepen understanding of this topic it is useful to study real failure in mines in this paper we describe how a roof bed failure in an underground mine excavated in a stratified rock mass was back analyzed using different approaches namely the empirical stability graph method the analytical voussoir techniques and the numerical discrete element method the study enabled us to better understand the conditions of failure and to define the most significant parameters affecting the failure it has also been shown how relaxation or loss of confinement stress can play an important role in roof bed deformation

an epeiric ramp low energy cool water carbonate facies in a tertiary inland sea murray basin south australia the murray supergroup records temperate water carbonate deposition within a shallow mesotrophic oligo miocene inland sea protected from high energy waves and swells of the open ocean by a granitic archipelago at its southern margin rocks are very well preserved and exposed in nearly continuous outcrop along the river murray in south australia most facies are rich in carbonate silt contain a background assemblage of gastropods especially turritellids and infaunal bivalves and are packaged on a decimetre scale defined by firmground and hardground omission surfaces bioturbation is pervasive and overprinted resulting in rare preservation of physical sedimentary structures facies are grouped into four associations large foraminiferan bryozoan echinoid bryozoan mollusc and clay facies interpreted to represent shallow water 50 m deposition under progressively higher trophic resource levels from low mesotrophy to eutrophy and restricted marine conditions from relatively offshore to nearshore regions a large scale shift from high to low mesotrophic conditions within lower miocene strata reflects a change in climate from wet to seasonally dry conditions and highlights the influence terrestrially derived nutrients had upon this shallow land locked sea overall low trophic resource levels during periods of seasonally dry climate resulted in a deepening of the euphotic zone a widespread proliferation of foraminiferan photozoan fauna and a relatively high carbonate productivity inshore heterozoan facies became progressively muddier and restricted towards the shoreline in contrast periods of wet climate led to rising trophic resource levels resulting in a shallowing of the euphotic zone a decrease in epifaunal and seagrass cover and widespread development of a mostly heterozoan biota dominated by infaunal echinoids rates of carbonate production and accumulation were relatively low the murray basin is best described as an epeiric ramp wide facies belts developed in a shallow sea on a low angled slope reaching many hundreds of kilometres in length grainy shoal and back barrier facies were absent internally generated waves impinged the sea floor in offshore regions and because of friction along a wide and shallow sea floor created a low energy expanse of waters across the proximal ramp storms were the dominating depositional process capable of disrupting the entire sea floor

temperate skeletal carbonate sediments on scott shelf northwestren vancouver island canada abstract scott shelf 2000 km 2 centred at scott islands northwestern vancouver island is mainly shallower than 150 m topographically diversified and floored by bedrock outcrops and terrigenous lithic gravels and sands left stranded following the post glacial rise in sea level 13 000 yrs b p it lies in a zone of vigorous wind wave currents and strong tidal flows but is largely starved of modern terrigenous sediment as a consequence it is slowly accumulating a thin discontinuous blanket of clean skeletal carbonate sands and gravels admixed to varying degrees with the underlying terrigenous deposits principal skeletal contributors are infaunal bivalves on coarse sandy and gravelly substrates barnacles on low amplitude gravelly ridges bryozoans on bedrock outcrops and boulders and benthic foraminifera on fine sands in deep 100 m waters south of the scott islands living carbonate benthos are scattered and generally sparse occupying specific ecologic niches and the shelf wide rate of carbonate production is low skeletons are fragmented transported and mixed during storms and are concentrated within bedrock hollows and crevices and shallow depressions between gravel ridges where infaunal bivalves are abundant the carbonates are dominated by aragonite but otherwise the skeletal hashes are predominantly calcitic many grains and especially aragonitic ones are corroded and weakened by epilithic and endolithic bioerosion and probably also by marine and dissolution the most corroded shells have ages of only about 1000 yrs so that their preservation potential is low the character of scott shelf skeletal carbonate deposits reflects their temperate latitude cold water heritage

halimeda dominance in the coastal wedge of pietra di finale ligurian alps italy the role of trophic conditions the middle to late miocene mixed carbonate siliciclastic coastal wedge of the pietra di finale unconformably overlying the ligurian alps succession displays a carbonate portion dominated by halimeda and porites fragments that fall in the photozoan assemblages photozoan assemblages typically develop under tropical and oligotrophic conditions while hetorozoan assemblages tend to thrive in high nutrient settings the pietra di finale formation shows however that high weathering and an increase of nutrient inputs related to alpine uplift and humid climatic conditions promoted halimeda over the seagrass carbonate factory in the photic zone the successful halimeda proliferation was due to its efficient competition for nutrients especially nitrogen thus the pietra di finale formation represents an interesting counter intuitive example in which increased nutrient concentrations promoted instead of inhibited a photozoan over a seagrass related heterozoan carbonate production

sedimentology and palaeoenvironment of the southeast sicilian tertiary platform carbonates abstract a thick succession of shelf and shelf slope carbonates is developed in southeastern sicily sedimentological aspects of the oligocene to tortonian sequence including distribution and palaeoenvironmental factors are considered a new formation and four new members are proposed in the upper part of the succession the region comprises a western half typically exhibiting the principal deeper water planktonic facies including marls and an eastern area displaying typically inner shelf carbonates and an attenuated succession coralline algal limestones and calcarenites are more typical of this latter region but there are also some volcanic intercalations an attempt is made to relate the hyblean succession to that of the maltese islands which lie at the southern end of this tertiary carbonate platform

mechanical degradation of emplacement drifts at yucca mountain a modeling case study part i nonlithophysal rock abstract this paper outlines rock mechanics investigations associated with mechanical degradation of planned emplacement drifts at yucca mountain which is the designated site for the proposed us high level nuclear waste repository the welded tuff emplacement horizon consists of two groups of rock with distinct engineering properties nonlithophysal and lithophysal units based on the relative proportion of lithophysal cavities the term lithophysal refers to hollow bubble like cavities in volcanic rock that are surrounded by a porous rim formed by fine grained alkali feldspar quartz and other minerals lithophysae are typically a few centimeters to a few decimeters in diameter part i of the paper concentrated on the degradation behavior of the generally hard strong and fractured nonlithophysal rock part ii concentrates on the host rock in the lithophysal units lithophysal rock is characterized by lithophysal cavities interconnected by fracturing fracture sets are not as clearly defined as in the nonlithophysal rock the rock mass porosity in the lithophysal units has been shown to be the primary physical factor that governs elastic and strength properties the degradation behavior of the tunnels in the lithophysal rock is controlled by the spalling of the surrounding rock mass a discontinuum material model has been developed to represent the drift scale rock mass properties in which slip and separation of contacting rock blocks can be estimated two dimensional discontinuum analyses were developed with the consideration of in situ thermal and seismic loads time dependent degradation was also considered in this study field and laboratory data and numerical analyses are well integrated to provide a solution for the unique problem of modeling drift degradation

carbonate deposition in restricted basins a pliocene case study from the central mediterranean northwestern apennines italy abstract carbonate depositional models are often informed by the study of platforms of good lateral continuity and sizable thickness because of their significance in petroleum geology however spatially restricted and more ephemeral carbonate accumulations can be an important but frequently overlooked component of otherwise siliciclastic dominated or mixed carbonate siliciclastic systems pliocene successions of tuscany and the tyrrhenian shelf northern apennines italy record a regional pulse of nontropical carbonate deposition across several restricted basins that has not yet been precisely constrained in its genesis and correlation this study investigates the stratigraphic expression of these carbonates to extract general aspects applicable to carbonate sedimentation across tectonically structured and physiographically complex shelves analyses of the extension composition facies and sequence stratigraphic architecture of the studied piacenzian carbonate units are complemented by new biostratigraphic and magnetostratigraphic data which document the slightly diachronous development of the carbonates within mediterranean planktonic foraminifera subzones mpl4b and mpl5a and magnetic polarity chron c2an the carbonate units are part of a regionally defined tectonically controlled sequence and represent the first transgressive unit overlying the basal sequence boundary but are also found in the regressive portion of the sequence collectively the units document the establishment of a shallow marine carbonate factory dominated by calcareous red algae the larger benthic foraminifer amphistegina and heterozoan skeletal components along the margins of a complex archipelago like coastal domain a review of the studied successions and other examples from the literature indicates that carbonate accumulations in settings with varied coastal physiography and active partitioning of depocenters are generally characterized by a spatial discontinuity b an overall skeletal association consistent across separate basins but with local variability in dominant skeletal components c preferential accumulation along basin margins or over isolated structural highs not in direct proximity to a hinterland with major drainage systems d predominance of low to moderate energy facies e preferential onset of deposition during transgression with possible development of mixed carbonate siliciclastic facies and f differing internal stratigraphic architecture tied to the specific subsidence and uplift history of coeval individual basins these observations built upon the study of mid piacenzian carbonate units from the central mediterranean contribute to the refinement of carbonate facies models and their application in the fields of sequence stratigraphy and basin analysis

strength reduction on saturation of coal and coal measures rocks with implications for coal pillar strength coal and associated coal measures rocks including shales mudstones and sandstones may lose significant strength on water saturation due to the absorption of water stress corrosion or mineralogical changes to the clays within the rock matrix as most coal seams are natural aquifers water ingress into underground mine workings is common and is typically controlled during mining by dewatering pumps after a mine has closed unless ongoing pumping is maintained workings will flood and coal pillars and the pillar roof and floor foundations will revert to fully saturated conditions this paper reports on a study of how flooding effects pillar strength in an abandoned coal mine in queensland australia the reduction in strength of coal and coal measures rocks between unsaturated and saturated water moisture contents has been quantified through physical testing these strength data along with the distribution of lithologies in a coal pillar from the mine were used as inputs for numerical modelling of the strength reduction of a coal pillar on water saturation it was found that the modelled pillar strength reduction could be estimated by the average strength reduction of all the lithological components of the pillar weighted by the thickness of each lithology

submarine lobes and feeder channels of redeposited temperate carbonate and mixed siliciclastic carbonate platform deposits vera basin almeria southern spain temperate carbonates and mixed siliciclastics carbonates of upper tortonian age were deposited on a narrow platform along the southeastern margin of the sierra de los filabres on the western side of the vera basin the temperate carbonates were unlithified or were only weakly lithified on the seafloor and so were easily prone to synsedimentary removal part of the shelf sediments were eroded reworked and redeposited in submarine lobes up to 40 m thick and 1 km wide the lobes consist of turbiditic carbonates calcarenites and calcirudites and mixed siliciclastics carbonates which contain up to 30 siliciclasts derived from the sierra de los filabres to the northwest and abundant bioclasts of coralline algae bivalves and bryozoans in the inner platform the feeder channels of the lobes cross cut beach and shoal deposits and are filled by strings of debris flow conglomerates up to 3 m thick and a few metres wide these channels presumably developed as the continuation of river courses entering the sea further towards the outer platform they pass into large channels up to several hundred metres wide and 20 m deep steeply cutting into the horizontally bedded strata of the platform significant quantities of platform sediment were removed by erosion during their excavation once abandoned they were filled by new platform sediments further towards the basin the channels associated with the lobes exhibit lateral accretion and internal cut and fill structures and are intercalated between hemipelagic deposits the channel filling sediments are in this latter case coarse grained carbonates and mixed siliciclastics carbonates lobe development concentrated first at cortijo grande on the western side of the

the influence of terrestrial run off on marine biotic communities an example from a thrust top carbonate ramp upper pennsylvanian foreland basin picos de europa nw spain article i nfo high diversity marine biotic communities characterize the lower kasimovian upper pennsylvanian carbonates of the las llacerias formation in the andara massif picos de europa province cantabrian mountains spain the carbonates accumulated on a small thrust top ramp system within the shallow low energy and euphotic realms biotic communities were characterized by abundant photozoans calcareous algae and cyanobacteria and heterozoans including filter and suspension feeders calcareous and siliceous sponges bryozoans brachiopods crinoids diverse other metazoans rugose solitary and colonial corals tabulate corals bivalves gastropods and echinoids benthic foraminifers including very abundant small incrusting tubiforms and conspicuous swarms of cement filled spheres calcispheres or penella small sized buildups of chaetetid sponges syringoporids branching rugose corals anthracoporella and phylloid algae commonly developed in these shallow water environments meanwhile mud mounds formed at greater water depths mostly below the lower limit of the phothic zone the occurrence of such diverse biotic communities and the grain composition of the shallow water deposits not recorded in the platform top successions of the antecedent bashkirian moscovian carbonate shelf valdeteja and picos de europa formations are interpreted as linked to increased nutrient levels mesotrophic to mildly eutrophic conditions in the actual sea surface water the nutrients are inferred to have resulted from land derived fluxes from the rivers draining the adjacent growing variscan orogenic chain nutrients were subsequently transported into the narrowed marine shallowing foreland basin located in the eastern side of pangea within the palaeoequatorial humid belt comparison to the pennsylvanian auernig group in the carnic alps allows the discrimination between the influence of land derived versus upwelling derived nutrients providing a useful tool in the interpretation of biotic assemblages in the fossil rock record

a preliminary analysis of failure mechanisms in karst and man made underground caves in southern italy abstract natural and anthropogenic caves may represent a potential hazard for the built environment due to the occurrence of instability within caves that may propagate upward and eventually reach the ground surface inducing the occurrence of sinkholes in particular when caves are at shallow depth the effects at the ground surface may be extremely severe apulia region southern italy hosts many sites where hazard associated with sinkholes is very serious due to presence of both natural karst caves and anthropogenic cavities the latter being mostly represented by underground quarries the pliocene pleistocene calcarenite a typical soft rock was extensively quarried underground by digging long and complex networks of tunnels with time these underground activities have progressively been abandoned and their memory lost so that many apulian towns are nowadays located just above the caves due to urban expansion in the last decades therefore a remarkable risk exists for society which should not be left uninvestigated the present contribution deals with the analysis of the most representative failure mechanisms observed in the field for such underground instability processes and the factors that seem to influence the processes as for example those causing weathering of the rock and the consequent degradation of its physical and mechanical properties aimed at exploring the progression of instability of the cavities numerical analyses have been developed by using both the finite element method for geological settings represented by continuous soft rock mass and the distinct element method for jointed rock mass conditions both the effects of local instability processes occurring underground and the effects of the progressive enlargement of the caves on the overall stability of the rock mass have been investigated along with the consequent failure mechanisms in particular degradation processes of the rock mass as a consequence of wetting and weathering phenomena in the areas surrounding the caves have been simulated the results obtained from the numerical simulations have then been compared with what has been observed during field surveys and a satisfactory agreement between the numerical simulations and the instability processes as detected in situ has been noticed

environmental factors influencing skeletal grain sediment associations a critical review of miocene examples from the western mediterranean the presence of foramol rhodalgal and bryomol skeletal grain associations in ancient shallow marine limestones is commonly interpreted as evidence for non tropical palaeoclimate despite temperature being only one of several factors influencing skeletal grain associations such interpretations neglect the multitude of factors other than temperature that influence carbonate producing biota these include nutrients water energy water transparency depth of the sea floor salinity oxygen ca2 and co2 concentrations mg ca ratio alkalinity substrate requirements competitive displacement as well as biological and evolutionary trends this uniformitarian approach also disregards the probability that conditions of present day biological systems may not be representative of past conditions of analogous systems here the importance of considering these other factors is illustrated through two examples of carbonate platforms in the western mediterranean these platforms are dominated by foramol rhodalgal and bryomol associations of miocene age in spite of having formed in tropical conditions the platforms discussed are 1 the lower tortonian ramp on menorca balearic islands and 2 the lower middle miocene ramps of the central apennines italy evidence for tropical conditions in the mediterranean during the period of growth of these platforms is provided by species of red algae and larger foraminifera by data from coeval continental basins and by global oxygen isotope data

water weakening behavior of hawkesbury sandstone in brittle regime abstract this paper investigates the effect of water on the mechanical behavior of intact hawkesbury sandstone a massive rock formation in sydney australia two sets of cylindrical samples air dried and water saturated were tested under the confining pressures of 4 10 18 and 25 mpa water saturated samples were tested under undrained conditions with initial pore water pressures of 1 4 7 2 and 10 mpa respectively initial pore water pressure was observed to increase with increasing deviatoric stress during undrained tests and the maximum induced pore water pressure was observed to increase with increasing effective confining pressure peak effective strength showed an increasing trend with increasing confining pressure for both sample sets and the strengths of dry samples were always greater peak strength drops of 13 36 25 27 34 70 and 38 12 were observed due to water at the confining pressures of 4 10 18 and 25 mpa respectively results for the residual strength of tested samples displayed that it increased with increasing confining pressure for both sample sets the volumetric strain response revealed that the volume reduction due to compaction increases with increasing confining pressure and dilatancy related volume increase close to sample failure was not significant at higher confining pressures for both sample sets the samples tested under dry conditions showed a considerably higher volume reduction by compaction than that for the samples tested under undrained conditions analysis of failure mechanisms indicated that all samples failed mainly by shear localization where the angle of the failure plane measured from the minor principal stress direction was varied from c 55 to c 45 for dry samples and from c 50 to c 40 for the samples tested under undrained conditions at 4 and 25 mpa confining pressures respectively fracture propagation behavior was studied using an acoustic emission detection system and the results demonstrated that the micro crack initiation occurred very close to the failure stress under low confining pressures leading to a more brittle sudden failure w hereas under higher confining pressures it occurred relatively earlier compared to the failure stress showing more quasi brittle characteristics

orbital forcing recorded in subtidal cycles from a lower miocene siliciclastic carbonate ramp system central italy metre scale siliciclastic carbonate cycles are the basic depositional motif of the lower miocene guadagnolo formation outcropping in the central apennines the mechanisms which formed the mixed lithology cycles are still a matter of debate the mixed siliciclastic carbonate system discussed in this paper provides a new case study to illustrate the role of orbital forcing in controlling the facies evolution and cyclic stacking of small scale sequences deposited on the outer sector of a ramp two sections are discussed that display mixed siliciclastics and carbonates arranged in upward shallowing cycles each cycle shows an upward decrease in the terrigenous input and a parallel increase in benthic fauna time series analyses indicate the cyclic carbonate terrigenous pattern to be largely controlled by orbital forcing in the milankovitch frequency band coupling of climate change and sea level fluctuations in tune with orbital cycles are proposed as driving mechanisms

paleoecology and dynamics of coralline dominated facies during a pleistocene transgressive regressive cycle capo colonna marine terrace southern italy abstract the upper pleistocene deposits of capo colonna marine terrace calabria southern italy contain a volumetrically important record of red algal facies developed during a transgressive regressive cycle well expressed along a nearshore offshore transect this setting presents an ideal opportunity for the acquisition and interpretation of paleoecological information on coralline dominated deposits and their response to relative sea level changes the capo colonna deposits include rigid build ups rhodolith accumulations and a maerl bed the build ups identified as a fossil example of the present day mediterranean coralligenous are primarily formed by mesophyllum alternans and subordinately by lithophyllum stictaeformae titanoderma pustulatum and lithothamnion sp rarely alternating with encrusting bryozoans fruticose praline rhodoliths occur in a packstone bed up to 160 cm thick 2 to 5 cm in size and composed of lithothamnion sp mesophyllum sp and rare t pustulatum the maerl bed is about 60 cm thick and laterally continuous for several tens of meters and consists of interlocked unattached red algal branches of the species lithothamnion corallioides phymatolithon sp lithophyllum sp and lithothamnion sp the lateral distribution along the shelf profile of different red algal facies was influenced by transgressive regressive trends while praline rhodoliths and the maerl bed developed on mobile substrates mostly during the early highstand respectively at intermediate and distal shelf sectors the mesophyllum dominated coralligenous build ups continued to grow for most of the regressive phase progressively occupying all the preserved paleoshelf profile during sea level fall and resulting in a characteristic ecological vertical succession of crustose algae facies in the distal segment of the transect differences in substrate types determined variability in the coralligenous morphologies with dome to mushroom shapes starting from discontinuous blocks of a basal conglomerate and we elongated platforms developing from a hardground and from rhodolith beds eventually the development of red algal deposits became in itself the dominant control on substrate type the red algae rich deposits of capo colonna marine terrace not only suggest a relationship between available substrate and geomorphological expression of the coralligenous build ups but also provide a framework for the paleoecological interpretation of other neogene and quaternary rhodalgal deposits from the mediterranean region

sedimentology and palaeoecology of a miocene coralline algal biostrome from the maltese islands abstract a large coralline algal biostrome 20 km 5 km 16 m thick is well exposed in western malta and eastern gozo the biostrome is composed of limestones largely constructed by in situ coralline algae or transported algal debris some sediments are dominated by rhodoliths and others by crustose coralline frameworks six facies are distinguished crustose algal marl crustose algal wackestone rhodolith pavement algal branch packstone crustose pavement and algal crust packstone each facies is characterised by different rhodolith morphologies and coralline crusts which are constructed mainly bymesophyllum commune the coralline morphogenesis is related to the palaeoenvironmental conditions the biostrome is thought to have developed from a series of relic sand ridges to form a low relief platform of moderate depths containing a mosaic of sedimentary facies the sequence is affected by growth faulting which divides the biostrome into eight units

kinetics of melting in peridotite from volume strain measurements abstract partial melting in the earth s mantle involves a combination of processes such as ionic diffusion and solid liquid transition these processes yield an array of characteristic times for the melting kinetics both the magnitude and time constant of melt induced volume strain affect seismic velocity attenuation and buoyancy in situ monitoring of samples during melting are enabled by multi anvil high pressure devices coupled with synchrotron x ray radiation in this study the volume strain induced in a sample from melting is measured as a function of time using x ray images we find a doubling of the effective thermal expansion for only 2 melt both from our data and from thermodynamic models of peridotite the characteristic time of melting is determined to be less than one second these findings have a direct impact on the effect of melting on seismic velocities

numerical simulation of progressive rock failure and associated seismicity in this paper a numerical approach to modeling progressive failure leading to collapse in rock and associated seismicity is reported in the first part a newly developed numerical code rfpaz rock failure process analysis is introduced the program allows modeling of the observed evolution of damage and associated seismic events due to progressive failure leading to collapse in brittle rock there are three features distinguishing the approach from conventional numerical methods such as fem 1 by introducing heterogeneity of rock parameters into the model rfpaz can simulate non linear behavior in rock using a linear method 2 by introducing elastic modulus reduction for failed elements rfpa2d can process discontinuum mechanics problems by a continuum mechanics method and 3 by recording the event rate of failed elements the seismicities associated with the progressive failure in rock can be simulated in the second part of the paper the applications of rfpa2d in simulating geological process and in solving mining design problems are illustrated numerical simulation of a fault initiation process indicates that some of the important phenomena such as coalescence of microfracture the nucleation and growth of crack clusters fault initiation and development elastic rebound dilatation uplift and seismic behavior etc can be simulated with this numerical code the simulation of progressive failure leading to collapse in underground openings demonstrates the capacity of this code in solving mining design problems