metre scale cycles in shallow water carbonate successions milankovitch and stochastic origins metre scale cycles are a common feature in precambrian and phanerozoic shallow water carbonate successions and astronomically forced changes in sea level milankovitch cycles may have been an important driver controlling their deposition nevertheless the degree to which potentially low amplitude astronomically paced sea level oscillations may have controlled carbonate accumulation in deep time is unclear in this study a stochastic model of carbonate accumulation demonstrates how metre scale exposure bound sequences can be generated under conditions of random sea level change these sequences have characteristic durations close to milankovitch cycles despite the absence of any astronomical control on their formation metre scale sequences with sub milankovitch millennial scale durations can also be generated by the model potentially shedding light on the origin of sub milankovitch sequences such as those recorded on the middle triassic latemar platform of northern italy sensitivity tests demonstrate how shallow water carbonates may be very sensitive to weak i e low amplitude astronomically forced sea level oscillations notably strong statistical evidence p 0 01 for astronomical cycles can be preserved in modelled successions even when astronomical forcing contributes 1 of the sea level variance on million year timescales taken together metre scale cycles with milankovitch scale durations in ancient carbonate successions may reveal very little about the amplitude or even the existence of astronomical forcing as a sea level driver

the nature of shallow water carbonate lithofacies thickness distributions carbonate lithofacies thickness distributions are of fundamental importance to understanding shallow water carbonate deposystems because they record evidence of the lateral distribution and migration of lithofacies elements as well as evidence for the various other intrinsic and extrinsic controls on stratal geometries and accumulation rates previous analyses of lithofacies thickness data led to the suggestion that exponential distributions are ubiquitous in the ancient record this has been interpreted to indicate deposition by stochastic poisson process lithofacies mosaics to further investigate these ideas statistical analysis of 56 outcrop and core examples was performed the kolmogorov smirnov test was used to identify the degree to which measured lithofacies thicknesses are well represented by a theoretical exponential distribution results from this analysis show that 16 of the 56 examples can be confidently shown to be exponential while 28 are very probably not exponential this indicates that stochastic poisson processes are a plausible explanation for many carbonate successions but they do not explain all of those tested here suggesting that other non poisson processes either stochastic or deterministic in nature or both must also be important thus lithofacies planform geometries and the processes controlling vertical stacking in ancient carbonate platform top deposystems were likely more diverse than has been suggested requiring significant further quantitative analysis and numerical forward modeling to properly understand

seismic and geologic characteristics of drowning events on carbonate platforms carbonate platform drowning events are recorded in upper jurassic lower cretaceous carbonates of the baltimore canyon area offshore united states east coast and lower miocene carbonates of the pearl river mouth basin offshore people s republic of china cursory examination of seismic data from both areas would indicate that the platforms fit the classic definition of a drowning unconformity however detailed lithologic and paleontologic data indicate that the depositional erosional hiatuses vary widely in each area from 0 25 m y in the baltimore canyon area to a condensed section with no hiatus in the pearl river mouth basin the sedimentary sequence produced during drowning the drowning sequence in both areas is gradational with underlying shallow platform carbo ates and in some places overlying deeper marine limestones and shales the generalized facies models proposed for drowning events suggest that they may appear as instantaneous or gradual changes in geologic and seismic data however high resolution seismic data across the baltimore canyon and pearl river mouth basins show that some drowning sequences may be masked on conventionally processed seismic sections because of this resolution problem a distinction should be made between seismically and geologically defined unconformity surfaces the geologic characteristics of drowning events on carbonate platforms include a gradational lower and sometimes upper contact chemical sedimentation glauconite phosphate open marine shelf sediments and a variable hiatus at the upper boundary late growth shelf margin reefs also can be a diagnostic feature of drowned platforms seismic characteristics include horizontal to sub horizontal basinal marine onlap basin parallel reflector continuity above the carbonate sequence boundary and downlap of later highstand units evidence from platforms adjacent to continental margins baltimore canyon indicates that drowning occurs in a step wise fashion advancing more or less symmetrically across the platform from shelf to nearshore environments data from isolated open ocean atolls pearl river mouth basin indicate that they respond differently to drowning showing an asymmetric decrease in shallow platform environments as drowning occurs proper recognition by a geoscientist of the seismic and geologic characteristics of drowning events can lead to better reservoir and seal estimates and the correct reconstruction of the depositional tectonic and eustatic histories of an area

chalcophile element geochemistry and petrogenesis of high ti and low ti magmas in the permian emeishan large igneous province sw china sulfide poor mafic layered intrusions sills dykes and lava flows in the funing region sw china are part of the 260 ma emeishan large igneous province they belong to either a high ti group tio2 1 6 4 4 wt with elevated ti y ratios 351 1 018 or a low ti group tio2 1 low y pd pm ratios 0 2 7 1 and nearly constant cu pd pm ratios 1 5 3 8 the even and parallel chalcophile element patterns of the high pge low ti subgroup rocks are likely a result of olivine dominated fractionation under s undersaturated condition the low pge low ti group rocks have low mgo 4 5 8 9 wt and very poor pge pt pd 0 5 1 6 ppb ir 0 004 0 02 ppb with low cu zr ratios 0 1 0 5 high y pd pm 26 70 and variable cu pd pm ratios 2 8 14 the trough like chalcophile element patterns of the low pge low ti subgroup rocks indicate that the magmas were sulfide saturation and sulfide melts were extracted from the magmas the extracted sulfide melts might be potential ni cu sulfide ores at depth in the funing region

exxon global cycle chart an event for every occasion the basic premise of the recent exxon cycle chart that there exists a globally correlatable suite of third order eustatic cycles remains unproven many of the tests of this premise are based on circular reasoning the implied precision of the exxon global cycle chart is not supportable because it is greater than that of the best available chronostratigraphic techniques such as those used to construct the global standard time scale correlations of new stratigraphic sections with the exxon chart will almost always succeed because there are so many exxon sequence boundary events from which to choose this is demonstrated by the use of four synthetic sections constructed from tables of random numbers a minimum of 77 successful correlations of random events with the exxon chart was achieved the existing cycle chart represents an amalgam of regional and local tectonic events and probably also includes unrecognized miscorrelations it is of questionable value as an independent standard of geologic time

recurrent hierarchical patterns and the fractal distribution of fossil localities understanding the spatial structure of fossil localities is critical for interpreting earth system processes based on their geographic distribution coordinates of marine and terrestrial sites in the conterminous united states for 17 time bins were analyzed using point pattern statistics lacunarity analysis shows that the spatial distributions of sites are fractal for almost every studied interval indicating that clumping of localities occurs at multiple scales random hierarchical multiplicative processes provide a theoretical null model for the distribution of collecting sites consistent with their occurrence being a complex product of numerous biological geological and anthropogenic processes acting at many spatial and temporal scales mechanistic models for the formation preservation and exposure of fossil localities and other geologic entities can be tested using point pattern and related spatial statistics

simplified process modeling of river avulsion and alluvial architecture connecting models and field data abstract modeling is an invaluable tool for studying sedimentary basin filling and for understanding depositional processes with long recurrence intervals including channel avulsion simplified modeling approaches such as cellular models and process analogue experiments are particularly useful for efficiently exploring alternative hypotheses and evaluating first order controls on river avulsion and alluvial architecture here we review the history and current state of the art in simplified avulsion and alluvial architecture models with a particular focus on how results and insights from these models can be incorporated into field and subsurface studies and vice versa simplified avulsion and alluvial architecture models have proliferated in the past decade providing a wide variety of models to serve as a basis for future coupled field modeling studies we compare features of leading models and discuss avenues for effectively pairing model capabilities with hypotheses and field data outstanding questions highlighted by recent modeling efforts include 1 what thresholds control avulsion initiation in different systems 2 how do floodplain processes and topography influence avulsion dynamics and alluvial architecture 3 what factors determine where avulsion channels stabilize answering these questions will require targeted modeling efforts coupled to data from ancient systems hence our model comparison emphasizes features that can be used to choose or design fit for purpose models and we outline how quantitative data useful for model selection and validation can be obtained from modern systems and ancient deposits matching model goals with targeted questions and model parameters and predictions with quantitative field data will help tighten communication between field and model oriented sedimentary geologists facilitating advances in our understanding of river avulsion and alluvial architecture

the devonian of the parana basin brazil sequence stratigraphy paleogeography and sw gondwana interregional correlations abstract the devonian period is characterized by an overall mean sea level higher than is observed today this pattern is recognized in several basins worldwide and permitted for example the flooding of the rheic ocean through sw gondwana s cratonic domain nonetheless this flooding was not purely eustatic the ordovician devonian geodynamic famatinian episode also played its role this tectonic eustatic interplay favored shallow marine deposition recorded in several sw gondwana basins such as the parana basin in brazil even so the evolution of the parana basin through the devonian and the factors responsible for the accommodation space remain speculative which leads to bias regarding the correlation of transgressive regressive events in sw gondwana this work aims by integrating outcrop and subsurface data to provide a basin scale stratigraphic framework and a paleogeographical reconstruction of the ponta grossa early devonian and sao domingos formations middle to late devonian of the parana basin it also correlates the studied interval with adjacent basins to identify the impact of tectonic and eustatic processes on the evolution of sw gondwana tectono sedimentary cycles we identified two 2nd order transgressive regressive sequences that correspond to the lithostratigraphic occurrence of ponta grossa and sao domingos formations respectively and whose maximum transgressive and regressive surfaces and high hierarchy unconformities are traceable through adjacent basins the ponta grossa sao domingos boundary also delineates an important tectonic event associated with far field stresses probably caused by precordilleran orogeny related phenomena the ponta grossa and sao domingos formations share several similarities with coeval strata in sw gondwana basins indicating that they can be extrapolated and correlated to contemporaneous processes of interregional scale the first namely precordilleran i early devonian was dominated by tectonics and encompasses the ponta grossa and las pavas composite sequence set the second precordilleran ii middle to late devonian was mostly eustatic and encompasses sao domingos and aguarave composite sequence sets both intervals are part of the famatinian geodynamic cycle

what is the use of the history of geology to a practicing geologist the propaedeutical case of stratigraphy abstracta practicing geologist can benefit from the history of geology professionally in two main ways by learning about past mistakes so as not to repeat them and by finding out about different ways to discovery in this article i discuss some aspects of the history of stratigraphy and point out that the concept of a stratum has shoehorned geologists into thinking time and rock equivalent which has led to some serious misinterpretations of geological phenomena such as the timing of orogenic events and the charting of sea level changes i call this the tyranny of strata the very name of stratigraphy comes from strata but what it does is simply deduce temporal relations from spatial relations of rock bodies including fossils by making certain assumptions about processes that is invoking inevitably a hypothetical step what we have learned from looking at the history of geology is that empirical stratal correlation even when well controlled by index fossils can never yield perfect temporal cor

quantifying the hierarchical organization of compensation in submarine fans using surface statistics abstract stratigraphy is often interpreted within hierarchical or scale dependent frameworks that subdivide deposits based on distinct jumps in characteristics such as duration of deposition or scale while the interpretation is logically valid few studies quantitatively demonstrate that the jumps exist rather recent work has quantitatively shown some characteristics of stratigraphy to be fractal or scale invariant compensational stacking the tendency for sediment transport systems to preferentially fill topographic lows is a concept widely used in stratigraphic interpretation here we use the compensation index a metric that quantifies the strength of compensational stacking in sedimentary deposits to describe the architecture of stratigraphy exposed in outcrops of submarine fan strata in the carboniferous ross sandstone representing contrasting architectural styles 1 predominantly lobe elements and 2 predominantly channel elements in both datasets the stratigraphic architecture is classified into hierarchical classes of beds stories and elements results are the following first at both sites we document statistically significant increases in the strength of compensation across larger hierarchical levels supporting the use of hierarchical interpretations of stratigraphy it is therefore plausible for some characteristics of sedimentary systems to be hierarchical and others to be fractal second we document that lobe elements stack more compensationally than channel elements we interpret this pattern to document that compensation increases along a longitudinal transect through this distributive submarine fan

power spectrum of sea level change over fifteen decades of frequency 1 the power spectrum of relative sea level change has been estimated over more than 15 orders of magnitude in frequency from a frequency of 1 591 ma to a frequency of 1 5 s although there are still regions of the spectrum where data sampling and duration do not allow the power to be calculated most notably between periods of 100 1000 years the general shape of the spectrum is that in which the power depends on the square of the reciprocal frequency apart from periods between 1 and 100 years where the power spectrum falls off less steeply with increasing frequency a spectrum in which power depends on reciprocal frequency squared is the same spectrum as that calculated from a random walk signal of finite length there are some causes that have defined frequencies such as those associated with tides and the milankovitch cycles of the ice ages but there is also a continuum of relative sea level change that requires other causes the implications of this are discussed in the light of global change and heating of the lithosphere from the bottom

stratal thickness frequencies and the prevalence of orderedness in stratigraphic sequences assuming the existence of discernable hierarchies in the thickness and or temporal recurrence of stratal units within sedimentary sequences has become an increasingly important axiom of sequence and cyclostratigraphic studies and multiple orders of stratigraphic cyclicity are now commonly associated with inferred durations and magnitudes of rhythmic variation in global sea level beyond the desire to establish an informal nomenclature relating stratigraphic thickness to periodicity of eustatic change an assumption of stratigraphic orderedness also supports the inference that groups of sedimentary units with distinct modal dimensions in fact do occur with some generally distinct frequency in stratigraphic sequences in contrast to such perceived patterns of stratigraphic order many groupings of sedimentary units exhibit lognormal frequency distributions wherein most of the population has an exponentially increasing frequency of occurrence with linearly decreasing class size such thickness distributions

depositional facies and aqueous solid geochemistry of travertine depositing hot springs angel terrace mammoth hot springs yellowstone national park u s a petrographic and geochemical analyses of travertine de positing hot springs at angel terrace mammoth hot springs yellow stone national park have been used to define five depositional facies along the spring drainage system spring waters are expelled in the vent facies at 71 to 73 8c and precipitate mounded travertine composed of aragonite needle botryoids the apron and channel facies 43 728c is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide oxidizing aquificales bacteria the travertine of the pond facies 30 62 8c varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures calcite ice sheets calcified bubbles and aggregates of aragonite needles fuzzy dumbbells pre cipitate at the air water interface and settle to pond floors the prox imal slope facies 28 54 8c which forms the margins of terracette pools is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face finally the distal slope facies 28 30 8c is composed of calcite spherules and calcite feather crys tals despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization the com positions of spring water and travertine predominantly reflect abiotic physical and chemical processes vigorous co 2 degassing causes a 12 unit increase in spring water ph as well as rayleigh type covariations between the concentration of dissolved inorganic carbon and corre sponding d 13 c travertine d 13 c and d 18 o are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher temperature 50 738c depositional facies conversely

ordered hierarchy versus scale invariance in sequence stratigraphy sequence stratigraphy has been applied in a wide range of scales of time and space from decimeter thick layers formed within hours to kilometer thick basin fills formed during hundreds of millions of years the traditional approach to practice sequence stratigraphy in this wide range of scales is to subdivide the sediment piles into an ordered hierarchy of sequence cycles of different duration and different architecture an alternative are scale invariant models with fractal characteristics published data confirm two predictions of the ordered hierarchy model sequences of very short duration 200 106 years are symmetrical transgressive regressive cycles however the sequence record in the range of 1 104 200 106 years the principal domain of sequence stratigraphy shows a rather irregular succession of sequences with variable symmetry and bounded by flooding surfaces or exposure surfaces for these time scales scale invariant models are a good first approximation particularly because the evidence for scale invariance and randomness in the stratigraphic record is strong frequency spectra of sea level change as well as rates of sedimentation and rates of accommodation change plotted against length of observation span show basic trends indistinguishable from random walk these trends combined with scale invariant sequence models may be the most efficient tools for across the board predictions on sequences and for locating islands of order in the sequence record

architecture and growth history of a miocene carbonate platform from 3d seismic reflection data luconia province offshore sarawak malaysia using 3d seismic reflection data and wireline logs we reconstruct in detail the architecture and growth history of a miocene carbonate platform in the luconia province offshore sarawak malaysia platform growth started in the late oligocene to early miocene by coalescence of isolated patch reefs the growth history includes phases of progradation backstepping and occasional collapsing of platform flanks guided by syndepositional faulting the most pronounced seismic reflections in the platform correspond to flooding events thin transgressive systems tracts subaerial exposure preceding the flooding could be demonstrated in only one case platform growth was terminated by gradual submergence drowning indicated by smooth concentric seismic reflectors forming a convex mound

forcing factors of the magnetic susceptibility signal in lagoonal and subtidal depositional cycles from the zachelmie section eifelian holy cross mountains poland eifelian dolomites in the zacheomie quarry exhibit metre scale depositional cyclicity both in the lower lagoonal part of the section and in the upper shallow subtidal portion magnetic properties were studied in 30 samples at c 1 m intervals including magnetic susceptibility ms and anhysteretic and isothermal remanent magnetization the rock magnetic parameters are com pared with the results of thin section study and elemental chemistry the forcing factors driving the ms pattern are identified the ms signal is mostly related to a finely dispersed hematite controlled by terrigenous input magnetite plays a subordinate role and it is confined to less terrigenous hor izons relatively enriched in uranium and phosphorus results of high resolution c 8 cm intervals ms field measurements show a good correlation with depositional shallowing upwards cycles especially in the lagoonal part of the section where variations of rock magnetic properties and geo chemical redox and productivity indices are very small high ms values occur in the bottom part of the cycles and they decrease upwards time series analyses of the ms signal reveal the domi nance of c 1 7 m cycles grouped into c 10 m bundles the former cycles probably reflect preces sion driven changes in monsoonal intensity whereas the latter may have been controlled by 100 kyr eccentricity

stress field in the ryukyu kyushu wadati benioff zone by inversion of earthquake focal mechanisms abstract the study addresses the space distribution of the stress field in the kyushu ryukyu wadati benioff zone based on homogeneous data of earthquake focal mechanisms and the inverse technique by gephart and forsyth j geophys res 89 1984 9305 the used data set consists of 148 harvard cmt solutions and 22 earthquake focal mechanisms listed in previous studies the stress field parameters are determined for 0 40 41 100 and h 100 km depth ranges the top 100 km layer of the wadati benioff zone wbz is characterized by strike normal maximum compression 1 and steeper than the slab minimum compression 3 the last indicating for unbalanced slab pull force the tokara channel divides the subduction into two parts of different stress regime at depth greater than 100 km to the south of the channel the slab is under slab parallel 1 and slab normal 3 while its northern part beneath kyushu is under slab parallel extension and slab normal compression the results of recent studies on the regional velocity structure and geochemistry of the volcanic lava indicate that the most plausible reason for the observed stress field difference below 100 km in the northern and rest part of the arc is the presence of hot low viscosity upper mantle west of kyushu the results of this study indicate that the forces involved in the contemporary subduction dynamics in the ryukyu kyushu wadati benioff zone are related to the convergence between the philippine sea plate and the eurasian plate the trench suction force slab pull the slab anchor force and in the southern central part of the arc mantle resistance

parasequences allostratigraphic misfits in sequence stratigraphy abstract parasequences were introduced as the building blocks of seismic scale systems tracts in the context of low resolution seismic stratigraphy pitfalls of this concept relate to the definition of parasequence boundaries as lithological discontinuities that mark episodes of abrupt water deepening with this general meaning flooding surfaces may be facies contacts within transgressive deposits or may coincide with different types of sequence stratigraphic surfaces maximum regressive transgressive ravinement or maximum flooding in all cases flooding surfaces are allostratigraphic contacts restricted to coastal and shallow water settings where evidence of abrupt water deepening can be demonstrated flooding surfaces may also be absent from the shallow water systems where conformable successions accumulate during gradual water deepening it follows that 1 parasequences have smaller extent than systems tracts and 2 systems tracts do not always consist of stacked parasequences these limitations prevent the dependable use of the parasequence concept in sequence stratigraphy advances in high resolution sequence stratigraphy show that the scales of sequences and parasequences are not mutually exclusive the two types of units define different approaches to the delineation of stratigraphic cycles at high resolution scales sequences that develop at parasequence scales provide a more reliable alternative for correlation both within and outside of the coastal and shallow water settings rendering parasequences obsolete every transgression that affords the formation of a flooding surface starts from a maximum regressive surface and ends with a maximum flooding surface observed at the scale of that transgression these systems tract boundaries are invariably more extensive than any facies contacts that may form during the transgression flooding surfaces remain relevant to the description of facies relationships but their stratigraphic meaning needs to be assessed on a case by case basis the use of sequences and systems tracts in high resolution studies provides consistency in methodology and nomenclature at all stratigraphic scales irrespective of geological setting and the types and resolution of the data available

major and trace element and sr nd isotope constraints on the origin of paleogene volcanism in south china prior to the south china sea opening abstract paleogene volcanic rocks crop out in three sedimentary basins namely sanshui heyuan and lienping in the attenuated continental margin of south china lavas from the sanshui basin which erupted during 64 43 ma are bimodal consisting of intraplate tholeiitic basalt and trachyte rhyolite associations similar to cretaceous a type granites from the nearby region the felsic member shows peralkaline nature na2o k2o 10 12 na k al 0 98 1 08 general enrichment in the incompatible trace elements and significant depletion in ba sr eu p and ti although both types of the sanshui lavas have rather uniform nd isotope compositions nd t 6 to 4 that are comparable to late cenozoic basalts around the south china sea the felsic rocks possess apparently higher initial sr isotope ratios isr up to 0 713 and form a horizontal array to the right in the nd vs sr isotope plot closed system differentiation of mantle derived magmas in a double diffusive magma chamber is considered for the bimodal volcanism in which the trachytes and rhyolites represent a type melts after extensive crystal fractionation in the upper portion of the chamber such a type melts were later contaminated by small amounts 1 3 of upper crustal materials during ascent on the other hand composition of lavas in the other two basins varies from tholeiitic basalt to andesite their sr and nd isotope ratios isr 0 705 to 0 711 nd t 1 to 5 and generally correlative nb ta depletions suggest a distinct magma chamber process involving fractional crystallization concomitant with assimilation of the country rock we conclude that these paleogene volcanic activities resulted from the lithospheric extension in south china that migrated southwards and eventually led to opening of the south china sea during 30 16 ma

drowning history of a miocene carbonate platform zhujiang formation south china sea abstract the identification and interpretation of drowning events in the geologic record can aid significantly to the reconstruction of the depositional tectonic and eustatic history of a study area and often improve reservoir and seal prediction in carbonate rocks the differentiation between drowned platforms showing a record of continuous deepening and those with a record of exposure followed by rapid deepening remains however problematic the zhujiang carbonate platform liuhua 11 1 field south china sea study shown here provides an example of an integrated approach combining high resolution geochemistry microfacies analyses and foraminiferal biostratigraphy in order to improve the reconstruction of environmental conditions prior during and after platform demise and drowning the zhujiang carbonate platform displays the following vertical succession of four facies types i skeletal grain facies with a miogypsinid lepidocyclinid dominated fauna deposited in a moderately deep heterostegina sp and spiroclypeids possibly capped by a subaerial exposure surface well rounded rhodoids representing a mesotrophic lagoon dominate the upper portions of the rhodoid facies iv pelagic marine shales of the hanjiang formation burying the carbonate platform after drowning this facies succession in combination with geochemical evidence suggests a deepening upward trend this trend might have been interrupted by transient subaerial exposure but no evidence for meteoric diagenesis was found at the drowning unconformity topping the carbonate platform instead microfacies analyses suggest that platform demise may be related to progressive changes in environmental conditions including increasing nutrient levels and or decreasing temperature up core towards the drowning unconformity these findings are of significance for those concerned with miocene carbonate factories and more specifically the demise of carbonate platforms in general

along strike variability of back arc basin collapse and the initiation of sedimentation in the magallanes foreland basin southernmost andes 53 54 5 s 1 the patagonian andes record the cretaceous demise of the quasi oceanic rocas verdes back arc basin and formation of the magallanes foreland basin for 500 km along the strike of the mountains this tectonic transition is marked by a sandstone mudstone package that records the beginning of turbiditic sand deposition and fan growth sandstone modal analyses and u pb detrital zircon spectra show changes in rock composition and provenance across the transition on a basin wide scale indicating it has tectonic significance and is related to orogenic uplift and the progressive evolution of the andean fold thrust belt spatial variations in transition zone characteristics indicate the foreland basin s central and southern sectors were fed by different sources and probably record separate fans at bahia brookes on tierra del fuego foreland basin sedimentation began at least after 88 89 ma and possibly after 85 ma several million years after it did 700 km away at the northern end of the basin this event coincided with increased arc volcanism and the partial obduction of the basaltic rocas verdes basin floor onto continental crust by 81 80 ma conglomerate deposition and increased compositional and provenance complexity including the abundance of metamorphic lithic fragments indicate that the obducted basaltic floor first became emergent and was eroding the results suggest that the beginning of turbidite sedimentation in the magallanes foreland basin and the progressive incorporation and exhumation of deeply buried rocks in the andean fold thrust belt occurred later in southern patagonia than in the north by a few million years

dolomitization and dolomite neomorphism trenton and black river limestones middle ordovician northern indiana u s a abstract the trenton and black river limestones are dolomitized extensively along the axis of the kankakee arch in indiana with the proportion of dolomite decreasing to the south and southeast of the arch planar and nonplanar dolomite replacement textures and rhombic type 1 and saddle type 2 void filling dolomite cements are present three stages of dolomitization involving different fluids are inferred on the basis of petrographic and geochemical characteristics of the dolomites nonferroan planar dolomite has relatively high 18o values 1 8 to 6 1o oo pdb and has 87sr 86sr ratios 0 70833 to 0 70856 that overlap those of middle ordovician seawater petrography geochemistry and the geometry of the dolomitized body suggest that the planar dolomite was formed in middle and late ordovician seawater during the deposition of the overlying maquoketa shale ferroan planar and nonplanar dolomite occurs in the upper few meters of the trenton limestone confined to areas underlain by planar dolomite this dolomite contains patches of nonferroan dolomite with cathodoluminescence cl characteristics similar to underlying planar dolomite ferroan dolomite has relatively low 18o values 5 1 to 7 3o oo pdb and has slightly radiogenic 87sr 86sr ratios 0 70915 to 0 70969 similar to those obtained for the overlying maquoketa shale these data indicate that ferroan dolomite formed by neomorphism of nonferroan planar dolomite as fluids were expelled from the overlying maquoketa shale during burial the absence of ferroan dolomite at the trenton maquoketa contact in areas where the earlier formed nonferroan planar dolomite also is absent indicates that the fluid expelled from the overlying shale did not contain enough mg2 to dolomitize limestone type 1 dolomite cement has isotopic compositions similar to those of the ferroan dolomite suggesting that it also formed from shale derived burial fluids cl growth zoning patterns in these cements suggest that diagenetic fluids moved stratigraphically downward and toward the southeast along the axis of the kankakee arch type 2 saddle dolomite cements precipitated late their low 18o values 6 0 to 7 0o oo pdb are similar to those of the type 1 dolomite cement however fluid inclusion data indicate that the saddle dolomite was precipitated from more saline basinal fluids and at higher temperatures 94 to 143 c than the type 1 cements 80 to 104 c a trend of decreasing fluid inclusion homogenization temperatures and salinities from the michigan basin to the axis of kankakee arch suggests that these fluids emerged from the michigan basin after precipitation of type 1 cement

a fractal model for the distribution of stratigraphic hiatuses several recent studies have suggested that there is a negative log linear relationship between sedimentation rates and the time span over which they are measured i e measured sedimentation rates are slow when measured over long time spans and rapid when measured over short time spans this relationship may be due to the inclusion of more and longer hiatuses over long time spans this paper proposes a mathematical model consistent with this relationship that is based upon the fractal cantor bar this model allows the estimation of the relative number and durations of stratigraphic hiatuses within a given section

geochemical and geochronological study of the sanshui basin bimodal volcanic rock suite china implications for basin dynamics in southeastern china abstract sanshui basin is one of the typical mesozoic cenozoic intra continental rift basins with voluminous cenozoic volcanic rocks in southeastern china thirteen cycles of volcanic eruptions and two dominant types of volcanic rocks basalt and trachyte rhyolite have been identified within the basin both basalt and trachyte rhyolite members of this bimodal suit have high values of end 2 3 to 6 2 and different sr isotopic compositions initial 87 sr 86 sr ratios are 0 70461 0 70625 and 0 70688 0 71266 for basalts and trachyte rhyolite respectively reflecting distinct magma evolution processes or different magma sources the results presented in this study indicate that both of the trachyte rhyolite and basaltic magmas were derived from similar independent primitive mantle but experienced different evolution processes the trachyte rhyolitic magma experienced significant clinopyroxene and plagioclase fractionational crystallization from deeper magma chamber with significant crustal contamination while the basaltic magmas experienced significant olivine and clinopyroxene fractionational crystallization in shallower magma chamber with minor crustal contamination new zircon u pb dating confirms an initial volcanic eruption at 60 ma and the last activity at 43 ma geologic geochemical and geochronological data suggest that the inception of the sanshui basin was resulted from upwelling of a mantle plume the sanshui basin widened due to subsequent east west extension and the subsequent volcanism constantly occurred in the center of the basin evidence also supports a temporal and spatial association with other rift basins in southeastern china the upwelling mantle plume became more active during late cenozoic time and most likely triggered opening of other basins including the young south china sea basin

empirical methods to estimate the strength of jointed rock masses abstract the ultimate strength and deformation of jointed rock mass are important parameters that designers look for in selecting sites for foundations of civil and mining engineering structures in rocks in the field it is extremely difficult to stress a rock mass to its ultimate failure stress consequently the field tests are performed up to a certain predefined stress level it is shown in this study that the results of these tests can be used to arrive at the ultimate strength of the rock mass a large number of uniaxial compressive strength ucs tests were conducted on the specimens of jointed block mass having various combinations of orientations and different levels of interlocking of joints four dominating modes of failure were observed the strength and the tangent elastic modulus values of the mass for a specific failure mode when plotted on the deere miller classification chart are found to follow an empirical straight line indicating strong correlation between them using the gradient of this empirical line correlations have thus been suggested to assess the ultimate strength of the jointed rock mass the findings of the study have been verified by applying it to estimate the ultimate rock mass strength of nine rock types from few dam sites in the lower himalayas the ultimate strength obtained by the present methodology is compared with that obtained through the q classification system it is concluded that reasonably good estimates on field strength of jointed rocks are possible by using the correlations suggested in this study

fractal nature of stratigraphic sequences orders of stratigraphic sequences are being used loosely and with widely varying definitions the orders seem to be subdivisions of convenience rather than an indication of natural structure it is proposed that at least at time scales of 103 106 yr sequences and systems tracts are scale invariant fractal features in which units bounded by exposure surfaces and units bounded by flooding surfaces are about equally likely support for this conceptual model derives from the well known facts that 1 sediment architecture is largely scale invariant over a wide range of scales in time and space 2 first order trends of sea level movements and sedimentation rates are fractal on all geologically relevant time scales and 3 detailed studies in carbonates indicate approximately equal abundance of flooding surfaces and demonstrable exposure surfaces among unit boundaries finally traces of prograding shelf edges that step up and step down in response to sea level changes are demonstrated in this study to have a fractal nature

evolution of deep water stratigraphic architecture magallanes basin chile abstract the 4000 m thick and 20 myr deep water sedimentary fill of the upper cretaceous magallanes basin was deposited in three major phases each with contrasting stratigraphic architecture 1 the oldest deep water formation punta barrosa formation comprises tabular to slightly lenticular packages of interbedded sandy turbidites slurry flow deposits and siltstone that are interpreted to record lobe deposition in an unconfined to weakly ponded setting 2 the overlying 2500 m thick and shale dominated cerro toro formation includes a succession of stacked conglomeratic and sandstone channel fill deposits with associated finer grained overbank deposits interpreted to record deposition in a foredeep axial channel levee system 3 the final phase of deep water sedimentation is characterized by sandstone rich successions of highly variable thickness and cross sectional geometry and mudstone rich mass transport deposits mtds that are interpreted to record deposition at the base of slope and lower slope segments of a prograding delta fed slope system the deep water formations are capped by shallow marine and deltaic deposits of the dorotea formation these architectural changes are associated with the combined influences of tectonically driven changes and intrinsic evolution including 1 the variability of amount and type of source material 2 variations in basin shape through time and 3 evolution of the fill as a function of prograding systems filling the deep water accommodation while the expression of these controls in the stratigraphic architecture of other deep water successions might differ in detail the controls themselves are common to all deep water basins information about source material and basin shape is contained within the detrital record and when integrated and analyzed within the context of stratigraphic patterns attains a more robust linkage of processes to products than stratigraphic characterization alone

relative scale and the strength and deformability of rock masses abstract the strength and deformation of rocks depend strongly on the degree of fracturing which can be assessed in the field and related systematically to these properties appropriate mohr envelopes obtained from the rock mass rating rmr classification system and the hoek brown criterion for outcrops and other large scale exposures of fractured rocks show that rock mass cohesive strength tensile strength and unconfined compressive strength can be reduced by as much as a factor often relative to values for the unfractured material the rock mass deformation modulus is also reduced relative to young s modulus a cook book example illustrates the use of rmr in field applications the smaller values of rock mass strength and deformability imply that there is a particular scale of observation whose identification is critical to applying laboratory measurements and associated failure criteria to geologic structures

a geo engineering classification for rocks and rock masses abstract in this article an attempt is made to assess the reliability of predicting the uniaxial compressive strength and the corresponding modulus of a rock mass by current approaches these two basic engineering properties when estimated from rock mass rating rmr q and geological strength index gsi indicate hardly any change in the modulus ratio with the change in the quality of the rock mass from very good to very poor however the modulus ratio obtained from the relations involving the joint factor j f indicate a definite decrease in the modulus ratio with a decrease in the quality of the rock mass the strength and modulus in the unconfined and confined states the modulus ratio and failure strain in the unconfined case were linked to j f in earlier publications based on a large experimental database some of these relations were adopted to verify the response of jointed test specimens the response of the rock mass during excavations for mining and civil underground chambers in establishing ground reaction curves including the extent of the broken zone and the bearing capacity of shallow foundations the joint factor is now linked to rmr q and gsi the prediction of compressive strength and modulus of the rock mass appears to be more suitable for classifying the rock based on these properties the deere and miller engineering classification applicable to intact rocks has been suitably modified and adopted the results of different modes of failure of jointed specimens establish definite trends of changes in the modulus ratio originating from the intact rock value on the modified deere and miller plot a geo engineering classification is evolved by considering strength modulus quantifiable weathering index and lithological aspects of the rock

a study on the uplift mechanism of tongjiezi dam using a coupled hydro mechanical model during filling in 1992 of the tongjiezi reservoir in southwest china it was noticed that the dam body and the rock masses on the right side of the valley were uplifted up to 22 2 mm and 24 3 mm respectively after reservoir filling in 1993 the uplift continued but the rate decreased and the measured maximum uplift increased from 22 2 mm to 27 5 mm in the dam body and from 24 3 mm to 28 9 mm in the rock masses from 1993 to 2004 based on the geological features of the dam site and observed geomechanics data a numerical method is used to evaluate the representative elementary volume rev and to identify the parameters related to the mechanical and hydraulic properties of the rock mass furthermore a coupled hydro mechanical model is presented to describe the uplift process the simulated results agree well with those measured in addition the time dependent deformation is studied in the laboratory and numerically it is concluded that with the specific hydrogeological conditions at the tongjiezi dam site hydro mechanical coupling during and after the reservoir impoundment is the main factor contributing to the uplift and the time dependent deformation is due to the rheological behavior of rock masses under seepage pressure

high resolution sequence stratigraphy the east coulee delta alberta abstract the fundamental concept on which sequence stratigraphy is based is that stratal architectures develop in response to the interaction between base level change and sediment flux a small lacustrine fan delta at east coulee alberta illustrates these principles and demonstrates that sequence stratigraphic concepts are scale and time independent this fan delta formed in a matter of days in a roadside drainage ditch as water level rose and then fell changes in the subaqueous space available for sediment to fill i e accommodation resulted in the development of a succession of systems tracts analogous to those formed within sedimentary basins over much longer time frames deposition began during lake level rise with progradation of a fan deltaic wedge accelerating lake level rise resulted in a backstepping of the shoreline and deposition of a transgress systems tract subsequent lake level fall resulted in subaerial exposure of the relatively steep delta front and caused incised valley formation and deposition of a lowstand delta this stratigraphic response to base level fall is typical of lowstand systems tract development on basin margins characterized by high relief slopes e g passive margins further lake level fall resulted in minor additional valley incision and development of a second lowstand delta on a surface characterized by lower relief as lowering water level exposed a flatter physiography this development of lowstand deltas and coa tlines during base level fall constitutes a forced regression of posamentier et al 1990 and is typical of lowstand systems tracts on basin margins characterized by gentle slopes in spite of its small size this example clearly illustrates that sequence stratigraphic principles apply to lacustrine as well as marine settings and at all spatial and temporal scales

on the geological significance of clastic parasequences abstract parasequences recognized in clastic sedimentary successions of shallow marine origin are considered by some geologists to be the fundamental building blocks of depositional sequences even though problems in their definition and application have been identified by others who instead advocate their abandonment as formal sequence stratigraphic units to elucidate the geological significance of clastic parasequences and inform the debate on their use in stratigraphy a quantitative characterization of the geometry facies characteristics and timescale of deposition of 1163 parasequences has been undertaken based on a synthesis of data from outcrop and subsurface studies that are available in the scientific literature through a database compilation the attributes of the studied parasequences are analysed with respect to the interpreted geological origin of the units and with consideration of sources of bias and uncertainty particular emphasis is placed on assessing the following i the importance of heuristics and of data types and coverage in the recognition of parasequences ii differences in parasequence characteristics observed across deltaic and shoreface depositional systems and between the quaternary and the ancient rock record iii possible explanations for the range in timescales of deposition of parasequences and iv the role of autogenic dynamics on the development of deltaic parasequences partly based on a comparison with the recent evolution of modern deltas the results demonstrate that parasequence definition and physical correlation suffer from subjectivity and that significant variability exists in the spatio temporal and architectural attributes of clastic parasequences this gives rise to uncertainty that affects the use of parasequences as a framework for comparison of the architecture of packages of strata originating via shoreline regression this uncertainty must be considered when using analogue data for subsurface predictions or when attempting comparative studies of clastic successions

estimation of completeness of stratigraphical sections using empirical data and theoretical models the completeness of a stratigraphical section is the fraction of time intervals of some specified length t that have left a record a record is left when some sediment is deposited during the interval and is not subsequently eroded a complete section contains no hiatuses longer than t the completeness of a section varies with t and its accumulation rate varies with the length of the time span over which it is measured plots of measured accumulation rate against time span are an empirical means of estimating completeness simple theoretical models help extrapolate meagre data and identify bias completeness at time scale t can depend upon three general properties of the accumulation history the age of the section the long term net accumulation rate drift and the unsteadiness of the sedimentation rate the way unsteadiness is measured depends upon the kinds of fluctuations that can be recognized in the accumulation rate to describe random fluctuations a standard deviation of rates is sufficient one dimensional brownian motion is a model of random fluctuations that explains many aspects of stratigraphical completeness regular periodic fluctuations in accumulation rate may be described in terms of wavelength and amplitude completeness is an increasing function of t drift and in the periodic case the wavelength of fluctuations it decreases with increasing standard deviation of accumulation rate and the amplitude of periodic fluctuations the completeness and thickness of stratigraphical sections are weakly positively associated

reciprocal sedimentation and noncorrelative hiatuses in marine paralic siliciclastics miocene outcrop evidence deepening upward paralic sequences present within a thicker record of shallowing upward shelf and nonmarine sequences in miocene siliciclastics of maryland provide rare stratigraphic evidence for 1 coastal trapping of sediment during marine transgression with simultaneous starvation on the open shelf recorded by condensed skeletal lags and 2 reciprocal switching of depositional and nondepositional conditions during regression it follows that the regressive disconformities that define hemicyclic coastal sequences are not laterally continuous with the transgressive disconformities and condensed lags that define open shelf hemicyclic sequences although they are commonly depicted or assumed as such nor are these disconformities age correlative marine to nonmarine correlations that assume lateral continuity of small scale sequences 1 to 10 m thick seismic parasequences will err by as much as one half cycle restricting the applicability of models of punctuated aggradational cycles the stratigraphic anatomy of parasequences is most comparable to reciprocal patterns inherent in hierarchically larger scale sequences in passive margins where subaerial unconformities and submarine condensed intervals have recently been biostratigraphically verified as offset in age

measured rates of sedimentation what exactly are we estimating and why abstract data on rates of sedimentation are essential in studies of sedimentation systems these data are obtained in three main study contexts 1 the study of sedimentation systems that are active today 2 the source to sink study of sedimentation systems that no longer are active and 3 the study of the relationship between accumulation rate and measurement timespan the aim of this paper is to question the meaning of measured rates of sedimentation and their interpretability particularly in these three contexts individual measurements of rate of sedimentation must always be interpreted with care firstly there are different definitions for instance with different statistical support or measurement dimension values that are defined differently cannot be compared directly secondly appropriate sampling schemes must have been used for the measurement this minimises sampling bias thirdly the inherent limitations of the data sources must be taken into account rates of sedimentation can usually be measured successfully in active sedimentation systems the same is not true for systems that are no longer active these can only be studied using the stratigraphic successions left behind rates of erosion can never be measured successfully in stratigraphic successions rate of sedimentation is essentially a ratio an amount of sedimentation per length of time therefore the obvious strategy to use in determining it is first to measure the amount and the time independently then to combine the values the amount can be measured in terms of thickness or volume or mass per unit area the duration of the time interval can be preset using quasi continuous measurement techniques or site reoccupation or it can be identified from interval specific sedimentary structures or it can be measured using dated horizons an alternative strategy is to use a surrogate measurement variable rates of erosion in ancient systems are usually measured in this way using cosmogenic radionuclide concentrations these two strategies are reviewed in this paper sets of measurements made in systems that are active today can certainly be used to estimate the rate of sedimentation for the system as a whole this estimation is best carried out using geostatistical estimation techniques the alternative is simply to average the measured rate values this latter approach should not be used however because the mean sedimentation rate in a system gives information only about the net sediment movement at the system boundaries it says nothing at all about how the system is operating or about its spatial and temporal variability measurements of rates of sedimentation made for source to sink studies are necessarily made in stratigraphic successions the measurements are used to estimate quantities in the sediment mass budget equation the amount of decumulation is inherently incapable of being measured in stratigraphic successions therefore there are always unknowns in the mass budget equation whenever the lithic surface at the start of the time interval considered cannot be recognised everywhere this means that the mass budget equation is applicable in practice only when all the systems involved in the study are entirely non erosional for that entire time interval a highly unrealistic situation the consistently inverse relationship documented between accumulation rates and measurement timespan is taken usually to indicate that this relationship is substantially scale invariant this in turn is often taken as indicating that the stratigraphic record is fractal in nature there are nevertheless grounds for doubt all of which relate to the ways that the data are collected and used for estimation the relationship is in fact the natural mathematical result of last in first out lifo operation and is produced in any type of system in which addition and removal processes both operate it says nothing particular about sedimentation processes the future analysis of accumulation rate data collected from stratigraphic successions will sensibly be framed in the context of estimating the parameters of a lifo model

global milankovitch cycles recorded in rock magnetism of the shallow marine lower cretaceous cupido formation northeastern mexico rock magnetic cyclostratigraphy was measured in the barremian aptian cupido cupidito formation northeastern mexico the goal was to develop an objective evaluation of palaeo environmental variability recorded in the formation that is independent of facies analysis and interpretation anhysteretic remanent magnetization arm was used to estimate magnetic mineral concentration variations for the upper 143 m of the formation which is characterized by metre scale carbonate cycles representative of innerand middle shelf marine environments isothermal remanent magnetization acquisition experiments and scanning electron microscope sem examination indicate that micron sized detrital magnetite from eolian dust carries the arm signal at the sampled sections from garcia and chico canyons 25 km apart arm records a synchronous 30 35 m oscillation with maxima coinciding with fourth order sequence boundaries superimposed with prominent high frequency variability calibrating the 30 35 m oscillation to a 405 kyr period long eccentricity cycle focuses the high frequencies into short eccentricity obliquity and precession index bands the precession band signal modulates with an eccentricity signature the arm signal is correlated between sections but decoupled from the interpreted fifthorder depositional cycles arm amplitudes diminish up section with facies suggesting deepening conditions that diluted magnetite concentration this probably signals a warming increasingly humid climate changing global circulation and or greater dispersal of magnetite grains earth s ancient shallow marine carbonate platforms are important archives of past global change their in situ biological genesis makes them sensitive indicators of physical conditions in shallow marine environments including temperature circulation and sea level wilson 1975 the accommodation space afforded by water depth is thought to govern the amount and type of sediment that accumulates at a given location water depth in turn is controlled by a combination of tectonic subsidence near shore deposition and global sea level which vary significantly through time schlager 2005 the commonly observed stacking of metrescale shallowing upward cycles in carbonate platform deposits has led to proposals of allocyclic v autocyclic forcing mechanisms the most widely cited allocyclic hypothesis is astronomically controlled eustasy fischer 1964 hardie et al 1986 autocyclic mechanisms involve infilling and oceanward progradation of sedimentation without eustatic change ginsburg 1971 to this day the allocycle v autocycle debate remains unresolved in understanding the origin of 10 10 year scale lithologic cyclicity in shallow marine carbonates schwarzacher 2000 burgess 2006 schlager 2010 full shallowing to sea level may not develop in response to every sea level oscillation subtidal missed beats resulting in amalgamated cycles conversely prolonged episodes of subaerial exposure may occur in inner platform settings that are only briefly or never flooded with every sea level oscillation leading to condensed or peritidal missed beats goldhammer et al 1990 ultimately facies analysis of shallow marine sections is limited in teasing apart the interplay of eustasy owing to climate change and subsidence arising from local tectonics this is in large part owing to the relatively subjective interpretation of lithofacies that is required from the stratigrapher therefore we need to develop facies independent from jovane l herrero bervera e hinnov l a housen b a eds 2013 magnetic methods and the timing of geological processes geological society london special publications 373 325 340 first published online april 25 2013 http dx doi org 10 1144 sp373 20 the geological society of london 2013 publishing disclaimer www geolsoc org uk pub ethics by guest on july 5 2013 http sp lyellcollection org downloaded from

the expected duration of upward shallowing peritidal carbonate cycles and their terminal hiatuses meter scale accommodation cycles which dominate the stratigraphic record of peritidal carbonate accumulation might provide a time scale of unusually high resolution but the duration of the hiatuses that cap the resulting cyclothems is difficult to determine thousands of rates of peritidal accumulation from many different carbonate sections have been combined according to the length of the time span of measurement to describe a hypothetical average section because all sections are interrupted by hiatuses the average accumulation rate falls progressively with increasing time span and most steeply at the time spans that capture the highest proportion of hiatuses the process of combining rates from many sections cancels local differences in the distribution of hiatuses only hiatuses that have similar spacing and duration in a majority of sections will stand out after compilation the size and position of a pronounced inflection in the combined plot of accumulation rates against time span identifies a dominant cycle period of 100 000 yr of which the terminal hiatus accounts for 80 90 the expected cyclothem is 10 m thick because peritidal accommodation cycles begin and end with the sediment surface at sea level the expected cycle period can be estimated by finding the time span at which accommodation and accumulation rates balance the maximum duration of the hiatus is the time span at which rates of subsidence and sea level fall balance compilations of many empirical measurements were again employed to determine the relationship between time span and the rates of subsidence sea level change and net accommodation this second method confirms the results of the first and can be modified to predict the expected cyclothem in different climatic tectonic and depositional settings because quaternary data dominate short term rates the hypothetical average section best describes a passive margin in an icehouse climate with strong glacio eustatic fluctuations in sea level after modification for an extreme greenhouse climate devoid of ice caps the second method predicts that 20 000 yr accommodation cycles will be preferentially recorded the expected cyclothem is 2 m thick and accounts for about 50 of the cycle period increased subsidence rates whether on active margins in the initial phase of passive margin formation or at the seaward edge of a platform tend to extend the limit of cycle duration increase cyclothem thickness and partition less time to the bounding hiatus increased subsidence however raises the risk that the sediment surface will drown

wave climate sediment supply and the depth of the sand mud transition a global survey abstract the influences of wave climate and sediment supply on the depths of sand mud transitions hsmt are investigated depths of sand mud transitions smt are based on published granulometric data from surface samples gathered from 14 sites in different wave dominated coastal environments with fluvial input including high energy columbia eel russian san lorenzo copper and nepean rivers moderate energy ebro nile santa clara tseng wen and kao ping rivers and low energy po pescara and tronto rivers regimes geometric mean diameter gmd and mud percent are compiled from samples along shore normal transects and significant correlation is found between these two textural descriptors nominally the smt is defined as the transition from gmd 63 m to 25 mud this dual definition is applied to the 14 systems and hsmt is tabulated for each system correlation is found between hsmt and the depth at which wave induced bottom shear stress equals the critical erosion shear stress of the largest mud particles and also between hsmt and significant wave height lack of correlation between hsmt and sediment load of nearby rivers indicates either that the influence of sediment supply on depth of the sand mud transition is small or is not adequately represented in this study shelf width and slope do not correlate with residuals from a formalized linear relationship between hsmt and significant wave height the relationship between hsmt and wave climate is useful for calibration of numerical models of erosion and deposition in wave dominated coastal environments for prediction of seabed properties in remote or inaccessible areas and for reconstruction of paleodepth based on facies changes from sand to mud in ancient rocks

stochastic and deterministic controls on stratigraphic completeness and fidelity compilations of sedimentation rates determined across a large range of time spans and different sedimentary environments attest to the discontinuous nature of sedimentation and support the reasoning that hiatuses pervade sedimentary successions at multiple spatial and temporal scales the relationship between sedimentation rate and time span of observation also emphasises how stratigraphic completeness is a time span dependent concept the scaling of stratigraphic completeness with time span alludes to the likely stochastic and fractal nature of the stratigraphic record it also implies that the relationship between stratal thickness and time is inherently non linear and this has obvious implications for the way we should expect temporal processes to be recorded stratigraphically order within the stratigraphic record may arise from deterministic processes in stratigraphy most notably through astronomically influenced sedimentation intuitively a strongly ordered stratigraphic record due to the presence of cyclicity in sedimentation increases stratigraphic completeness at time spans equal to and longer than the time span of the cyclicity and minimises the non linearity between stratal thickness and time here geological data and simple modelling are used to support this supposition but these results also highlight how stochastic variability inherent in depositional processes may sensitise certain successions to missed cycles and incompleteness even in the presence of strong cyclicity this stochastic variability has the potential to mask evidence of astronomical forcing of sedimentation it is also shown how hiatuses affect the ability of a succession to faithfully record temporal processes and this is true regardless of whether hiatuses are deterministically controlled or random or indeed whether a succession is considered complete or not consequently stratigraphic completeness and stratigraphic fidelity are not synonymous terms

on the labeling length and objective basis of fischer plots abstract fischer plots of the accumulation of shallow marine carbonate cycles track the cumulative departure from mean cycle thickness through a vertical sequence of contiguous upward shallowing units this is a simple objective treatment of residuals in a time series and is applicable to other stratigraphic phenomena to reflect the noninterpretive construction of fischer plots the vertical axis should be labeled cumulative departure from mean cycle thickness and the horizontal axis cycle number the typical fischer plot is an erratic bridge that begins and ends at the same elevation but has the form of an irregular train of asymmetric waves which rise steeply and fall gradually the asymmetry of the individual waves arises because thinner than average cycles typically outnumber thick r cycles two to one the overall form of the wave train is sensitive to mean cycle thickness but can guide correlation and may have considerable interpretive potential provided that enough cycles are included to ensure a robust estimate of mean thickness runs tests demonstrate that fischer bridges for peritidal carbonates are unlikely to be the result of random stacking processes since this anticipated result does not emerge unequivocally for fischer plots of less than 50 cycles however we recommend against plotting such short sections

determining the size and shape of blocks from linear sampling for geotechnical rock mass classification and assessment classifying and assessing geotechnical aspects of rock masses involves combining parameters in various ways guided by empirical considerations to derive quantitative geotechnical parameters geological structures and the deformation history of rocks underpin the nature of rock masses the kinematics of a deforming rock mass may occur as sliding along throughgoing discontinuities or as distributed sliding on block faces distributed sliding will tend to disrupt the continuity of planar structures such that data on the size and shape of blocks is needed rather than relying on discontinuity orientation data alone orientation and spacing data can be combined to provide a geometric analysis of block systems from linear samples such as drill core dihedral angles and spacing of sequential pairs of discontinuities provides a sample of the size and shape of blocks that can be interpreted stereologically further detail can be derived by combining neighbouring intersections that enclose or partially enclose individual blocks the shape and size of a block can be represented on a stereograph with the enclosing faces shown as poles and their perpendicular distance from an arbitrary point inside the block shown as a number identifying the size and shape of specific blocks rather than relying on statistical methods is beneficial to critical aspects of design such as analysing keyblocks that would be exposed during excavations the detailed characterization of block size and shape is also a step toward interpreting the kinematics of rock mass deformation and the analysis of rock masses as ultra close packed dilatant granular systems

characterization lateral variability and lateral extent of discontinuity surfaces on a carbonate platform barremian to lower aptian oman hiati of various duration in carbonates are commonly expressed as discontinuity surfaces the understanding of processes that form and affect these surfaces leads to an improved sequence stratigraphic interpretation a reliable outcrop correlation and better models for reservoir compartmentalization various intraformational discontinuities were analysed and interpreted in a well exposed study window 2 5 km in lateral length and 60 m in height comprising the barremian aptian qishn formation haushi huqf area central oman this study focuses on the lateral extent and morphology of the surfaces the petrography of the underlying rocks and the facies changes and geochemical trends across these discontinuities furthermore the lateral variability of discontinuity surfaces was documented three genetic types of discontinuities are differentiated i erosion surfaces ii omission surfaces hard and firmgrounds and iii composite surfaces with evidence for both subaerial exposure and submarine boring field observations combined with petrographic and geochemical data suggest that 17 surfaces are laterally extensive for at least 20 km and record relative sea level fluctuations of regional scale in contrast a large number of laterally limited surfaces 1 km are related to locally active processes such as waves and current erosion the lateral variability along extensive surfaces is the result of the depositional environment below the discontinuity the sea floor topography waves and currents and differential erosion the most pronounced lateral variability is present along six laterally extensive composite surfaces that record terrestrial exposure and subsequent flooding of a tidal flat environment this variability is caused by spatial variability in the tidal flat environment meteoric alteration and differential erosion this study emphasizes the spatial and temporal complexity of processes that form and modify discontinuity surfaces this variability must be kept in mind when interpretations and correlations are based on one dimensional sections or cores 2005 international association of sedimentologists

estimation of rev size and three dimensional hydraulic conductivity tensor for a fractured rock mass through a single well packer test and discrete fracture fluid flow modeling abstract a new methodology is presented to determine the representative elementary volume rev size and three dimensional 3 d hydraulic conductivity tensor for a fractured rock mass first a 3 d stochastic fracture network model was built and validated for a gneissic rock mass based on the fracture data mapped from scanline surveys at the site this validated fracture network model was combined with the fracture data observed on a borehole to generate a stochastic deterministic fracture network system in a cubic block around each packer test conducted at a different depth region in the same borehole each packer test was simulated numerically applying a developed discrete fracture fluid flow model to estimate the influenced region or effective range for the packer test a cubic block of size 18 m with the packer test interval of length about 6 5 m located at the centre of this block was found to be suitable to represent the influenced region using this block size the average flow rate per unit hydraulic gradient defined as the transmissivity multiplied by mean width of flow paths field for fractures was calibrated at different depth regions around the borehole by numerically simulating the packer tests conducted at different depth regions the average flow rate per unit hydraulic gradient of the fractures that intersect the borehole was considered to be quite different to the average flow rate per unit hydraulic gradient of the fractures that do not intersect the borehole a relation was developed to quantify the ratio between these two parameters by studying the directional hydraulic conductivity behaviour of different cubic block sizes having the validated stochastic fracture network and calibrated hydraulic parameters a rev for the hydraulic behaviour of the rock mass was estimated to be a block size of 15 m the hydraulic conductivity tensor in 3 d computed through regression analysis using the calculated directional hydraulic conductivity values in many directions was found to be significantly anisotropic the principal directions of the hydraulic conductivity tensor were found to be agreeable with the existing fracture system of the site further the geometric hydraulic conductivity calculated was found to be comparable to the hydraulic conductivity estimated through the radial flow assumption in continuum porous media

estimation of rock mass deformation modulus and strength of jointed hard rock masses using the gsi system abstract rock mass characterization is required for many applications in rock engineering practice including excavation design support design stope design amongst others for these purposes it is necessary to obtain design input parameters such as deformation moduli and strength parameters for numerical modeling although such parameters can ultimately be determined from in situ tests at the preliminary design stage where access to underground is limited the practical way to obtain these parameters is to apply a rock mass classification system to characterize the rock mass and estimate the rock mass properties over the years many classification systems such as rqd rock mass rating q and geological strength index gsi systems have been developed amongst them the q system is widely used for rock support system design and the gsi system is used for estimating design parameters the gsi system is the only rock mass classification system that is directly linked to engineering parameters such as mohr coulomb hoek brown strength parameters or rock mass modulus however the application of the existing gsi system is hindered by the facts that the use of the system is to some extent subjective and requires long term experience in the present study a quantitative approach to assist in the use of the gsi system is presented it employs the block volume and a joint condition factor as quantitative characterization factors the approach is built on the linkage between descriptive geological terms and measurable field parameters such as joint spacing and joint roughness the newly developed approach adds quantitative means to facilitate use of the system especially by inexperienced engineers the gsi system is applied to characterize the jointed rock masses at two underground powerhouse cavern sites in japan gsi values are obtained from block volume and joint condition factor which in turn are determined from site construction documents and field mapping data based on gsi values and intact rock strength properties equivalent mohr coulomb strength parameters and elastic modulus of the jointed rock mass are calculated and compared to in situ test results the point estimate method is implemented to approximate the mean and variance of the mechanical properties of the jointed rock masses it is seen that both the means and variances of strength and deformation parameters predicted from the gsi system are in good agreement with field test data

cenozoic basalts in se china chalcophile element geochemistry sulfide saturation history and source heterogeneity abstract cenozoic basalts in se china may be derived from a mixture of depleted morb mantle dmm and enriched mantle 2 em2 sources but whether these basalts share a common mantle source or magmatic history remains unknown to investigate these unresolved issues this study sampled basalts from niutoushan and mingxi fujian province xilong zhejiang province and penghu taiwan for geochemical analysis the basalt samples show oib like trace element patterns and have low pge contents with 0 02 0 7 ppb ir and pd 0 05 1 4 ppb ru 0 01 0 2 ppb rh and 0 06 1 1 ppb pt all samples have high cu pd ratios ranging from 69 000 to 3 500 000 and low cu zr ratios ranging from 0 1 to 0 8 suggesting sulfur saturated fractionation model calculations indicate that the basalts are depleted in pge due to the retention of 0 001 to 0 1 sulfide in the mantle and the removal of up to 0 0022 sulfide during magma ascent the crystallization of olivine and spinel and partial melting are insufficient to account for the observed pge variation in these basalts thus the distinct pge patterns in basalts with different ages may reflect the heterogeneity of the mantle source beneath se china the source heterogeneity may be due to compositional heterogeneity particularly variations in oxygen fugacity and pge mineral phases or due to variable fluid melt metasomatic agents in the sub continental lithospheric mantle this heterogeneity is possibly related to the westward subduction of the paleo pacific plate

platinum group element fractionation in a komatiitic basalt lava lake precise pge os ir ru pt pd abundance data for bulk rock samples and mineral separates from a deep differentiated komatiitic basalt lava lake in the vetreny belt baltic shield were obtained using an icp ms id technique the composition of the erupted liquid mgo 5 15 is characterized by a highly fractionated pge pattern pd os n 5 48 with subchondritic os ir n 5 0 43 analysis of separated olivine and chromite revealed that ru os and ir were slightly compatible to moderately incompatible in olivine d 5 1 7 0 8 and were compatible with chromite d 5 100 150 platinum and pd were highly incompatible with olivine d 5 0 08 0 03 and moderately compatible with chromite d 5 1 6 3 3 bulk solid liquid partition coefficients for pges ni cr and cu estimated from the whole rock regressions were os 7 9 ir 6 6 ru 4 5 pt 0 53 pd 0 09 ni 6 2 cr 4 4 and cu 0 01 the highly incompatible behavior of cu and pd indicates that there was no separation of fenicu immiscible sulfide liquid during the differentiation of the lava lake comparison of the bulk partition coefficients with those calculated from the olivine and chromite compositions implies that the fractionating mineral assemblage included 10 2561 mass fraction of pyrrhotite the data obtained provide new constraints on the effects of fractional crystallization on the pge compositions of mafic ultramafic magmas copyright 2001 elsevier science ltd