oolitic sandbody depositional models and geometries mississippian of southwest britain implications for petroleum exploration in carbonate ramp settings abstract a 1000 m thick early mississippian carbonate supersequence the carboniferous limestone of southwest britain consists of three third order depositional sequences these comprise parasequences in various configurations and the whole forms a carbonate ramp stack within this framework five major oolitic carbonate sandbodies developed a castell coch limestone b stowe oolite c brofiscin oolite d gully oolite and e high tor limestone the depositional regime was storm and wave dominated throughout and the major sandbodies represent a range of progradational carbonate beaches barriers and detached subtidal shoals analysis of the three dimensional shapes and distribution of these five examples shows that they evolved to produce three major carbonate sandbody geometries a strings b sheets and c wedges these geometries are characterised using the five field examples and offered as a template which may assist in the exploration and reservoir modelling of petroleum rich high energy ramp systems progradation for up to 40 km of barrier islands stowe oolite and beach ridge plains gully oolite formation generated strings and thick sheets individually up to 10 20 m thick thin shoreface retreat carbonate packstone grainstone sheets up to 5 m thick high tor limestone developed during transgressions as veneers across flooding surfaces these are comparable with sheet sands developed in siliciclastic shelf depositional systems progradation for up to 30 km and vertical aggradation of shoreline detached oolite shoals castell coch limestone brofiscin oolite generated basinwards expanding or thinning wedges up to 30 m thick tectonically controlled stacking of strandplain sheets produced a composite carbonate sandbody up to 80 m thick gully oolite the intrinsic sedimentary and extrinsic eustacy tectonism climate factors which controlled these sandbody geometries are addressed establishing the positions of the sandbodies accurately within depositional sequences allows them to be located within inferred seismic sequence geometries and provides one possible solution to the difficult problem of predicting carbonate facies distribution in subtle stratigraphic plays in this ramp system the most homogeneous sandbodies up to 30 m grainstones with greatest reservoir facies potential are represented by shoal belt wedges potential grainstone reservoir facies in the prograding shorelines are limited to the upper parts of individual shoreface sequences max 10 m grainstones for shoreline carbonate sandbodies the greatest reservoir and stratigraphic trapping potential exists in the earliest ramp parasequences where enveloping offshore sediments are siliciclastic mudstones in later stages potential seals are likely to be less reliable low porosity outer ramp carbonates

regional variations of seismic attenuation of lg waves in southern mexico attenuation of lg waves is estimated using 61 events located in the subduction zone of the middle american trench and recorded by the seismic network of laguna verde veracruz mexico we estimate the anelastic attenuation coefficient of lg waves or equivalently qlg by calculating the rate of acceleration spectra decay with distance we consider paths from two regions guerrero veracruz ne sw direction and oaxaca veracruz north south direction assuming a frequency dependence of of the form 0 we find that 0 175 0 05 for both regions and that 0 was lower for paths from guerrero to veracruz 0 0 0071 0 002 than for paths from oaxaca to veracruz 0 0 0161 0 003 in the frequency range from 2 to 7 hz in terms of the quality factor qlg values of qlg 134 30 0 83 0 2 and qlg 59 10 0 81 0 2 were found for the guerrero veracruz and the oaxaca veracruz paths respectively this difference in attenuation may be due to the state of stresses that prevails in both regions including the density and fluid content of fractures which are attenuation mechanisms also suggested for other regions mitchell 1995

an inversion of lg wave attenuation and site response in the north china region a joint inversion method for determining the lg wave attenuation along the propagation path and site response based on seismic spectral ratios was developed and applied to invert the lg wave attenuation and site response in the north china region is related to the quality factor q by f uq where u is the velocity waveform data of 200 earthquakes during 2006 2008 with m l 1 7 5 5 in the area of 38 41 n 114 120 e were selected for this study more than 1500 three component records chosen from 81 stations on the basis of the signal to noise ratio were used in the inversion the waveform data were processed in the frequency range of 1 6 hz with an interval of 0 2 hz the results indicate that there is remarkable heterogeneity in lg wave attenuation in the study area we divided the area into four regions according to the lg wave propagation paths lower values are found in the tectonic mountain region higher values occur in the tectonic basin region and moderate values are found for the propagation paths passing through both the mountain and basin regions on the vertical component was found to be frequency dependent and in the form graphic 1 and graphic 2 for propagation paths in the mountain and basin regions respectively and graphic 3 and graphic 4 for paths passing through both mountain and basin regions with seismic ray direction from the mountain to the basin and vise versa respectively the absolute quality factor q ranges from 125 to 306 the response of rock sites is smooth and flat and less than five at low frequency while that for soil sites is higher than for rock sites for soil sites the amplification of low frequency waves is higher than that for high frequency waves for both site response and attenuation no significant differences were observed between different components online material source parameters of the studied earthquakes 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif 4 embed inline graphic 4 gif

the ml scale in northern baja california mexico abstract we found that the attenuation functions proposed for southern california by richter 1958 and hutton and boore 1987 are not entirely suitable for local magnitude calculation for earthquakes in northern baja california in this study we used zero to peak amplitudes from synthetic wood anderson seismograms to determine appropriate log a 0 attenuation functions and station magnitude corrections through a multiple linear regression analysis our data were grouped so that each energy path was entirely contained in either the granitic peninsular ranges of baja california prbc or the sedimentary environment of the mexicali imperial valley miv the best solutions of the regression analysis are log a 0 1 0134 0 0288 log r 100 0 0025 0 0005 r 100 3 0 for miv and log a 0 1 1319 0 0197 log r 100 0 0017 0 0002 r 100 3 0 for prbc where r is hypocentral distance a comparison of these functions with those for southern california revealed the following a a remarkable agreement between richter9s function and the function for miv at distances between 40 and 450 km b hutton and boore9s function and the function for prbc are quite similar in the whole distance range considered 10 to 450 km and c for both areas at distances shorter than 50 km the log a 0 richter function was as much as 0 5 units lower than the others thus as for other regions the use of richter9s function results in understimation of local magnitudes at near source distances additionally the attenuation function for prbc was 0 30 units lower than richter9s at 400 km which means that at such longer distances the richter function overestimates the magnitude of prbc earthquakes finally station magnitude corrections from 0 42 to 0 26 units were obtained suggesting significant effects due to station site properties

the complete synthesis of seismic crustal phases at regional distances using a new method to evaluate green s functions for elastic layered media we compute complete synthetic seismograms at regional distances for an earthquake in the earth crust we choose as source parameters the ones inferred for an earthquake in central france and compare the computed seismograms to the ones recorded at several short period stations of the french seismic network the major features of the records including complexity and duration are well reproduced by the synthetics lg waves which are the prominant phase are shown to be guided waves made up of sh and sv waves incident on the moho at angles of incidence more grazing than the critical angle and multiply reflected within the crust the length of the computed lg wave coda extends between group velocities of 3 5 and 2 8 km s and is in good agreement with the data

attenuation of coda waves in new england abstract seismic wave attenuation was measured in new england from the time domain decay of coda wave amplitudes on narrow bandpass filtered seismograms of local earthquakes the frequency band of interest was 0 75 to 10 hz q c f was found to increase with frequency across this band but there was also a difference between the q c f values for short t t 100 sec lapse times of coda wave propagation for the short lapse time data corresponding to wave paths primarily in the upper crust q c f increases from 400 at 3 hz to 1300 at 10 hz for the large lapse time data corresponding to wave paths in the lower crust and upper mantle q c f was found to vary from 660 at 1 hz to 1500 at 10 hz if we interpret this dataset in terms of a model incorporating both scattering and anelastic attenuation we find that the mean free path of seismic waves over this frequency band is 80 km for short lapse times and 400 km for long lapse times if we assume that scattering is entirely responsible for the observed attenuation we find that the minimum mean free path for short lapse times is about 75 km over all frequencies whereas for long lapse times the minimum mean free path decreases from 400 km at 0 75 hz to 90 km at 10 hz

temporal change in coda q before the tangshan earthquake of 1976 and the haicheng earthquake of 1975 a new earthquake precursor called coda q is demonstrated for the tangshan earthquake of 1976 and for the haicheng earthquake of 1975 the precursor is based on the measurement of coda decay rate for small local earthquakes in the general area that is preparing for a major earthquake during the 3 year period preceding the tangshan earthquake the coda q was about 3 times lower than it was before or after this period a comparable change also occured at the time of the haicheng earthquake the observed change cannot be due to the change in the source parameters such as the focal depth or the source spectrum the coda q precursor appears to detect the same physical process detected by other precursors such as b value quiescence radon water quality vp vs and animal behavior but has advantages over them in its clearer physical mechanism easier sampling and better defined anomalous region

genesis of terrestrial oncoids cayman islands british west indies terrestrial oncoids up to 4 3 mm long are common in sinkholes that penetrate the dolostones of the oligocene miocene bluff formation on grand cayman and cayman brac the vaguely laminated terrestrial oncoids which generally lack a nucleus are formed of detrital material micrite clays dolomite calcified filaments and spores and insect fragments the abundant diverse assay of microorganisms includes six different types of filaments and five different types of spores which can be attributed to fungi algae and or cyanobacteria thin mats of mucus are commonly associated with the microorganisms the microorganisms contribute to the formation of the terrestrial oncoids by i calcification of the filaments and spores ii trapping and binding detrital material and iii binding with their mucus detrital material to the surface of the oncoids identification of terrestrial oncoids relies on i the recognition of a microbial assemblage ii the demonstration that the microorganisms played an ac

calcrete in quaternary coastal dunes in southwestern australia a capillary rise phenomenon associated with plants abstract non pedogenic calcrete is forming as a thin sheet 10 50 cm thick just above the water table in the subsurface of a barrier dune terrain in south western australia the calcrete is forming in response to the regional evapo transpirative regime the annual rainfall is high but of short duration and it infiltrates rapidly into the sandy substrates relatively high air temperatures and evaporation coupled with wind stress combine to produce a water vapor deficit across the dune terrain the vegetation responds by drawing upon phreatic water and pellicular water of the vadose zone thereby precipitating caco3 where plants are not drawing phreatic water calcrete is developing by evaporation of water at the top of the zone of capillary rise various structure types of calcrete are developed in the study area namely rhizoconcretionary mottled massive and laminar forms these occur in a definite stratigraphic sequence related to maturity of profile vegetation cover and thickness of the vadose zone rhizoconcretionary calcrete forms in the vadose zone mottled and massive calcrete frequently capped by laminar calcrete develop in the zone of capillary rise these latter calcrete types form a sheet that is ubiquitous and parallel to the water table since it is a feature of the water table the calcrete sheet may potentially transect regional stratigraphic boundaries and unconformities at the local level the various structural types of calcrete may he used as paleowater table indicators

calcrete palaeosols from the lower carboniferous llanelly formation south wales abstract three calcrete bearing palaeosol units are described from the lower carboniferous llanelly formation in south wales and are named the tyle r bont pedocomplex the cwm dyar pedoderm and the llanelly pedocomplex these units were formed on semi arid to arid floodplains and are associated with sheet flood stream flood and meandering channel deposits three major processes operated during pedogenesis calcification pedoturbation and solution pedoturbation resulted in the formation of brecciated horizons pseudo anticlinal and prismatic structures and a predominance of disorthic nodules the soils developed in smectite rich clays under a seasonally arid climate resulting in strong argillipedoturbation

ferrolysis in arundian alluvial palaeosols evidence of a shift in the early carboniferous monsoonal system an unusual clay mineral assemblage from early carboniferous arundian palaeosols in south wales contains a three component kaolinite chlorite like material smectite mixed layer clay this is interpreted as the product of ferrolysis a complex process involving dissolution of clays a d the subsequent production of interlayered varieties from the repetitive reduction and reoxidation of iron compounds in seasonally waterlogged surface water grey soils support for this interpretation comes from the distribution of iron species iron concretions and vertic features in the palaeosol profile which indicate formation under strongly seasonal dry hydromorphic conditions the appearance of the ferrolytic pa iaeosol indicates a shi from a dry to a wet type monsoonal regime in late arundian times

estimates of q in central asia as a function of frequency and depth using the coda of locally recorded earthquakes digital recordings of microearthquake codas from shallow and intermediate depth earthquakes in the hindu kush region of afghanistan were used to determine the attenuation factors of the s wave coda qc and primary s waves q an anomalously rapid decay of the coda shortly after the s wave arrival observed also in a study of coda in central asia by rautian and khalturin 1978 seems to be due primarily to depth dependent variations in qc in particular we deduce the average qc in the crust and uppermost mantle 100 km depth is approximately four times lower than the deeper mantle 400 km depth over a wide frequency range 0 4 to 24 hz further while qc generally increases with frequency at any depth the degree of frequency dependence of qc depends on depth except at the highest frequency studied here 48 hz the magnitude of qc at a particular frequency increases with depth while its frequency dependence decreases for similar depths determinations of q and qc agree suggesting a common wave composition and attenuation mechanism for s waves and codas comparison of these determinations of qc in afghanistan with those in other parts of the world shows that the degree of frequency dependence of qc correlates with the expected regional heterogeneity such a correlation supports the prejudice that qc is primarily influenced by scattering and suggests that tectonic processes such as folding and faulting are instrumental in creating scattering environments

paleosols capping regressive carbonate cycles in the pennsylvanian black prince limestone arizona abstract the lower pennsylvanian morrowan to early derryan black prince limestone exposed in southeastern arizona consists of shallowing upward regressive carbonate cycles that accumulated on a shallow shelf platform a typical complete cycle from the base upward consists of the following fades mixed skeletal mudstones to grainstones subtidal shelf open circulation mixed skeletal to nonskeletal packstones and grainstones restricted shelf lagoon nonskeletal fenestral mudstones to grainstones intertidal nonskeletal cryptalgally laminated brecciated mudstones to wackestones supratidal and paleosol horizons terrestrial two paleosol types occur calcrete and terra rossa calcrete occurs as thin 5 10 cm profiles consisting of laminar micrite coated grains aggregate grains and vadose diagenetic features terra rossa paleosols consist of subspherical nodules derived from pedogenic alteration of parent limestones separated by a reddish insoluble accumulation ofclays iron oxides calcite skeletal debris and quartz silt the terra rossa paleosols occur as in situ preserved c horizons and as reworked soil residuum the first occurrence is marked by parent limestone in completely brecciated into nodules whereas reworked paleosols consist of nodules enveloped in red matrix both calcrete and terra rossa paleosols record subaerial exposure although the terra rossa paleosols suggest that signi icant amounts of limestone were removed during pedogenesis the terra rossa paleosols also favor an extrinsic versus anintrinsic mechanism for the origin of the cycles

attenuation of coda waves in western mexico using local seismicity coda waves are an important instrument to study the elastic properties of the lithosphere the attenuation of coda waves in western mexico is analyzed using seismograms recorded during the mapping of the rivera subduction zone experiment the coda wave attenuation is measured by means of q within the single backscattering model and the single isotropic scattering model schemes the frequency dependence of q is analyzed using the power fit formulation q f q f the resulting q q and are then used to study the seismic attenuation properties in western mexico we compare our results with the crustal structure by means of the surface geology seismic activity crustal thickness and p wave velocity patterns in the study area there is a poor correlation of the attenuation parameters with such crustal features however an analysis of the variations of the p wave velocity shows that the seismic attenuation parameters correlate to some extent with seismic velocity variations previously noted in the study area where low attenuation and weak frequency dependence correlate with low velocity variation

an upper pennsylvanian desert paleosol in the d zone of the lansing kansas city groups hitchcock county nebraska abstract this study suggests that the upper shale regressive shale in the upper pennsylvanian missourian lansing kansas city groups d zone from hitchcock county nebraska is a paleosol pedogenesis of this unit occurred during prolonged subaerial exposure on a semiarid to arid alluvial flood plain pedogenesis occurred during maximum retreat of the late pennsylvanian sea during the d zone sedimentary cycle initially clays in this unit were deposited in marine environments but as eustatic sea level continued to drop deposition became dominated by continental alluvial processes characteristics which distinguish the upper shale as a paleosol are the presence of 1 a basal subsoil caliche c soil horizon characterized by weathered limestone regolith clasts soil nodules thin laminated calcrete beds with pseudo fenestral fabric pelleted and clotty calcareous and dolomitic caliche weathered clays circumgranular cracks and root casts and 2 an upper unit b soil horizon characterized by authigenic hematite intensely weathered clays soil nodules slickensides and gypsum root casts

attenuation of multiphase surface waves in the basin and range province part i lg and lg coda summary broad band data recorded by the lawrence livermore laboratory network are used to investigate whether or not lg q and lg coda q have similar values in the basin and range province of north america in order to retrieve spectral estimates of the broad band lg and lg coda signals a hybrid method is used which retains high fidelity at lower frequencies while strongly smoothing the spectral estimates and minimizing the number of spectral points at high frequencies a stochastic approach is used to model the lg signal and ambient noise and to analyse results from two station determinations of lg q in the basin and range the effects of ambient noise frequency dependent station site response and focusing defocusing on lg q inversion are analysed it is shown that after averaging spectral ratios determined from repeated observations over four two station paths a modest site effect will not cause significant errors in the resulting lg q relation using this inversion scheme and spectral ratio estimates averaged over those paths at frequencies between 0 2 and 2 5 hz we obtain the relation qlg f 267 f 56 f0 37 0 06 for the basin and range province further constraints on lg q were obtained from lg coda which due to the natural averaging effect of scattering is insensitive to effects of focusing defocusing to investigate the validity of the single isotropic scattering model for lg coda in the basin and range province we calculated ischrons for scatterers corresponding to later lg coda signals as required by the single scattering model it is found that when significant portions of these isochrons are oceanic lg coda amplitude decay becomes irregular and abnormally slow suggesting a strong scattering reflection effect caused by the rapidly changing crustal structure along the coast applying the single isotropic scattering model to lg coda records with isochrons mostly confined to the continental crust results in q f 275 f 26 f 0 36 0 03 which is nearly identical to our qlg relation this indicates that even in a complicated geological province a joint interpretation of the dynamic properties of lg and lg coda can be successful and fruitful inconsistent lg q and coda q relations found in earlier studies in the basin and range province may be attributed to different settings of parameter trade offs different seismic phases or different dynamic properties being used

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

a rendzina from the lower carboniferous of south wales a thin calcrete crust horizon from the lower carboniferous llanelly formation of south wales consists of two parts an upper laminated unit and a lower peloidal unit the former is interpreted as a subaerial stromatolite and the latter as an a horizon of a palaeosol comparisons are made with the a horizons of rendzinas and it is concluded that the calcrete crust represents a complete rendzina profile this fossil rendzina contains abundant evidence of a soil fauna in the form of fecal pellets and small burrows

an inversion of lg wave attenuation and site response from seismic spectral ratios in the eastern china region abstract both lg wave attenuation and site responses are determined in the eastern china region the region ranges from 26 n to 33 n and 117 e to 124 e we analyze over 1360 three component seismograms from 92 local and regional earthquakes the seismograms are recorded in the distance range of 100 600 km the earthquakes occurred between 2002 and 2012 in the region and varied in magnitude between 2 0 and 4 7 m l a combined inversion method which can simultaneously estimate attenuation and site response from seismic spectral ratios is implemented in the study modeling errors are determined using a delete j jackknife resampling technique fourier spectral amplitudes are measured from lg phases windowed between the group velocity limits 2 6 and 3 6 km s the inversion are performed in a frequency range of 1 6 hz with an interval of 0 2 hz the frequency dependent quality factor is modeled in the form of q q 0 f the eastern china region displays high q 0 and a weaker frequency dependence characterized by the functions q 335 16 f 0 45 0 02 q 411 21 f 0 26 0 01 and q 432 26 f 0 24 0 01 for vertical north south and east west components respectively the values are similar to the average for other stable regions of the globe site responses from 32 stations are estimated in the region most stations do not show obvious amplification the site responses are mainly smooth flat and less than 5 in the frequency range of 1 6 hz

calcrete breccia floatstone in holocene sand developed by storm uprooted trees abstract calcrete breccia floatstone occurs as a surficial sheet overlying calcrete caliche in southwestern australia the sheet is composed of calcrete clasts of variable size dispersed within a sand or soil matrix the calcrete breccia floatstone is developed as trees are uprooted and toppled by periodic severe storms these trees disrupt a portion of the underlying calcrete in which their roots are imbedded and subsequent decay or burning releases calcrete clasts to the surficial sand environment this process provides an additional mechanism for producing calcrete breccia the configuration of calcrete sheet and overlying breccia floatstone also provides useful information for interpretation of palaeo environmental conditions and processes

pedogenic calcrete as it occurs in quaternary calcareous dunes in coastal south australia abstract laminar and massive calcretes are forming in the vadose zone of the quaternary calcarenite coastal dunes of south australia calcrete formation is intimately associated with a near surface soil zone of intense plant root growth and an abundant soil biota the calcretes contain many fabrics indicative of caliche formation including meniscus cements micrite envelopes rhizoconcretions dissolved grains nodules zones of fractured sediment and intraclast breccias within pleistocene dunes and especially within calcrete zones the individual sand grains including quartz grains are often coated with a rind or envelope of micrite this envelope is perhaps formed by fluctuations in the volume and chemistry of the film of attached water which surrounds each grain on the mesoscale many so th australian coastal calcretes contain intraclast horizons which show interesting clast within clast fabrics and some of the clasts show an unusual stellate form the formation of these intraclasts is controlled by the episodic nature of calcrete development and dune sand emplacement within a coastal dune setting recognition of these various calcrete fabrics in pre quaternary carbonate sequences can be used to refine further the distinction between subaerial exposure surfaces and marine hardgrounds

s wave coda q from 3 to 20 hz and p wave q for foreshocks and aftershocks of the petatlan earthquake in order to understand better the variations of mechanical properties close to the source and the failure process in the upper portion of the crust in a geologically very young subduction zone the seismic s wave coda qc from 3 to 20 hz and p wave half pulse width qp from 6 to 12 hz were determined for selected foreshocks and aftershocks of the 1979 petatlan mexico ms 7 6 earthquake to limit the region being sampled the quality factor of s coda qc was obtained from the first 10 s following the s onset qc exhibited a strong spatial temporal and frequency dependence and in the small foreshock portion of the aftershock area qc and to a lesser extent qp were significantly lower before the mainshock than afterward the frequency dependence n in qc qo n was practically constant for aftershocks in four different regions n 1 32 0 03 and for foreshocks n 1 43 0 07 only in one peripheral region station pair did we find a significantly different n n 0 97 0 09 our observations indicate that qc and perhaps the frequency dependence n are sensitive to the physical property changes in the source region and might be useful as predictors of large earthquakes in a shallow subduction zone environment

terra rossa catenas in wisconsin usa abstract the soils in the unglaciated part of wisconsin have a loess cover over sedimentary rock mostly dolostone of ordovician age the dolostone has weathered and produced layers of red clay or terra rossa we have sampled 144 pedons of 16 catenas with different slope aspects and curvatures in a 70 km 2 area half of all the pedons had a red clay subsoil mostly 5yr 3 4 and had on average over 40 clay the mean thickness of the loess above the red clay was 50 cm but it ranged from 7 to 130 cm the thickness of the red clay ranged from 4 cm to 60 cm with an average thickness of 25 cm the red clay was found in every part of the landscape except the valley bottoms it was present in soils on summits shoulders backslopes and footslopes the red clay is only found over dolostone but not present on all dolostone ridges it was concluded that there is large variation in the terra rossa soilscapes of wisconsin and this variation can only partly be explained by topography

calcrete and other soils in quaternary limestones structures processes and applications quaternary limestones commonly include descriptions of calcrete caliche and soils which embrace both surficial deposits in which dissolution and cementing phenomena interact on a calcareous substrate and soils or other sediments where carbonates are precipitated as cements three genetic groups are recognized in which 1 a soil profile is developed by surface alteration of existing marine sediments 2 deposits accumulate superficially on a lithified surface and 3 soil like materials have been added to unconsolidated marine sediments by surface processes including infiltration sediments range from unaltered marine grainstones through poorly sorted wackestones to mudstones diagnostic structures include pisoliths and other glaebules laminae grain aggregates birdseyes and other vugs and rootlets as well as fractures and brecciation not found in other environments the most common precipitated carbonates are micrites but needle fibres whiskers and prismatic crystals occur crystal morphology is controlled in part by the level of supersaturation rapid evaporation leading to micrite precipitation and whiskers but also by the pressure of organic contaminants distribution of cements and structures is irregular relating to percolating groundwater streams cements may be isopachous but meniscus structures cement bridges and microstalactites occur these vadose textures may not be developed where evaporation rates are high irregular areas of replacive neomorphic spar and displacive calcite growths occur in some examples but criteria for recognition are not firmly established dated recent examples lie between 400 and 18 300 years b p but deposits on aldabra and in kenya are intercalated with marine sediments which extend to 200 000 years b p the recognition of these terrestrial intervals within otherwise marine sequences enables sea level changes to be identified and correlated with other climatic data to separate local patterns of uplift or subsidence

geochemical evidence of saharan dust parent material for soils developed on quaternary limestones of caribbean and western atlantic islands abstract most previous workers have regarded the insoluble residues of high purity quaternary limestones coral reefs and oolites as the most important parent material for well developed clay rich soils on caribbean and western atlantic islands but this genetic mechanism requires unreasonable amounts of limestone solution in quaternary time other possible parent materials from external sources are volcanic ash from the lesser antilles island arc and saharan dust carried across the atlantic ocean on the northeast trade winds soils on quaternary coral terraces and carbonate eolianites on barbados jamaica the florida keys united states and new providence island bahamas were studied to determine which if either external source was important caribbean volcanic ashes and saharan dust can be clearly distinguished using ratios of relatively immobile elements al 2 o 3 tio 2 ti y ti zr and ti th comparison of these ratios in 25 soils where estimated ages range from 125 000 to about 870 000 yr shows that saharan dust is the most important parent material for soils on all islands these results indicate that the northeast trade winds have been an important component of the regional climatology for much of the quaterary saharan dust may also be an important parent material for caribbean island bauxites of much greater age

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

genesis of calcrete in quaternary soil profiles hutt and leeman lagoons western australia abstract soil profiles exposed along the margins of hutt and leeman lagoons contain a succession of calcrete horizons that exhibit oolitic pisolitic grainstone lithoclast breccia and pelloidal wackestone mudstone stone lithologies the typical coastal profile consists of an upper laminar calcrete horizon which is usually overlain by a transitional pisolitic loose soil horizon underlying the laminar calcrete is breccia and or massive calcrete downward gradation into the host is through a mottled calcrete horizon structure textures and fabrics are utilized to classify the following different calcrete types pisolitic loose soil is composed of sandy soils calcrete ooids and pisolites eolianite clasts and shell fragments laminar calcrete is composed of parallel laminated sheets of micritic carbonate that develop by segregation processes massive calcrete is dense relatively structureless calcrete with a secondary mudstone fabric resulting from diagenetic alteration of primary constituents calcrete mottles form in response to localized diagenesis in the host sediment breccia calcrete develops as a result of prolonged weathering involving repeated episodes of calcretization dissolution and brecciation diminution of permeability of the host sediment by development of massive calcrete is a major process in genesis of the profile and occurs in the lowermost part of the zone of alternate wetting and drying where the effect of water input overcomes the cumulative effects of evapotranspiration profile development is thereafter topographically controlled and restricted to horizons overlying the massive calcrete redevelopment of zones of alternate wetting and drying in older deposits may produce multiple soil profiles

lacustrine carbonates and pedogenesis sedimentology and origin of palustrine deposits from the early cretaceous rupelo formation w cameros basin n spain the berriasian rupelo formation of the w cameros basin consists of a 2 200 m thickness of marginal and open lacustrine carbonate and associated deposits open lacustrine facies contain a non marine biota with abundant charophytes both stems and gyrogonites ostracods gastropods and rare vertebrates carbonate production was mainly biogenic the associated marginal lacustrine palustrine facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history the succession was laid down in a low gradient shallow lake complex characterized by wide fluctuations of the shoreline carbon and oxygen stable isotope analyses from the carbonates show non marine values with ranges of 13 from 7 to 11 and 18 from 3 to 7 5 differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake analyses from the entire sample suite plot on a linear trend isotopic compositions become lighter with increasing evidence of pedogenic modification this suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil derived co2 the stable isotope data thus support evidence from petrography and facies relations that palustrine limestones form through pedogenic modification of lake carbonates

time partitioning in cratonic carbonate rocks dissimilarity in relations between thickness duration and accumulation rate in holocene sections metre scale phanerozoic cycles and epoch interval phanerozoic sequences reflects variation in the distribution of depositional and hiatal time at different scales of observation modern accumulation rates are strongly dependent on duration of deposition lower rates correspond to longer durations phanerozoic cycle thicknesses are similar to those of holocene sections suggesting that both formed while filling similar amounts of accommodation space however accumulation rates of phanerozoic cycles and sequences are about two orders of magnitude less than in modern settings and they show neither strong dependence on duration of accumulation nor significant variation over phanerozoic time hence net accumulation is primarily controlled by regional subsidence rate these relations also allow for determination of that fraction of cycle period recorded as rock and that corresponding to hiatal time at intercycle boundaries depending on subsidence rate and amount of compaction most cratonic carbonate units accumulated over 3 to 30 of the time represented by sequences in which they occur

source characteristics of a 5 5 magnitude earthquake that occurred in the transform fault system of the delfin basin in the gulf of california portable and permanent broadband seismic stations in the neighborhood of the gulf of california recorded a moment magnitude mw 5 5 event on 26 novem ber 1997 this is the first time that a moderate event located in the gulf of california extensional province was well recorded by local broadband seismic stations the event was located at 29 754 n and 113 708 w and at a focal depth of 5 0 km in the southeastern end of the transform fault that connects the lower and upper delfin basins the hypocentral location and the results of the wave modeling indicate that this is a complex event that originated in the pull apart delfin basin the focal mech anism estimated from first motions 310 d 83 k 97 and body wave modeling of p waves in the frequency band 0 05 0 5 hz suggests that the rupture started with dip slip reverse faulting motion and ended releasing the bulk of energy through strike slip motion synthetics of surface waves in the frequency band 0 05 0 1 hz were also calculated using a triangular source time function of 3 sec the best match between the synthetics and observed surface waves recorded at 90 km from the epicenter was obtained using a fault geometry defined by a strike of 330 15 dip 85 5 and slip of 165 15 the spectral analysis of the lg phase recorded at stations in the peninsular ranges gives a seismic moment of 1 28 10 17 n m 1 28 10 24 dyne cm a source radius of 6 3 km and a stress drop of 0 22 mpa 2 2 bar the source parameters inferred with s wave spectra and the same model brune 1970 give similar values

terrestrial stromatolites and laminar calcretes a review abstract laminated carbonates are prominent features of subaerial exposure profiles and many types of calcareous soils including calcretes previously much attention was given to differentiating these laminites from marine or lacustrine microbial stromatolites and oncoids however recent research has shown that many subaerial laminated carbonates are biogenically formed mainly but not wholly by microbial activity this paper reviews the criteria for distinguishing terrestrial carbonate laminites from non terrestrial stromatolites and oncoids and for differentiating biogenic from abiogenic terrestrial laminites

on the attenuation of lg waves in western and central asia and their use as a discriminant between earthquakes and explosions data from earthquakes and explosions in the western and central parts of the soviet union are used to determine the values of the coefficient of anelastic attenuation of 1 sec period lg waves from the russian uplands region and for the region from the caspian sea to the southern perimeter of the soviet union for the former region the value is approximately 0 15 deg 1 and for the latter 0 35 deg 1 using the empirical veith and clawson 1972 curve for the amplitude of p waves at regional distances and theoretical curves for the attenuation of higher mode surface waves for lg curves are constructed which show the variation of the amplitude ratio of lg to p with epicentral distance with the coefficient of anelastic attenuation as a parameter when data from explosions and earthquakes in the soviet union are compared with the calculated curves the amplitude ratios of lg and p on the average are larger for earthquakes than explosions however there is much overlap so that this ratio by itself does not appear to be a useful discriminant between earthquakes and explosions

crustal in south korea using the source pair receiver pair method graphic 1 has been studied extensively because its regional variations reflect geological structure values around 1 hz show close correlation with tectonic seismicity we analyze graphic 2 in south korea by applying the source pair receiver pair sprp method to 39 korean earthquakes and 32 far regional earthquakes we obtain nearly 1500 source receiver pairs with the combined difference of epicentral distance d ranging from 16 to 657 km seismograms are filtered by using an eight pole bandpass butterworth filter with five center frequencies 0 375 0 75 1 5 3 and 6 hz the obtained graphic 3 for all frequencies are less than 0 002 which is a reasonable value for a seismically inactive region in spite of the short range of d the results of the sprp method show reliable values especially at 1 5 and 3 hz 1 embed inline graphic 2 gif 2 embed inline graphic 3 gif 3 embed inline graphic 4 gif

contrasting diagenesis of two carboniferous oolites from south wales a tale of climatic influence two oolites in the dinantian mississippian lower carboniferous of glamorgan sw britain were deposited in similar depositional environments but have contrasting diagenetic histories the brofiscin and gully oolites occur in the upper parts of shallowing upward sequences formed through strandplain progradation and sand shoal and barrier growth upon a southward dipping carbonate ramp the brofiscin oolite is characterized by a first generation cement of equant calcite spar preferentially located at grain contacts and forming non isopachous fringes around grains interpreted as meteoric vadose and phreatic in origin isopachous fibrous calcite fringes of marine origin are rather rare and occur only at a few horizons burial compaction was not important and porosity was occluded by poikilotopic calcite spar fitted grain grain contacts locally occur and could be the result of near surface vadose dissolution compaction syntaxial overgrowths on echinoderm debris are common pre compaction overgrowths are cloudy inclusion rich and probably of meteoric origin and post compaction overgrowths are inclusion free by contrast the gully oolite has little first generation cement however marine fibrous calcite is common in oolitic intraclasts as isopachous fringes of acicular calcite crystals closely associated with peloidal internal sediment and early equant drusy calcite spar occurs in the uppermost part of the gully beneath a prominent palaeokarst where pedogenic cements also occur the major feature of gully diagenesis is burial compaction resulting in extensive grain grain dissolution and microstylolitic grain contacts and post compaction poikilotopic spar occluded remaining porosity the brofiscin oolite is pervasively dolomitized up dip but the gully oolite for the most part only contains scattered pre compaction dolomite rhombs and late veins of baroque dolomite with less pervasive dolomitization the difference in diagenetic style of the two dinantian oolites is attributed to prevailing climate the paucity of early meteoric cements in the gully is a result of an arid climate and this is supported by the nature of the capping palaeokarst the abundant meteoric cements in the brofiscin reflect a more humid climate and effective meteoric recharge also resulted in up dip pervasive mixing zone dolomitization the style of early diagenesis in these two oolites exerted a major control on the later burial diagenesis in the brofiscin the early cements inhibited grain grain dissolution and pressure solution while these processes operated extensively in the gully oolite thus prevailing climate can influence a limestone s diagenetic history from near surface through into deep burial

stemflow influences on the formation of solution pipes in bermuda eolianite abstract soil filled pipes consisting of calcite casings were found in all of the eolianite formations of bermuda except the rocky bay formation the pipes are cylindrical in shape taper vertically downwards and occur in aggregated clusters they are most commonly exposed in areas of shoreline erosion in the form of soil filled cylindrical rims of calcite projecting up from the surrounding host eolianite in the early literature on the geology of bermuda it was suggested that these features were fossilized stumps of the bermuda palmetto tree sabal bermudiana in the study presented here this hypothesis is rejected on the basis of the morphology and stratigraphic position of these geomorphic features and their basal area and areal density compared with existing natural stands of s bermudiana the soil filled pipes of bermuda however cannot be simply explained as random solutional features that correspond to points where percolating soil water happened to converge and cause localized subsurface dissolution in situ measurements of stemflow from indigenous tree species suggest that the soil filled solution pipes of bermuda may be the product of stemflow drainage from particular tree species stemflow from s bermudiana was the most acidic with ph values as low as 4 29 compared to the gross rainfall in the open which had a ph of 5 58 the crowns of the bermuda cedar juniperus bermudiana and the subtropical tree species eugenia axillaris had the most significant funnelling effect stemflow volumes from individual trees representing these two species were 20 times greater than the volume of water that would have been collected in rain gauges with orifice areas equivalent to the trees trunk basal areas tree species capable of acidifying intercepted rainwater and funnelling large quantities down their trunks as stemflow may be the cause of subsurface dissolution loci extending vertically downward through bermuda s soluble eolianite formations stemflow from long lived trees representing these species could account for the diameters the cyclindrical shape the vertical orientation and the soil filled interiors of the pipes successive generations of these trees in preferred habitats could explain their clustered distribution and high areal densities 103 pipes ha

the role of fungal biomineralization in the formation of early carboniferous soil fabrics paleosols in the lower carboniferous limestones of south wales commonly contain needle fibre calcite which is an unusual form of calcite recently shown to form by the calcification of fungal hyphae in present day soils the needle fibre calcite occurs in two associations in the paleosols as coatings on sediment grains and as rhizocretions the former can be compared with the microbial grain coatings of quaternary calcretes the latter represent the sites of fungal coats on roots and are interpreted as probable ectomycorrhizae a symbiotic fungal sheath root association these findings suggest that biomineralization was important in the formation of soil fabrics during the carboniferous as it is in present day soils

penetrative calcretes and their stratigraphic implications multiple calcrete horizons previously considered representative of true subaerial exposures may in fact be false penetrative calcretes related to only one subaerial exposure event individual subaerial exposure periods can produce a true surficial calcrete plus a series of penetrative calcretes although penetrative calcrete horizons are not laterally traceable over long distances they are very similar to surficial calcretes are commonly found at sequence and or lithologic boundaries permeability anomalies and can be easily misinterpreted in core borings as representing individual exposure events recent penetrative calcretes are common on elevated limestone ridges of the caicos islands where roots penetrate downward seeking ground water moisture in glacial times penetrative calcretes may have been present throughout carbonate platforms as ground water levels were much lower penetrative and surficial calcretes can be differentiated by the lower concentrations of insoluble al and fe in penetrative calcretes

palaeosols in microtidal carbonate sequences sierra de utiel formation upper cretaceous se spain abstract the sierra de utiel formation upper coniacian to lowermost campanian of the prebetic and iberian ranges consists of a thick 70 120 m carbonate series of stacked thin shallowing up cycles 0 4 0 6 m average that were developed in an extensive shallow epeiric sea control was mainly by a humid climate and by the virtual absence of tides each of these cycles basically consists of a shallow subtidal unit capped by a supratidal unit characterized by calcrete development by considering the maturity of the soils as a guide to its formation time palaeosol analysis emerges as a useful tool for the analysis of these monotonous peritidal series a statistical study of the variations of degree of calcrete maturation and of other variables such as cycle thickness and subtidal facies up through the sierra de utiel formation allows the recognition of three transgressive regressive sequences that correspond to three successive 3rd order cycles further each small cycle could be the result of 5th order sea level changes in tune with milankovitch orbital rhythms the available data however do not allow the rejection of a sedimentary autocyclical origin for the smaller cycles

stability of coda q in the region of parkfield california view from the u s geological survey parkfield dense seismograph array many investigators have proposed that changes in the rate at which the coda decays may be an intermediate term precursor to moderate to large earthquakes parkfield california on the san andreas fault is a promising location for studying premonitory changes in coda q qc because a large earthquake is likely to occur there we have investigated qc using recordings from the u s geological survey parkfield dense seismograph array which is a digital array with 14 triaxial sensors and an aperture of about 1 km for each earthquake we can measure qc from up to 42 recordings their average is more stable than the measurement from a single station using clustered seismicity we have developed criteria for selecting events and reducing scatter in the measurement the qc value determined from a seismogram depends on the position and length of the analysis window thus qc should always be measured from the same length window starting at the same lapse time regardless of the source location in addition the band limited signal to noise ratio at the end of the analysis window is important qc determined in two frequency bands 4 8 hz and 8 16 hz from a tight cluster of 26 events which occurred between december 1989 and january 1994 has not changed despite m 4 7 and m 4 6 events in october 1992 and november 1993 qc measured from local events 60 km in three frequency bands shows larger scatter but has also not changed during this period for monitoring qc observations should include array averaged measurements from a single lapse time because qc measurements made using an analysis window that starts at a constant multiple of the s wave lapse time depend on epicentral distance a procedure combining the evaluation of the time and distance dependences of qc also gives stable observations

black pebble occurrence and genesis in holocene carbonate sediments florida keys bahamas and tunisia abstract black carbonate lithoclasts along with blackened peloids ooids skeletal fragments and entire limestone beds are found in the shallow subtidal intertidal and supratidal zones of modern and ancient carbonate environments they are often associated with pedogenic features such as root traces or caliche the blackening is due to impregnation of the sediment by dissolved colloidal or finely particulate organic substances in an anoxic and alkaline environment or microenvironment the organic matter is derived from decayed algae and or decayed or burnt higher terrestrial plants iron sulfides contribute to the blackening especially in samples containing algal matter a complex interplay of adsorption of organic matter on carbonate crystal surfaces neomorphism and microcrystalline cementation in the vadose or freshwater phreatic zones is thought to fix the organic matter and make the black coloration relatively resistant to oxidation black pebbles form through reworking of the preferentially cemented and blackened sediment by coastal erosion they are mostly relics because the less consolidated host sediment is washed away black pebbles may thus be valuable indicators of ancient coastal and terrestrial environments

measurement of frequency dependent lg attenuation in the great basin measurement of the spatial decay of spectral amplitudes of the higher mode seismic surface wave train lg indicates that in the great basin the apparent seismic quality factor q is a function of frequency observations along a 300 km profile recording of a nuclear explosion yield the function q 206 0 68 over the band 0 3 10 0 hz similar analysis using numerous recordings of earthquakes along paths which provide a good average sampling of the great basin crust gives q 214 15 0 54 0 09 for 0 3 5 0 hz if the crustal sampling by lg energy from nuclear explosions surface sources is primarily in the shallow crust as has been suggested then these results indicate a greater frequency dependence of apparent q there than at depth

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

the structure and diagenesis of rhizoliths from cayman brac british west indies abstract rhizoliths from the pleistocene ironshore formation are formed of a brown micrite core surrounded by sediment that is well cemented with 1 calcite rhomb chains 2 isolated calcite rhombs 3 calcified spherical bodies 4 types i and ii calcified epilithic and chasmolithic filaments and 5 grain coating calcite needle mats the friable host sediment has significantly less cement and lacks the grain coating calcite needle mats and type ii calcified filaments of the rhizoliths the sediment however contains calcite needles and a cryptocrystalline cement which do not occur in the rhizolith the contrast in the amount and type of cement between the rhizoliths and the encasing sediment points to the significant role that plants can play in carbonate diagenesis not only do the plant roots act as conduits for water of varying composition they also provide sites at which algae fungi and bacteria thrive these microorganisms serve to promote diagenesis in the rhizoliths the occurrence of the sediments in a coastal setting means that they are subjected to many different types of water ranging from freshwater to saltwater such variability along with the associated changes in the water chemistry may be responsible for the considerable variation in the cement associated with the rhizoliths

frequency dependent attenuation in the crust beneath central france from lg waves data analysis and numerical modeling abstract the quality factor of shear waves in the crust beneath central france is evaluated by the combined use of data analysis and theoretical modeling the measurement is made from lg wave records of 18 earthquakes at 22 short period vertical seismic stations of the french seismic network the geometrical attenuation of lg waves has been calculated through a numerical simulation in a perfectly elastic model the station responses including site effects have been evaluated from lg waves and from records of the seismic noise q has been calculated for a set of 11 frequencies between 0 5 and 10 hz and has been found to be in the form q 290 f 0 52 where f is the frequency the numerical simulation leads to the interpretation of q of lg waves as the mean value of q within the crust theoretical and experimental decay of energy with distance are in very good agreement the lg waves present a different sensitivity to a low q zone whether this zone is associated with the sediments or with scattering in the lower crust the lower crust beneath central france appears from our experimental results to be associated with high values of q

paleosols in shallow marine carbonate sequences abstract shallow water carbonate sequences in the geological record commonly exhibit numerous exposure surfaces reflecting emersion of sediment due to progradation processes and sealevel oscillations some ancient platform sequences contain hundreds of such surfaces associated with paleosols fossil soils typically calcretes a wide range of macro and microstructures are associated with these calcretes which are reviewed profile types and stages in profile development can be defined the nature of the exposure surface and associated paleosols can be used to identify the nature of the prevailing climate although hydromorphic effects related to marine flooding of the platforms can modify the paleosols a potentially important use of paleosols is to define the nature of sequence boundaries several studies have identified sets of paleosols with varying maturities reflecting changes in rates of accommodation space creation during sealevel rises and falls

paleoclimate controls on stratigraphic repetition of chemical and siliciclastic rocks climate is a primary control on sediment flux from continental sources into sedimentary systems in warm climates siliciclastic input is greatest under highly seasonal rainfall nonseasonal conditions favor formation of end member chemical rocks perennially wet climates are conducive to coal formation whereas dry climates produce carbonates and or evaporites stratigraphic repetition of siliciclastic and chemical rocks therefore appears to be related to paleoclimate cycles as well as to transgressive regressive events and tectonics

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

regional variations of seismic attenuation from coda and l g waves in northern baja california attenuation of coda and lg waves was estimated from events recorded by the seismic network of northern baja california red sismica del noroeste de mexico resnom in the frequency band 1 to 12 hz in order to find a regional variation of qc crustal quality factor for s waves in northern baja california mexico we used the single scattering model of sato 1977 in the time domain to estimate quality factor qc and a spectral approach to relate acceleration spectra with distance to estimate the anelastic attenuation coefficient of lg waves we calculated qc for short 10 s and long lapse times 70 s using local events and the events that originated at the main tectonic features of the area assuming a frequency dependence of qc of the form qc qc we observed for short lapse times a regional variation of q0 with low values from about 53 in the inner continental borderland icb province to about 115 in the peninsular ranges pr and 144 in the gulf of california depression gcd province the values range from 0 70 and 0 85 for events in the icb and pr to 0 44 in the gcd region for long lapse times and for events located in the pr we found q0 values from 49 at stations within the icb to 101 at stations within the gcd attenuation coefficient of lg waves between 1 and 6 hz was also estimated using events located in southern california with source station distances up to 420 km we found that frequency dependence of was higher for source receiver paths going from a typical continental structure to a pull apart basin the gcd province than for paths within the pr using all data in a linear inversion process and assuming a group velocity vlg of 3 4 km s we obtained a power law dependence of the form qlg 288 20 0 32 02

aluminous lateritic soils eleuthera bahamas a modern analog to carbonate paleosols abstract aluminous lateritic soils from governor s harbour eleuthera bahamas are described these soils are forming on eolian ridges under a humid tropical savanna climate the parent material is carbonate eolianite plus airborne dust from north africa the soils are thin discontinuous and concentrated in shallow solution pits they are stony have a crumb texture and are underlain by pedogenically altered limestones the solum has a low sio2 al2o3 ratio and is composed of boehmite hydroxy interlayered clay hic al hematite al goethite calcite and minor quartz the presence of carbonates in the solum buffers the ph and inhibits gibbsite precipitation resulting in a high availability of aluminum for incorporation in hic and iron minerals the moisture egime of these soils is characterized by frequent wetting and drying due to the high porosity and permeability of the underlying carbonates and the intermittent nature of the rainfall boehmite is the stable al phase within cryptovoids where the h2o activities are less than one the dominant pedogenic features in the altered limestones are voids produced by solution of limestone around plant roots these voids are subsequently infilled with overlying solum material and cemented with equigranular calcite alteration rinds containing micritized carbonate grains and laminations of micrite and iron rich clay develop around the voids features observed in aluminous lateritic soils are compared to other carbonate soils and paleosols preserved within carbonate sequences

repeated subaerial exposure of subtidal carbonate platforms triassic northern italy evidence for high frequency sea level oscillations on a 104 year scale triassic carbonate platforms in northern italy ladinian latemar carnian durrenstein norian dolomia principale consist of hundreds of stacked meter scale cycles each made of a subtidal unit with a cap rock that carries vadose cements pisoids and tepee structures these diagenetic caps are interpreted to be due to subaerial exposure of the subtidal sediments the absence of peritidal deposits rules out progradation as the cause of the exposure i e these are not ginsburg autocycles thus the repeated exposure must be the result of relative sea level oscillations which based on the number of cycles and time intervals involved occurred with an average frequency in the 104 year range we postulate a combination of small scale high frequency eustasy and local tectonic movements e g differential subsidence in the norian and infrequent pulses of uplift in the ladinian to explain the cyclicity and its internal variations

a holocene calcrete from north yorkshire england implications for interpreting palaeoclimates using calcretes glacial gravels of late devensian dimlington stadial age 26 000 13 000 years bp at west tanfield north yorkshire england have been cemented by carbonate rich solutions to produce a strongly indurated calcrete horizon the low mg cements occur as drusy spar needle fibres alveolar septal structures micrite and micropinnacles indicative of vadose zone cementation some complex pore partition structures attributed to precipitation along meniscus films also occur these partitions separate air dominated and water dominated microenvironments of the vadose zone the abundance of vadose fabrics shows that the accumulation is not a groundwater calcrete in addition much of the carbonate appears to have been precipitated by biological mediation carbon and oxygen isotopic data suggest that the carbonate did not form as a result of freezing as has been suggested for some arctic soil carbonates the pollen history of the area since the devensian suggests that this calcrete precipitated at low temperatures this contrasts with widely reported occurrences of calcrete in soils of hot arid or semi arid regions and suggests that palaeo calcretes should not be used as absolute palaeoclimatic indicators the unusual occurrence albeit localized of a thick calcrete under a cool and wet climate probably reflects the well drained nature of the gravels the abundance of caco3 as limestone clasts in the gravel and a high degree of biological activity beneath a forest cover which created a local environment favouring carbonate precipitation