the apparent paradox of abundant foramol facies in low latitudes their environmental significance and effect on platform development recent studies of low latitude carbonates from se asia and australia have revealed deposits and platform types that do not fit easily into the perceived view of warm water tropical carbonates the sediments are classified as a foramol or foralgal facies and are dominated by non framework building light dependent biota such as perforate larger benthic foraminifera coralline algae and sometimes halimeda although ancient foramol deposits are often interpreted as an indication of non tropical conditions foramol facies have long been known from the tropics yet the environmental conditions in which they form are poorly known the aims of this paper are to evaluate how these deposits are best classified and more importantly whether there are any overriding controls that influence their common development in low latitude areas and if resultant platform development is affected the deposits are all best grouped within the photozoan association james n p 1997 the cool water depositional realm in james n p clarke j a d eds cool water carbonates sepm special publication 56 1 20 an assignment synonymous with warm water conditions the facies were also found to develop in conditions of limited light or oligophoty all the platforms described are characterised by having extensive areas of oligophotic facies generally in water depths extending down from 20 m but sometimes in shallower waters platforms types vary from land attached rimmed shelves homoclinal and distally steepened ramps to isolated banks and platforms but all have extensive moderate to deep photic zone development of oligophotic facies some workers might assign these platforms to the incipiently drowned platform type read j f 1985 carbonate platform facies models american association of petroleum geologists bulletin 69 1 21 however a morphological assignment is preferred here to signify that many of the deposits did not or may not form through drowning limited light in moderate to deeper depths of the photic zone often in regions with a reduced depth euphotic high light zone is seen as key to the extensive development of these deposits and the resultant platforms these conditions are often developed in humid low latitude areas of high terrestrial runoff and therefore regions of reduced water salinity or in areas of nutrient upwelling reduced water clarity due to nutrients plankton blooms suspended particulate matter upwelling and strong currents all promote the development of oligophotic conditions and facies on a regional scale time periods of relative rises in sealevel can also promote oligophotic facies development the findings of this study have broader implications for the development of low latitude platforms beyond australasia and during time periods when non framework building oligophotic biota are dominant sediment contributors the reconstruction of past climatic conditions based on study of foramol grain assemblages requires careful study to distinguish warm water deposits from those formed in cool waters

ionospheric electron enhancement preceding the 2011 tohoku oki earthquake 1 the 2011 march 11 tohoku oki earthquake mw9 0 caused vast damages to the country large events beneath dense observation networks could bring breakthroughs to seismology and geodynamics and here i report one such finding the japanese dense network of global positioning system gps detected clear precursory positive anomaly of ionospheric total electron content tec around the focal region it started 40 minutes before the earthquake and reached nearly ten percent of the background tec it lasted until atmospheric waves arrived at the ionosphere similar preseismic tec anomalies with amplitudes dependent on magnitudes were seen in the 2010 chile earthquake mw8 8 and possibly in the 2004 sumatra andaman mw9 2 and the 1994 hokkaido toho oki mw8 3 earthquakes but not in smaller earthquakes

a statistical investigation of preearthquake ionospheric anomaly 1 empirical evidence of the preearthquake ionospheric anomalies peias is reported by statistically investigating the relationship between variations of the plasma frequency at the ionospheric f2 peak fof2 and 184 earthquakes with magnitude m 5 0 during 1994 1999 in the taiwan area the peia defined as the abnormal decrease more than about 25 in the ionospheric fof2 during the afternoon period 1200 1800 lt significantly occurs within 5 days before the earthquakes moreover the odds of earthquakes with peia increase with the earthquake magnitude but decrease with the distance from the epicenter to the ionosonde station these results indicate that the peia is energy related

relationship between diagenesis and reservoir quality in sandstones of the garn formation haltenbanken mid norwegian continental shelf a quantitative model is proposed for the dependence of porosity and permeability on diagenesis in subarkosic arenites of the middle jurassic garn formation porosity variation is controlled by the combined effects of compaction and quartz cementation in general more porosity has been lost by compaction than by quartz cementation but compactional porosity loss appears to have occurred relatively early in the burial history before burial below 2 km below the sea floor thus progressive reduction of the total porosity with increasing burial below 2 km results mainly from quartz cementation permeability is a function of the abundance of intergranular macroporosity which is interpreted to be a measure of effective porosity at depths less than 3 5 km below the sea fl or intergranular macroporosity generally comprises more than 50 percent of the total porosity but at greater depth as total porosity decreases below about 16 percent the ratio of effective to ineffective porosity drops below one this depth corresponds to the onset of extensive illitization and grain dissolution which results in major reorganization of the pore system generation of secondary porosity by feldspar dissolution appears not to have been beneficial to reservoir quality in the garn formation but it is regarded as an intrinsic part of the overall process of porosity destruction with increasing diagenesis

holocene landscape history and palaeohydrology evidenced by stable carbon isotope δ13c analysis of alluvial sediments in the mbari valley 5 n 23 e central african republic abstract pleistocene to holocene as well as recent trends in climate have an influence on the composition of savanna forest vegetation fringes in africa dominated mainly by savanna c 4 and mainly forest c 3 groups of plants the modified vegetation cover plays an important role on the runoff processes and on the discharge of the draining river systems because the majority of forest savanna borders in central africa is situated on geologically old planation surfaces the main sources of palaeoenvironmental information are alluvial sediments of rivers therefore this study focuses on the examination of alluvial soils and the determination of stable carbon isotopes 13 c of organic sediments on the mbomou plateau and in the mbari valley in the southeast of the central african republic car it has been shown that there is some evidence for an ongoing increase in c 3 dominated forest plants reducing the recent extension of savannas in the study area the most important reasons for this trend are sufficient amount of annual rainfall 1500 mm decrease in bushfire frequency and negative migration processes of the rural population due to the economic crisis in central africa 13 c values in fossil soil horizons show that a greater extent of forest on the mbomou plateau occurred around 7 7 5 ka and between 2 5 and 3 ka drier savanna dominated vegetation patterns were found at 5 ka and from 1 ka to the present the more humid and arid climate periods during the holocene partly correspond with high and low lake levels of lake chad the findings also seem to be confirmed by other studies neighbouring central african regions as cameroon gabon and congo brazzaville bateke plateau which indicate a more general validity of the findings from the mbomou plateau especially for the period since 3 ka

potassium leached zones at the contacts of the garn formation mid norwegian continental shelf evidence for the role of shale in sandstone diagenesis abstract

textural and geochemical alternations in late cenozoic bahamian dolomites dolomitized intervals of a core from san salvador island bahamas exhibit variations of two texturally and geochemically distinct end members in the pliocene section of the dolomitized interval the two end members alternate in a pattern that may reflect originally and or diagenetically modified depositional facies formerly mud free intervals locally capped by exposure surfaces are massive crystalline mimetic dolomites cm muddier sediments are replaced by friable microsucrosic dolomites ms cm and ms dolomites also differ in porosity 30 permeability 100 md mol mgco3 44 9 vs 47 7 mol oxygen isotopic composition 1 7 vs 2 7 and strontium content 241 vs 106 ppm these data indicate that depositional and diagenetic fabric are the principal controls governing the distribution of dolomite types differences in texture and geochemistry are suggested as arising through differential rates of crystallization produced as a result of variations in permeability and reactivity of the precursor sediments and rocks

reef exploration in the east sengkang basin sulawesi indonesia abstract reconnaissance seismic shot in 1971 72 showed a number of well defined seismic anomalies within the east sengkang basin which were interpreted as buried reefs subsequent fieldwork revealed that upper miocene reefs outcropped along the southern margin of the basin a drilling programme in 1975 and 1976 proved the presence of shallow gas bearing upper miocene reefs in the northern part of the basin seismic acquisition and drilling during 1981 confirmed the economic significance of these discoveries with four separate accumulations containing about 750 10 9 cubic feet of dry gas in place at an average depth of 700 m kampung baru is the largest field and contains over half the total both reservoir quality and gas deliverability are excellent deposition in the east sengkang basin probably started during the early miocene a sequence of lower miocene mudstones and limestones unconformably overlies acoustic basement which consists of eocene volcanics during the tectonically active middle miocene deposition was interrupted by two periods of deformation and erosion carbonate deposition became established in the late miocene with widespread development of platform limestones throughout the east sengkang basin thick pinnacle reef complexes developed in the areas where reef growth could keep pace with the relative rise in sea level most reef growth ceased at the end of the miocene and subsequent renewed clastic sedimentation covered the irregular limestone surface late pliocene regression culminated in the holocene with erosion the walanae fault zone part of a major regional sinistral strike slip system separates the east and west sengkang basins both normal and reverse faulting are inferred from seismic data and post late pliocene reverse faulting is seen in outcrop

seismoionospheric gps total electron content anomalies observed before the 12 may 2008 mw7 9 wenchuan earthquake 1 the global ionospheric map gim is used to observe variations in the total electron content tec of the global positioning system gps associated with 35 m 6 0 earthquakes that occurred in china during the 10 year period of 1 may 1998 to 30 april 2008 the statistical result indicates that the gps tec above the epicenter often pronouncedly decreases on day 3 5 before 17 m 6 3 earthquakes the gps tec of the gim and electron density profiles probed by six microsatellites of formosat3 cosmic f3 c are further employed to simultaneously observe seismoionospheric anomalies during an mw7 9 earthquake near wenchuan china on 12 may 2008 it is found that gps tec above the forthcoming epicenter anomalously decreases in the afternoon period of day 6 4 and in the late evening period of day 3 before the earthquake but enhances in the afternoon of day 3 before the earthquake the spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650 km and 2850 km from the epicenter in the latitudinal and longitudinal directions respectively the f3 c results further show that the ionospheric f2 peak electron density nmf2 and height hmf2 significantly decreases approximately 40 and descends about 50 80 km respectively when the gps tec anomalously reduces

a statistical study of ionospheric earthquake precursors monitored by using equatorial ionization anomaly of gps tec in taiwan during 2001 2007 abstract in this paper we examine pre earthquake ionospheric anomalies by the total electron content tec derived from a ground based receiver of the global positioning system gps a network of eight gps receivers is used to construct daily latitude time tec ltt plots to monitor the crest of equatorial ionization anomaly eia in the taiwan area three parameters of the strength location and formation time of the eia crest are extracted a 15 day running medians of the three parameters and the associated upper and lower quartiles are utilized as the references for identifying abnormal signals for all of the 150 m 5 0 earthquakes in the taiwan area during 2001 2007 results show that the eia crest significantly moves equatorward poleward and appears in an earlier later time of the afternoon period a few days before after the earthquakes along the taiwan longitude the two parameters of the eia crest location and occurrence time can be employed to detect ionospheric earthquake precursors the results further imply that atmospheric electric fields generated around the epicenter of a forthcoming earthquake during the preparation period are essential

spatiotemporal variations in hydrological regimes within central africa during the xxth century abstract using several statistical tests we divided into homogeneous segments the xxth century long discharges data series and the rainfall data series of the congo river and of several of its right bank sub catchments these tests revealed that the river congo at brazzaville experienced a phase of so called stable discharge from the beginning of the xxth century until 1960 a phase of surplus discharge during the 1960s testimony to its centennial flooding and then from 1971 onwards two successive phases of lower discharge the second one stretching from 1980 up to now being the most accentuated with a 10 drop in the total series interannual discharge 40 600 m 3 s 1 it has only been very recently in 1990 that the river dropped to its lowest level of the century the dates at which hydrological discontinuities appear are observed to be globally similar within practically all of the tributaries studied the most significant being that of 1970 already well known in west africa during the second half of the century these discontinuities occur roughly every ten years at the beginning of the 1960s 1970s and 1980s rainfall discontinuities are not as numerous as discharges ones they separate homogeneous phases whose variations between them are less pronounced than that of those separated by discharges discontinuities this underlines the major importance of the geographical location and of the physiographical characteristics of river basins on hydrological spatiotemporal variations lastly we show that the effects of the recent drought are more visible and pronounced in the northern areas of this vast basin than in the southern ones

physiogeographic features of the oubangui catchment and environmental trends reflected in discharge and floods at bangui 1911 1999 central african republic abstract varying discharges of large rivers observed over long periods can reflect environmental trends like climate change within the catchment e g ongoing aridification results in a reduced discharge the present study on the oubangui river in central africa first lines out some physiogeographic features of the almost 500 000 km2 large catchment situated on the vast north equator rise subsequently a discharge record from 1911 1999 of qmax and qmin covering data for 73 years from the gauge station bangui is examined annual variability of oubangui floods is generally high and shows over the past years especially since the mid to end 1960s a less significant trend to a slight depletion of maximum discharge frequency analysis gauss gumbel weibull of floods resulted in return periods between 7 and 35 years distributions calculated after gumbel generally gave the best results no linear and simple evidence exist of the tendency of the river to reduce discharge because of a depletion of rain fall as the oubangui s floods are again increasing since the mid 1990s finally the consequences of oubangui flood hazards for the growing town of bangui are discussed flooding of urban areas from exceptional high qmax discharge is spatially reconstructed for the floods in 1916 1962 and 1999

the role of sea surface temperature as a control on carbonate platform development in the western coral sea the derivation of a detailed sea surface paleotemperature curve for the middle miocene holocene 10 0 ma from odp site 811 on the queensland plateau northeast australia has clarified the role of sea surface temperature fluctuations as a control on the initiation and development of the extensive carbonate platforms of this region this curve was derived from isotopic analyses of the planktonic foraminifer globigerinoides ruber and converted to temperature using the surface water paleotemperature equation accounting for variations in global ice volume the accuracy of these data were confirmed by derivation of paleotemperatures using the water column isotopic gradient 13o corrected for salinity and variations in seafloor water mass temperature results indicate that during this period surface water temperatures were on average greater than the minimum required for tropical reef growth 20 c veron 1986 with the exception of the late miocene and earliest early pliocene 10 4 9 ma when there were repeated intervals of temperatures between 18 20 c tropical reef growth on the queensland plateau was extensive from the early to early middle miocene 21 13 ma after which reef development began to decline a lowstand near 11 ma probably exposed shallower portions of the plateau after re immersion near 7 ma the areal extent of reef development was greatly reduced 50 paleotemperature data from site 811 indicate that decreased sea surface temperatures were likely to have been instrumental in reducing the area of active reef growth on the queensland plateau reduced reefal growth rates continued until the late pliocene or quaternary despite the increase of average sea surface paleotemperatures to 22 23 c studies on modern corals show that when sea surface temperatures are below 24 c as they were from the late miocene to the pleistocene off northeast australia corals are stressed and growth rates are greatly reduced consequently when temperatures are in this range corals have difficulty keeping pace with subsidence and changing environmental factors in the late pliocene sedimentation rates increased due to increases in non reefal carbonate production and falling sea levels it was not until the mid quaternary 0 6 0 7 ma that sea surface paleotemperatures increased above 24 c as a result of the formation of a western coral sea warm water pool because of age discrepancies it is unclear exactly when an effective barrier developed on the central great barrier reef the formation of the warm water pool was likely to have either assisted the formation of this barrier and or permitted increased coral growth rates fluctuations in sea surface temperature can account for much of the observed spatial and temporal variations of reef growth and carbonate platform distribution off northeast australia and therefore we conclude that paleotemperature variations are a critical control on the development of carbonate platforms and must be considered an important cause of ancient platform drowning

statistical evidences of seismo ionospheric precursors applying receiver operating characteristic roc curve on the gps total electron content in china abstract evidence of the seismo ionospheric precursor sip is reported by statistically investigating the relationship between the total electron content tec in global ionosphere map gim and 56 m 6 0 earthquakes during 1998 2013 in china a median based method together with the z test is employed to examine the tec variations 30 days before and after the earthquake it is found that the tec significantly decreases 0600 1000 lt 1 6 days before the earthquake and anomalously increases in 3 time periods of 1300 1700 lt 12 15 days 0000 0500 lt 15 17 days and 0500 0900 lt 22 28 days before the earthquake the receiver operating characteristic roc curve is then used to evaluate the efficiency of tec for predicting m 6 0 earthquakes in china during a specified time period statistical results suggest that the sip is the significant tec reduction in the morning period of 0600 1000 lt the sip is further confirmed since the area under the roc curve is positively associated with the earthquake magnitude

observations and simulations of seismoionospheric gps total electron content anomalies before the 12 january 2010 m7 haiti earthquake 1 in this paper the total electron content tec of the global ionosphere map gim is used to detect seismoionospheric anomalies associated with the 12 january 2010 m7 haiti earthquake and an ionospheric model is applied to simulate the detected anomalies the gim temporal variation shows that the tec over the epicenter significantly enhances on 11 january 2010 1 day before the earthquake the latitude time tec ltt plots reveal three anomalies 1 the northern crest of equatorial ionization anomaly eia moves poleward 2 the tecs at the epicenter and its conjugate increase and 3 the tecs at two dense bands in the midlatitude ionosphere of 35 n and 60 s further enhance the spatial analysis demonstrates that the tec enhancement anomaly appears specifically and persistently in a small region of the northern epicenter area the simulation well reproduces the three gim tec anomalies which indicate that the dynamoelectric field of the ionospheric plasma fountain might have been perturbed by seismoelectric signals generated around the epicenter during the earthquake preparation period

structure of optimal strategies in earthquake prediction abstract prediction of a stationary sequence of strong events is considered the prediction uses any information that is related in a stationary way to the sequence the goal of prediction is stated as minimization of a loss function which is a function of two long term errors the fraction of failures to predict and the fraction of alarm time we describe the structure of optimal prediction strategies for any convex loss function given a time varying hazard function prediction stability is analyzed within the framework of this loss function approach the main result of this work may be regarded as a rigorous formulation and refinement of some earthquake prediction algorithms

temporal and spatial precursors in the ionospheric global positioning system gps total electron content observed before the 26 december 2004 m9 3 sumatra andaman earthquake 1 we report seismo ionospheric precursors of anomalous decreases in the total electron content tec appearing day 5 prior to an m9 3 earthquake the largest one in the last five decades which occurred in sumatra andaman indonesia on 26 december 2004 sequences of global ionosphere maps of the tec derived from worldwide ground based receivers of the global positioning system gps are used to statistically study the temporal and spatial precursors of the earthquake it was found that the temporal precursor of the gps tec around the epicenter was significantly reduced during the afternoon period on d 5 before the earthquake the spatial precursors prominently persistently and simultaneously appear around the epicenter and its conjugate areas of the sumatra andaman earthquake

variations of ionospheric total electron content during the chi chi earthquake on 20 september1999 ut 21 septemberin local time lt a large earthquake mw 7 7 struck central taiwan nearthe small town of chi chi the greatest plasma frequency in the ionosphere fof2 observed by the chung li ionosonde 25 0 n 121 2 e reveals three clear precur sors at 1 3 and 4 days prior to the earthquake this paper examines the ionospheric total electron content tec ob served by a network of the global positioning system gps receivers in taiwan area it is found that variations in fof2 and overhead tec recorded at chung li have a similar ten dency combining the data of the network of 13 gps re ceivers time and spatial variations of tec prior to the chi chi earthquake are examined results show that the equa torial anomaly crest moves equatorward and its tec value significantly decreases 1 3 and 4 days before the earth quake a comparison between the disturbed and reference previous 15 day median days confirms that tec decreases significantly around the epicenter in the afternoons of these days finally possible mechanisms are proposed and dis cussed

pore networks in holocene carbonate sediments abstract permeabilities of holocene carbonate sediments from florida and the bahamas determined for 74 samples by water flow rates in a variable head permeameter range from 0 6 to 57 000 millidarcies porosities range from 40 to 78 percent these parameters are related to depositional texture as follows table the muddiest sediments i e the finest grained have the highest porosities but lowest permeabilities this negative correlation between porosity and permeability is the reverse of the situation found in carbonate rocks even as young as pleistocene high porosity and low permeability in sediments show a strong correlation with percentage of fines 62 m from capillary pressure curves it is inferred that many of the pore throats of muddy carbonate sediments are less than 1 m in diameter at least after drying measured permeabilities are used to calculate cementation rates for simple models of upper phreatic zone cementation the calculated rates would require excessive time to produce the degree of cementation seen in late pleistocene rocks of florida and the bahamas the amounts of rainfall and evaporation are the most important factors in the degree of cementation

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

deposition and diagenesis of miocene limestones senkang basin sulawesi indonesia abstract miocene knoll reef limestones form gas reservoirs in the east senkang basin of southwest sulawesi they are composed predominantly of packstones and wackestones but grainstones and boundstones also occur uplift and exposure of the reef occurred during deposition this together with burial resulted in dissolution of bioclasts precipitation of meniscus and blocky spar cements extensive fissuring of the rock and filling of the fissures by internal sediment predominantly carbonate silts the meniscus cements are unusual in that they occur mostly within biomouldic pores particularly after corals the meniscus form of the cement may be a result of air bubbles trapped within the complex pore system formed from the dissolution of corals the fissures which are probably a product of fracturing associated with local fault movements form complex networks linking biomouldic pores carbonate internal sediments mostly crystal silt but also pelleted which form thin graded layers in places completely fill the fissures and adjacent biomouldic pores these features in association with bioclasts dissolution and meniscus cements suggest a vadose origin this interpretation is supported by the variation in the 18 0 and 13 0 stable isotope values of the internal sediment compared with the depositional matrix equant sparry calcite cements are locally extensive on the basis of only moderately depleted 8 0 values and elevated strontium values they are tentatively interpreted to be of marine phreatic origin

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

porosity permeability relationships in miocene carbonate platforms and slopes seaward of the great barrier reef australia odp leg 194 marion plateau this paper reports a series of 700 porosity permeability analyses and supporting petrographic and sedimentologic descriptions from early to late miocene carbonate strata cored on the marion plateau offshore from north eastern australia during ocean drilling program odp leg 194 the samples analysed are not only mainly coarse bioclastic limestones and dolomitized equivalents from platform top facies but also include 79 plugs from deeper water slope to hemipelagic drift facies outstanding characteristics of this data set are the wide ranges of porosity and permeability in both limestones and dolostones the large degree of short range heterogeneity typical of these strata and the better porosity permeability correlation of dolostones than limestones the platforms have experienced widely varying calcite cementation dolomitization and dissolution but show little clear evidence of meteoric diagenesis suggesting that subaerial exposure may have played little role in porosity permeability evolution permeability for given porosity is controlled by grain size and calcite cement content in grainstones and by occurrence of larger shelter pores and vugs in mud rich samples dolomitization tends to reduce the variation of permeability for given porosity by recrystallizing mud matrix to form intercrystalline macroporosity that connects vugs and moulds to become integrated with the effective pore system as a result there are no differences in permeability porosity trends for different dolostone textures whether dominated by intercrystalline vuggy or preserved intergranular pore types two platform top sites separated by only 5 km display a major lateral variation in dolostone porosity permeability characteristics within the youngest dolostone units this difference is interpreted as reflecting a relatively windward current facing setting of the site with the overall higher permeability for given porosity site 1199 that led to less muddy depositional facies greater cementation and lesser grain dissolution pore geometry parameters measured by petrographic image analysis confirm that the windward dolostones have pores that are both larger and less intricate than dolostones comprising the more current protected location

is an unusual large enhancement of ionospheric electron density linked with the 2008 great wenchuan earthquake 1 on 12 may 2008 at 0628 ut a major earthquake ms 8 0 struck wenchuan county 31 0 n 103 4 e in southwest china the maximum ionospheric electron density at f2 peak nmf2 recorded an unusual large enhancement during the afternoon sunset sector by the chinese ionosondes over wuhan 30 5 n 114 4 e and xiamen 24 4 n 123 9 e which are close to the earthquake epicenter an averaged increase at these two stations is about 2 times on a geomagnetic quiet day 9 may kp 2 3 days prior to the earthquake relative to the median value of 1 12 may whereas the increase was much less significant over yamagawa 31 2 n 130 6 e and okinawa 26 7 n 128 2 e in japan combining the data from the network of 58 global positioning system receivers around china and the global ionospheric map the variations of the total electron content reveal the region where enhancement persisted for a long period to be within longitudes 90 130 e our results suggest that this abnormal enhancement is most possibly a seismo ionospheric signature

seismo ionospheric signatures prior to m 6 0 taiwan earthquakes this paper examines variations of the greatest plasma frequency in the ionosphere fof2 recorded by the chung li ionosonde 25 0 n 121 1 e before m 6 0 earthquakes during 1994 1999 the 15 day running median and the associated inter quartile range are utilized as the reference and the upper or lower bounds to monitor the ionospheric fof2 variations for finding seismo ionospheric signatures precursors of the earthquakes it is found that precursors in the form of the recorded fof2 falling below its associated lower bound around 1200 1700 lt appear 1 6 days prior to these earthquakes on september 20 1999 ut september 21 taiwan local time a large mw 7 7 earthquake struck central taiwan near the small town of chi chi we analyzed the fof2 and found three clear precursors 1 3 and 4 days prior to the chi chi earthquake

the relative roles of compaction and early cementation in the destruction of permeability in carbonate grainstones a case study from the paleogene of west central florida u s a abstract how compaction can yield a progressive decrease in the permeability and pore structure of carbonate grainstones is not well documented in this study the destruction of permeability by compaction relative to early cementation is examined in forty five shallow buried 30 440 m grainstones with a range in permeability of 12 to 5180 md compaction and cementation indices calculated from thin section point count data indicate a group of grainstones dominated by cementation and another by compaction log linear cross plots of permeability versus these indices suggest that permeability loss in these two groups occurs by different processes the nature of those processes is elucidated by capillary pressure data and the distribution of cement and compaction fabrics as a function of permeability as cement abundance increases in the cement dominated samples a continuous distribution of cement develops along grain surfaces which is followed by the development of partial and then complete pore filling mosaics permeability is progressively reduced with this succession of cement fabrics and an increasingly greater percentage of pore space is positioned behind progressively smaller throats permeability loss results from porosity reduction progressive constriction of pore throats and increased tortuosity of flow paths once permeability is reduced to tens of millidarcies effective pore radii are all less than 1 m and many are less than 0 1 m but there is no evidence for complete blocking of all pore throats in this suite of samples in absolute terms the pore lining cements reduce permeability by thousands of millidarcies whereas the pore filling cements reduce permeability only by hundreds of millidarcies mechanical compaction is the dominant cause of permeability reduction between 5000 and about 500 md in the compaction dominated samples linear grain contacts and embayed grains become more abundant and close to overly close packing textures become more homogeneously distributed as permeability decreases however there is no concurrent change in the amount of pore space accessed by large or small throats indicating that mechanical compaction does not uniformly constrict or seal pore throats instead the data suggest that mechanical compaction reduces permeability by reducing porosity lengthening pore throats and increasing tortuosity at about 500 md the compaction dominated trend steepens on the log linear plot of permeability versus porosity a change that corresponds to the development of grain to grain pressure solution unlike mechanical compaction grain to grain pressure solution constricts and eliminates pore throats and isolates pore space resulting in a loss of large throats and an increase in the amount of pore volume accessed by small throats in contrast to cement dominated samples the most effective pore radii are still greater than 1 m at tens of millidarcies of permeability such low amounts of permeability can be reached even when pressure solution is not pervasively distributed throughout a sample