fluid flow and late diagenesis of fault infill carbonates in the aptian dolostones at jabel semmama kasserine area western central tunisia abstract in western central tunisia kasserine area dolomitization of jabel semmama aptian limestones of the serj formation fm led to the dolostones of the orbata fm these dolostones are cross cut by several generations of faulting and fracturing the current study focused on e w trending faults and fractures system incorporating carbonate infills and freshwater flows which have stimulated continental diagenetic processes the faulting fracturing and rock fluid interactions yielded nine fault infill diagenetic and tectonic sedimentary phases the purpose of studying the tectonic stresses and the nine phases was to elucidate their late impact on the aptian dolostone reservoir quality this enquiry was based on lithological tectonic microfacies and oxygen carbon o c isotopes investigations analyses of stable o c isotopes are performed on crushed and dedolomitized dolostones as well as on calcite cement laminae and spherulites c1 c2 the crushed and dedolomitized dolostones 18o and 13c data averages 4 0 v pdb 1 75 v pdb remain close to the moderately depleted results of the aptian replacive dolostone host rocks averages 3 6 v pdb 2 0 v pdb inversely calcite cement laminae and spherulites c1 c2 yielded strikingly depleted oxygen values 18o averages 7 77 v pdb 8 0 v pdb pointing out to freshwater controlled diagenesis the discrepancy between the two records 0 23 v pdb is ascribed to cooling during the precipitation of calcitic cement spherulites the divergence between the two depleted 13c values of the two cements c1 c2 averages 6 19 v pdb and 4 0 v pdb is attributed to climatic control wet dry alternations that controlled the micritization phenomenon the latter orchestered the release of ca12co3 being more mobile than ca13co3 this process is in agreement with the strong variation of fluid flow supplies vadose phreatic transcribed in the lithology as cement phases lamellar spherulites gelatinous vadose and granular the study series record two major climatic changes a wet period encompassing phases p1 p4 and a dry period extending on phases p5 p9 two short cool and wet episodes accompany this period the nine tectonic sedimentary and diagenetic phases occurred into two periods through the telogenetic stage uplift they started at the miocene pliocene during the atlasic foldings along e w faults and fractures phases p1 p6 and continued throughout the quaternary period villafranchian along a reactivation of the same direction phases p7 p9 we believe that the nine phases arose after the oae s organic matter maturity and thus had nearly no impact on any early oil migration while the earlier diagenesis phases remain the most useful for the reservoir quality

early carboniferous of the solway basin a tectonostratigraphic model and its bearing on hydrocarbon potential abstract the solway basin forms the western portion of the northumberland trough a carboniferous basin system trending wsw ene across northern england a study of the tectono stratigraphic variations along the margins allows certain predictions to be made regarding the hydrocarbon prospectivity of the dinantian it is proposed that earliest carboniferous extension initiated a series of half grabens separated by transfer zones that have subsequently formed fold culminations and fault belts within the basin a model for the proposed graben polarity switching in the basin system is outlined differential subsidence across active faults led to pronounced facies variations in the courcevan chadian which subsequently declined in importance until in brigantian pendleian times deposition was governed by regional subsidence the initial stages of graben formation led to the deposition of subaerial coarse clastic facies associations followed by a cyclical series of marine transgressions and regressions the model anticipates that the best development of reservior facies is in the distal nearshore equivalent of the early dinantian alluvial coarse clastics one of the hydrocarbon objectives identified is stratigraphic trapping in these sands enhanced by courceyan chadian rollover early carboniferous algal source rocks are considered as lateral equivalents to the reservoirs and are calculated as oil generating from the permo trias onwards the westphalian coals are unlikely to have generated significant gas in the basin

a 44 kyr paleoroughness record of the antarctic surface two 788 m conductivity records from ice cores drilled at dome c antarctica provide an unprecedented opportunity to examine the past roughness of the antarctic surface by measuring the distribution of depth differences between synchronous events in the cores the surface height distribution can be estimated during time intervals in the past for the first time we publish a record of this type and consider its paleoclimatic implications the paleoroughness originating from sastrugi and dunes on the ice sheet surface is hypothesized to be related to the wind speed temperature and accumulation rate during the period of preservation the roughness record indicates only a slight decrease in the preserved surface roughness from the last glacial period 0 031 m root mean square r m s of surface deviation to the present 0 029 m r m s this result is surprising given the large change in temperature and accumulation rate that occurred during the last climatic transition however it could be consistent with modeling results suggesting low wind speeds on the east antarctic plateau during the last ice age if the possible influences of the accumulation and temperature changes are ignored additionally the reliability of the dome c ice core record is assessed and the probability of short term events being missing from the profile is determined these results are of particular interest when constraining the proportion of events that may be synchronously matched with other ice cores the principles and results present here allow inferences about the natural variation in ice core records generally

spatial distribution of sheet flow velocity along slope under simulated rainfall conditions abstract velocity of sheet flow is an important parameter for understanding the process of inter rill erosion on a hill slope under rainfall conditions a solute centroid method was employed to measure velocity distribution of sheet flow basing on solute transport process in the flow in an 8 m long flume the flow velocity measurements were made at slope lengths of 3 5 6 and 7 m under slope gradients of 5 10 and 20 and rainfall intensities of 80 120 and 160 mm h 1 respectively the measurements clearly showed that mean flow velocity ranged from 0 050 to 0 352 m s 1 and increased with slope gradient and rainfall intensity velocity of sheet flow increased with slope length while the increase rate slowed down before approaching a steady velocity the distance for sheet flow velocity to reach its maximum became shorter under greater slope gradient and rainfall intensity water depth was

dedolomitization in the taum sauk limestone upper cambrian southeast missouri abstract coarse dolomite crystals in the taum sauk limestone upper cambrian southeast missouri contain both calcite and iron oxides in rhombohedral zones and along fractures and cleavage traces the dolomite crystals are demonstrably nonstoichiometric averaging 57 mole percent caco3 and are compositionally zoned ranging from 1 40 to 4 56 mole percent feco3 cathodoluminescene study and microprobe analyses of the dolomite coupled with scanning electron microscope sem examination of etched fracture surfaces reveal that 1 scattered dolomite within the calcite iron oxide zones is the most iron rich 2 calcite within dolomite rhombs is brightly luminescent nonferroan and is intergrown with iron oxides 3 the iron oxides display two crystal habits thin red hematite circular plates typically 0 7 to 1 0 microns across grouped in rosettes and prismatic bundles and prismatic radiating aggregates of brown crystals goethite typically 1 to 3 microns in length 4 narrow veinlets of dolomite associated with calcite and iron oxides along cleavage traces form a three dimensional network this feature which aided in interpreting the iagenetic history of the dolomite was not observed during petrographic examination but was readily observed with the sem the occurrence of nonferroan calcite and ferric oxides in rhombohedral zones in taum sauk dolomite suggests that dedolomitization occurred by the oxidation and alteration of ferroan dolomite zones and probably reflects alteration related to recent weathering

dolomitic breccia veins as evidence for extension and fluid flow in the dalradian of argyll veins of red dolomite occur extensively in the dalradian rocks of argyll scotland and adjacent areas the veins represent brittle extensional deformation preferentially reactivating caledonian quartz veins the dolomite is associated with reddening of the adjacent dalradian country rock which it partially replaced dolomite was also precipitated in overlying old red sandstone and probably dates to late carboniferous early permian fluid inclusion studies show that the veining involved moderate temperature 75 to 115 c fluids stable isotope data suggest that these fluids were basinal brines traces of chalcopyrite paragenetically late in the veins may reflect the mineralization which occurs more widely in the dalradian rocks of argyll the red colour of the dolomite is due to abundant haematite crystallites that grew in the dolomite crystal fabric palaeomagnetic analysis yields a consistent late permian early triassic age for the haematite growth in the dolomite veins and the reddened dalradian country rocks this age represents the time of haematite precipitation from iron rich dolomite that may have been related to deep oxidizing weathering gold anomalies associated with reddened basement rock must be of this age or younger

defining the geochemical composition of the epica dome c ice core dust during the last glacial interglacial cycle the major element composition of the insoluble windborne long range dust archived in the european project for ice coring in antarctica dome c ice core has been determined by particle induced x ray emission analyses the geochemistry of dust from the last glacial maximum lgm and from the holocene is discussed in terms of past environmental changes throughout the last climatic cycle antarctic dust from glacial and interglacial climate clearly reveals different geochemical compositions the weathered crustal like signature of lgm dust is characterized by a low compositional variability suggesting a dominant source under the glacial regime the close correspondence between the major element composition of antarctic glacial dust and the composition of southern south american sediments supports the hypothesis of a dominant role of this area as major dust supplier during cold conditions conversely the major element composition of holocene dust displays high variability and high al content on average this implies that an additional source could also play some role comparison with size selected sediments suggests that a contribution from australia is likely during warm times when a reduced glacial erosion decreases the primary dust production and a more intense hydrological cycle and larger vegetation cover inactivates dust mobility in a large part of southern south america weakening its contribution as a massive dust supplier to antarctica

significance of secondary porosity in interpreting sandstone composition secondary porosity resulting from dissolution of unstable framework grains such as feldspar and rock fragments including chert is common in sandstones extensive dissolution of framework grains may result in misinterpreting the original composition of a sandstone and hence in misinterpreting its provenance to avoid these problems secondary porosity caused by grain dissolution must be recognized sandstone composition may be properly evaluated by including the dissolved portion of a framework grain as a grain rather than as porosity while point counting this should be useful in interpreting original composition of sandstones and in paleogeographic reconstruction of prospect areas

absolute dating of dedolomitization by means of paleomagnetic techniques paleomagnetic analysis in conjunction with petrographic studies is an approach whereby absolute dates can be placed on diagenetic events hematite is associated with dedolomite in the lower ordovician kindblade formation in south central oklahoma and is interpreted as a by product of the dedolomitization of ferroan dolomite paleomagnetic results date the time of dedolomitization as late pennsylvanian early permian dedolomitization was probably caused by oxidizing fluids with high calcium contents that migrated through the kindblade formation following uplift of the arbuckle mountains

south pole paleowind from automated synthesis of ice core records 1 we develop a fully automated reconstruction of south pole surface roughness as a measure of past wind intensity using dynamic warping feature recognition and internal consistency checks to reduce subjectivity and analysis time we synchronized millimeter resolution optical profiles of deep south pole glacial dust together with ice core data between the ages 26 and 90 thousand years b p the images were captured using a laser dust logger in six boreholes of the icecube neutrino detector array a massive construction project in the ice at south pole and an unusual opportunity for glaciology and paleoclimate research south pole surface roughness anticorrelated with curves of antarctic pco2 and temperature which we propose were connected through secular migrations of the southern hemisphere westerlies this new paleoclimate signal may be direct evidence of atmospheric reorganization during the glacial helping to deconvolve the thermodynamics and biogeochemistry of climate change we also found that local intensity of atmospheric circulation roughly tracked the quantity of wind borne particulates deposited in antarctic ice during the glacial period although the largest dust increases were likely furnished by the source regions

constraints on the development of secondary porosity in the subsurface re evaluation of processes abstract secondary porosity formed by the dissolution of grains and cements is of great economic importance in both clastic and carbonate reservoirs a review of the commonly proposed mechanisms for the production of secondary porosity indicates that meteoric water penetration and mixing corrosion may be able to create significant volumes of secondary porosity in the shallow subsurface leaching by acidic fluids generated by solution of co 2 or monocarboxylic acids both derived during the thermal maturation of organic matter or by acidic fluids created by clay mineral reactions in shales are the most commonly proposed mechanisms by which secondary porosity is said to form in the deep subsurface however these mechanisms suffer from great difficulties in producing significant volumes of secondary porosity once mass balance and fluid migration problems are taken into account it is highly likely that the correct mechanism for the creation of economically significant amounts of secondary porosity in the deep subsurface is yet to be found

multiphase reddening and weathering events in upper carboniferous red beds from the english west midlands sediments of the halesowen and salop formations westphalian d stephanian in the west midlands were deposited on the southern margin of the pennine basin during a period of relative tectonic quiescence during the variscan orogeny the clastic framework of the predominantly red sandstones and mudstones in the salop formation includes large detrital hematite grains these yield a primary component of magnetization indicating that sediments were deposited close to the carboniferous palaeo equator variscan uplift erosion and subsequent deep oxidation in an arid climate during the permian resulted in the precipitation of finer hematite in rocks of both formations which are now found at depths of over 150 m below the present day ground level these grains carry secondary magnetizations which indicate formation at palaeolatitudes of between 5 and 15 n the position that britain occupied during the permian the pattern of permian remagnetization particularly in borehole samples suggests that the secondary fine grained hematite was precipitated as a result of lateral flow of meteoric water through connected permeable sandstone units rather than downward percolation through the entire succession present day surface weathering has resulted in the dissolution of the finer grains of hematite and in some cases where permeabilities are relatively high it has also affected the coarser fraction consequently the record of late carboniferous and permian magnetization events is commonly incomplete in strata close to the present day ground level