the measurement and modelling of rill erosion at angle of repose slopes in mine spoil the process of rill erosion causes significant amounts of sediment to be moved in both undisturbed and disturbed environments and can be a significant issue for agriculture as well as mining lands rills also often develop very quickly from a single rainfall event to a season and can develop into gullies if sufficient runoff is available to continue their development this study examines the ability of a terrestrial laser scanner to quantify rills that have developed on fresh and homogeneous mine spoil on an angle of repose slope it also examines the ability of the siberia erosion model to simulate the rill s spatial and temporal behaviour while there has been considerable work done examining rill erosion on rehabilitated mine sites and agricultural fields little work has been done to examine rill development at angle of repose sites results show that while the overall hillslope morphology was captured by the laser scanner with the morphology of the rills being broadly captured the characteristics of the rills were not well defined the digital elevation model created by the laser scanner failed to capture the rill thalwegs and tops of the banks therefore delineating a series of ill defined longitudinal downslope depressions these results demonstrate that an even greater density of points is needed to capture sufficient rill morphology nevertheless siberia simulations of the hillslope demonstrated that the model was able to capture rill behaviour in both space and time when correct model parameters were used this result provides confidence in the siberia model and its parameterization the results demonstrate the sensitivity of the model to changes in parameters and the importance of the calibration process copyright 2007 john wiley sons ltd

stable isotope stratigraphy of brachiopods from pennsylvanian shales in texas stable isotope stratigraphies have been generated for brachiopods from five late pennsylvanian sections upper winchell cycle finis shale colony creek shale necessity cycle and wayland shale in north central texas to examine the relationship between isotopic composition paleoenvironment and sea level change nonluminscent calcite from more than 300 specimens of 4 species of brachiopod composita subtilita crurithyris planoconvexa eridmatus texana neospirifer cameratus was analyzed sedimentological and paleontological data are used as evidence for paleoenvironmental change higher 18 o values of brachiopod shells occur in intervals of greatest paleodepth as indicated by fossil content and lithology these higher 18 o values reflect a decrease in bottom temperature with increased water depth normalized for paleodepth the 18 o values of the brachiopods are similar in all of the units except the wayland shale for which they are 0 5 higher this suggests either cooler temperatures or greater continental ice volume during the time of wayland deposition brachiopod 13 c values do not correlate with paleodepth the 13 c values of composita are consistently higher than those of crurithyris and eridmatus composita 13 c values are similar in the upper winchell cycle necessity cycle and wayland shale averaging 4 8 to 4 9 in contrast crurithyris 13 c values range from 2 5 in the necessity cycle to 4 4 in the wayland shale eridmatus values are also lowest in the necessity cycle 3 4 and greatest in the wayland shale 3 9 these differences between species do not correlate with susceptibility to diagenesis and appear to reflect a pore water influence on semi infaunal crurithyris forms the 13 c values of composita shells suggest that the late pennsylvanian ocean off eastern laurussia was enriched in 13 c by about 1 relative to the ocean off western laurussia

meteoric diagenesis below a submerged platform implications for δ13c compositions prior to pre vascular plant evolution middle ordovician alabama u s a abstract the middle ordovician chickamauga formation at red mountain expressway rme and tidwell hollow twh sections in alabama u s a has a complex early diagenetic history early diagenetic history of the buildup facies consisted of two phases of marine cementation separated by two generations of meteoric equant calcite with moldic dissolution separating equant calcite generations a third generation of meteoric equant drusy calcite is present after secondary marine diagenesis equant drusy calcite is interpreted as meteoric because its stable isotopic composition 13 c 0 1 to 1 6 18 o 4 8 to 7 3 is too variable to be accounted for by marine or mixing zone precipitation equant drusy calcite from buildup facies is mostly non luminescent and non ferroan this is unlike early ferroan equant calcite dull to bright luminescent from below the unconformity that overlies the chickamauga formation at rme meteoric diagenesis below the unconformity is unrelated to early diagenesis in the underlying buildup facies equant drusy calcite from the buildup facies at rme has a covariation of 13c and 18o values that forms a truncated inverted j and has elevated mg values these geochemical signatures indicate precipitation at a site that was distal from the recharge zone meteoric diagenesis at rme occurred during rising relative sea level and flow of meteoric fluids under a submerged platform is the only mechanism able to reconcile available stratigraphic petrologic and geochemical data ordovician meteoric 13c values from twh and other formations are slightly depleted 2 4 relative to coeval marine carbonate especially when compared with post silurian meteoric carbonate minor depletion of ordovician carbonate is the result of limited generation of light soil gas co2 before the development of vascular plants

geochronological evidence supporting antarctic deglaciation three million years ago the response of the antarctic ice sheets to increased global temperatures is an important unresolved issue in the assessment of future climate change in particular considerable controversy exists as to whether the east antarctic ice sheet suffered extensive deglaciation during the mid pliocene epoch 3 myr ago when temperatures were only slightly warmer than today although the ice sheet is widely assumed to have existed in something like its present form for the past 14 myr ref 1 marine diatoms eroded from the antarctic interior have been found in glacial till deposits high in the transantarctic mountains2 3 and have been bio stratigraphically dated at 3 myr before present this age has been disputed4 because it implies marine deposition in the antarctic interior and hence substantial deglaciation at a time when other evidence has been marshalled for the persistence of cold polar conditions4 here we report k ar and 40ar 39 ar ages for a volcanic ash bed in diatom bearing glaciomarine strata cored in ferrar fiord east antarctica by the ciros 2 drill hole5 which confirm the age of the diatoms at 3 myr and hence also confirm the mid pliocene deglaciation

the genesis of nodular limestones in the ordovician and silurian of the oslo region norway nodular limestones have been studied from the lower chasmops shale middle ordovician and the rytteraker formation lower silurian observations on nodule host rock relations and variations of ferroan non ferroan calcite cements help explain the role of precipitation dissolution and redistribution of carbonate distribution and frequency of nodules depends on environmental parameters such as carbonate clay ratio grain size distribution and bioturbation though final shapes are the result of pressure dissolution and cleavage

dolomitization and isotope stratigraphy of the vazante formation sao francisco basin brazil the vazante formation consists of approximately 1700 m of mainly microbial mats and stromatolitic reefal lenses that were deposited on shallow marine platform and have been entirely dolomitized samples representing different dolomite generations were taken from three boreholes covering the entire spectrum of the vazante carbonates dolomites can be classified based on petrography and geochemistry into four generations ranging in crystal size between 4 m almost micritic and 3 mm and occurring as both replacements and cements the sr ca molar ratios calculated for the dolomitizing fluid 0 0006 0 0138 suggest a contribution from a non marine possibly meteoric water component the 18 oa nd 13 c values vary from 0 1 to 14 3 pdb and 0 2 to 2 3 pdb respectively fluid inclusion study suggests that dolomitization must have commenced at a temperature lower than about 50 c a mixing zone model of dolomitization for dolomites i iii satisfies the constraints from elemental chemistry 18 o 87 sr 86 sr and fluid inclusions the petrographic and chemical criteria of the latest generation dolomite iv reflect conditions of deep burial environment at temperatures above 120 130 c the 13 c values show only small variations at the base of the formation followed by a major negative plunge 4 at the top this plunge correlated with the sturtian glacial phase in contrast to c isotopes only few samples may have retained their near primary 87 sr 86 sr values of 0 70614 0 70734 the lowest 87 sr 86 sr value 0 70614 from fibrous cement in the upper part of the formation correlates with the negative 13 c shift and is also consistent with the sr isotope signature proposed for the glacial sturtian seawater the 34 s values obtained from sulfates trapped in carbonates range between 10 8 and 16 9 with a jump to 21 3 in the overlying formation all isotope signals are within the range suggested for the early neoproterozoic seawater but the precambrian baseline is poorly known and additional work is required to confirm this tentative assignment 2001 elsevier science b v all rights reserved

textural elemental and isotopic variations among constituents in middle devonian limestones north america abstract biogenic components brachiopods crinoids and corals in middle devonian limestones were manually separated from their enclosing matrix and analyzed by textural elemental and isotopic methods in order to assess the preservational state of these components in general brachiopods in these rocks are better preserved texturally than other constituents as determined by sem and cathodoluminescence observations elemental variations among the major components are compatible with a differential response to diagenesis governed by the relative stability of the original mineralogy of the component however among the most stable low mg calcite brachiopods the relationship between textural preservation and trace element content is complex this apparent complexity may be due at least par ially to our method of textural characterization of whole brachipod samples the nonluminescent portions of a set of well preserved brachipods have textural characteristics and elemental contents which are virtually indistinguishable from modern representatives consequently their 18o values 3 7 0 2 are assumed to represent primary biogenic calcite these 18o values are in the heavy end of the range of values from texturally well preserved whole brachiopods 6 6 to 2 5 texturally altered whole brachiopods 6 7 to 3 7 and texturally altered crinoids and cora s 6 7 to 2 7 this comparison suggests that marine derived pore waters were a predominant component during the principal phase of diagenesis the relatively low l8o values of well preserved brachiopods compared with modern representatives implies that middle devonian seawater was either warmer by about 10 c or depleted in 18o by about 2 3 relative to modern seawater

eustatic sea level patterns from the lower silurian llandovery series of southern norway and estonia this study demonstrates the utility of checking for eustatic sea level events correlated between passive epicontinental seas and those on the margin of orogenic activity bathymetric profiles interpreted on the basis of stratigraphic data from the lower silurian llandovery series in five districts of the oslo region of southern norway are compared with similar data derived from five bore hole sites in the baltic region of estonia these regions preserve extensive marine strata deposited on the silurian continent baltica the data are tested for intra regional and inter regional conformity despite the fact that the oslo region was affected by the caledonide orogeny the same four highstands in sea level were recorded there as on estonia9s comparatively stable platform expressed in terms of the established geochronologic standard and its faunal zones coeval highstands in sea level occurred across baltica during latest rhuddanian time in mid aeronian time as marked by the basal monograptus sedgwickii or stricklandia lens progressa zones in early telychian time m turriculatus or s laevis zones and in late telychian time near the llandovery wenlock boundary this timing corresponds to four highstands in sea level previously documented in north america and to at least three high stands found in south china claims for early silurian eustasy now rest on data collected from three independent paleocontinents if the llandovery epoch lasted 10 m y then sea level cyclicity was on the order of 2 5 m y a combination of tectono eustastic and glacioeustatic causes probably was responsible for these cycles

cathodoluminescene at low fe and mn concentrations a sims study of zones in natural calcites abstract point analyses of natural calcite cements by sims confirm the earlier suggestions that 20 ppm mn is required to activate luminescence whereas fe concentrations in excess of 1400 ppm quench it partly independently of the mn content below this fe threshold luminescence is bright at mn concentrations in excess of 225 ppm in the range 20 225 mn all types of luminescence dull luminescent and nonluminescent can occur this undifferentiated domain is evident also from a compilation of literature data the type of luminescence is not a simple function of fe and mn concentrations other parameters influence cl sinc most diagenetic calcite cements have fe and mn concentrations that place them within the field of mixed cathodoluminescence these results force reassessment of models that equate the type of luminescence with the redox state of the diagenetic environment

meteoric burial diagenesis of middle pennsylvanian limestones in the orogrande basin new mexico water rock interactions and basin geothermics abstract stable isotopic compositions of cyclic middle pennsylvanian gobbler formation limestones record two stages of alteration early open system meteoric diagenesis during episodic subaerial exposure stabilized cycle top carbonate in the presence of meteoric fluid at high water rock ratios 400 4000 subsequent closed system burial diagenesis stabilized meteoric and residual marine carbonate in the presence of connate pore fluids at elevated temperatures to 150 c and low water rock ratios 1 0 10 present 18o distributions record normal to high geothermal gradients 27 86 c km during burial stabilization high basin center geothermal gradients probably resulted from elevated heat flow due to rapid crustal extens on and subsidence of the orogrande basin during the late pennsylvanian a dike injection lithospheric extension model with 40 oceanization best accounts for subsidence and geothermal patterns of the orogrande basin

comparing oxygen isotope records of silurian calcite and phosphate δ18o compositions of brachiopods and conodonts oxygen isotope compositions of silurian calcitic brachiopod shells from gotland are compared with those of phosphatic inarticulate brachiopod shells and conodonts from identical stratigraphic horizons the 18ophosphate values of inarticulate brachiopod shells vary widely 13 0 to 17 5 v smow and are significantly lower than those of coeval conodont samples 17 5 to 19 5 v smow conodont samples from individual beds have homogenous 18ophosphate values with variations close to the analytical precision 0 2 together with a significant correlation of conodont 18ophosphate and articulate brachiopod shell 18ocarbonate values r 0 85 this observation suggests that primary marine oxygen isotope compositions are better preserved in conodont apatite than in inarticulate brachiopod shell apatite however with decreasing 18ocarbonate values the 18ophosphate values of conodonts are higher than expected for theoretical isotopic equilibrium with brachiopod calcite different habitats of conodonts and brachiopods cannot account for the observed offset in 18o because both organisms were thriving on a broad shallow marine carbonate platform whereas 18ophosphate values of silurian conodonts are close to 18ophosphate values of modern and mesozoic tropical biogenic apatites most silurian calcitic brachiopod shells from gotland are depleted in 18o when compared to modern or mesozoic brachiopods we therefore suggest that silurian conodonts from gotland record paleotemperature and 18o of silurian sea water more faithfully than coeval calcitic brachiopod shells

transporting capacity of overland flow on plane and on irregular beds in this paper the transporting capacity of thin flows in the laminar and transitional flow regime is studied experiments were carried out on irregular as well as on plane beds using two totally different set ups the results of these two types of experiment were convergent in both cases sediment concentration was clearly related to grain shear velocity and unit stream power expressed as the product of mean velocity and slope yang 1973 the data agreed with those of kramer and meyer 1969 for a sandy bed the unit stream power relationship was able to predict reasonably well the sediment concentrations measured on a mulched surface for laminar and transitional flows both the unit stream power and the shear velocity are related in the same way to slope and unit discharge the unit stream power is a parameter which in particular can be very easily measured and might therefore become useful in obtaining a quick estimate of the transporting capacity of a thin flow however before a sediment transport equation for thin flows can be developed more information is needed about the influence of the flow regime and grain size and density

cenozoic marine sedimentation and ice volume variation on the east antarctic craton recycled cretaceous and cenozoic marine microfossils have been recovered from samples of the pliocene sinus formation samples were collected from outcrops in the reedy beardmore and ferrar glacier areas of the transantarctic mountains between lat 77 and 86 s the glaciogene sediments contained diatoms foraminifera calcareous nannoplankton silicoflagellates radiolarians sponge spicules palynomorphs and ostracodes of late cretaceous paleocene eocene late oligocene late miocene and pliocene age this suggests the presence of open marine basins on the east antarctic craton during late mesozoic and cenozoic time the apparent absence of early oligocene and early through middle and earliest late miocene assemblages suggests either that marine regression exposed the basin floors or that ice filled the basins during these times the high elevation setting of sirius formation outcrops suggests one of two hypotheses for their origin 1 they are in situ pliocene glaciomarine deposits that were uplifted 1 750 2 500 m with the transantarctic mountains to their present elevation 2 the sirius formation deposits are a mixture of derived sediments stripped from sub ice intracratonic basins and subsequently redeposited by ice flowing up the inland slope of the transantarctic mountains we favor the second hypothesis with transport to sites sometime within the past 3 m y

fibrous calcite from the ordovician of tennessee preservation of marine oxygen isotopic composition and its implications three categories of fibrous calcite from early to middle caradoc platform marginal buildups in east tennessee can be delineated using cathodoluminescent microscopy minor element chemistry and stable c o isotopic composition bright luminescent fibrous cement has elevated mn 1000 p p m negative 13c and intermediate 18o values relative to other types of fibrous calcite this cement reflects fibrous calcite that interacted with reducing mn rich fluids dully luminescent fibrous cement has elevated fe 400 p p m positive 13c and negative 18o values relative to other fibrous cements this cement was stabilized by burial fluids nonluminescent fibrous cement has low mn and fe generally below 400 p p m and positive 13c and 18o values relative to other types of fibrous calcite the latter cement is interpreted to be the best material for determining the isotopic composition of calcite precipitated in equilibrium with early to middle caradoc seawater which is 13c 1 pdb and 18o 4 to 5 pdb results from this study and ashgillian brachiopods indicate that the average 18o composition of the ordovician ocean during nonglacial periods was probably never more negative than 3 smow assuming an ordovician seawater 18o value of 1 smow holston formation fibrous cements would have precipitated at temperatures between 27 and 36 c which is near the upper temperature limit for metazoans a seawater 18o value of 2 smow yields temperatures ranging from 23 to 31 c while a 3 smow value yields temperatures of 18 26 c

thermal metamorphism of the silurian strata of the oslo region assessed by conodont colour conodont elements from silurian limestones in the oslo region norway range from brown to grey samples from the south of the region contain black and grey conodonts indicative of high palaeotemperatures there is a general decrease in thermal metamorphism towards the north with the lowest palaeotemperatures recorded from toten ringsaker and parts of the ringerike district there is a close correlation between thermal metamorphism and the proximity of permian intrusions modified journal abstract

derivation of the original isotopic composition of permian marine cements abstract diagenesis of former aragonite and magnesian calcite marine cements of the permian reef complex has resulted in a fine scale intermixture of two distinct secondary phases a luminescent and a nonluminescent calcite multiple carbon and oxygen isotopic analyses of these marine cements from any single sample result in a linear covariant trend reflecting random proportions of the two calcite phases contained in individual analyses the convergence of four trends derived from samples of former aragonite marine cement collected at four sites along a single upper capitan paleoslope fixes the isotopic composition of the nonluminescent calcite at a value of 2 518o 5 313c likewise covariant trends from former aragonite cements in the lower capitan and the youngest upper capitan yield nonluminescent calcite compositions of 2 818o 5 213c and 0 718o 5 813c respective y the single covariant trend generated from former magnesian calcite cements does not converge with equivalent former aragonite covariant trends indicating that the precursor mineralogy influences the isotopic composition of the nonluminescent calcite considered as a whole the invariance of the nonluminescent calcite signature the timing of luminescent calcite emplacement and the fine scale of the fabric retention suggest that the precipitation of the nonluminescent calcite occurred while isolated from effective isotopic exchange with external diagenetic fluids a direct consequence of this low water rock ratio closed system is that the isotopic signature of the nonluminescent calcite also represents the original isotopic composition of the marine cement this is further support d by the preservation of primary differences between the original isotopic compositions of aragonite and magnesian calcite cements the constancy of the marine isotopic signature throughout the reef massive and foreslope facies requires that the delaware basin water mass was relatively well mixed comparison of marine compositions throughout the range of the capitan samples indicates that although the oxygen composition of the marine cements was apparently constant through much of the guadalupian a substantial enrichment in 18o occurred at the very end of the guadalupian this relatively abrupt change recording a concomitant change in the oxygen composition of the delaware basin water mass was probably the result of increased restriction of the delaware basin and marked the first step in the sequence of events which led to the deposition of the deep basin evaporites of the castile formation

burial cementation is it important a case study stuart city trend south central texas the stuart city trend is a shelf edge buildup of lower cretaceous bioclastic and reefal carbonates that is currently buried to depths of between 3 300 and 5 000 m 11 000 and 16 000 ft compaction and cementation have generally reduced rock porosities to less than 9 sediments were cemented in the marine environment by finely crystalline bladed isopachous cement and volumetrically important 14 volume coarse to very coarsely crystalline fibrous to bladed isopachous mg calcite cement these cements have been neomorphically altered end page 536 to low mg calcites forming an unusual radiaxial texture observed in the coarse to very coarsely crystalline bladed calcite cement evidence of their marine origin consists of a relative 1 mole mg memory a marine like isotopic character dgr18o approx 2 5 and dgr13c approx 2 0 and early relative timing of precipitation diagenetic alteration of these carbonate sediments by the interaction with meteoric water in lenses that formed within topographic highs along the shelf margin changed the initial marine chemical isotopic and textural character of the sediments secondary porosity formation mineral stabilization aggrading neomorphism and equant spar calcite cementation are the important products of meteoric diagenesis the equant spar calcite cements make up approximately 16 by volume of the limestones studied they are iron and manganese poor the majority have a dgr13c composition which falls in the range of modern marine carbonates i e 0 9 to 3 5 pmil the dgr18o compositions range from 1 3 to 6 6 pmil relative to the pdb standard oxygen stable isotopic and petrographic data suggest that over 50 of the equant spar calcite cements were formed in a near surface meteoric environment a large percentage of the remaining equant spar calcite cements formed at shallow burial depths in a water limited system where mass transfer was dominated by diffusional processes thermally induced dgr18o depletion of the equant spar calcites indicating significant fluid flow was of minimal importance pyrobitumen pore fillings and inclusions in the outer 1 0 mm thick rims of the very coarsely crystalline equant spar calcite cements indicate that only minor amounts of cementation have occurred since the introduction of hydrocarbons deep burial diagenesis i e post hydrocarbon migration consisted of the precipitation of minor amounts of galena fluorite and sr rich equant spar calcites these diagenetic products can be directly related to the present day formation water the chemical isotopic and textural characteristics of the stuart city trend limestones contain the imprints of their initial marine composition and shallow diagenetic alterations in a hydrodynamic system burial diagenesis has not significantly altered these limestones fault and fracture control on the movement of formation waters in this system determine the location and intensity of late stage diagenetic events end of article last page 537

diagenetic evolution of the carnian wetterstein platforms of the eastern alps the carbonate platforms of the wetterstein formation of the eastern alps drau range and northern calcareous alps show a distinct facies zonation of reefs and lagoons while some lagoonal areas were episodically emerged and formed lagoonal islands others remained permanently flooded the scale of near surface meteoric or marine diagenesis was related to this lagoonal topography at shallow burial depth cementation was dominated by altered marine solutions which additionally caused recrystallization of metastable constituents of the sediment and earlier marine cements high magnesian calcite aragonite connected with a carbon and oxygen isotopic change to more negative values deeper burial cementation shows a succession with two types of saddle dolomite and three types of blocky calcite carbon and oxygen isotopic values of these cements show a trend towards more negative values from the first to the last generation in the following succession clear saddle dolomite zoned blocky calcite cloudy saddle dolomite post corrosion blocky calcite replacive blocky calcite fluid inclusion studies of the carbonate cements are interpreted to indicate a deeper burial temperature development that first increases from 175 to 317 c followed by a temperature decrease to 163 260 c and subsequent increase up to 316 c whereby the samples of the drau range always show the lowest values calculations of the isotopic composition of the water from which the carbonate cements were precipitated yielded positive 18o values from 6 66 to 17 81 o smow which are characteristic for formation and or metamorphic waters also the isotopic compositions of the palaeofluids probably changed during deeper burial diagenesis following the temperature development

mass transfer between mudstone sandstone interbeds during diagenesis as revealed from the type and distribution of carbonate cements in the eocene beach bar sandstones bohai bay basin abstract the characteristics heterogeneous distribution and origins of carbonate cements within beach bar sandstones in the boxing sag and implications on the mass transfer from mudstone to sandstone during diagenetic process was investigated systematically by an integrated analysis invoking petrography carbon and oxygen stable isotopes and porosity permeability with specific references to the contrasts among the sharp s change lithology s mudstone s sandstone interbeds the gradual g change lithology g mudstone g sandstone interbeds and the center of sandstones there are distinct differences in the occurrence content distribution carbon and oxygen isotopic compositions and precipitation temperatures of the carbonate cements among the s sandstone g sandstone and center of sandstone material sources of carbonate cements in the s sandstones are mainly derived from the diagenetic alterations of the nearby s mudstones through mass transfer with the participation of organic co2 while in the g sandstones the material sources are mainly internal and originated from the calcareous matrix dissolution of feldspars and conversion of clay minerals provided the main materials for the precipitation of carbonate cements in the center of sandstones mass transfer of carbonate cements mainly occurred between the s mudstones and the s sandstones with limited transmission distance which controlled the distribution of carbonate cements in the s mudstones there was almost no mass transfer between the g mudstones and g sandstones because of the small concentration gradient instead the depositional components and recrystallization controlled the carbonate distribution of the g sandstones

submarine cementation and subaerial exposure in oligo miocene temperate carbonates torquay basin australia abstract at least four hardgrounds are present throughout the 27 m thick exposed oligo miocene cool water point addis limestone of the torquay basin in southeastern australia they range from thin a few centimeters thick incipient layers that have a nodular fabric to thick up to 1 m thick continuous hardgrounds the hardgrounds tend to be at the top of coarsening upward cycles and are typically overlain by low relief erosion surfaces the uppermost hardground is the best developed and most widespread in the point addis limestone and can be observed in all exposures of the succession at some localities it shows evidence of karstification such as dissolution pits clints and grikes and dissolution pinnacles whether karstified or not well developed hardgrounds are overlain by a lag c nglomerate that consists of hardground intraclasts with marine fe oxide crusts the hardgrounds are cemented by a first generation isopachous inclusion rich columnar and fibrous radiaxial calcite of marine origin with trace element compositions mg2 0 68 1 74 mole mgco3 fe2 800 4690 ppm sr2 0 260 ppm mn2 0 230 ppm and cathodoluminescence dull blotchy indicative of stabilized mg calcite the isopachous cements are invariably overlain by homogeneous peloidal or microbioclastic micrite having trace element compositions mg2 0 77 1 54 mole mgco3 fe2 760 10 030 ppm sr2 0 240 ppm mn2 60 340 ppm and cathodoluminescence dull blotchy again indicative of stabilized mg calcite this micrite is always closely associated wi h the isopachous cements and appears to be of marine origin perhaps being analogous to the micritic precipitates described from reefal settings clear calcite is the last cement generation in the hardgrounds and has attributes of meteoric cements nonluminescent mg2 0 12 0 87 mole mgco3 fe2 0 230 ppm sr2 and mn2 below detection limits the whole rock stable isotope compositions of the hardgrounds and host limestone indicate that the whole unit has been subjected to pervasive alteration by meteoric fluids the least altered carbonates analyzed from the point addis limestone are brachiopods d13c 1 5 to 2 2 pdb d18o 1 7 to 0 9 pdb and the unkarstified hardgrounds d13c 3 8 to 1 0 pdb d18o 0 6 to 0 6 pdb these hardground occurrences help promote the validity of a unique sea level driven model for the formation of hardgrounds in cool water settings we propose that the development of these hardgrounds was an entirely marine process produced by relative sea level drop and entry of the sea floor into the zone of wave reworking marine cementation may begin in the form of nodules at and below the seawater sediment interface and involves both slow sedimentation and shallowing of the cool waters the nodules can later merge to form continuous hardgrounds in such a high energy environment nondeposition and erosion are the dominant processes and marine cementation can occur further sea level drop would lead to subaerial exposure of the previously formed hardgrounds as found in one inst nce in the point addis limestone at coastal exposures

δ18o values 87sr86sr and sr mg ratios of late devonian abiotic marine calcite implications for the composition of ancient seawater abstract late devonian frasnian abiotic marine calcite has been microsampled and analyzed for 87 sr 86 sr ratios 18o and 13c values and minor element concentrations portions of marine cement crystals from the alberta and canning basins have escaped diagenetic alteration and preserve original marine 18o values 4 8 0 5 pdb 13c values 2 0 to 3 0 pdb 87 sr 86 sr ratios 0 70805 3 and sr mg weight ratios 0 04 to 0 05 marine 87 sr 86 sr ratios are globally consistent and can be correlated within the alberta basin and among the alberta canning and williston basins correlation of isotopic and chemical data strengthen the conclusion that marine cements from the leduc formation preserve original marine 18o values which are 3 to 4 lower than those of modern marine cements these low 18o values are best explained by precipitation from 18o depleted seawater and not by elevated seawater temperature or diagenetic alteration for comparison with devonian data analogous data were collected from holocene mg calcite and aragonite marine cements from enewetak atoll marshall islands mg calcite and aragonite marine cements are in isotopic equilibrium with ambient seawater and mg calcite cements are homogeneous with respect to sr and mg contents empirically derived homogeneous distribution coefficients for mg and sr in modern abiotic mg calcite from enewetak atoll are 0 034 and 0 15 respectively an equation describing the dependence of dsr on mg content was based on a compilation of sr and mg data from holocene abiotic marine calcite dsr 3 52 10 6 ppm mg 6 20 10 3 unlike that derived from experimental data this sr mg relation is consistent over a range of 4 to 20 mol mgco3 and may represent precipitation phenomena which are minimally controlled by kinetic effects comparison of sr and mg contents of analogous devonian and holocene marine cements suggests that the mg ca ratio of late devonian seawater was significantly lower and that the sr ca ratio was significantly higher than that of modern seawater

bathymetric and isotopic evidence for a short lived late ordovician glaciation in a greenhouse period the end ordovician glaciation is distinct among phanerozoic glaciations in that co 2 levels were generally high yet major continental ice sheets accumulated on the gondwana supercontinent new oxygen isotopic data indicate substantial changes in sea water temperatures and ice volume coinciding with glacio eustatic changes in sea level reflecting the growth and decay of the gondwana ice cap major glaciation was apparently confined to the hirnantian and was 0 5 1 m y long rather than the 35 m y of earlier estimates carbon isotope values indicate significant changes in carbon cycling as the oceans changed from a state with warm saline bottom waters to a state with cold deep water circulation and then back again we believe that the changes in the carbon cycle effected a reduction in p co 2 levels in the oceans and atmosphere and thus promoted glaciation but were unable to sustain icehouse conditions in a greenhouse world

oxygen and carbon isotopic composition of ordovician brachiopods implications for coeval seawater one hundred and two articulate brachiopods and twenty one marine cements from ordovician strata were analyzed for oxygen and carbon isotopes these together with 200 previously published analyses of ordovician brachiopods mostly of upper ordovician age define a general trend of increasing 18o values with decreasing age from a minimum of 10 5 in the earliest ordovician to a maximum of 1 5 at the ordovician silurian boundary the 13c values show a general positive correlation with 18o and increase from 2 5 in the earliest ordovician to as high as 7 at the ordovician silurian boundary the magnitudes of ordovician excursions for both 18o and 13c are similar to those reported previously for the entire phanerozoic different genera of brachiopods from the same stratigraphie level did not yield any large differences in their isotopic compositions suggesting that vital effects did not influence decisively the isotope values of the studied skeletal parts petrographic examination and trace element analyses indicate that brachiopod shells from llandeilo to ashgill strata are well preserved and thus may have retained their primary isotopic signatures the same criteria for the tremadoc arenig and some llanvirn brachiopods suggest partial diagenetic alteration of 18o values in these samples but this does not preclude their utility as a recorder of a primary 13c signal the observed 18o trend for the well preserved portion of the record may reflect progressive cooling during ordovician perhaps complemented by a changing 18o values of seawater the latter could have been a consequence of a net increase in the rate of high temperature water rock interaction relative to its low temperature counterpart as indicated also by the large coeval decrease of marine 87sr86sr superimposed on the above long term 18o trend is a positive excursion of about 2 at the end of the ordovician probably reflecting a large expansion of polar ice caps the magnitude of this excursion indicates a degree of glaciation comparable to that at the height of the quaternary glacial episodes the secular 13c trend may reflect a progressive increase in marine organic productivity and or enhanced organic deposition in the ordovician oceans particularly noticeable at the time of the terminal ordovician glaciation

the diagenesis of the late dinantian derbyshire east midland carbonate shelf central england carbonate cements in late dinantian asbian and brigantian limestones of the derbyshire carbonate platform record a diagenetic history starting with early vadose meteoric cementation and finishing with burial and localized mineral and oil emplacement the sequence is documented using cement petrography cathodoluminescence trace element geochemistry and c and o isotopes the earliest cements pre zone 1 are locally developed non luminescent brown sparry calcite below intrastratal palaeokarsts and calcretes they contain negligible fe mn and sr but up to 1000 ppm mg their isotopic compositions centre around 18o 8 5 13c 5 0 calcretes contain less 13c subsequent cements are widespread as inclusion free low mg low fe crinoid overgrowths and are described as having a dead bright dull cathodoluminescence the dead cements zone 1 are mostly non luminescent but contain dissolution hiatuses overlain by finely detailed bright subzones that correlate over several kilometres across dead bright subzones there is a clear trend in mg 500 900 ppm mn 100 450 ppm and fe 80 230 ppm zone 1 cements have isotopic compositions centred around 18o 8 0 and 13c 2 5 zone 2 cement is bright thin and complexly subzoned it is geochemically similar to bright subzones of zone 1 cements dull zone 3 cement pre dates pressure dissolution and fills 70 or more of the pore space it generally contains little mn fe and sr but can have more than 1000 ppm mg increasing stratigraphically upwards the 18o compositions range from 5 5 to 15 and the 13c range is 1 to 3 20 00 zone 4 fills veins and stylolite seams in addition to pores it is synchronous with pb ba f ore mineralization and oil migration zone 4 is ferroan with around 500 ppm fe up to 2500 ppm mg and up to 1500 ppm mn isotopic compositions range widely 15o 2 7 to 9 and 13c 3 8 to 2 50 unaltered marine brachiopods suggest a dinantian seawater composition around 15o 0 smow but vital isotopic effects probably mask the original 13c pdb value pre zone 1 calcites are meteoric vadose cements with light soil derived 13c and light meteoric 18o an unusually fractionated pluvial 15o smow value of around 6 is indicated for local dinantian meteoric water calcrete 18o values are heavier through evaporation zone 1 textures and geochemistry indicate a meteoric phreatic environment fe and mn trends in the bright subzones indicate stagnation and precipitation occurred in increments from widespread cyclically developed shallow meteoric water bodies meteoric alteration of the rock body was pervasive by the end of zone 1 with a general resetting of isotopic values zone 3 is volumetrically important and external sources of water and carbonate are required emplacement was during the namurian early westphalian by meteoric water sourced at a karst landscape on the uplifted eastern edge of the derbyshire east midland shelf the light 18o values mainly reflect burial temperatures and an unusually high local heat flow but an input of highly fractionated hinterland derived meteoric water at the unconformity is also likely relatively heavy 13c values reflect the less altered state of the source carbonate and aquifer zone 4 is partly vein fed and spans burial down to 2000 m and the onset of tectonism light organic matter derived 13c and heavy 18o values suggest basin derived formation water combined with textural evidence of geopressures this relates to local high temperature ore mineralization and oil migration low water to rock ratios with host rock buffering probably affected the final isotopic compositions of zone 4 masking extremes both of temperature and organic matter derived co2

palaeokarst tidal erosion surfaces and stromatolites in the silurian eke formation of gotland sweden irregular scalloped erosion surfaces in the shelf carbonate sequences of the lower eke formation ludlow series upper silurian in the east of gotland sweden comprise series of shallow hollows separated by sharp crested ridges and cavities with sculptured undercut walls cut into lithified sediment these represent analogues of the solution basins formed in modern coastal and subaerial karst terrains discrete erosional cavities merge on enlargement by breaching of the intervening walls to leave remnant tapering ridges sets of the ridges and basins seen in surface view show an average width of basins of 1 2 m with relief of 40 50 cm and pronounced n s axes for the ridges this alignment may reflect the local drainage direction the lowermost erosion surface passes laterally into a planar mineralized horizon at the top of the underlying hemse group that was resistant to and forms the base level of erosion because of restricted exposure of higher eke formation sediments the upper limit of erosion remains unknown there is no evidence of caliche or subaerial diagenetic textures but solution vugs are common in the eroded limestones marine hard bottom biota attached to some surfaces and transition from scalloped to planar surfaces indicate erosion in tidal zones but subaerial karstic erosion is also inferred the resubmerged karst eroded topography is overlain by shallow marine carbonates including small organic buildups finely layered stromatolitic mats developed over the initial infill in subtidal environments and grew to form domed mounds within the erosional cavities they abut sharply against bounding side walls and overhangs some emergence is evident from desiccation features in the upper parts of mounds biostratigraphical evidence dating the events from initial uplift and karstic erosion to covering of the drowned relief topography places the whole sequence within upper ludlow times

diagenetic alteration of early marine cements of upper silurian stromatactis stromatactis is a spar network whose elements in cross section have flat to undulose lower surfaces and digitate upper surfaces the network is composed principally of isopachous crusts of centripetal cement and commonly occurs embedded in finely crystalline limestone it is the cement filling of interconnected cavities stromatactis of upper silurian red stromatactis limestone from gaspe peninsula quebec appalachians exhibits two types of cements 1 an isopachous cement that lined the walls of the conduits and is interpreted as early marine and 2 a later blocky cement that occupies the centres of cavities the first cement is composed exclusively of non ferroan calcite whereas the second cement is mixed non ferroan and ferroan calcite the early isopachous cement is white on polished slabs and has a turbid aspect under transmitted light in a few samples the relative homogeneity of this early cement is broken by the presence of distinctive grey clear calcite under cathodoluminscence the grey clear calcite is non luminescent and exhibits well defined bladed crystal shapes whereas the white turbid cement has a dull orange luminescence and indistinct crystal shapes the relationships between the two cements indicate that the dull luminescent cement is a secondary form of the non luminescent cement and it is concluded that the dull cement is the product of alteration of the non luminescent cement by burial or meteoric fluids the later blocky cement has the same dull luminescence as the white turbid cement and is thought to have been precipitated from the same fluids as those responsible for the alteration of the early marine cements oxygen isotopic values of the dull cement of the early isopachous crusts mean 18o 6 8 o are intermediate between those of the non luminescent early marine cement mean 18o 5 3 o and the dull luminescent blocky cement mean 18o 11 8 o while carbon isotopic values do not differ significantly 13c 2 9 2 4 and 2 6 o respectively the alteration also has affected the distribution of some trace elements particularly mg both unaltered and altered cements contain less than 1 microdolomite inclusions but the mg content of the background calcite of unaltered cement is three times that of altered cement 14171 vs 5502 ppm precursor early marine cement is thought to have been low mg calcite the mean 18o value 5 3 o of unaltered early marine cement is higher than values for the oxygen isotopic signature of silurian oceans provided by brachiopod shells

carbon oxygen and strontium isotopes in paleozoic carbonate components an evaluation of original seawater chemistry proxies abstract brachiopods trilobites cements and whole rock matrix material were evaluated for their reliability as proxies of original seawater carbon oxygen and strontium isotope chemistry in this process coeval material was evaluated from individual horizons of formations spanning the permian to cambrian unaltered shells of low mg calcite articulated brachiopods retain original seawater oxygen carbon and strontium isotope compositions as old as late ordovician assessments of older specimens are hampered by a lack of suitable material coeval brachiopod whole rock sets a definitive assessment of cement marine chemistry is difficult due to the paucity of material but despite this caveat cements hold some promise for retaining original carbon and possibly strontium isotope seawater values in contrast the potential of whole rock material as a proxy of original seawater chemistry is quite complex in some but not all instances the carbon isotopic composition of whole rock after detailed scrutiny and evaluation appears to represent an original seawater chemistry signal in a few instances their oxygen isotope compositions reflect original seawater values unlike the stable isotope compositions the strontium isotopes of all studied whole rock material permian to upper cambrian appear not to reflect original seawater chemistry values thus the potential for retaining original seawater isotope chemistry and serving as specific proxies in order of decreasing reliability are 1 unaltered low mg calcite brachiopods c o and sr isotopes 2 pristine marine cements c and sr isotopes and 3 whole rock material c isotopes carbon oxygen and strontium isotope compositions of ordovician trilobites mirror those of coeval unaltered brachiopods cambrian trilobites hold significant promise as an important proxy of original seawater isotope chemistry but further studies are needed to ascertain their full potential the survey of isotopes in some ordovician and cambrian intermediate low mg calcite trilobites demonstrates their potential as an important proxy of original seawater chemistry

effects of rock fragment cover on hydrological response and soil loss from regosols in a semi humid environment in south west china abstract controlling soil hydrological processes and combating soil erosion on agricultural fields are high priorities for crop production and ecological environments in this research the effect of land application of rock fragments on surface runoff subsurface runoff infiltration and soil loss on regosols had been investigated under field conditions using a portable rainfall simulator experimental twin plot two subplot with 1 m wide by 2 m long 32 slope with different rock fragment covers ranging from 0 40 were exposed to three rainfall intensities low 57 2 mm h 1 medium 91 3 mm h 1 and high 122 5 mm h 1 fifteen treatments were conducted in the experiments in duplicates surface runoff subsurface runoff soil moisture and sediment were measured results show that surface rock fragment cover retarded surface runoff increased infiltration and subsurface runoff and diminished sediment concentration and soil loss the final infiltration rates which increased with increasing rock fragment covers were 16 5 42 7 mm h 1 at low intensity 19 7 50 8 mm h 1 at medium intensity and 23 8 56 4 mm h 1 at high intensity compared with bare soils surface runoff rates were reduced to 24 51 and 64 in soils with 40 rock fragment cover at low medium and high intensity rainfall respectively subsurface runoff volume was significantly higher and time to start subsurface runoff was shorter as surface rock fragment cover increased compared with bare soils subsurface runoff coefficients increased to 3 5 3 3 and 2 9 times in soils with 40 rock fragment cover at low medium and high intensity respectively sediment concentrations increased from 9 8 g l 1 for 40 rock fragment cover under high intensity rainfall to 51 5 g l 1 for bare soils with rain falling at high intensity the erosion rate was 15 g m 2 min 1 for bare soils under low intensity the relationship between rock fragment cover and soil loss ratio can be expressed by an exponential function with a high degree of reliability regardless of rainfall intensities overall results indicate the surface rock fragments can be influential in shaping hydrological processes and soil loss from sloping farmland

the origin of late spar cements in the lincolnshire limestone jurassic of central england the carbon and oxygen isotopic compositions of the lincolnshire limestone bajocian of the east midlands are shown to be determined largely by two end member components marine precipitates and later sparry burial cements the origin of major quantities of such burial cement is controversial the extreme possibilities ranging from calcite precipitation from meteoric groundwaters to precipitation from highly saline brines with contrasting flow regimes this study demonstrates how formation wide sampling and mapping of stable isotopic compositions of burial cements from the lincolnshire limestone combined with a detailed knowledge of its burial history and associated thermal evolution can be employed to distinguish the influence of different water types two 9provinces9 are differentiated with respect to the stable isotopic compositions of the latest volumetrically most significant ferroan burial cements 1 a 9southern province9 associated with thinning of the limestone shallower depths of maximum burial approx 300 m and light 18 o and i3 c cement compositions 2 a 9central province9 associated with deeper burial approx 550 m but less 18 o and 13 c depleted cement compositions the relative isotopic depletion of the southern province ferroan burial cements is considered to be a function of their precipitation from meteoric waters with a depleted i8 o signature relative to seawater at temperatures of approximately 24 c 13 c depletion is tentatively ascribed to the persistence of 13 c depleted soil gas co 2 in the precipitating waters in the central province basinal waters of both meteoric and marine derivation are considered to have precipitated the late spar with associated up dip fluid movement at temperatures between 29 and 39 c 13 c depletion is believed to be controlled by the input of co 2 derived from thermal oxidation of organic matter

new isotopic data solving an old biostratigraphic problem the age of the upper ordovician brachiopod holorhynchus giganteus recent work has shown that there is a pronounced positive late ordovician excursion in both 13 c and 18 o which appears to be global and identifies a clear chemostratigraphic interval that is confined to part of the hirnantian stage pre hirnantian rawtheyan brachiopod carbonate values of 13 c are typically in the range 1 to 1 pdb and lower hirnantian values are typically in the range of 4 to 7 o pdb this contrast in isotopic values has been used to assess the age of the distinctive late ordovician brachiopod holorhynchus giganteus the age of the holorhynchus association is important in terms of its relationship to the major late ordovician extinction that was initiated at the start of the hirnantian the species which traditionally was regarded as uppermost ordovician hirnantian in age has been shown on stratigraphic evidence to be pre hirnantian at many locations if this is so it predates the first phase of extinction and is not associated with the hirnantia fauna which characterizes the interval between the two main episodes of late ordovician extinction however at its type locality in the asker district of norway the stratigraphic evidence has pointed to it being hirnantian in age to resolve this ambiguity analyses have been made on holorhynchus at three locations 1 in the east baltic region where holorhynchus occurs below demonstrable hirnantian rocks 2 in the boda limestone of central sweden where holorhynchus occurs high on a carbonate mud mound where its age is unclear and 3 in the type area of the species in norway at all three locations the 13 c values are low indicating a pre hirnantian pre extinction age for holorhynchus the re assessment of the age of the asker sequence in norway implies the presence of a cryptic unconformity there and suggests uplift rather than subsidence during the latest ordovician this study emphasizes the value of chemostratigraphy in high resolution stratigraphy

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

application of the trace element and isotope geochemistry of strontium to studies of carbonate diagenesis carbonate rocks and natural waters exhibit a wide range in the concentration and isotopic composition of strontium this wide range and the quantifiable covariation of these parameters can provide diagnostic tools for understanding processes of fluid rock interaction careful consideration of the uncertainties associated with trace element partitioning sample heterogeneity and fluid rock interaction mechanisms is required to advance the application of the trace element and isotope geochemistry of strontium to studies of diagenesis goundwater evolution ancient seawater chemistry and isotope stratigraphy a principal uncertainty involved in the application of sr concentration variations to carbonate systems is the large range of experimental and empirical results for trace element partitioning of sr between mineral and solution this variation may be a function of precipitation rate mineral stoichiometry crystal growth mechanism fluid composition and temperature calcite and dolomite in ancient limestones commonly have significantly lower sr concentrations 20 70 p p m than would be expected from published trace element distribution coefficient values and sr ca ratios of most modern sedimentary pore waters this discrepancy probably reflects the uncertainties associated with determining distribution coefficient values as techniques improve for the analytical measurement and theoretical modelling of sr concentration and isotopic variations the petrological analysis of carbonate samples becomes increasingly important the presence of even small percentages of non carbonate phases with high rb concentrations and high 87 sr86 sr values such as clay minerals can have significant effects on the measured 87 sr 86 sr values of carbonate rocks due to the decay of 87rb to 87 sr for example a permian marine limestone with 50 p p m sr and 1 p p m rb will have a present day 87 sr 86 sr value that is 2 10 4 higher than its original value this difference is an order of magnitude greater than the analytical uncertainty and illustrates the importance of assessing the need for and accuracy of such corrections a quantitative evaluation of the effects of water rock interaction on sr concentrations and isotope compositions in carbonates strengthens the application of these geochemical tracers geochemical modelling that combines the use of trace elements and isotopes can be used to distinguish between different mechanisms of water rock interaction including diffusive and advective transport of diagenetic constituents in meteoric pore fluids during the recrystallization of carbonate minerals quantitative modelling may also be used to construct diagnostic fluid rock interaction trends that are independent of distribution coefficient values and to distinguish between mixing of mineral end members and fluid rock interaction

carbon isotope event markers through the wenlock pridoli sequence at ohesaare estonia and priekule latvia abstract the ohesaare borehole in the northern part of the silurian baltic gulf penetrates shallow and deep shelf marlstones limestones and dolostones the priekule borehole in the deep shelf belt of the basin was drilled through marlstones and graptolitic mudstones most of the successions except the upper part are characterized by a high sr ca ratio close to marine calcites suggesting good preservation of carbonate material conodont alteration indices are low 1 2 carbon isotopes were measured using whole rock samples in the ohesaare core section two distinctive 13 c positive excursions were established one in the early wenlock riccartonensis and low rigidus ellesae standard graptolite zones 4 2 and the second in the late wenlock nassa zone 4 6 before and after the latter there are also intervals with low 13 c values the first just above the lundgreni zone 1 8 and another in the ludensis perhaps reaching into nilssoni zone 3 8 in the priekule section the early wenlock 13 c peak is well represented 3 1 but in the late wenlock early ludlow 13 c values show little variation from 2 0 to 1 in this section a high peak of 13 c values 5 9 was determined in the nova beds correlated with the topmost gorstian and lowermost ludfordian ludlow the carbon isotope positive excursions show good correlation with lows of the global sea level curve and with most of the biotic and supposed climatic events glaciation ocean state

the effects of rock fragment shapes and positions on modeled hydraulic conductivities of stony soils abstract mountainous soils usually contain a large number of rock fragments particles with a diameter larger than 2 mm which can influence soil hydraulic properties that are required to quantitatively describe soil water movement in stony soils the objective of this study was to numerically estimate both the saturated hydraulic conductivity of a stony soil and its dependence on a relative content of rock fragments stoniness and the shape position and distribution of rock fragments in a soil matrix the assessment method was based on a numerical version of darcy s classic experiment that involved steady state flow through a porous material under a unit hydraulic gradient our experiments involving hypothetical stony soils in this particular case were simulated using mainly the two dimensional 2d numerical model hydrus 2d a limited number of simulations were carried out using a three dimensional hydrus model three different shapes of hypothetical rock fragments were used in the study a sphere an ellipsoid with two different positions and a pyramid all represented by their 2d cross sections i e a circle an ellipse and a triangle respectively the mean relative effective saturated hydraulic conductivity k rs for the same stoniness was almost the same for all simulated scenarios and fine soil textures a stoniness between 0 07 and 0 5 cm 3 cm 3 can cause a decrease of k rs in the range of 0 17 0 70 numerical experiments were divided into 3 scenarios the largest and the smallest values of k rs were different for different shapes of rfs scenario a different orientations of the slab sided elliptical rfs scenario b and regular or irregular distributions of spherical rfs scenario c the largest difference between k rs values 0 26 was found in scenario b when the slab sided elliptical rfs were oriented either horizontally or vertically for stoniness of 0 24 or 0 31 cm 3 cm 3 simulated k rs values were underestimated in all scenarios as compared to the ravina and magier 1984 function the smallest differences 1 1 2 5 between numerically simulated and calculated the corring and churchill 1961 method for a cylindrical shape of rfs k rs values were found for scenario a with its 2d representation of spherical rock fragments calculated the corring and churchill 1961 method for a spherical shape of rfs k rs values corresponded well with those simulated using a 3d representation of spherical rock fragments numerical models provide a unique opportunity to evaluate the effects of different factors on the saturated hydraulic conductivity of stony soils that may be nearly impossible to measure in practice

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

stable isotopic results from paleosol carbonate in south asia paleoenvironmental reconstructions and selective alteration article i nfo we measured 18 o and 13 c values of paleosol carbonate nodules from a variety of sedimentary units in southern asia in order to reconstruct paleoenvironmental conditions and to evaluate for possible diagenetic alteration paleosol carbonate nodules were collected from lower to upper cretaceous strata exposed in two locations in southern tibet and from lower to middle miocene strata in northern india and nepal additional samples were collected from stratigraphically adjacent marine carbonate units to test for possible resetting of stable isotope values based on the implausibly low 18 o values 13 of most of the marine carbonate samples we interpret the 18 o values of the associated paleosol carbonate nodules as being reset and therefore unreliable for paleoenvironmental or paleoelevation reconstruction importantly the 18 o values of 13 c values of marine carbonate rocks fall within the expected primary

differential preservation of primary isotopic signatures in silurian brachiopods from northern europe abstract isotopic and geochemical compositions of silurian calcitic brachiopod shells carbonate host rocks and calcite cements from two northern european sites with different diagenetic histories are compared gotland sweden oslo graben norway the sequence exposed on gotland is characterized by repeated synsedimentary subaerial exposure and meteoric influence but only insignificant thermal alteration during shallow burial diagenesis in contrast silurian sediments exposed in the oslo area show only few signs of early exposure but were severely affected by thermal alteration during burial of the succession the preservation potential of brachiopod shells in each basin is different most nonluminescent brachiopods from gotland show well preserved microstructures and trace element contents very similar to those of modern brachiopod shells tightly clustered isotope values of individual brachiopod populations do not suggest significant meteoric alteration of primary marine isotope signatures in contrast there is strong evidence that all brachiopod shells from the oslo area contain diagenetically altered 18o values alteration of norwegian brachiopods is not always reflected in their trace element contents and cathodoluminescence characteristics but under sem the shells often display corrosion and recrystallization scattered oxygen isotope values in nonluminescent brachiopods 18o 18 to 5 5o oo together with low 18o values the case study from the oslo graben demonstrates that high fluid rock ratios and thermal overprinting during burial diagenesis may result in pervasive diagenetic alteration of 18o values in nonluminescent brachiopod shells this alteration can be detected by combined petrographic and geochemical investigations on brachiopod shells diagenetic cements and carbonate host rocks brachiopods from deeply buried and hydrothermally altered sites should not be used for deciphering marine 18o signals however the data presented here argue against a general rejection of lower paleozoic brachiopods as indicators of marine isotope signatures

microspar development during early marine burial diagenesis a comparison of pliocene carbonates from the bahamas with silurian limestones from gotland sweden comparison of ultrastructures in pliocene periplatform carbonates from the bahamas with silurian limestones from gotland sweden reveals that despite the differences in primary sediment composition and age they reflect a similar mechanism of lithification in both sequences calcite microspar was formed as a primary cement at an early stage of marine burial diagenesis neither significant compression nor meteoric influence are necessary for the formation of calcite microspar a model is proposed for the process of microsparitic cementation of fine grained aragonite needle muds comprising four stages 1 unconsolidated aragonite dominated carbonate mud 2 precipitation of microspar that engulfs aragonite needles 3 dissolution of aragonite resulting in pitted surfaces of the microspar crystals and 4 slight recrystallization our results contradict the widespread opinion that microspar necessarily is a product of secondary recrystallization of a previously lithified micrite

a sediment transport equation for interrill overland flow on rough surfaces a model for predicting the sediment transport capacity of turbulent interrill flow on rough surfaces is developed from 1295 flume experiments with flow depths ranging from 3 4 to 43 4 mm flow velocities from 0 09 to 0 65 m s 1 reynolds numbers from 5000 to 26 949 froude numbers from 0 23 to 2 93 bed slopes from 2 7 to 10 sediment diameters from 0 098 to 1 16 mm volumetric sediment concentrations from 0 002 to 0 304 roughness concentrations from 0 to 0 57 roughness diameters from 1 0 to 91 3 mm rainfall intensities from 0 to 159 mm h 1 flow densities from 1002 to 1501 kg m 3 and flow kinematic viscosities from 0 913 to 2 556 10 6 m2 s 1 stones cylinders and miniature ornamental trees are used as roughness elements given the diverse shapes sizes and concentrations of these elements the transport model is likely to apply to a wide range of ground surface morphologies using dimensional analysis a total load transport equation is developed for open channel flows and this equation is shown to apply to interrill flows both with and without rainfall the equation indicates that the dimensionless sediment transport rate is a function of and therefore can be predicted by the dimensionless shear stress its critical value c the resistance coefficient u u the inertial settling velocity of the sediment wi the roughness concentration cr and the roughness diameter dr the model has the form 1 where and testing reveals that the model gives good unbiased predictions of in flows with sediment concentrations less than 0 20 flows with higher concentrations appear to be hyperconcentrated and to have sediment transport rates higher than those predicted by the model copyright 2001 john wiley sons ltd

diagenesis of fibrous magnesian calcite marine cement implications for the interpretation of δ18o and δ13c values of ancient equivalents fibrous high mg calcite hmc marine cement from the pliocene hope gate formation jamaica occurs as 1 2 mm thick isopachous coatings on skeletal grains in local occurrences of halimeda grainstone and is commonly syntaxially overgrown by clear prismatic low mg calcite lmc interpreted as a mixing zone cement the presence of inclusions at discrete levels in the fibrous marine cement produces internal growth banding wherein clear inclusion free zones alternate with cloudy inclusion rich zones clear zones have uniform mg contents 13 7 0 2 mol mgco3 and stable isotopic compositions 18o 0 8 0 1 13c 3 2 0 1 consistent with a marine origin in contrast inclusion rich zones contain fine scale intergrowths of lmc dolomite and hmc and have carbon and oxygen isotopic compositions that define a linear mixing trend between compositions of inclusion free hmc and prismatic lmc cement overgrowths petrographic observations indicate that the mixing trend defined by isotopic data from inclusion rich zones is related to the addition of large volumes of secondary lmc as cement in primary pore space as intergrowths among fibers of primary hmc marine cement and or as replacements of primary hmc crystallites dolomite is present in inclusion rich zones in volumes generally compatible with amounts predicted to result from the closed system stabilization of hmc to lmc and dolomite in addition isotopic and geochemical data from some areas of inclusion rich zones are consistent with mass balance constraints assuming a closed system which require that bulk isotopic and geochemical compositions are retained these relations suggest that small remnants of hmc in inclusion rich zones of hope gate marine cement have altered to lmc and dolomite while isolated from system pore fluids such that primary marine isotopic signatures were imparted on diagenetic products similar petrographic geochemical and isotopic relations have been noted in ancient occurrences suggesting that 18o and 13c values from some former marine cements should be useful for the determination of isotopic compositions of original marine cements and ultimately for the determination of ocean chemistry in the geologic past

brachiopods as indicators of original isotopic compositions in some paleozoic limestones the original stable isotopic composition of paleozoic marine carbonate rocks is important to establish a baseline for evaluating diagenetic alteration and providing a reliable data base for modeling exogenic geochemical cycles of the elements we have compared the 18 o and 13 c values in the nonluminescent portions of brachiopods with similar published data of whole brachiopods other whole fossils and estimates of original isotopic composition of marine cements the oxygen and carbon isotopic records for each of these paleozoic components show generally good internal consistency significant discrepancies however were noted between results on the different components isotopic and trace element data presented in this study suggest that permo carboniferous whole brachiopods are little altered chemically nonetheless a more reliable but not fool proof approach for obtaining pristine isotopic values is microsampling of least altered regions based on cathodoluminescence in conjunction with staining techniques and elemental analyses the carbon and oxygen isotopic compositions of all components decrease in 18 o and 13 c in geologically older material neither temporal trend is monotonic however oxygen isotopic results suggest an important positive shift in 18 o of about 2 during the early carboniferous whereas the carbon isotope trend shows a major positive shift 2 3 during the mid carboniferous

runoff characteristics and soil erosion dynamic processes on four typical engineered landforms of coalfields an in situ simulated rainfall experimental study abstract large engineered landform tracts formed during coalfield development and construction cause serious soil erosion and threaten the ecological security of the coalfield area a series of in situ simulated rainfall experiments with rainfall intensities ranging from 1 0 to 3 0 mm min 1 were conducted to explore the runoff characteristics and erosion dynamic processes of four engineered landforms namely waste slag heap with more gravel wsg waste slag with more sand wss waste soil heap wsh and disturbed land dl with undisturbed land ul as the control ck compared with ul the wss wsg and wsh runoff rates rrs increased by 38 83 71 39 and 63 16 respectively but decreased by 9 25 for dl the slope flow of ul was in the subcritical laminar and subcritical transition flow regimes while the four engineered landform flow regimes were mainly subcritical transition and subcritical turbulent flow regimes the ul and dl soil loss rates slrs followed a declining fluctuating levelling off trend while the wss wsg and wsh slrs followed a trend of multiple early stage peaks and valleys before levelled off the mean wss wsg wsh and dl slrs were 11 19 times 138 67 times 73 47 times and 2 82 times that of ul respectively ul disturbance significantly increased the runoff ability to detach sediments by 2 48 94 90 times based on the relationships between runoff rate and soil loss rate the shear stress stream power and unit stream power up critical values initiating dl soil erosion were 58 86 37 06 and 56 67 lower than those of ul respectively while higher critical hydrodynamic values were required to detach wsg wss and wsh particles the rainfall intensity ri slope gradient median particle size d50 fractal dimension fd and up were employed to develop an empirical model for predicting engineered landform slrs

the influence of landscape connectivity and landslide dynamics upon channel adjustments and sediment flux in the liwu basin taiwan catchment scale analyzes of spatial and temporal variability in landscape connectivity are critical considerations in appraisals of landscape evolution and disaster mitigation in tectonically active mountain belts such as taiwan this study uses historical aerial photographs flow discharge and seismic data to analyze landslide changes and channel adjustments over a 30 year period in the liwu basin recurrent earthquakes and typhoon events trigger frequent landslide activity channel adjustment and sediment reworking in this system spatial variability in magnitude frequency relations of hillslope valley floor lateral and upstream downstream longitudinal connectivity during the study period are shown to reflect annual reworking in source and accumulation zones while partly confined valleys in the mid catchment area trap sediment behind landslide induced dams that are formed and breached on an approximately decadal basis this promotes partial longitudinal connectivity in these areas landscape responses to disturbance events were especially pronounced following combinations of seismic and typhoon events prior to the 1998 and 2005 images although single high magnitude events and series of moderate events affect patterns of landscape connectivity in the liwu basin residence times for sediment storage are very short in this highly connected river system where confined valley settings extend virtually to the coast copyright 2014 john wiley sons ltd

primary and diagenetic isotopic signals in fossils and hemipelagic carbonates the lower jurassic of northern spain stable isotope and trace element analyses of 230 jurassic pliensbachian toarcian samples from northern spain have been performed to test the use of geochemical variations in fossils belemnites and brachiopods and whole rock hemipelagic carbonates as palaeoceanographic indicators although the succession analysed reinosa area westernmost basque cantabrian basin has been subject to severe thermal alteration during burial diagenesis the samples appear to be well preserved the degree of diagenetic alteration of the samples has been assessed through the application of integrated petrographic chemical and cathodoluminescence analyses it is demonstrated that brachiopods and whole rock carbonates although widely used for palaeoceanic studies do not retain their primary marine geochemical composition after burial diagenesis in contrast there is strong evidence that belemnite rostra preserve original isotopic values despite pervasive diagenesis of the host rock well preserved belemnite shells non luminescent to slightly luminescent typically show stable isotope values of 4ae3 to 0ae7 d 13 c 0ae7 to 3ae2 d 18 o and trace element contents of 950 l gg 1 sr and sr mn ratios 80 this study suggests that the degree to which diagenesis has affected the preservation of an original isotopic composition may differ for different low mg calcite fossil shells and hemipelagic bulk carbonates behaviour that should be considered when marine isotopic signatures from other ancient carbonate rocks are investigated multiple non luminescent contemporaneous belemnite samples passed the petrographic and geochemical tests to be considered as palaeoceanic recorders yet their d 13 c and d 18 o values exhibited moderate scatter such variability is likely to be related to the palaeoecological behaviour of belemnites and or highfrequency secular variations in sea water chemistry superimposed on the longterm isotopic trend a pronounced positive carbon isotope excursion up to 4ae3 is documented in the early toarcian serpentinus biozone which correlates with the toarcian d 13 c maximum reported in other european and tethyan regions

geochemistry of brachiopods oxygen and carbon isotopic records of paleozoic oceans abstract combined trace element and isotope studies of 319 brachiopods covering the ordovician to permian time span show that 13c and 18o in well preserved specimens varied during the paleozoic the overall 13c secular trend is in accord with the previously published observations but its details are obscured by vital isotopic fractionation effects at generic level nonetheless the results suggest that the negative correlation between marine 13ccarbonate and 34ssulphate deteriorates at time scales of 106 years due to the long residence time and thus slow response of so42 in the ocean for oxygen isotopes all devonian and older specimens have 18o of 4 while the well preserved permian samples have near present day 18o of about 1 pdb this isotopic dichotomy is probably not due to post depositional phenomena salinity or biogenic fractionation effects this leaves open the perennial arguments for a change in 18 o 16 o of sea water versus warmer ancient oceans the present data are difficult to explain solely by the temperature alternative the coincidence of the proposed shift in 18o with the large late paleozoic changes in marine 87 sr 86 sr 13 c 12 c 34 s 32 s and sea level stands argues for a tectonic cause and for a change in 18 o 16 o of sea water although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites whatever the precise cause or combination of causes the implications for tectonism and or paleoclimatology are of first order significance

depth and seasonal variations in the thermal properties of antarctic dry valley permafrost from temperature time series analysis 1 we present the first dedicated study of the thermal properties of perennially frozen ice cemented subsurface dry valley permafrost from time series analysis of 14 months temperature measurements we resolve depth and seasonal variations in the thermal properties at two nearby sites at table mountain with different origin composition and polygonal ground patterning we determine apparent thermal diffusivity atd profiles directly from thermistor array measurements at 13 5 cm depth intervals and 4 hour time intervals in the top 2 m we treat the system as purely conductive year round due to the cold temperatures and compare the performance of several common analysis schemes with a graphical finite difference method that we present in detail this comparison is facilitated by one site showing strong depth variations including an abrupt twofold increase in atd across a sharp compositional boundary we characterize the composition of the inhomogeneous ground from recovered cores and estimate an ice fractiondependent heat capacity in the range c 1 7 0 1 to 1 8 0 1 mj m 3 c 1 we calculate apparent thermal conductivity profiles that correlate very well with the core compositions the conductivity generally lies in the range 2 5 0 5 w m 1 c 1 but is as high as 4 1 0 4 w m 1 c 1 for a quartose sirius sandstone unit at one site the seasonal variation in the atd is consistent with its expected temperature dependence index terms 3299 mathematical geophysics general or miscellaneous 5134 physical properties of rocks thermal properties 5194 physical properties of rocks instruments and techniques keywords dry valleys antarctica thermal properties of frozen ground permafrost

marine burial and meteoric diagenesis of early silurian carbonate ramps quebec appalachians canada the coeval early silurian platformal sayabec and la vieille formations covered 10 000 and 20 000 km 2 respectively in the gaspe basin in the appalachian orogenic belt field studies petrography and carbon and oxygen stable isotopes have been used to document the diagenetic evolution of the carbonate platforms significant diagenetic features included marine cements shallow burial marine to possible meteoric phreatic cements burial cements pressure solution stylolites fractures and minor fracture fill cements meteoric dissolution and meteoric vadose cements cementation started in the marine environment lf1 it was minor 18 o 5 3 per thousand delta 13 c 3 8 per thousand is taken as the best value for early silurian marine composition the upper part of the radiaxialoptic cement layers is composed of an initial non luminescent equant to prismatic spar lf2 passing into complexly banded luminescent scalenohedral spar lf3 these two cements constitute the bottom of cement successions in other lithofacies of both the sayabec and la vieille formations they are interpreted as likely shallow marine burial cements but a possible meteoric phreatic origin is not ruled out both hypotheses rely on cl petrographic similarities with known examples their depleted delta 18 o signature and wide range of delta 13 c values ferroan cements lf4 fill over 85 of the pore space occlusion of which was completed at burial depths of around 450 m lf4 cements are 18 o depleted delta 18 o 8 1 per thousand and 8 7 per thousand for sayabec and la vieille formations respectively when compared to lf2 delta nearly equal 2 3 per thousand and lf3 delta nearly equal 1 3 per thousand cements for both formations the delta 13 c values for the lf2 to lf4 la vieille cements are much higher than those of the sayabec this is explained by early methanogenesis related to the paleogeographic nature of the platform stylolitization fracturing and minor calcite cementation minor dolomitization and sulfatization occurred in the burial environment and postdate lf4 cements post initial burial lf5 gravitational and lf6 cements delta 18 o 10 7 per thousand and 10 1 per thousand delta 13 c 3 7 per thousand and 4 4 per thousand respectively are interpreted to be meteoric vadose cements filling solution vugs of the la vieille limestones in the western part of the ramp they are related to late silurian uplift in the gaspe belt

variability in geochemical provenance and weathering history of sirius group strata transantarctic mountains implications for antarctic glacial history abstract the major element and trace element geochemistry of 57 diamicts and muds of the sirius group is evaluated to determine the provenance and stratigraphic relations of geographically widespread outcrops in the transantarctic mountains the origin and age of the sirius group are heavily debated because of the presence of marine diatoms inferred to indicate a reduced east antarctic ice sheet as recent as the pliocene a key question is whether glaciers transported sediments and the enclosed diatoms from the east antarctic interior to the transantarctic mountains major element and trace element ratios indicate that the greater part of the sirius group sediments have an east antarctic provenance and that a few high elevation deposits are locally derived the degree of chemical weathering of the materials in the sirius group expressed as the chemical index of alteration cia has a wide range 41 70 on the basis of geochemical provenance weathering intensity and morphostratigraphic position the sirius group can be subdivided into three subgroups which probably represent multiple glacial phases 1 sediments with a local provenance from high elevation outcrops on spurs and mountain summits 2000 m which contain abundant weathered materials 2 sediments in high elevated outcrops 2000 m with intermediate cias originating from an east antarctic ice sheet which was overriding parts of the transantarctic mountains and 3 sediments recovered within or on the margins of the present glacial troughs at 1500 1800 m with low cias and an east antarctic provenance comparison with the weathering history inferred from drilling records in the nearby victoria land basin reveals that glaciation in the transantarctic mountains probably commenced with small ice caps and alpine glaciers prior to the eocene oligocene transition and from the oligocene onward continued with multiple phases of continental glaciation these results and interpretations contribute considerably to the understanding of the landscape evolution of the transantarctic mountains the sirius group debate and the history of east antarctic glaciation

provenance geochemistry and grain sizes of glacigene sediments including the sirius group and late cenozoic glacial history of the southern prince albert mountains victoria land

the silurian of gotland sweden facies interpretation based on stable isotopes in brachiopod shells the silurian of gotland sweden consists of 440 m of carbonate deposits repeatedly uniform sequences of micritic limestones and marls are interrupted by complex structured reefs and by adjacent platform sediments generally the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the purpose of this study is a facies interpretation based on both field observations and stable isotope measurements of brachiopod shells approximately 700 samples from stratigraphically arranged localities in different facies areas have been investigated the carbon and oxygen isotopes show principally parallel curves and a close relationship to the stratigraphic sequence lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than to paleotemperature carbon isotope ratios are believed to have been connected to global changes in the burial of organic carbon in black shales during periods of euxinic deep water conditions consequently the facies succession on gotland results from global paleoclimatic conditions changes in terrigenous input due to different rates of weathering and freshwater runoff rather than sea level fluctuations control the carbonate formation of the silurian on gotland

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

brachiopod δ18o values do reflect ambient oceanography lacepede shelf southern australia although commonly used as proxies for attributes of ancient ocean waters the 18 o values of brachiopods from modern seas are little studied to evaluate the utility of brachiopods as recorders of regional oceanography modern shells from the lacepede shelf 25 000 km 2 of southern australia were analyzed for 18 o and the results were compared to the values of ambient seawater southern ocean waters cover this area of extensive cool water carbonate deposition but there are distinct sectors of seasonal upwelling and lesser fluvial outflow 18 o values of brachiopods across the environmental spectrum from 40 to 300 m water depth are in general isotopic equilibrium with surrounding seawater nevertheless 18 o values from individual sample sites vary as much as 0 60 the area of cold water upwelling in particular is clearly delimited by a group of high 18 o values the range of values across this one shelf on the order of 2 5 is similar to the range of values postulated on the basis of similar results for secular changes in many ancient oceans

comment on oxygen and carbon isotopic composition of ordovician brachiopods implications for coeval seawater by h qing and j veizer

the isotopic record of ocean chemistry and diagenesis preserved in non luminescent brachiopods from mississippian carbonate rocks illinois and missouri fossil brachiopod shells are commonly used as a faithful record of the chemical and isotopic composition of the ancient ocean water in which they grew owing to their stable mineralogy and their presence in marine strata throughout phanerozoic time the utility of these fossils for preserving ocean water compositions is evaluated through analyses of multiple specimens that grew in contemporaneous sea water at individual stratigraphic horizons in the mississippian age burlington keokuk formation of mid continent north america significant variations in sr c and o isotopic compositions are observed in contemporaneous non luminescent shells indicating that apparently pristine brachiopod shell material has been altered by post depositional processes of diagenesis the least altered compositions at each horizon are used to estimate secular variations of 87 sr 86 sr in early mississippian ocean water the estimated rates of change of ocean water 87 sr 86 sr are comparable in magnitude to the rapid sr isotopic changes documented for cenozoic ocean water for which high frequency glacial cycles are inferred as a driving mechanism the rigorous assessment of diagenetic effects on the isotopic signatures of marine phases is requisite for the advancement of high resolution reconstructions of paleo ocean chemistry

carbon and oxygen isotopic composition of silurian brachiopods gotland sweden palaeoceanographic implications abstract one hundred and seventy two non luminescent brachiopod shells from the silurian sequence of gotland were investigated for their carbon and oxygen isotopic composition diagenetic alteration of the shell calcite was excluded by means of petrographic trace element and cathodoluminescence analysis oxygen and carbon isotopic signals vary considerably within the uppermost llandovery to the ludlow average 18o and 13c values of well defined stratigraphic units range from 2 4 to 5 9 and 1 to 8 respectively we observed parallel trends in the carbon and oxygen isotope curves with the most prominent shifts occurring in the lower wenlock upper wenlock and middle ludlow average 18o values 2 4 to 2 9 recorded in the middle ludlow are among the highest 18o values reported for the early palaeozoic the recorded 18o variations cannot solely be explained by changes in sea surface temperature and salinity the variations in the isotopic signals correlate negatively with changes in sea level heavy carbon and oxygen signals coincide with sea level lowstands whereas light signals are recorded during sea level highstands sea level highstands were probably characterized by the formation of warm saline waters on subtropical epicontinental shelves inducing oxygen deficiency in the basins alumshale facies the low 18o values are attributed to 18o depletion in surface waters owing to the storage of 18o enriched saline waters in the basins low 13c values are explained by a low surface water productivity since nutrients were not supplied to the photic zone but rather stored in the deeper ocean during sea level lowstands colder waters that formed in higher latitudes may have represented the main intermediate water source a better ventilation of the basins is documented by the deposition of well aerated sediments whereas the high 18o values are explained by the change in oceanic circulation the high 13c values are attributed to an enhanced primary productivity and possibly to an enhanced burial of corg the model discussed here may provide an attractive scenario for accounting for the recorded short term variations in the isotopic signals without the necessity of introducing an isotopic correction factor for silurian sea water

fabric retentive non luminescent brachiopods as indicators of original delta 13 c and delta 18 o composition a test abstract fabric retentive non luminescent helderbergian brachiopods from open marine deposits analogous to brachiopods used in other studies to determine paleo oceanic stable isotopic composition exhibit depleted 13c values immediately below the erosional contact and more enriched values of 13c at greater stratigraphic distances below this surface in addition 13c values of these brachiopods display a marked shift across the erosional surface and values above it are essentially the same as those 30 m or more beneath the surface complementing these trends whole rock analyses metastable high agnesian calcite constituents echinoderms as well as early equant calcite cement also exhibit an increased depletion trend in 13c values as the helderberg oriskany contact is approached from below fabric retentive luminescent as well as obviously recrystallized brachiopods display stable isotopic values similar to those of fabric retentive non luminescent brachiopods thus best preserved fabric retentive non luminescent brachiopods exhibit values similar to obviously recrystallized brachiopods diagenetically altered metastable constituents echinoderms stable early meteoric cements and whole rock samples helderberg strata of new york state were affected by early meteoric diagenesis during a siegenian exposure event prior to deposition of the overlying marine oriskany sandstone meteoric diagenesis during this exposure gave rise to a characteristic carbon isotopic depletion trend approaching the helderberg oriskany contact all of the skeletal constituents underwent isotopic exchange during early diagenetic exposure to meteoric waters consequently the practice of using fabric retentive non luminescent brachiopods as indicators of their original chemistry and by extension paleo oceanic chemistry is questioned

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

effect of antecedent conditions and fixed rock fragment coverage on soil erosion dynamics through multiple rainfall events the effect of antecedent conditions and specific rock fragment coverage on precipitation driven soil erosion dynamics through multiple rainfall events was investigated using a pair of 6 m 1 m flumes with 2 2 slope four sequential experiments denoted e1 e2 e3 and e4 involved 2 h precipitation rates of 28 74 74 and 28 mm h 1 respectively and 22 h without rainfall were conducted in each experiment one flume was bare while the other had 40 rock fragment coverage the soil was hand cultivated and smoothed before the first event e1 only and left untouched subsequently sediment yields at the flume exit reached steady state conditions over time scales that increased with sediment size experiments were designed such that both steady and non steady effluent sediment yields were reached at the conclusion of e1 results from subsequent experiments showed that short time soil erosion was dependent on whether steady state erosion was achieved during the preceding event although consistent steady state effluent sediment yields were reached for each sediment size class steady state erosion rates were however dependent on the rainfall intensity and its duration if steady state sediment yields were reached for a particular size class that class s effluent sediment yield peaked rapidly in the next rainfall event the early peak was followed by a gradual decline to the steady state condition on the other hand for size classes in which steady state was not reached at the end of the rainfall event i e e1 in the following event e2 the sediment yields for those classes increased gradually to steady state i e the sharp peak was not observed the effect of rock fragment cover 40 on the soil surface was also found to be significant in terms of the time to reach steady state i e their presence reduced the time for steady conditions to be attained effluent sediment yields for the bare and rock fragment covered flumes e1 showed steady conditions were reached for the latter in contrast to the former we used the hairsine rose h r model to simulate the experimental data as it explicitly models soil particle size classes experiments e1 and e2 involved soil compaction by raindrops and in this case the model predictions were found to be unsatisfactory however compaction was effectively completed by the end of experiment e2 and the model provided reasonable predictions for experiments e3 and e4

vein cements and the geochemical evolution of subsurface fluids in the visean of the campine basin poederlee borehole belgium upper visean reef mound carbonates from the campine basin northern belgium have a complex diagenetic history which reflects the evolution of subsurface fluids in the basin primary pores became cemented by marine fibrous stage a and shallow burial stage b c and d scalenohedral and blocky calcites tectonic deformation then created successive networks of fractures which acted as conduits for aggressive fluids and which were subsequently cemented by six stages of carbonate cement fluid inclusion evidence suggests that the first cloudy columnar calcite cements in fractures stage e formed at or below 50 c these calcites have a 18 o of 13 3 pdb and they are interpreted to have grown in meteoric waters 18 o 6 7 to 7 4 smow after a further period of fracturing and dissolution white blocky calcites stage f 18 o 9 1 pdb precipitated around 60 c from fluids with a 18 o 0 9 smow later fractures contain brown columnar and blocky calcites stage g with a 18 o of 12 1 pdb and a minimum homogenization temperature t h of c 90 c giving a pressure corrected precipitation temperature of 95 c an oxygen isotopic composi tion of 0 6 smow is indicated for the fluid granular to bladed ferroan calcites stage h blocky ferroan calcites stage i 18 o 9 8 pdb and t h 128 c and saddle dolomites stage j 18 o 10 0 pdb and t h 147 c are the last diagenetic carbonate phases methane has been detected in the vapour phase of the fluid inclusions in the blocky ferroan calcites the ferroan calcites and the saddle dolomites are interpreted to have formed respectively at 150 c and 200 c in 18 o rich fluids 7 9 smow and 10 9 smow the stable isotope values of the fluids indicate an abrupt change from a meteoric composition towards marine derived compactional fluids and basinal brines enrichment in 18 o is mainly attributed to the dewatering dehydration of clay minerals in the adjacent upper carboniferous strata the paragenetic sequence of cements described here is comparable to that encountered in other lower carboniferous limestones where there is not such an extensive data base of fluid inclusion and stable isotopic data it is suggested that the large change in the pore fluid composition documented here might be a common subsurface process and that the interpretation of diagenetic temperatures from isotopic data alone can be very misleading

diagenesis of middle devonian carbonate mounds of the mader basin eastern anti atlas morocco abstract in the mader basin of the eastern anti atlas middle devonian carbonate mounds were established on a gently sloping ramp at moderate water depths primary stromatactis cavities in these mounds exhibit early marine shallow burial and deeper burial cementation the mound matrix was affected by neomorphic alteration stylolitization and dolomitization earliest cementation occurred in the marine environment nonluminescent to blotchy luminescent cloudy radiaxial calcites of originally high mg calcite composition coat the walls of stromatactis cavities and take up more than 50 of the primary pore space the isotopic signature d18o 2 6 0 2 pdb d13c 2 7 0 5 pdb is close to that of nonluminescent fabric retentive brachiopod shells in the same mounds and taken as the nearly pristine stable isotopic signature of mader basin seawater the high d18o values compared with middle devonian data of north america are interpreted to result from the mid latitudinal ca 35 s temperate water settings of the mader basin carbonate mounds the transition to the shallow burial realm is indicated by a typical non bright dull luminescence sequence nonluminescent scalenohedral cements pass into bright luminescent and banded luminescent scalenohedral cements which are overgrown in turn by dull to moderate luminescent blocky spar meteoric influence on that cement sequence can be excluded deeper burial diagenesis is represented by stylolitization ferroan calcite cementation and neomorphic alteration of the fine grained mound carbonates pressure solution and or outgassing of co2 are possible ion sources for ferroan calcite precipitation in the remaining pore space 18o depletion d18o 6 8 to 8 9 pdb of these cements can be calculated to elevated precipitation temperatures of 21 33 5 c and burial depths of 420 670 m microspar making up the bulk of the mounds was formed by a one step transformation of a precursor calcitic micrite low d18o values 6 9 p 2 1 pdb mottled luminescence and high fe concentrations indicate that this transformation also took place in the deeper burial realm

spatial distribution of rock fragments on steep hillslopes in karst region of northwest guangxi china abstract rock fragments 5 mm in diameter at the soil surface and within the topsoil have a large effect on the intensity of various hydrologic and geomorphic processes however little information is available on the spatial distribution of rock fragments in subtropical regions the objective of this paper was to investigate the relationship between the spatial distribution of rock fragments and landforms on two different steep karst hillslopes in northwest guangxi southwest china on the first hillslope a disintegrated landslide failure with the presence of several large rock outcrops 2 m in height the spatial distribution of rock fragment cover had no obvious relationship with topographic position except that the mean cover percentage of small rock fragments 5 20 mm decreased from bottom to top on the second hillslope an avalanche slope without the presence of large rock outcrops the mean total rock fragment cover 5 600 mm increased from bottom 5 to top 21 with decreasing variability and rock fragments with various sizes 5 20 20 75 and 75 250 mm showed a similar increasing trend the mean total rock fragment cover increased linearly with slope gradient on the second hillslope and tended to increase and then decrease with gradient but their relationship was not obvious on the first hillslope this indicated that the spatial distribution of surface rock fragment cover had a close relationship with the presence of large rock outcrops and slope gradient however the median diameter d50 of the surface rock fragments had an increase decrease trend with slope gradient but there was no obvious relationship on both hillslopes with low overland flow therefore the dominant factor for the spatial distribution of rock fragment cover and size at the soil surface might not be soil erosion by water but slope gradient vegetation and geomorphologic condition of the slope the mean total volumetric rock fragment content 5 250 mm within the topsoil 10 20 cm thick increased linearly from bottom 16 to top 39 with slope gradient on the first hillslope and had a logarithmic increase from bottom 10 to top 27 with gradient on the second hillslope this suggested that rock fragment content within the topsoil was mostly controlled by slope gradient and topographic positions and had not a close relationship with the presence of large rock outcrops

petrogenesis of early cambrian reef limestones labrador canada through petrography cathodoluminescence and microprobe analysis three styles of particle preservation can be differentiated 1 skeletons with excellent fabric retention as nonferroan calcite trilobites and salterella or both ferroan and nonferroan calcite echinoids and sponge spicules 2 skeletal molds completely filled by nonferroan calcite spar or occasionally a second stage of equant ferroan calcite and dolomite as well archaeogastropods hyolithids brachipods coelenterates and chancelloria 3 fibrous to microcrystalline components which are now either well preserved as nonferroan calcite or are molds filled by equant ferroan calcite and dolomite or both ooids archaeocyathans and the alga renalcis synsedimentary cements localized to reefs are 1 rays or botryoids in which each acicular crystal is a spar filled mold or 2 rinds of fibrous calcite commonly with fascicular optic properties or a partially dissolved fabric in which the solution voids are now filled with iron rich equant calcite cement those cambrian particles and cements which are now only spar filled molds were originally aragonite those without a void stage and retaining original fabric were calcite or mg calcite those with a fibrous to microcrystalline habit in some instances and spar filled molds in other cases were probably mg calcite alteration to calcite occurred as the sediments reacted with meteoric and marine groundwaters in a phreatic lens and then with percolating meteoric waters in a vadose diagenetic environment either conditions of carbonate precipitation have been similar since the earliest paleozoic or that the ocean atmosphere system in early cambrian time was coincidentally similar to that of today but may have been quite different at other times during the phanerozoic modified journal abstract

18o16o and 13c12c in lower paleozoic articulate brachiopods implications for the isotopic composition of seawater three hundred and eleven articulate brachiopods with extensive geographic coverage spanning the cambrian to silurian stratigraphic interval were analyzed for oxygen and carbon isotopic composition cambrian samples have 18o 7 ordovician samples 2 4 and silurian samples 1 9 confirming the previously established trend towards lighter isotopic compositions with increasing age throughout the lower paleozoic forty nine best preserved ordovician and silurian samples were identified based on scanning electron microscopy and trace element analysis they were found to bracket the isotopic compositions of over 85 of specimens from these stratigraphic intervals supporting widespread preservation of the isotopic signal some latest ordovician and lower ludlovian samples associated with shale sequences are apparently enriched in 18o these are interpreted as an environmental phenomenon perhaps related to water temperature and glaciation a number of silurian samples of varying genera and stratigraphic levels are highly enriched in 13c up to 6 some are shale related but some are associated with carbonate bearing basins these are also thought to represent near original compositions but a single environmental cause is unknown the present data show that luminescence is not a decisive criterion for evaluating the degree of brachiopod preservation whole shell values were isotopically similar to their nonluminescent portions for both oxygen and carbon

boron isotope geochemistry of paleozoic brachiopod calcite implications for a secular change in the boron isotope geochemistry of seawater over the phanerozoic abstract boron isotope composition of marine carbonates has been proposed as a paleo ph proxy and potential tool to reconstruct atmospheric pco2 the precise knowledge of the boron isotopic composition of ancient seawater represents the fundamental prerequisite for any paleo ph reconstruction this contribution presents boron isotope values for silurian to permian brachiopod calcite that might be used to reconstruct ph or boron isotope composition of past oceans all brachiopod shells were screened for diagenetic recrystallization by means of cathodoluminescence microscopy trace element geochemistry b fe mn sr as well as sem only nonluminescent shells revealing well preserved microstructures high strontium and boron concentrations as well as low iron and manganese contents were accepted for boron isotope analysis the boron isotope ratios of silurian devonian pennsylvanian and permian brachiopod calcite range from 6 8 to 11 0 7 3 to 14 9 12 4 to 15 8 and 10 1 to 11 7 respectively these 11b values are significantly lower in comparison to 11b values of modern biogenic carbonates and indicate that the paleozoic oceans were depleted in 11b by up to 10 box modeling of the boron geochemical cycle suggests that the significant depletion of 11b in the oceanic reservoir may have been initiated by an enhanced continental boron discharge our data support the earlier made conclusion that boron isotopes may not be used in the geological past as reliable paleo ph proxy unless the boron isotopic composition of ancient oceans can be constrained by further studies

silurian conodont based correlations between gotland sweden and saaremaa estonia correlations between the silurian successions of gotland and the east baltic are based on the narrowest stratigraphic units that can be distinguished in both areas in order further to increase precision true ends of ranges in measured sections have been used instead of pooled formational faunas where outcrops and collections permit some previous correlations are confirmed in other cases there are considerable changes both in levels of correlation and in precision the major differences are found mostly when one or more of the major gaps have remained unrecognized and stratigraphic units therefore have been extended and translated upwards or downwards at least some of these gaps decrease in magnitude southwards in estonia gaps at these levels are also noted on gotland although they are small and probably do not extend across the island the patterns through time of deposition during secundo episodes and gaps during primo episodes agree very well with what can be predicted from a model of oceanic and climatic cyclicity

δ18o and δ13c values of modern brachiopod shells abstract researchers have not rigorously tested the hypothesis that calcite from modern brachiopod shells is precipitated in oxygen isotope equilibrium with ambient seawater isotopic variability at the intraspecimen and intertaxon levels has not been examined without such data for modern brachiopods similar data from ancient brachiopods cannot be accurately interpreted in this study a survey is made of 18 o and 13 c values of terebratulid rhynchonellid thecideidine and craniacean brachiopods from antarctica the bay of fundy curacao japan new zealand norway puget sound palau sicily and south africa this suite of samples provides a wide range of taxonomic levels temperatures salinities and depositional environments for evaluating the degree of isotopic equilibrium attained during precipitation of brachiopod calcite new data indicate that modem brachiopod calcite is not always precipitated in oxygen and carbon isotope equilibrium with ambient seawater calcite from the primary layer and specialized shell structures hinge brachidium foramen interarea muscle scars are depleted in both 18 o and 13 c a characteristic of biological fractionation or vital effects often found in other calcerous marine organisms our findings suggest that these portions of the brachiopod shell should be avoided during sampling of ancient brachiopods secondary layer calcite the material most often analyzed in ancient brachiopods has higher 18 o and 13 c values which approach and sometimes correspond with predicted equilibrium values therefore secondary layer calcite is the most suitable portion of the brachiopod shell for use as an ancient seawater proxy although near equilibrium precipitation in secondary layer calcite is encouraging to those studying the isotopic composition of ancient oceans these data come with caveats large intraspecimen variability in the 18 o values of secondary layer calcite 1 in some samples limits the use of brachiopods as precise indicators of the 18 o value or temperature of ancient seawater the 18 o and 13 c values of secondary layer calcite deviate from predicted equilibrium values toward the lower values of the primary layer and specialized shell structures indicating a measurable vital effect in most cases measured 18 o values are lower than the calculated equilibrium values dictated by seasonal variations in the 18 o value and temperature of seawater ontogenetic variations in the 13 c values of secondary layer calcite have also been measured and must be assessed when interpreting ancient data modern brachiopods occur in a wide range of seawater salinities and temperatures therefore the relation between salinity and the 18 o value of seawater must be known to correctly calculate the temperature of calcite precipitation from secondary layer 18 o values errors of up to 15 c are found if ambient seawater is assumed to have a constant 18 o value e g 0 smow and the 18 o values of secondary layer calcite are used to calculate temperature coupled with vital effects and intraspecimen variability these errors can obscure the resolution of secular variations in the rock record

environmental and physiological influences on isotopic and elemental compositions of brachiopod shell calcite implications for the isotopic evolution of paleozoic oceans abstract brachiopods from the demissa bed middle devonian hamilton group biologically regulated the incorporation of mg sr and na into their shell calcite significant taxonomic differences in the elemental contents of three species athyris spiriferoides mediospirifer audacula and mucrospirifer mucronatus may be related to differences in calcification processes in contrast no significant difference or vital effects were observed between the isotopic values of mediospirifer audacula and athyris spiriferoides from erie 18o 0 03 p 0 949 13c 0 76 p 0 083 and genessee counties 18o 0 39 p 0 471 13c 0 06 p 0 854 this suggests that these brachiopods did not exert a biological control over their isotopic compositions and that their shell calcites reflect ambient physicochemical conditions isotopic compositions in unaltered shell calcites of brachiopods from genessee county which was close to the basin depocentre are heavy for carbon 13c x 5 01 pdb and oxygen 18o x 2 85 pdb compared to the species sampled at the basin s edge erie county 13c x 2 79 pdb 18o x 3 83 pdb there is a significant separation in isotopic values between the deeper and shallower water brachiopods of the basin 18o 0 98 p 0 0005 13c 2 22 p 0 0005 the 18o variation suggests a temperature salinity change with water depth whereas the change in 13c composition probably records an enrichment depletion of organic matter with water depth this observation has significant implications for paleozoic ocean isotopic evolution studies because many global changes in marine 18o and 13c are based on isotopic shifts of similar magnitude