rock composition dolomite stoichiometry and rock water reactions in dolomitic carbonate rocks dolomitic carbonate rock units from a variety of phanerozoic localities and depositional environments throughout north america were evaluated with respect to their dolomite content and dolomite composition by x ray diffraction analysis dolomite compositions range from 48 to 57 mole caco 3 with well defined modes at 51 nearly stoichiometric dolomite and 55 distinctly calcian dolomite caco 3 values of percentage of dolomite also exhibit a pronounced albeit less well defined bimodal distribution with modes at 97 dolostones and 20 dolomitic limestones dolomite similar distributions characterize most other published data on phanerozoic dolomitic carbonates these data suggest that two separate processes may lead to two distinct populations of sedimentary dolomite 1 dolomitic limestones originate in diagenetically closed systems during magnesian calcite dissolution calcite and dolomite precipitation reactions and 2 dolostones originate in diagenetically open systems during th

syn and postkinematic cement textures in fractured carbonate rocks insights from advanced cathodoluminescence imaging abstract in calcite and dolomite deposits in fractures transmitted light and optical cathodoluminescence methods detect crack seal texture in some fractures but scanning electron microscope based cathodoluminescence sem cl combined with secondary electron images and element maps reveals crack seal and cement growth textures where previous sem cl imaging methods found massive or featureless deposits in a range of fractured carbonate rocks patterns and textures of calcite and dolomite cements precipitated during and after fracture growth resemble complex accumulation patterns found in quartz in sandstone fractures suggesting that some apparent differences between carbonate mineral and quartz deposits in fractures reflect the limits of previous imaging methods advances in delineating textures in widespread carbonate mineral deposits in fractures provide evidence for growth and occlusion of fracture porosity

shallow burial dolomitization and dedolomitization of cenozoic cool water limestones southern australia geochemistry and origin abstract the gambier limestone a bryozoan rich cool water carbonate of late eocene to early miocene age in the otway basin of southeastern australia is about one third variably dolomitized limestone and dolostone individual dolomite crystals range from 10 to 500 m and are of three types 1 silt size crystals 4 64 m diameters having a brightly luminescent core 10 20 m of nearly stoichiometric dolomite with 1 mol mnco3 and sio2 but no fe surrounded by a thin dull or alternating dark and bright cl cortex that is nonstoichiometric with 44 46 mol mgco3 but sharp to diffuse zoning in mn and fe 2 sand size crystals which also have a brightly luminescent and stoichiometric core and dark and bright non stoichiometric thin inner cortex but are mostly a thick outer cortex at ca 50 m diameter that is nonluminescent and nonstoichiometric with some fe but no mn and 3 identical sand size crystals with a variably leached core and inner cortex that is either a void or a void filled with late calcite cement these three crystal populations represent two distinct dolomites and their alteration product the smallest of the silt size crystals which are rarely preserved are also the cores of the larger crystals upon which grew an inner and outer cortex of somewhat different composition the 18o values of dolomite rhombs 1 6 to 2 9 correlate positively with 13c values 0 7 to 3 0 with the lowest values from silt size or small sand size crystals and the highest values from large sand size crystals with leached unfilled cores low and variable 18o and 13c values in conjunction with high and variable mn and fe contents in both the core and inner cortex of all crystals are consistent with formation from a mixture of brackish water and seawater higher values for the outer cortex in sand size crystals are typical of those expected for precipitation from normal or near normal seawater low sr mn and fe contents in the largest crystals in conjunction with fluid inclusions of seawater salinity in the outer cortex are also consistent with the bulk of the large crystals having precipitated from seawater using the sr isotope evolution curve for cenozoic seawater sr isotope ratios of the dolomites can be divided into four distinct groups which correspond to times of major transgressions this cenozoic example in which dolomite petrography and crystal chemistry can be explained in terms of simple transgression regression offers a simple sedimentological explanation for many similar dolomites where processes of formation cannot be so easily constrained

temperate carbonate debrites and short lived earliest miocene yo yo tectonics eastern taranaki basin margin new zealand abstract this study examines two unconformity bound earliest miocene temperate shallow marine limestones at remote gibson beach western north island on the eastern margin of taranaki basin new zealand s only producing hydrocarbon province the local geology comprises an upper limestone of up to 6 m of spectacular conglomeratic limestone rudstone papakura limestone whose pebble to boulder sized clasts were derived from cannibalisation of the lower skeletal limestone bryomol grainstone otorohanga limestone multiple lines of evidence require the otorohanga limestone to have been well indurated before erosion and clast generation cementation occurred from pressure dissolution of calcitic skeletons at burial depths of probably 400 m or more subsequent uplift led to local subaerial exposure and karstification of a fault block cliffed coastline where physical erosion sourced talus limestone debris onto adjacent high energy pocket beaches storm and or seismic events periodically triggered mass flows of the limestone clasts offshore onto the contemporary mixed siliciclastic carbonate shelf as channelised carbonate debrites lithification of these papakura limestone debrites occurred via pressure dissolution and required a second burial episode karst pinnacles preserved on the eroded upper surface of the papakura limestone demand uplift again and erosion in a subaerial setting before subsequent deep burial by early miocene siliciclastic shelf sand and turbidite deposits strontium isotope dating of brachiopod fossils suggests the two postulated burial uplift cycles involving movements up to 400 100 m occurred very rapidly within several 100 kyr speculative drivers of the yo yo tectonic events are earliest miocene movements on the nearby major taranaki fault thrust in association with regional changes in subduction tectonics at the australian pacific plate boundary along with pulsed emplacement of obducted gravity slide deposits northland allochthon onto northern north island the two limestones record a previously undocumented degree of eastern taranaki basin margin tectonic mobility relevant to a fuller appreciation of petroleum system development in that basin

formation of dolomite mottling in middle triassic ramp carbonates southern hungary abstract the middle triassic carbonates of the villany mountains were deposited on a homoclinal carbonate ramp many of the carbonates from the 700 m thick sequence show partial or complete dolomitization the present paper describes dolomites that occur in a limestone unit as irregular mottles and as pore and fracture filling cements replacement type scattered dolomite rhombs in the mottles having inclusion rich very dull luminescent cores and limpid non luminescent outer zones represent the initial phase of dolomitization the isotopic composition of these dolomites 13 c 2 30 vpdb 18 o 3 60 vpdb is similar to that of the calcitic micrite 13 c 2 6 vpdb 18 o 4 00 vpdb indicating that no external fluids were introduced during dolomite formation the elevated sr content of the micrites implies that sediment was originally aragonite or high mg calcite dolomitization took place in the burial realm from a marine pore fluid in a partly closed system later fracture related saddle dolomite reflects elevated formation temperatures and increasing burial five calcites were identified multiple generations of calcite filled fractures were formed during burial diagenesis generally having dull or no luminescence 13 c 1 80 vpdb 18 o 6 40 vpdb the latest phase calcites are related to karst formation having a very negative isotopic composition 13 c 5 0 to 7 2 vpdb and 18o 7 4 vpdb the karst related processes include dissolution calcite precipitation and partial replacement of dolomites by complex zoned bright yellow calcite the timing of dolomitization is uncertain but the first phase took place in a partly closed system prior to stylolite formation late stage saddle dolomites were precipitated during maximum burial in the cretaceous the dissolution of dolomites and karst related calcite replacement was not earlier than late cretaceous

the succession of ice flow patterns in north central quebec labrador canada abstract quebec labrador canada is one of the postulated dispersal centres of the late wisconsinan laurentide ice sheet and also contains an unusually complex and rich glacial geological record a reliable reconstruction of glaciation history represented by this record would improve our comprehension of the dynamics of the eastern sector of the laurentide ice sheet such as the evolution of the basal thermal regime and the timing of enhanced ice flow into ungava bay we mapped glacial landforms over a 200 000 km2 area using aerial photographs and conducted a detailed field based survey of the central part of the area to establish the relative age of crosscutting glacial geological features the position of the last ice remnant was south of ungava bay well north of what has commonly been perceived as the location for this dispersal centre southward radial flow from a northward migrating and predominantly cold based dispersal centre was the last glacial event in north central quebec labrador a widespread occurrence of older ice flow traces towards the southwest was detected in some areas large drumlins formed during this ice flow event occur in alignment with landforms formed during the last deglaciation this older southwestward flow is however overprinted by and therefore predates traces of northward convergent flow into ungava bay ungava bay flow traces of a northeastward flow event and in some areas traces of the deglacial flow event flutes and glacial striae indicating ice flow towards northeast are superimposed on the ungava bay flow the northeastward ice flow system has been recognised across the mapped area and because of its direction and regional significance we infer formation approximately during the last glacial maximum

the mixed bed glacial landform imprint of the north sea lobe in the western north sea 2018 john wiley sons ltd during the last glacial cycle an intriguing feature of the british irish ice sheet was the north sea lobe nsl fed from the firth of forth and which flowed south and parallel to the english east coast the controls on the formation and behaviour of the nsl have long been debated but in the southern north sea recent work suggests the nsl formed a dynamic oscillating terrestrial margin operating over a deforming bed further north however little is known of the behaviour of the nsl or under what conditions it operated this paper analyses new acoustic sedimentary and geomorphic data in order to evaluate the glacial landsystem imprint and deglacial history of the nsl offshore from ne england subglacial tills af2 3 form a discontinuous mosaic interspersed with bedrock outcrops across the seafloor with the partial excavation and advection of subglacial sediment during both advance and retreat producing mega scale glacial lineations and grounding zone wedges the resultant mixed bed glacial landsystem is the product of a dynamic switch from a terrestrial piedmont lobe margin with a net surplus of sediment to a partially erosive quasi stable marine terminating ice stream lobe as the nsl withdrew northwards glaciomarine sediments af4 drape the underlying subglacial mixed bed imprint and point to a switch to tidewater conditions between 19 9 and 16 5 ka cal bp as the north sea became inundated the dominant controls on nsl recession during this period were changing ice flux through the firth of forth ice stream onset zone and water depths at the grounding line the development of the mixed bed landsystem being a response to grounding line instability 2018 john wiley sons ltd

the relationship between drumlins and other forms of subglacial glaciotectonic deformation this paper brings together the field data from 33 drumlins to show the relationship between drumlin formation and other subglacial deforming bed processes it is shown that there is a drumlin structure continuum a depositional which are similar to flutes formed by sediment flowing into the low pressure area behind a large obstacle and these conditions are mostly found within rock cored drumlins b deformational which contain different styles of deformation associated with a relatively weak core including stoss side deformation including both small and large scale brittle and ductile deformation stoss and lee side deformation compressive deformation and extensional deformation c erosional which consist of either truncated stratified sequences or homogeneous tills with distinct ice flow patterns furthermore it is suggested that if more sediment enters the deforming layer than can be removed then there will be net subglacial deposition which will result in the build up of a deforming bed till but if more sediment leaves the deforming layer then net erosion will occur under net erosional conditions any obstacle to flow may be left behind as a drumlin thus although individual drumlins have different internal structures they are formed associated with subglacial net erosion 0 1997 elsevier science ltd all rights reserved

late stage dolomitization of the lower ordovician ellenburger group west texas abstract petrography of the lower ordovician ellenburger group both in deeply buried subsurface cores and in outcrops which have never been deeply buried documents live generations of dolomite three generations of microquartz chert and one generation of megaquartz regional periods of karstification serve to subdivide the dolomite into early stage which predates pre middle ordovician karstification and late stage which postdates pre middle ordovician karstification and predates pre permian karstification approximately 10 of the dolomite in the ellenburger group is late stage the earliest generation of late stage dolomite dolomite l1 is interpreted as a precursor to regional dolomite l2 l1 has been replaced by l2 and has similar trace element o c and sr isotopic signatures and similar cathodoluminescence and backscattered electron images it is possible to differentiate l1 from l2 only where cross cutting relationships with chert are observed replacement dolomite l2 is associated with the grainstone subarkose and mixed carbonate siliciclastic facies and with karst breccias the distribution of l2 is related to porosity and permeability which focused the flow of reactive fluids within the ellenburger fluid inclusion data from megaquartz interpreted to be cogenetic with dolomite l2 yield a mean temperature of homogenization of 85 6 c on the basis of temperature 18owater plots temperatures of dolomitization ranged from approximately 60 to 110 c given estimates of maximum burial of the ellenburger group these temperatures cannot be due to burial alone and are interpreted to be the result of migration of hot fluids into the a ea a contour map of 18o from replacement dolomite l2 suggests a regional trend consistent with derivation of fluids from the ouachita orogenic belt the timing and direction of fluid migration associated with the ouachita orogeny are consistent with the timing and distribution of late stage dolomite post dating dolomite l2 are two generations of dolomite cement c1 and c2 that are most abundant in karst breccias and are also associated with fractures subarkoses and grainstones 87sr 86sr data from l2 c1 and c2 suggest rock buffering relative to sr within dolomite l2 and a retention of a lower ordovician seawater signature while cements c1 and c2 became increasingly radiogenic it is hypothesized that reactive fluids were pennsylvanian pore fluids derived from basinal siliciclastics the precipitating fluid evolved relative to 87sr 86sr from an initial pennsylvanian seawater signature to radiogenic values this evolution is due to increasing temperature and a concomitant evolution in pore water geochemistry in the dominantly silic clastic pennsylvanian section a possible source of mg for late stage dolomite is interpreted to be from the dissolution of early stage dolomite by reactive basinal fluids

conditions of meteoric calcite formation along a variscan fault and their possible relation to climatic evolution during the jurassic cretaceous two calcite cements filling karst cavities and replacing lower carboniferous limestones at the variscan front thrust were precipitated after mid jurassic cimmerian uplift and subsequent erosion but before late cretaceous strike slip movement the first calcite stage a is nonferroan and crystals are coated by hematite and or goethite these minerals also occur as inclusions along growth zones the calcite lattice contains 0 07 mol fe but mn concentrations can be as high as 0 72 mol in bright yellow luminescent zones primary originally one phase all liquid aqueous inclusions have a final melting temperature between 0 2 and 0 2 c indicating a meteoric origin of the ambient water the 13c and 18o values of the calcites are between 7 3 and 6 3 7 8 and 5 5 on the vienna peedee belemnite vpdb scale respectively the second calcite stage b consists of ferroan 0 13 0 84 mol fe blocky crystals with mn concentrations between 0 34 and 0 87 mol primary single phase aqueous fluid inclusions indicate precipitation from a meteoric fluid below 50 c the 13c values of stage b calcites vary between 7 3 and 2 1 vpdb and the 18o values between 7 9 and 7 2 vpdb a precipitation temperature below 50 c for the stage a calcites and the presence of iron oxide hydroxide inclusions in the crystals indicate near surface precipitation conditions within this setting the geochemistry of the nonferroan stage a calcites reflects precipitation under oxic to suboxic conditions the ferroan stage b calcites precipitated in a reducing environment the evolution from the stage a to stage b calcites and the associated geochemical changes are interpreted to be related to the change from semiarid to humid conditions in western europe during late jurassic cretaceous times a change in humidity can explain the evolution of groundwater from oxic suboxic to reducing conditions during calcite precipitation the typically higher 13c values of the stage b compared to the stage a calcites can be explained by a smaller contribution of carbon derived from soil zone processes than from carbonate dissolution in the groundwater under humid conditions the small shift to lower 18o between stage a and b calcites may be caused by a higher precipitation temperature or a decrease in the 18o value of the meteoric water this decrease could have been caused by a change in the source of the air masses or by an increase in the amount of rainfall during the early mid cretaceous although the latter interpretation is preferred it cannot be proven

natural fractures in the spraberry formation midland basin texas the effects of mechanical stratigraphy on fracture variability and reservoir behavior horizontal cores from sandstone siltstone reservoirs in the spraberry formation midland basin west texas have documented two systems of dramatically different yet dynamically compatible natural fractures in reservoirs separated vertically by only 145 ft 44 m each system is capable of producing a different degree of the northeast trending permeability anisotropy recognized in spraberry reservoirs one fracture system consists of two vertical fracture sets with an apparent conjugate geometry striking north northeast and east northeast the other system consists of evenly spaced northeast striking vertical fractures nearly bisecting the acute angle of the first system although lithologically similar differences in quartz overgrowth and clay content in the layers resulted in a yield strength of the lower bed that is only half of that of the upper layer producing different fracture systems in the two reservoirs despite their proximity such differences in the mechanical properties due to variations in diagenetic and depositional histories of the strata are probably widespread within the formation they have the potential to cause significant vertical and lateral variation in the spraberry fracture system across the basin low present day in situ stresses in the reservoirs allow the fractures to open to become more conductive and even to propagate under very low injection pressures

geochemistry of vein and wallrock carbonates from the ediacaran system in south china insights into the origins of depositional and post depositional fluids abstract a combined study of carbon oxygen isotopes and major trace elements was carried out for vein and wallrock carbonates from the lantian formation of the ediacaran system in south china the results provide geochemical constraints on the origins of depositional and post depositional fluids with respect to recognition of the post depositional alteration the lantian formation was subdivided into the upper and lower carbonate units for the upper unit uu petrographic observations indicate that wallrock carbonates only experienced limited post depositional alteration the wallrock exhibits 18 o values of 19 2 to 13 1 and 13 c values of 9 6 to 8 9 both relative to vpdb the vein carbonates are divided into groups a and b based on their 18 o values and ree y patterns group a veins show nearly similar 18 o and 13 c ranges to but different ree y patterns from the wallrock these data indicate that the origin of fluids for group a veins may be similar to that of wallrock which was probably the mixture of continental and marine glacial meltwaters group b veins show both different 18 o values and ree y patterns from but similar 13 c values to the wallrock this indicates that post depositional fluids are different from the depositional fluids and thus of external origin low 18 o values 23 7 to 18 1 for group b veins indicate that the post depositional fluids were derived from continental glacial meltwater there is no correlation between 18 o and 13 c values for these vein and wallrock carbonates suggesting that the wallrock was not extensively altered by the post depositional fluids for the lower unit lu veins exhibit different c o isotope compositions and ree y patterns from wallrock carbonate indicating that post depositional fluids have different geochemical compositions from depositional fluids and thus are of external origin the simultaneous changes in 18 o and 13 c values with different laminations in the wallrock carbonates suggest the preservation of the primary geochemical compositions the 18 o values and ree y patterns for the lu veins indicate that the post depositional fluids were probably the mixtures of continental and marine glacial meltwaters therefore the lantian carbonates record the incorporation of continental glacial meltwater into the marginal sea of ediacaran age nevertheless the geochemical screening can provide constraints on the preservation of primary signatures and thus on the origins of depositional and post depositional fluids in the neoproterozoic marine carbonates

climate controlled early dolomite late triassic cyclic platform carbonates hungary abstract the 2 km thick late triassic hungarian carbonate platform has a completely dolomitized lower part and a limestone dominated upper part the platform succession is made up of meter scale possibly precessional 20 ky carbonate cycles in the lower platform main dolomite cycles are completely dolomitized and capped by caliche laminites and pisolites in the upper platform dachstein limestone dolomite is confined to laminite caps of cycles that are bounded by clayey paleosols most of the dolomitization in the platform interior occurred early in tidal flat settings during each high frequency cycle subtidal dolomites are slightly coarser grained are low in fe2 and mn2 and have the heaviest 18o signature this indicates they formed from evaporative oxidizing brines sourced from supratidal flats intertidal supratidal dolomites are fine grained commonly fe2 and or mn2 rich and slightly enriched in 18o compared to the marine calcite cement they formed from marine water that was weakly to moderately reducing dachstein paleosols have light 18o and 13c signatures reflecting meteoric soil waters repeated emergence stabilized the dolomites to low sr2 and na dolomite similar to cenozoic platform dolomites in contrast to these early cyclic dolomites coarse grained platform margin dolomites with very low mn2 and fe2 and light 18o signatures formed as thermally driven warm oxidizing marine water associated with jurassic rifting of the neo tethys pennini ocean circulated through the margin early dolomitization of cycles may have been controlled by high frequency sea level changes but the overall vertical distribution of early dolomite on the platform does not reflect long term eustasy rather the intense dolomitization of the lower platform reflects a semiarid hot subtropical seasonal setting and megamonsoonal climate global cooling and increased humidity toward the latest triassic and early jurassic inhibited pervasive early dolomitization leaving the upper platform largely as limestone

burial dominated cementation in non tropical carbonates of the oligocene te kuiti group new zealand abstract cementation of bryozoan echinoid benthic foraminiferal temperate shelf carbonates of the oligocene te kuiti group north island new zealand occurred mainly during subsurface burial the calcite cements in the limestones are dominated by equant and syntaxial rim spar which typically becomes ferroan given an iron supply and compared to the skeletal material with normal marine 18o values from 2 to 1 more depleted in 18o with depth of burial the 18o composition of bulk cement samples ranging from 1 to 7 these trends reflect the establishment in pore waters during sediment burial of reducing conditions and gradually increasing temperatures 20 50 c respectively the 13c values 0 to 3 of the cements remain the same as the host marine shells suggesting the source of carbon in the cements was simply redistributed marine carbonate derived from shell dissolution two gradational burial diagenetic environments influenced by marine derived porewaters are arbitrarily distinguished shallow burial phase and moderate burial phase during the shallow burial phase down to 500 600 m sub bottom depth the carbonates lost at least 25 of their original porosity by mechanical compaction and were selectively cemented by non ferroan or usually ferroan variably luminescent slightly 18o depleted sparry calcite cement 18o 2 to 4 mainly as syntaxial rims about echinoid grains these shallow burial cements form less than about 10 of total cement in the majority of the limestones and their source was probably mainly mild intergranular dissolution of calcitic skeletal fragments accompanying the onset of chemical compaction during the moderate burial phase between about 600 and 1100 m sub bottom depth porosity loss continued typically to about 70 of its original value as a result of pressure solution of calcitic bioclasts associated with more advanced stages of chemical compaction this involved development of a wide variety of non sutured and microstylolitic solution seams including both single and composite wispy or continuous bedding parallel types and non parallel reticulate forms the released carbonate was precipitated as ferroan or non ferroan where iron supply was negligible dull luminescent strongly 18o depleted 18o 4 to 7 mainly equant calcite spar cement occluding available pore space in the limestones

the influence of fracture cements in tight paleogene saline lacustrine carbonate reservoirs western qaidam basin northwest china paleogene saline lacustrine carbonate rocks are important fractured reservoirs in the western qaidam basin core data show that most fractures are small steeply dipping faults bedding plane slip faults and subvertical opening mode fractures other fractures are diagenetic in origin fracture occurrence and abundance patterns are controlled by lithology bed thickness and proximity to larger faults fractures are generally filled with calcite gypsum or glauberite na2ca so4 2 the degree of fracture filling determines the effectiveness of fractures as fluid conduits and the distribution of high quality reservoirs open fractures not only provide the main pathways for fluid flow but also enhance the free fluid index and the free fluid saturation measured by nuclear magnetic resonance and determine the potential production rates of tight carbonate reservoirs the open fractures are parallel to and occur near faults and many do not coincide with the present day direction of the maximum horizontal compressive stress

burial dolomitisation in a non tropical carbonate petroleum reservoir the oligocene tikorangi formation taranaki basin new zealand abstract the oligocene tikorangi formation is a subsurface non tropical limestone rich fracture producing oil reservoir in taranaki basin new zealand the formation is distinct from uplifted and exposed age equivalent new zealand limestones due to partial dolomitisation by modest quantities of silt sized scattered inclusion rich euhedral dolomite rhombs occasionally displaying idiotopic fabrics rhombs commonly have dull luminescent fe rich cores and oscillatory bright and dull concentric outers the dolomites are non stoichiometric high calcian and highly ferroan varieties dolomite 18 o and 13 c values are moderately depleted while associated precursor calcite phases are less depleted petrographic geochemical and geohistory evidence suggest that the dolomite formed during and following the later stages of pressure dissolution cementation in a relatively closed moderately deep burial environment ca 0 85 1 9 km burial depth ca 33 65 c in the early miocene ca 24 18 ma from warm saline enriched pore fluids by mainly mimic fabric selective replacement of interparticle and rarely intraparticle micrite matrix dolomitisation did not affect skeletal grains or calcite cements or develop any secondary porosity mg supply was restricted and was likely sourced internally from micritic inter and intraparticle precursor material and from the pressure dissolution of calcitic skeletons importantly dolomitisation occurred prior to compression related brittle fracturing of the carbonates responsible for creating extensive hydrocarbon bearing fracture networks because of the greater susceptibility of the dolomitised limestones to brittle fracturing their location and distribution may have important implications for hydrocarbon prospectivity and production within the tikorangi formation

outcrops as guides to subsurface natural fractures example from the nikanassin formation tight gas sandstone grande cache alberta foothills canada abstract outcrop studies are essential for understanding subsurface fractures because some key attributes such as length and height distribution cannot be measured using wellbores discrepancies between outcrop and subsurface fracture attributes arise because loading paths due to burial exhumation and thermal paths differ consequently even where rock type and structural setting are close matches differences may exist in mechanical properties and fracture growth here we investigate petrologic criteria and disseminated arrays of quartz filled microfractures as tools for comparing and contrasting fractures in outcrop with those as sampled by core for tight gas sandstones fracture cements are key diagnostic criteria for proving correspondence between outcrop and core we offer guidelines on selecting suitable outcrop analogs that differ markedly from current practice our illustration uses outcrops and core samples of late jurassic to early cretaceous nikanassin formation a tight gas sandstone but aspects of the outcrop vetting procedure can be applied to other rock types in some core and outcrops nikanassin formation fractures contain quartz and ankerite cement assemblages crack seal and rind textures and aperture size distributions that show that the outcrop and subsurface localities we examined share the same fracture stratigraphy and similar diagenesis these outcrops can thus be used to measure attributes including those that are unlikely to be captured in core such as fracture height and length distributions relative and absolute fracture intensity with structural position and degree of fill by synkinematic cement in our example absolute fracture intensity and distribution of postkinematic carbonate cements are site specific and differ between outcrop and core but in ways that can be quantified

enhanced carbonate petrography using fluorescence microscopy abstract fluorescence microscopy can recognize depositional facies and delineate diagenetic fabrics and porosity relationships in certain highly dolomitized or recrystallized limestones previously uninterpretable using standard petrographic techniques this tool has other valuable applications in the study of carbonate rocks these other applications include differentiating carbonate cements from neomorphic spar enhancing depositional and diagenetic fabrics rapidly evaluating mineralogical stabilization and recrystallization in holocene and pleistocene deposits and improving delineation of porosity and pore geometries in sedimentary rocks fluorescence microscopy is a rapid easily used and nondestructive technique that can be applied to unpolished thin sections or rock slabs by itself or in conjunction with other petrographic and geochemical tools it has the potential to expand our understanding of carbonate diagenetic processes and products in particular dolomitization and neomorphism and carbonate porosity evolution we strongly encourage routine usage of fluorescence microscopy in future carbonate petrographic studies

patterns of quaternary ice sheet erosion and deposition in fennoscandia and a theoretical framework for explanation it has long been recognised that the formerly glaciated area of fennoscandia shows large spatial differences in thicknesses of quaternary deposits mainly tills and exhibits distinct patterns of glacial scouring and deep linear erosion the reasons for this striking zonation have been elusive and in particular the relative roles of mountain ice sheets mis and full sized fennoscandian ice sheets fis in shaping the landscape surface need clarification on the basis of current advances in our understanding of the climate evolution and basal thermal organisation of ice sheets we perform spatio temporal qualitative modelling of ice sheet extent and migration of erosion and deposition zones through the entire quaternary and proceed to suggest an explanatory model for the current spatial pattern of quaternary deposits and the two different types of erosion zones we use the spatial distribution of fjords and deep non tectonic lakes for delineating zones of deep glacial erosion and relict landscapes as markers for frozen bed conditions on the basis of the amount of exposed bedrock the landscape was classified into a tripartite system of drift thickness thick drift intermediate drift thickness absence of drift scoured zones it is found that a centrally placed central and northern sweden zone of thick drift cannot be explained by deposition under fis style ice sheets but is instead likely to be the combined result of marginal deposition of fluctuating mis style ice sheets primarily during the early and middle quaternary and the inefficiency of later east centered fis style ice sheets in evacuating this drift from underneath their central low velocity and possibly frozen bed areas the western fjord zone of deep glacial erosion formed underneath both mis and fis style ice sheets during the entire quaternary while the eastern lake zone of deep glacial erosion is exclusively related to mis style ice sheets and formed largely during the early and middle quaternary the scouring zones formed under conditions of rapid ice flow towards bathymetrically defined calving margins of fis style ice sheets they likely reflect process patterns of the last two or three fis style ice sheets the three landscape zones differ in their degree of permanence with the deep erosion zones being a long lasting legacy in the landscape more likely to be enhanced than obliterated by subsequent glacial events the thick drift cover zone once established appears to have been surprisingly robust to erosion by subsequent glacial events the scouring zones appear to be the most recent and ephemeral of the three zones with possible major alterations during single glacial events

micromorphology clay mineralogy and geochemistry of calcic soils from western thar desert implications for origin of palygorskite and southwestern monsoonal fluctuations over the last 30 ka abstract the thar desert with intense aeolian activity and calcrete formation is one of the hottest arid regions of the world little is known about the formation of calcic soils with a large amount of palygorskite in the western thar in this study we have used microscopy sub microscopy clay mineralogy and geochemistry of three calcic soils from western thar to understand the pedogenesis in response to fluctuating southwestern monsoon over the last 30 ka thin sections of the soils show a dominance of weakly developed pedofeatures with powdery to well indurated pedogenic calcium carbonate that influenced weathering of primary mineral grains sub microscopy of the calcretes shows a large amount of fibrous palygorskite in pore spaces of micritic and sparitic nodules xrd of the total clay

multiple phase fracture and fault controlled burial dolomitization upper devonian wabamun group alberta abstract recent data from the subsurface tangent eaglesham and normandville fields located east of the peace river arch in northern alberta indicate that these wabamun group subtidal carbonates have undergone a complex diagenetic history related to multiple stages of fracturing and faulting burial dolomitization which generated mainly matrix dolomites was responsible for the development of porous reservoir rocks which are spatially highly variable primary porosity was reduced by marine and early burial diagenesis which formed micrite syntaxial overgrowths granular blocky and coarse fracture filling calcite cements minor amounts of microdolomite and floating dolomite rhombs formed during shallow burial further porosity reduction by mechanical compaction and cementation except for minor dissolution and initial fracturing resulted in predominantly tight limestones matrix dolomitization is associated with the second most extensive phase of fracturing which greatly increased both the porosity and permeability of the tightly cemented wabamun limestones dolostones which comprise 85 matrix dolomite are the principal reservoir rock but have highly variable porosity large dissolution cavities developed locally after formation of the matrix dolomites the third phase of fracturing crosscuts the matrix dolomites in the tangent field these fractures locally form irregular cavity systems which are partly filled with finely crystalline and saddle dolomites these fine crystalline dolomites probably represent dolomite silt and sand derived from brecciation of the earlier matrix dolomite during faulting renewed faulting was responsible for rotation of breccia clasts saddle dolomite was precipitated during at least two phases on the sides and undersides of some clasts and in fractures late stage bladed anhydrites and fracture filling coarse calcites precipitated during hydrocarbon generation presumably in the late cretaceous except locally where source rocks may have been heated by ascending hot brines the timing of dolomitization and fracturing is difficult to determine early fractures most likely occurred in the late devonian to early carboniferous during early burial and mechanical compaction the second phase of fracturing probably occurred during the mississippian to pennsylvanian when the normandville and dunvegan faults underwent movement during the foundering of the peace river arch the third phase of fracturing is linked to the more rapid subsidence and burial by the cretaceous and early tertiary clastic wedge which presumably reactivated some of the earlier faults the combined stratigraphic petrophysical and geochemical data support the following interpretations 1 early dolomite rhombs and patches resulted from the movement of seawater through semi lithified sediment near the sediment water interface or during early compaction 2 matrix dolomites formed at temperatures of between 40 and 65 c and depths of about 500 to 1500 m probable fluid sources for matrix dolomites were devonian brines buried with these and underlying sediments and expelled by mechanical compaction possibly aided by seismic pumping along stage ii fracture fault conduits 3 sucrosic saddle and reworked dolomites postdate stage iii fractures and occurred during deep burial most saddle dolomites formed at temperatures around 100 c but a few formed near 200dc these dolomites formed from warm highly saline basin brines and or from hot brines that ascended along fractures and faults and other stratigraphic conduits from deeper parts of the basin and or the crystalline basement

tertiary evolution of the intra carpathian area a model abstract the outer carpathian flysch nappes encircle an intra carpathian domain which can be divided into two megatectonic units north pannonian and tisza mostly on the basis of contrasting mesozoic and palaeogene facies development we see two major kinematic problems to be solved 1 1 the present distribution of the mesozoic and palaeogene facies is mosaic like and some belts form exotic bodies within realms of austroalpine affinity 2 2 late eocene palinspastic reconstruction of the outer carpathian flysch nappes suggest that the entire intra carpathian area must have been located several hundreds of kilometres to the south and to the west of its present position neogene extension can account for shortening in the external carpathian nappes but is unable to explain mesozoic facies anomalies and offsets of palaeogene formations we suggest that evolution of the intra carpathian area involved first late palaeogene early miocene juxtaposition of the north pannonian and tisza megatectonic units accompanied by the closure of the external carpathian flysch troughs thereafter extension of this amalgamated unit occurred which was compensated by thrusting of flysch nappes onto the european foreland and formation of molasse foredeeps eastward escape of the north pannonian unit from the alpine collisional belt involved left lateral shear along the pieniny klippen belt and right lateral shear along the mid hungarian zone parts of the late palaeogene basin and an early miocene volcanic edifice were dissected offset and elongated by several 100 kms the driving mechanism of the eastward escape of the intra carpathian area can be related to the collision of apulia and europe and the subduction of the external carpathian crust under the pannonian units the escape ceased gradually in the early miocene when oblique collision between the north pannonian unit and european continent occurred neogene extension of the pannonian region was an areal deformation the extension at locally variable rate resulted in the break up of the heterogenous floor of the neogene basin the driving mechanism of basin extension and contemporaneous compressional deformation of the external carpathians is thought to be related to ongoing subduction involving the marginal part of the attenuated european continental crust tectonic activity in the carpathians and basin subsidence and volcanism shifted in time and in unison from the west toward the east southeast

intraformational fluid flow in the thuringian syncline germany evidence from stable isotope data in vein mineralization of upper permian and mesozoic sediments abstract vein mineralization observed in boreholes quarries and outcrops of upper permian and mesozoic sediments in the thuringian syncline germany was investigated for the first time by petrography electron microprobe analysis and stable isotope analysis the objective was a characterization of paleo fluid systems within this basin veins are mostly restricted to nw se trending fault systems and comprise carbonates calcite dolomite minor sulfates gypsum anhydrite celestite barite and rarely sulfides they are variably distributed within the late paleozoic to mesozoic succession calcite vein mineralization occurs in almost all triassic strata though dominating in the lower muschelkalk subgroup mu gypsum anhydrite veins occur in the middle keuper subgroup km middle muschelkalk subgroup mm middle and upper buntsandstein subgroup sm so as well as in the upper permian zechstein sulfate and carbonate isotope analyses indicate that most vein mineralization dominantly crystallized from intraformational fluids within the upper permian and triassic sediments crystallization from descending meteoric waters was observed especially for calcite veins in the lower muschelkalk but also for gypsum anhydrite veins in the upper buntsandstein mineralization from ascending carbonate ph buffered warm waters was restricted to individual parts of the southern deep reaching main border fault zone of the thuringian syncline mixing and fault crossing fluid movements are subordinate within the thuringian syncline we conclude that no large scale cross formational fluid flow occurred in thuringian syncline over the last millions of years

the impact of quaternary glaciations on inselbergs in northern sweden we investigate the glacial modification of inselbergs large isolated bedrock hills in northern sweden inselbergs are generally regarded as products of deep weathering etching and stripping under warm and humid climates unlike inselbergs found in the tropics the inselbergs in northern sweden were exposed to ice sheet glaciation for long periods of the quaternary we used dems to examine 794 inselbergs in our study area and they were classified according to their degree of glacial modification bedrock structural control was assessed using gis data on the regional geology clusters of inselbergs were mapped in the field for features indicative of glacial erosion such as glacial cliffs and stripped bedrock surfaces and for features indicative of limited erosion such as tors and blockfields the results of the study indicate that inselbergs in the area were mostly modified by quaternary ice sheets only to a low or moderate extent and that the degree of glacial erosion is dependent on their relief and location inselbergs with a relative relief of 100 m and in areas of lower absolute relief experienced the strongest glacial modification where the strongest glacial modification can result in lateral erosion of the inselberg flanks inselberg summits often display signs of minimal glacial erosion such as torlike bedrock outcrops with signs of strong weathering in summary we argue that inselbergs in northern sweden have largely retained their pre quaternary shape despite long periods of ice sheet cover

the role of carbonate complexes and crystal habit on rare earth element uptake in low temperature calcite in fractured crystalline rock abstract this study focuses on rare earth element ree geochemistry of low temperature calcite coatings occurring on the walls of fractures throughout the upper kilometer of crystalline rocks of the baltic shield fifty one calcite coatings were sampled from cores drilled with the triple tube technique which successfully preserved the fragile calcite coatings on the fracture walls the calcites which based on geological and isotopic evidence were precipitated over the last 10 million years had highly variable ree concentrations 0 61 2276 ppm that decreased weakly with the depth the calcite was sampled from when normalized to shale and host rock the ree concentrations of habits with c axis a axes and the closely associated c axis a axes the most abundant crystal morphologies in the system decreased strongly and smoothly across the series in contrast the rees of habits with c axis a axes identified only in fractures in the uppermost 260 m of the bedrock were flatter and occasionally expressed a weak middle ree enrichment by using calcite water partition coefficients derived for rees in previous laboratory experiments the la yb of the paleogroundwater from which the calcites precipitated was back calculated and found to be overall similar range 0 15 452 overlap to the corresponding ratio of the present groundwater range 2 1 36 4 in terms of ree ca the values for the back calculated paleogroundwater la ca 9 9 10 11 3 9 10 7 yb ca 1 5 10 10 2 2 10 7 were similar to those of laco3 ca 4 5 10 10 8 5 10 7 and ybco3 yb co3 2 ca 5 4 10 11 1 8 10 8 respectively in the present groundwater these patterns indicate that the lree to hree and ree to ca ratios in the groundwater at the site are broadly similar to those existing when the calcites precipitated and that carbonate complexes present in the paleogroundwater played a crucial role in sequestration and fractionation of rees in calcite the findings have implications for bedrock storage of high level radioactive waste which contains actinides for which the rees can be used as natural analogues

pedogenesis and clay mineralogical investigation of soils formed on gypsiferous and calcareous materials on a transect southwestern iran abstract this study examined pedogenesis as well as the clay mineralogy of soil and rock samples obtained from a transect of gypsiferous and calcareous materials the main objectives of this research were to study the relationship between clay minerals and physiographic units as well as the relative importance of key pedogenic processes in controlling clay mineralogy palygorskite chlorite illite smectite quartz and interstratified minerals were observed in both soil and rock samples using xrd tem and edx analyses illite chlorite and interstratified minerals are inherited largely from parent rocks most of the smectite is inherited from highly smectite marl formations although some may be the product of palygorskite weathering and transformation of illite particularly at the surface horizons neoformation of palygorskite as a result of calcite and gypsum precipitation seems to be a major pathway for the occurrence of this mineral especially on plateau physiographic units although inheritance has less importance gypsiferous soils showed more pedogenic palygorskite as compared to calcareous soils three morphological forms of palygorskite related to degree of weathering were identified in the studied pedons new great groups and subgroups of ustepts aridic gypsiustepts and aridic calcic gypsiustepts are suggested to be included in soil taxonomy based on the properties of some of the studied pedons dissolution and transport of anhydrite from outcrops is considered the main source of pedogenic gypsum in these soils micromorphological studies including thin section observations and sem analyses indicated variable habits of gypsum crystals suggested a dynamic soil environment

alteration of cenozoic cool water carbonates to low mg calcite in marine waters gambier embayment south australia abstract the oligo miocene gambier limestone is a poorly lithified fine grained bryozoan rich grainstone wackestone and marl allochems in these rocks which are typical of many modern and ancient cool water carbonates were originally calcite lmc mg calcite imc and hmc and minor aragonite but most are now neomorphosed to lmc with the exception of calcretes most limestones have 5 cement 13c and 18o values from 0 to 1 5o oo and preserved 87sr 86sr ratios that indicate that neomorphism occurred in seawater rather than meteoric or evolved pore waters marine diagenesis of the limestones was facilitated by their slow accumulation rates which were ca 15 mm ky based on sr isotope stratigraphy relatively fine grain size and high porosities which locally reach 50 the sr and mg contents of grainstones are significantly lower than in the original sediments whereas a less porous marl has higher sr and mg contents the grainstones have about 300 ppm sr and 6000 ppm mg consistent with slow abiotic precipitation of calcite under near equilibrium conditions with seawater which is the thermodynamic drive for this diagenesis the higher sr and mg content of the marl results from variable preservation of original allochems of biotic calcite the results from this study and others on modern cool water carbonates indicate that the extent of diagenesis varies with lithology but much neomorphism occurred in seawater with minimal effects from meteoric waters as such the chemical characteristics of seawater may be effectively preserved in some ancient cool water carbonates

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

stochastic modeling for the stress inversion of vein orientations paleostress analysis of pliocene epithermal veins in southwestern kyushu japan plio pleistocene epithermal quartz veins in southern kyushu japan include gold deposits the coherent trend of the ore veins suggests tectonic control for their formation however the stress regime during the formation has been controversial to solve this problem we improved existing methods for inferring paleostresses from vein orientations it was assumed that veins making a cluster were formed intermittently from thermal fluids with various pressures the present method determines stress ratio and stress axes with 95 confidence regions the method was applied to mid pliocene quartz veins cropping out at hashima southwestern kyushu we obtained a normal faulting regime of stress with the trend of sigma3 at 167 10 and the stress ratio at 0 20 0 13 0 09 the low stress ratio and the lack of slickenlines and slickenfibers on vein walls suggest that the host rock was subject to a small differential stress i e a weak tectonic stress when the veins were formed

non tropical carbonate deposits on the modern new zealand shelf abstract extensive ca 50 000 km 2 shallow marine platforms 70 caco 3 despite proximity to a tectonically active plate margin in these regions the terrigenous sediment supply is presently low and growth of epibenthos is fostered by firm substrates rock gravels shells seaweeds and the generally energetic nature and high nutrient levels of open shelf waters rapid transition into adjacent terrigenous dominated facies is characteristic irrespective of water depth the carbonates are coarse grained and fragmental carbonate mud is rare calcite dominates over aragonite high mg calcite widespread off northern new zealand is rare in the south skeletal material is dominated by bryozoans and bivalve molluscs with significant local contributions from foraminifers barnacles calcareous red algae and echinoderms the name bryomol is suggested for this distinctive temperate region skeletal carbonate facies which can be usefully subdivided based on dominant zoarial growth forms of the bryozoan component known to be habitat related bioerosion is an important mechanism of skeletal fragmentation and degradation many grains especially aragontic bivalves are infested by endolithic borers and have low preservation potential ages of skeletal material in the surficial deposits range from more than 20 000 years b p to modern which is consistent with both low rates of carbonate production and sediment accumulation and the wide range in preservation state of grains some data suggest that the skeletal carbonates are dispersed and mixed mainly during infrequent movement of sand ribbons sand waves and sand sheets driven by storm assisted tidal flows tracts of modern palimpsest and relict carbonates can occur in juxtaposition the facies characteristics of the new zealand shelf carbonate deposits contrast significantly with those of the classical bahaman type carbonate model however they are similar to those reported from many other mid to high latitude carbonate shelves and afford good analogues for most onland occurrences of new zealand cenozoic limestones

natural fractures in tight gas volcanic reservoirs and their influences on production in the xujiaweizi depression songliao basin china lower cretaceous volcanic rocks that contain major natural fractures are the main natural gas reservoirs in the deep xujiaweizi depression of the northern songliao basin in china natural fractures are mainly tectonic fractures in addition to some shrinkage dissolution and cryptoexplosive fractures analyzing various sources of data revealed that fractures are generally better developed in the rhyolites and trachytes of the crater and near crater group also tectonic fractures are developed to a higher degree in the hanging wall of faults with the degree of development decreasing with increasing distance from the fault planes more than 85 of these fractures are found to be unfilled and when connected by pores provide the main effective storage volume for these volcanic reservoirs up to 75 natural gas production is closely related to the linear density p10 of unfilled tectonic fractures and the angle between the orientation of unfilled tectonic fracture and the corresponding direction of the maximum horizontal stress component the results show that natural gas production is elevated when the average p10 exceeds 2 m 1 and the average included angle is less than 30 finally it was concluded that within the study area unfilled tectonic fractures of near east west strikes which have smaller included angles 30 with respect to the maximum horizontal stress direction are under minimal compressive stresses and make the best fluid flow pathways in the reservoir

modification of fracture porosity by multiphase vein mineralization in an oligocene nontropical carbonate reservoir taranaki basin new zealand the nontropical oligocene carbonate rich tikorangi formation is an important oil producer in the taranaki basin new zealand hydrocarbons are hosted and produced from mineralized natural fracture systems petrographic trace element stable isotope 18o and 13c and fluid inclusion data have enabled a complex sequence of eight paragenetic events to be determined the tikorangi formation host rock was cemented by low mg calcite event 1 during burial diagenesis from temperatures of 27c corresponding to 0 5 km burial and continued until 37c 1 km burial depth producing tight pressure dissolved fabrics with essentially no porosity and permeability the host rock was partially dolomitized 5 50 event 2 by ca and fe rich dolomite rhombohedra at burial depths and temperatures of 1 0 1 5 km and 35 50c without secondary porosity development subsequent brittle fracturing formed by neogene compression event 3 is constrained to a period following lithification and dolomitization but before precipitation of first generation vein calcite event 4 this initial ferroan low mg vein calcite formed after a period of burial from fe rich meteorically modified fluids at temperatures of about 50 60c and 1 4 1 9 km burial depth baroque dolomite formed event 5 following a period of mg enriched basinal fluid input precursory to hydrocarbon emplacement per se the dolomite formed mainly as a primary cement but also as a calcite replacement at temperatures following further burial to 2 2 5 km and temperatures of 65 80c formation of celestite and quartzine phases event 6 coincided with or marginally postdated dolomite at similar depths and temperatures to event 6 and formed as both replacements and cements second generation ferroan vein calcite formed event 7 at cooler temperatures 53 65c perhaps resulting from the introduction of cooler meteoric fluids from upsection the presence of petroleum fluid inclusions in the second generation calcite suggests precursory hydrocarbon bearing fluids have migrated along with aqueous fluids from about 10 ma with hydrocarbon emplacement event 8 occurring in the last 6 m y following a period of rapid late miocene burial an improved understanding of the paragenesis of the tikorangi formation may assist in hydrocarbon production from its reservoirs

modification of peripheral mountain ranges by former ice sheets the brecon beacons southern uk abstract the brecon beacons in southern wales is a large upland area 900 km 2 close to the periphery of the former british irish ice sheet the geomorphology of the brecon beacons highlands and surrounding areas was mapped using satellite imagery and a digital elevation model dem a fragmentary pattern of glacial lineations is inferred to represent ice build up in the mountains a more coherent set of glacial lineations formed by southward ice flow across the area from the welsh ice cap represents recession from the last glacial maximum lgm during this phase the brecon beacons acted as an obstacle deflecting the ice around higher terrain most of the higher terrain in the brecon beacons therefore appears to have escaped significant glacial erosion during both phases of ice flow due to cold based ice or low basal ice velocities beneath a local ice cap landforms previously interpreted as cirques in fact have v shaped profiles and lack evidence of major over deepening they are interpreted to have been formed primarily by processes other than glacial erosion the overall impact of glaciation in the brecon beacons appears to be limited primarily to the time when the area was over run by the welsh ice cap and the influence of local glaciation has been minimal this study has two main implications for landscape evolution in mountain ranges that lie at the periphery of former ice sheets first due to the presence of cold based ice or low basal ice velocities beneath a local ice cap it may be possible to find fragmentary traces of pre lgm ice flow second the pattern of glacial lineations in and around the brecon beacons indicates that peripheral mountain ranges may have deflected ice flow at the lgm resulting in low basal ice flow velocities and possible frozen bed conditions over higher terrain which consequently resulted in ineffective glacial erosion within the mountains themselves

karst controlled reservoir heterogeneity in ellenburger group carbonates of west texas petroleum production from restricted shelf carbonates of the lower ordovician ellenburger group is commonly considered to have been a result of a pervasive relatively homogeneous tectonic fracture system within the reservoir rock however regional facies and diagenetic paleokarst studies of ellenburger strata based on cores and wireline logs have demonstrated that significant reservoir compartmentalization was caused by karst modification in the upper part of the unit ellenburger group carbonates which attain a thickness of over 1 700 ft 520 m record sedimentation on a shallow water restricted shelf occupying most of west texas logging of over 10 000 ft 3 050 m of core from 63 wells has allowed recognition of six facies assemblages 1 lithic arenite 2 mixed siliciclastic carbonate packstone grainstone 3 ooid peloid grainstone 4 mottled mudstone 5 laminated mudstone and 6 gastropod intraclast packstone grainstone these facies assemblages record initial transgression and subsequent progradation and aggradation paleoslope was generally south and east from the texas arch toward the ouachita and marathon orogenic belts all facies assemblages with the local exception of the ooid peloid grainstone assemblage are characterized y very low intergranular and intercrystalline porosity porosity development in ellenburger group carbonates is directly related to a prolonged period of subaerial exposure that coincided with a middle ordovician eustatic lowstand prior to transgression of simpson group siliciclastics during this episode a widespread system of caves sinkholes joint controlled solution features and collapse breccias developed of particular importance to reservoir development was the formation of a regionally extensive cave system between 100 and 300 ft 30 and 90 m beneath the exposed ellenburger surface infill of this cave system by simpson group sand and clay segmented the upper ellenburger into three karst facies which are in descending order 1 cave roof dolomites fracture and mosaic breccias 2 laterally persistent cave fill facies siliciclastic matrix supported and carbonate matrix supported breccias and 3 lower collapse facies chaotic clast supported breccias of the cave floor pronounced vertical segregation of permeable zones defined by the three karst facies is evident in the emma andector martin block 13 and several other major ellenburger reservoirs lateral reservoir heterogeneities formed by localized laterally extensive collapse structures such as in the shafter lake reservoir also contribute to compartmentalization of producing zones within the upper ellenburger group secondary and tertiary recovery programs in these ellenburger reservoirs can be optimized by integrating concepts of lateral and vertical heterogeneity predicted by the karst model

diagenesis and reservoir quality of paleocene sandstones in the kupe south field taranaki basin new zealand paleocene reservoir sandstones in the kupe south field taranaki basin contain a diagenetic mineral assemblage that records major shifts in pore water composition during the burial history of the basin early calcite formed at shallow burial largely from meteoric depositional pore waters whereas later chlorite smectite records the downward passage of marine pore waters into the sandstones from overlying marine mudrocks prior to significant sandstone compaction during the late miocene late calcite and ferroan carbonates may record the presence of connate meteoric water expelled upward from nonmarine sedimentary rocks of the underlying cretaceous sequence whereas later kaolinite and secondary porosity formation are related to localized meteoric influx resulting from la e miocene to early pliocene uplift and erosion of the reservoir section hydrocarbon entrapment occurred during further pliocene to holocene sediment accumulation labile grain alteration has been less severe in the lower part of the hydrocarbon bearing section lower sands than in the upper part upper sands with the result that the lower sands contain mainly chlorite smectite and the upper sands contain mainly ferroan carbonates and kaolinite formed by extensive alteration of labile grains and earlier formed chlorite smectite reservoir quality in the lower sands is controlled mostly by grain size and the presence of chlorite smectite but in the upper sands the presence of kaolinite is the single most important cause of poor reservoir quality

geology and geothermal origin of grant canyon and bacon flat oil fields railroad valley nevada eastern nevada s grant canyon and bacon flat oil fields show strong evidence of formation in a still active moderate temperature geothermal system modern manifestations of this system include unusually elevated oil reservoir temperature at shallow depth 116 122 c at 1 1 1 6 km and dilute na hco3 cl thermal waters directly associated with hot oil hydrogen and oxygen isotopic compositions indicate that these thermal waters are meteoric in origin but were probably recharged prior to the holocene before 10 ka the waters apparently ascended to oil reservoir elevations after deep heating in response to the normal regional thermal gradient there is no evidence for a modern magmatic heat source the beginning of oil reservoir evolution at both fields is recorded by late stage fracture filling quartz in the vuggy brecciated paleozoic dolostone reservoir rocks oil and aqueous solutions were trapped as fluid inclusions in the quartz at temperatures comparable to those now prevailing in the reservoirs apparent salinities of the aqueous inclusions closely match the actual concentrations of current oil field waters and the quartz has the oxygen isotopic composition predicted for its crystallization from these waters at contemporary temperatures present day and fluid inclusion temperatures define essentially coincident isothermal profiles through and beneath the oil reservoir interval a phenomenon consistent with near constant convective heat transfer since inception of the eothermal system textural and mineralogic clues indicate that hot waters circulating in this system also increased porosity by dissolving carbonate minerals and helped seal reservoir margins by precipitating silica and kaolin more importantly the rising thermal waters may have aided oil transport and accelerated source rock maturation through an increase in the shallow 3 km local thermal budget along with the aforementioned fluid inclusion and isotopic evidence radiometrically dated life spans for numerous extinct geothermal systems epithermal ore deposits in the basin and range make it likely that the grant canyon bacon flat system and associated oil reservoirs are no older than 2 5 ma

evidence for a relict glacial landscape in quebec labrador abstract two major glacial landform systems occur in labrador these are the radial lineation and esker swarm reflecting late wisconsinan decay and the ungava bay lineation and esker swarm reflecting convergent northward flow in some sectors the two landform systems give conflicting evidence regarding deglaciation pattern we have interpreted the ice sheet dynamics in labrador from morphological data using a new inversion model that treats spatial patterns of deglacial meltwater landforms separately from lineation patterns in the george river area we have found that the ungava bay swarm of deglacial landforms has been overprinted at a right angle by a younger regional meltwater pattern from the last deglaciation a similar overprint also exists along the intersection line in west central labrador these relations show that the previously accepted relative ages of the two landform systems hughes 1964 boulton and clark 1990a b klassen and thompson 1993 have to be reversed we interpret the ungava bay lineation and esker swarm to represent a 0 25 106km2 pre late wisconsinan relict landscape formed during the deglaciation of an older ice sheet and later preserved in a dry based central zone of the labrador dome

massive dolomitization of a late miocene carbonate platform a case of mixed evaporative brines with meteoric water nijar spain late miocene platform carbonates from nijar spain have been extensively dolomitized limestones are present in the most landward parts of the platform in stratigraphically lower units and topographically highest outcrops suggesting that dolomitizing fluids were derived from the adjacent nijar basin the dolomite crystals range from 10 to 100 m existing as both replacements and cements na cl and so4 concentrations in the dolomites range from 200 to 1700 p p m 250 650 p p m and 600 7000 p p m respectively comparable with other tertiary and modern brine dolomite values and also overlapping values from mixing zone dolomites sr concentrations range between 50 and 300 p p m and the molar sr ca ratios of dolomitizing fluids are estimated to range between 7 seawater brine to freshwater ratios the 18o and 13c of the dolomites range from 1 0 to 4 2 pdb and 4 0 to 2 0 pdb respectively 87sr 86sr values 0 70899 0 70928 of the dolomites range from late miocene seawater to values greater than modern seawater mixtures of freshwater with seawater and evaporative brines probably precipitated the nijar dolomites modelled covariations of molar sr ca vs 18o and na ca vs 18o from these mixtures are consistent with those of the proposed nijar dolomitizing fluids complete or partial dolomite recrystallization is ruled out by well preserved cl zoning nonstoichiometry and quantitative water rock interaction modelling of covariations of na vs sr and 18o vs 13c the possibility of multiple dolomitization events induced by evaporative brines seawater and freshwater respectively is consistent with mineral mineral mixing modelling the basin derived dolomitizing brines probably mixed with freshwater in the nijar basin or mixed with fresh groundwater in the platform and were genetically related either to deposition of the yesares gypsum or the feos gypsum dolomitization occurred during either the middle messinian or the early upper messinian nijar dolomitization models may be applicable to dolomitization of other late miocene platform carbonates of the western mediterranean moreover the nijar models may offer an analogue for more ancient evaporite absent platform carbonates fringing evaporite basins

a highly mobile laurentide ice sheet revealed by satellite images of glacial lineations satellite images of the north american continent reveal previously unrecognized patterns of crossing drift lineations reflecting unexpected shifts of centres of mass of the laurentide ice sheet throughout the last glacial cycle such shifts must must have been associated with major global atmospheric circulation changes

a skeletal assemblage classification system for non tropical carbonate deposits based on new zealand cenozoic limestones abstract cenozoic limestones in new zealand are mainly skeletal grainstones and packstones formed under non tropical climatic conditions in open marine shelf or ramp environments following petrographic analysis of the nature and abundance of the skeletal components in nearly 500 samples of these limestones a complete linkage cluster analysis identified seven major skeletal assemblages that may be regarded as subdivisions of the single foramol skeletal association defined by lees and buller 1972 for temperate region carbonate deposits the seven assemblages are given contracted names as follows a barnamol barnacle bivalve dominated b bimol bivalve dominated c bryomol bryozoan bivalve dominated d echinofor echinoderm benthic foraminiferal dominated e nannofor nannofossil planktonic foraminiferal dominated f rhodalgal calcareous red algal dominated and g rhodechfor calcareous red algal echinoderm benthic foraminiferal dominated a composite triangular classification diagram has been devised for naming the skeletal assemblage of an unknown sample on the basis of its three main skeletal components the diagram successfully characterises more than 85 of the new zealand cenozoic limestone samples and also appears to be applicable for the skeletal assemblage designation of many overseas examples of non tropical carbonate deposits limitations relate mainly to locally common skeletal types e g serpulids brachiopods that are presently not incorporated into the new zealand based scheme the general ecological preferences of the main skeletal contributors in each of the seven skeletal assemblages form a basis for relating the assemblages to broad shelf habitats consequently as well as the benefits of providing a more consistent skeletal assemblage terminology for comparative studies between different workers the scheme can assist with the paleoenvironmental interpretation of non tropical skeletal carbonate facies

glacial erosion and geomorphology in the northwest sierra nevada ca pleistocene glacial erosion left a strong topographic imprint in the northwestern sierra nevada at many scales yet the specific landforms and the processes that created them have not been previously documented in the region in contrast glaciation in the southern and central sierra was extensively studied and by the end of the 19th century was among the best understood examples of alpine glaciation outside of the european alps this study describes glacially eroded features in the northwest sierra and presents inferred linkages between erosional forms and pleistocene glacial processes many relationships corroborate theoretical geomorphic principles these include the occurrence of whalebacks in deep ice positions roches moutonnees under thin ice and occurrence of p forms in low topographic positions where high subglacial meltwater pressures were likely some of the landforms described here have not previously been noted in the sierra including a large crag and tail eroded by shallow ice and erosional benches high on valley walls thought to be cut by ice marginal channels

geochemical characterization of contemporary fine detritus in the dead sea watershed abstract reconstruction of paleo synoptic conditions e g past atmospheric circulation involves tracing the origins and routes of transport of particles comprising eolian archives i e desert dust lacustrine deposits that accumulated in the quaternary lakes filling the dead sea basin include remobilized eolian desert dust that was washed to the lakes by floods here we analyze the mineralogical chemical compositions e g mg al ratios and 87sr 86sr and 143nd 144nd end values isotope ratios of fine siliciclastic particles that form the modern surface cover of the dead sea watershed e g loess mountain soils and flood particles that are mobilized to the lake during distinct synoptic conditions the data comprises reference data set that can be used for paleo synoptic interpretation enhancing our ability to decipher the paleoclimate history during the quaternary in the levant the end values and 87sr 86sr ratios of the fine detritus lie between 8 and 6 and 0 7035 to 0 7188 reflecting the values of erosional products of granitoids that are exposed in the sahara and arabia deserts and the unradiogenic sr from local soils in the dead sea watershed particles with low mg al ratios i e 0 17 0 31 are transported by the western winds associated with the mediterranean cyclones transporting dust from the sahara while particles with high mg al ratios 0 27 0 68 are associated with storms blowing dusts from east to the dead sea watershed saudi arabia and syrian deserts during red sea trough synoptic conditions fine particles blown from the sahara deserts during winter storms are rapidly washed to the lake by subsequent floods whereas the particles blown during dry storms associated with red sea trough synoptic conditions accumulate on the surface of the dead sea watershed and can be washed later to the lake during extensive rain events

multiphase partial and selective dolomitization of carnian reef limestone transdanubian range hungary partially dolomitized carbonate successions provide a good opportunity to understand the commonly multistage process of dolomitization petrographic methods fluid inclusion microthermometry and stable isotope measurements were applied to reconstruct the diagenetic evolution and dolomitization of a partially dolomitized carnian reef limestone from the transdanubian range hungary the diagenetic history began with reef diagenesis and formation of dolomite micro aggregates in microbial fabric elements this was followed by the development of euhedral porphyrotopic dolomite crystals through overgrowths around the previously formed dolomite micro aggregates during the earliest burial stage increasing burial resulted in the extension of the dolomite patches via formation of finely crystalline replacement dolomite from the late norian when the carnian reef carbonates reached the depth of 1 0 to 1 8 km the diagenetic evolution continued in an intermediate to deep burial setting contemporaneously an extensional regime was established leading to fracturing the progressive burial resulted in the recrystallization of the pre existing dolomite with increasing temperature while saddle dolomite cement was precipitated in fractures in connection with the alpine orogeny intense denudation took place during the late cretaceous accompanied by fracturing similar tectonically controlled denudation and fracturing occurred in several stages during the cenozoic as a result of these processes the studied carnian carbonates were raised to a near surface position or became subaerially exposed leading to dedolomitization of the last dolomite phase and precipitation of calcite cement in cavities and fractures this study revealed that by investigating partially and selectively dolomitized rock types it is possible to document and understand those stages of the multiple dolomitization process which can barely be detected in the completely dolomitized rock bodies recognition of the dolomitization phases could provide the basis for the analysis of their relations with the depositional diagenetic and tectonic processes and stages of basin evolution

fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model the evolution of ice sheet configuration and flow pattern in fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model i e a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets the model uses mapped flow traces and deglacial melt water landforms as well as relative chronologies derived from cross cutting striae and till lineations as input data flow trace systems were classified into four types i time transgressive wet bed deglacial fans ii time transgressive frozen bed deglacial fans iii surge fans and iv synchronous non deglacial event fans using relative chronologies and aggregation of fans into glaciologically plausible patterns a series of ice sheet configurations at different time slices was erected a chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume geological evidence exists for several discrete ice sheet configurations centred over the scandinavian mountain range during the early weichselian the build up of the main weichselian fennoscandian ice sheet started at approximately 70 ka and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern norway this configuration had a flow pattern which is poorly reproduced by current numerical models of the fennoscandian ice sheet at the last glacial maximum the main ice divide was located overthe gulf of bothnia a major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the scandinavian mountain chain widespread areas of preserved pre late weichselian landscapes indicate that the ice sheet had a frozen bed core area which was only partly diminished in size by inward transgressive wet bed zones during the decay phase

characteristics and origins of lee side stratification sequences in late pleistocene drumlins northern ireland spindle and parabolic shaped drumlins examined at fifty five localities in northern ireland possess stratification sequences on their lee side flanks these forms lack the distinctive steep stoss and tapering lee ends of classical drumlins and tend to occur in linear zones transverse to late pleistocene ice flow in most cases 90 per cent the stratified deposits infill embayments excavated in the lee side of barkhanoid forms and in the remainder 10 per cent they are superimposed on the lee side of whaleback forms the stratification sequences developed as a result of sedimentation in interconnected subglacial water filled cavities and are unlike remanie proglacial sediments moulded by ice into drumlin form stratigraphic evidence indicates that the lee side sequences developed during drumlin streamlining which supports the view that subglacial hydraulic processes played an important role in drumlin formation

heterozoan carbonates when where and why a synthesis on parameters controlling carbonate production and occurrences abstract in modern and phanerozoic times heterozoan carbonates group a large array of depositional environments from the poles to the tropics this global assessment reviews the critical parameters and controlling factors of heterozoan carbonates i stratigraphic and global distributional trends ii oceanographic and trophic relationships and iii biological and sedimentary processes well documented case studies n 129 have been investigated when facies and stratigraphic attributes were available and when environmental settings such as oceanography climate and paleogeography were clearly identified these case studies occur during specific periods of time in the sedimentary record e g late ordovician early carboniferous early permian and neogene while they are absent during others e g triassic and jurassic periods during greenhouse to icehouse transitions and those with active thermohaline circulation are particularly conducive for heterozoan carbonates based on global oceanographic patterns and existing ecological and hydrodynamic regime classifications hallock 2001 pedley and carannante 2006 james and jones 2015 a process based classification scheme is proposed that distinguishes two main heterozoan carbonate systems i a highly productive system characterized by suspension feeding biota and ii an oligo mesotrophic warm temperate system characterized by red algal and seagrass derived biota eight depositional models are proposed that combine i the source of energy for metabolic activities that allow the carbonate producing biota to thrive and ii hydrodynamics and physiography of the depositional system that control the sediment accumulation the local and platform scale based profiles can be used to complement the facies approach of james and jones 2015

strain response and re equilibration of ch4 rich synthetic aqueous fluid inclusions in calcite during pressure drops abstract aqueous fluids in sedimentary basins often contain dissolved methane particularly in petroleum environments pvtx pressure volume temperature composition reconstructions performed using fluid inclusion data are largely based on the assumption that inclusions do not change from the time of trapping until the present many authors however consider that fluid inclusions can re equilibrate particularly in fragile minerals like calcite in order to understand this re equilibration phenomenon in the metamorphic domain previous experiments have been performed under high pt conditions but few have been performed at low to medium pt conditions such as those associated with sedimentary burial diagenesis and no previous studies have examined ch 4 bearing aqueous inclusions in calcite an experimental study of the preservation modification of ch 4 rich synthetic fluid inclusions in calcite during isothermal decompression was conducted an autoclave was used for accurate ptx control allowing equilibrium between liquid and vapour in the ch 4 h 2 o system ptx conditions were maintained at four stages of decreasing pressure with each stage held for 7 days to simulate an isothermal pressure drop in order of decreasing pressure the pressure temperature conditions monitored were 276 10 bar at 180 7 c 176 10 bar at 180 7 c 76 10 bar at 180 7 c and 10 3 bar at 180 15 c at the end of the experiment the calcite was recovered and analyzed by microthermometry and raman microspectroscopy for ptx reconstruction a careful procedure was adopted to limit re equilibration of inclusions during analytical procedures four types of inclusion shapes and four types of strain patterns were differentiated classification of the petrographic strain patterns was carried out these strain patterns were associated with inclusion stretching and or leakage regarding ch 4 t h and p h compared to experimental conditions factors controlling the preservation or acquisition of strain patterns included the initial shape and size of the inclusion and the pressure differential p between the confining pressure p cf and the internal pressure p i within the inclusion most fluid inclusions seemed to be trapped during the first 7 days of the experiment although few 4 of these preserved the initial pt conditions of 276 10 bar whereas 8 preserved the second and third run of pt conditions overall the majority of inclusions 88 did not reflect accurately the ptx trapping conditions a petrographic guide to the inclusions is presented here that allows strain identification for pvt reconstructions re equilibration patterns and evidence for preferential methane leakage from aqueous inclusions in calcite are important findings revealed by this study and may be useful for the reconstruction of post trapping events in investigations of natural samples and in other experiments using synthetic inclusions in calcite

calcite vein system and its importance in tracing paleowater flow and hydrocarbon migration in the ordovician carbonates of the tazhong area tarim basin china it is difficult to determine flow pathways of paleofluids in sedimentary basins petrography fluid inclusion and isotopic compositions from different phases of calcite veins in the ordovician in the tazhong area were studied our results reveal a complex diagenesis process with two importantly crossformational fluid movements coupled with three phases of calcite veins c1 c2 and c3 precipitation and thermochemical sulfate reduction by hydrocarbons fluids that precipitated c2 and c3 calcites were saline and enriched in 18o and thus may have originated from underlying evaporates whereas fluid that precipitated c3 had an additional contribution from 87sr rich ba rich and zn rich precambrian basinal clastic units fluid inclusion homogenization temperatures salinities and 18owater values of c2 veins show decreasing trends with increasing distances from strike slip faults this may indicate that c2 fluid might migrate into ordovician carbonate reservoirs through strike slip faults within 6 km during late hercynian orogeny late permian the similarly decreasing trends are observed in c3 veins indicating that the eastern part of no 1 fault seemed to be the main fluid flow pathway for c3 calcite precipitation during himalayan orogeny hydrocarbon may have migrated along the similar pathways as supported by 1 abundant primary hydrocarbon bearing fluid inclusions in the c2 and c3 calcites and 2 well documented hydrocarbon migration and mixing this is an ideal case showing how spatial variation in geochemical data from fracture fillings can be used to trace paleowater and likely hydrocarbon flows in sedimentary basins it thus may be useful in predicting fluid flow and distribution of hydrocarbons in the tarim basin and other basins

are drumlins a product of a thermo mechanical instability abstract of numerous theories of drumlin genesis none has been widely accepted it seems evident however that some form of positive feedback process is involved under certain circumstances perturbations are amplified herein we suggest that patchy areas of frozen bed provide the initial perturbation such frozen patches may occur in local areas underlain by material of lower thermal conductivity or on slight topographic highs drag exerted by the frozen patch deflects ice flow into its lee dragging with it mobile till eroded from the thawed area the energy balance is such that this till likely refreezes either producing a topographic perturbation or amplifying an existing one the resulting topography then deflects more of the geothermal heat away from the developing hill and into the adjacent trough resulting in a positive feedback once the thermal perturbation exceeds a critical though as yet undefined level melting may decouple the ice from the bed preventing further entrainment of till from thawed areas and thus limiting the height and length of the drumlin

chemical and textural controls on the formation of sepiolite palygorskite and dolomite in volcanic soils abstract a 3 m deep soil profile from gran canaria canary islands has been studied the profile is interesting because soil development on mafic tephra produced a pattern of clay mineral and carbonate distribution carbonates precipitated abundantly increasingly towards the bottom making up 20 90 wt of the soil sepiolite and calcite are dominant at the top whereas palygorskite and dolomite are the major components at the lower part of the profile quartz is present in low amounts in most of the profile and smectite and non crystalline partially altered tephra occur in low amounts towards the bottom mineralogical chemical and textural investigations indicate that sepiolite and calcite precipitated in the space between the original tephra grains from ca mg and si dissolved in situ and transported in the runoff palygorskite and smectite precipitated within tephra grains from in situ tephra weathering as well as dolomite the distribution of the clay minerals is due to clay composition and ion mobility sepiolite consisting only of si and mg precipitated outside tephra grains where the mobile si and mg ions were abundant in the interstitial waters palygorskite and smectite contain si al fe and mg and only precipitated within the tephra grains where the immobile al and fe were available calcite precipitation in solution is kinetically favored over that of dolomite and thus calcite precipitated between the grains dolomite precipitated within altering tephra grains and spherical clay structures because tephra and clay generated a viscous medium where dolomite supersaturation increased and the kinetic barrier for precipitation was overcome these results are relevant to the dolomite problem as they illustrate how dolomite can precipitate in surface conditions and to co 2 sequestration because dolomite can immobilize higher co 2 amounts both ca and mg are involved and not only ca and in a much more stable manner dolomite is eight orders of magnitude less soluble than calcite

quantifying vein attributes in massive mudstones triassic sw england implications for progressive evolution of opening mode fracture networks abstract attributes of gypsum vein arrays in the triassic massive mudstones of sw england were analyzed to infer the process of vein network evolution field data demonstrate that there is no clear correlation between vein orientation and thickness however sub horizontal veins have a higher average thickness than the inclined veins vein thickness distribution is best characterized by a log normal distribution the fractal dimensions d of vein networks analyzed range from 1 44 to 1 71 vein networks which contain abundant bridging veins between neighbouring sub horizontal veins to form an anastomosing pattern exhibit a higher d value the fraction of vein volume derived from image analysis ranges from 6 75 to 17 94 a positive correlation is revealed by plotting the fractal dimensions of the vein networks versus the number of vein intersection points suggesting that an anti clustering distribution of veins could contribute to more interactions and also intersections of the gypsum veins the vein attribute data presented indicate that mineralization in the massive mudstones is mainly localized to some of the largest veins as a result of mechanical interaction of neighbouring veins during vein propagation hindering the nucleation of new veins as a consequence accommodation of the bulk rock strain could be facilitated mainly by expansion of the large backbone veins which follow a positive feedback mechanism of growth this study reveals a strong link between the geometric parameters of opening mode fractures with the history of their formation propagation and intersection

geomorphological reconstruction of the labrador sector of the laurentide ice sheet abstract the labrador sector formed one of three major domes of the laurentide ice sheet during the last wisconsinan glaciation reconstruction of its evolution is important because it modulated atmospheric and oceanic circulation over 1 100 ka time scales this paper reports new geomorphological evidence of ice flow which is used to reconstruct glimpses of the behaviour of the labrador sector during its evolution flow evidence indicates a southern position 51 n of the labrador ice divide presumed to be the usual location when the ice sheet was close to its maximum extent a previously inferred dramatic surge of labrador ice across hudson strait and onto baffin island at 9 9 9 4 ka is verified seemingly contradictory evidence regarding deglaciation in northern quebec has been analysed and a reconstruction developed that solves this problem deglacial retreat of the labrador ice sheet was highly asymmetric with rapid retreat of the southern margin northwards migration of the centre of mass by 500 km and slow retreat along the northern margin as it shrank its thermal regime changed from cold centred to entirely cold based and it finally fragmented into many residual ice caps and glaciers this dynamic and asymmetric behaviour may be due to destabilisation of the labrador ice sheet triggered by heinrich event ice streaming through hudson strait

early holocene glacial lakes and ice marginal retreat pattern in labrador ungava canada abstract the existence of glacial lakes naskaupi mclean minto melezes and wapussakatoo during the deglaciation of labrador ungava canada was recognized at the end of 1950s however glacial lakes have seldom been included in regional reconstructions to constrain the outline of successive ice margins during the glacial retreat in labrador ungava reconstruction of the ice flow succession in labrador ungava has often primarily focused on till lineation systems these reconstructions often depict a late glacial ice dispersal center situated over central labrador ungava more recent studies on glacial geomorphology including meltwater features however suggest that north central labrador ungava exhibited cold based conditions at least during the latest deglaciation cold based conditions inhibit basal sliding and formation of landforms except for meltwater traces such as meltwater channels glacial lake shorelines and deltas this situation implies that meltwater traces are the main source of information when reconstructing the spatial retreat pattern during a cold based deglaciation evidence presented in this study such as glacial lake shorelines fossil deltas and spillway and drainage channels in north central labrador ungava indicates the existence of numerous previously unmapped glacial lakes the mapped glacial lake features are synthesized to a reconstruction of several glacial lake stages which in turn are used to constrain the late glacial ice margin retreat pattern over the inferred cold based areas of north central labrador ungava a total of 26 glacial lakes 65 sub stages existed during the deglaciation of labrador ungava these lakes were impounded along the southern margin of the shrinking ice sheet the required damming ice margins indicate that the last ice remnant of the laurentide ice sheet in labrador ungava was situated over the southern ungava bay and the adjacent southern shore

shallow burial dolomitization and dedolomitization of mid cenozoic cool water calcitic deep shelf limestones southern australia abstract oligocene to mid miocene deep shelf bryozoan rich limestones across southern australia are variably altered to gray to orange ca rich medium crystalline sucrosic dolomite degree of replacement ranges from scattered rhombs to complete dolostone units several tens of meters thick and many kilometers in areal extent the locale and timing of dolomitization are tightly constrained to shallow burial and mid to late miocene dolostone varies from friable to dense and well lithified dolomitization is fabric specific muddy sediments are preferentially replaced calcite bryozoans and brachiopods form biomolds geochemistry suggests that dolomitization was predominantly by seawater limestone interaction but admixing of continental possibly meteoric groundwater is required by data on stable and radiogenic isotopes and trace elements sr isotopes confirm a mid miocene age for the dolomite if precipitated from seawater with no inherited limestone values dolomite crystals have undergone variable degrees of dissolution and meteoric calcite cement has locally filled the resultant rhombic voids dissolution began in the crystal cores implying some sort of metastability and expanded outward until in some ins ances the whole dolomite crystal was dissolved leaving dolomolds in otherwise unaffected limestone this dolomite occurrence well constrained by regional geology shows that widespread porous and permeable fabric destructive medium crystalline sucrosic dolostone can form in the shallow subsurface soon after sediment deposition such dolomite however may be metastable in the presence of variably mixed continental marine waters and newly formed crystals can undergo dedolomitization soon after precipitation

mechanism of palygorskite formation in the red clay formation on the chinese loess plateau northwest china abstract the morphological characteristics and microstructures of the authigenic palygorskite occurring with smectite and carbonate minerals in the late miocene red clay formation on the chinese loess plateau have been investigated with the powder x ray diffraction xrd scanning electron microscopy sem and high resolution transmission electron microscopy tem the xrd results indicate that the red clay sediments contain quartz feldspar calcite dolomite illite kaolinite chlorite palygorskite and smectite and sem analyses show that palygorskite is a common component delicate palygorskite fibers radiate from the margins of platy smectite suggesting a pedogenic origin during the weathering of pre existing smectite a process that involved intense dissolution of the smectite and an adjustment in its structure moreover palygorskite occurs as coatings pore fillings and pore bridging cements among dolomite rhombs suggesting that the fibrous palygorskite was formed by a direct dolomite precipitation from pore fluids mostly after dolomite crystallization there is evidence to show that these two mechanisms took place synchronously in the red clay formation and that the two processes are related under alkaline conditions with high ph 8 0 fluids rich in magnesium magnesium ions occupy the interlayer positions in the smectite and this results in a misfit between the mg octahedral sheet and the smectite layer thereby allowing interaction between the magnesium ions and smectite layers and a reorganization of the structure to form palygorskite then with this kind of palygorskite as a crystal nucleus more palygorskite grows through a direct chemical deposition process according to previous studies the red clay sediments experienced a steady dry warm climate with periods of high rainfall and evaporation the warm climate would have increased the rate of weathering of minerals and subsequently enhanced the ions content and ph in the soil solutions during dry periods this soil environment is favorable for smectite transformation and palygorskite deposition this study has improved our understanding of the environmental and paleoclimatic changes during the time that palygorskite formed in the arid soils of the chinese loess plateau

the effects of palygorskite on chemical and physico chemical properties of soils a review abstract very little was known about how palygorskite affects soil properties when it constitutes a significant component of the soil clay fraction this constituted a serious impediment for the proper management of palygorskite containing soils under irrigated agriculture the present review is intended to summarize studies on the effects of palygorskite on chemical and physico chemical properties of soils carried out in recent years and to discuss future research required in this area when palygorskite containing soils are involved in irrigation practices release of mg from palygorskite into the soil solution will occur magnesium as an exchangeable cation in turn is known to decrease aggregate stability and to enhance the dispersivity of the soil clay fractions on the other hand magnesium as a dissolved cation is known to improve phosphorus availability in arid soils knowledge of factors affecting rheological properties of soil clay suspensions is essential for understanding of mechanisms of water and solid particle transfer through the soil profile the rheological behavior of soil clay suspensions is however complex and cannot be predicted from that of suspensions of standard clays although the flocculation value of palygorskite at near neutral ph is significantly lower than that of smectite the presence of palygorskite in the soil clay fraction will not affect the flocculation value of the soil clay since smectite which is always present in the clay fraction of palygorskite containing soils has a dispersive effect on palygorskite palygorskite has the strongest disaggregation potential and the highest ability to migrate in the soil among common phyllosilicates such as smectite and kaolinite palygorskite particles are thus likely to move preferentially over smectite and kaolinite downward in the soil profile and eventually to clog soil pores disaggregation and migration of palygorskite from the surface soil during rainfall and or irrigation may have an effect on the degree of erosion as well palycretes duripans in which the cementing material is dominantly composed of palygorskite can be formed in some landscapes where palycretes occur close to the surface plant growth is severely impeded palycretes also reduce water permeability of the soils creating water logged conditions that necessitate drainage installation although some progress has been made recently in understanding the effects of palygorskite on chemical and physico chemical properties of soils much research remains to be done performing some additional studies on disaggregation potential and migration ability of palygorskite under conditions close to those in the field is strongly desirable scanning electron microscopy observations on possible changes in aggregation of palygorskite in soils following intensive irrigation might be useful studies of the rheological behavior of soil clays with different mineralogical composition and palygorskite containing soil clays in particular are strongly encouraged there is a need as well to study interactions of various contaminants both organic and inorganic with palygorskite containing soil clays

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete