hydrothermal dolomitization of jurassic cretaceous limestones in the southern alps italy relation to tectonics and volcanism dolomitization has affected up to 750m of the jurassic and cretaceous pelagic carbonate sequence of the southern continental margin of the alpine tethys the sequence crops out in the southern alps of italy monti lessini late paleocene to miocene extrusion of basaltic tuffs breccias and lavas was contemporaneous with the dolomitization was was associated with extensive tectonism in an ancient back arc basin more than 200 samples were analyzed by x ray diffraction cathodoluminescence scanning electron microscopy stable isotope ratios carbon oxygen strontium and clay mineralogy the dolomite contains 40 to 50 mgco sub 3 in thin sections the crystal size distribution is unimodal about 100 mu m possibly indicating a single nucleation for the main crystallization phase the delta sup 13 c of the dolomite is not appreciably different from the undolomitized pelagic limestone 1 0 per thousand to 2 0 per thousand peedee belemnite pdb the delta sup 18 o variation 5 0 per thousand to 13 0 per thousand pdb is due to temperature variation in the system the sup 87 sr sup 86 sr ratio in the dolomite 0 70839 0 70867 is consistent with the ratio in late oligocene miocene marine water clay minerals in limestone and dolomite differ in the presence of neoformed mg chlorite indicating a maximum temperature of about 150c for dolomitization the dolomite is suggested more to have a hydrothermal origin the heat flow associated with the volcanism allowed marine water to penetrate the system and circulate in convective cells through the tectonic breccias locally dolomitizing the limestone less

change in climate ocean and ice sheet conditions in the ross embayment antarctica at 6 ka evidence from the ross embayment antarctica suggests an abrupt cooling and a concomitant increase in sea ice cover at about 6000 sp 6 ka stable isotope delta d concentrations in the taylor dome ice core at the western edge of the ross embayment decline rapidly after 6 ka and continue to decline through the late holocene methanesulfonic acid concentrations at taylor dome show opposite trends to delta d sediment cores from the western ross sea show a percentage minimum for the sea ice diatom fragilariopsis curta between 9 and 6 ka when taylor dome delta d values are highest followed by an increase through the late holocene radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the ross embayment ceased atabout 6 ka coincident with the environmental changes inferred from the sediment and ice core records the similarity in timing suggests an important role for climate in controlling the evolution of ice shelf margins following the end of the last 9 glaciation

abandoned penguin rookeries as holocene paleoclimatic indicators in antarctica penguins are sensitive indicators of the antarctic climate and of the environmental parameters that limit their presence and distribution paleoenvironmental data obtained from the study of abandoned penguin rookeries pygoscelis adeliae along the victoria land coast in antarctica indicate 14c date of 11 13 ka for the oldest abandoned rookery and supply new information about the timing of glacier retreat in southern victoria land after the last glacial maximum the continuous presence of the adelie penguins is documented from 7 ka according to our data the limiting factors that control the presence of penguins along the coast of victoria land changed during the holocene whereas several colonies were occupied for very long periods other sites were used for more or less extended periods and then abandoned the greatest diffusion of rookeries occurred between 3 and 4 ka a period of particularly favorable environmental conditions that has never been repeated it was followed by a sudden decrease in the number of penguin rookeries shortly after 3 ka this event has been attributed to an increase of the sea ice extension and may have been correlated to a worldwide phase of climate change near the subboreal subatlantic boundary a minor phase of penguin reoccupation occurred locally in the eighth to fourteenth centuries a d because the presence and number of penguins reflect the state of health of the antarctic marine ecosystem it is important to evaluate the variations in their distribution in the past in the absence of human induced changes

detection of temperature and sea ice extent changes in the antarctic and southern ocean 1949 96 abstract some global climate models indicate that future global warning from increased atmospheric concentrations of greenhouse gases may be greatest in the polar regions over areas where the sea ice cover is reduced the reduction of sea ice area in the models also gives rise to a strong positive feedback to the warming from the increase of atmospheric greenhouse gas concentration to date and the results of transient climate models an estimate of the expected change in the antarctic temperatures and sea ice extent can be made the existing data for observed changes in temperatures of the antarctic and southern ocean extending back to approx 1956 and approx 1945 respectively are analyzed along with the data of sea ice cover commencing in 1973 to examine the extent to which the anticipated warming trends and sea ice decrease are being realized in spite of high temporal and spatial variability the data does support small significant trends of temperature increase and sea ice cover decrease compatible in magnitude to those expected as a consequence of atmospheric greenhouse gas increase the seasonal cycle shows a delayed period of autumn winter sea ice growth with a longer period of open water this supports a mechanism for positive feedback between decreasing sea ice cover and increasing temperature

the tectonic history of drake passage and its possible impacts on global climate this study provides an integrated review of plate tectonic models of the evolution of the antarctica patagonia connection compared to geological records collected on land in patagonia and tierra del fuego and offshore along the northern edge of the scotia sea a temporal framework for the sedimentary and tectonic events of the north scotia ridge and tierra del fuego is constructed with additional data compiled from entire patagonia and the austral basin this review provides robust correlations of seaways and tectonic events along the scotia and south america plates and indicates that the opening of the drake passage was not steady state since ca 30 ma rather the regions forming the present day northern limit of this gateway experienced important paleogeographic changes from deep marine basins to shallow ridges and emerged regions during the late oligocene and early middle miocene time our compilation of geological data shows that emergence along the north scotia ridge and tierra del fuego was achieved at 23 22 ma and has been followed by elimination of the patagoniano sea in patagonia starting at 22 23 ma and achieved at 20 ma this transition towards more continental sedimentation in southern south america is correlated with more shallow marine conditions in the austral basin this succession of events had a strong influence on the general geometry of the drake passage corresponding to a constriction of its northern limit starting in the window 29 22 ma and achieved at 21 ma this period of active deformation in southern south america also corresponds to a period of the global climate having two anomalies well known from the isotopic records the late oligocene warming around 26 ma and the mid miocene climatic optimum which ended between 15 and 14 ma the possible effects of the post oligocene tectonic evolution of the drake passage region on general oceanic circulation are discussed causes for the synchronicity between tectonic events and these global warming events are examined

site information and initial results from deep ice drilling on law dome antarctica the aim of deep ice drilling on law dome antarctica has been to exploit the special characteristics of law dome summit i e low temperature and high accumulation near an ice divide to obtain a high resolution ice core for climatic environmental studies of the holocene and the last glacial maximum lgm drilling was completed in february 1993 when basal ice containing small fragments of rock was reached at a depth of 1196 m accurate ice dating obtained by counting annual layers revealed by fine detail 18 o peroxide and electrical conductivity measurements is continuous down to 399 m corresponding to a date of ad 1304 sulphate concentration measurements made around depths where conductivity tracing indicates volcanic fallout allow confirmation of the dating for agung in 1963 and tambora in 1815 or estimates of the eruption date from the ice dating for the kuwae vanuatu eruption 1457 the lower part of the core is dated by extrapolating the layer counting using a simple model of the ice flow at the lgm ice fabric measurements show a large decrease 250 to 14 mm 2 in crystal size and a narrow maximum in c axis verticality the main zone of strong single pole fabrics however is located higher up in a broad zone around 900 m oxygen isotope 18 o measurements show holocene ice down to 1113 m the lgm at 1133 m and warm 18 o about the same as holocene ice near the base of the ice sheet the lgm holocene 18 o shift of 7 0 only 1 larger than for vostok indicates that law dome remained an independent ice cap and was not overridden by the inland ice sheet in the glacial

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

fault controlled and stratabound dolostones in the late aptian earliest albian benassal formation maestrat basin e spain petrology and geochemistry constrains this study was developed under the exxonmobil fc2 alliance fundamental controls on flow in carbonates the authors wish to thank exxonmobil production company and exxonmobil upstream research company for providing funding the views in this article by sherry l stafford are her own and not necessarily those of exxonmobil this research was supported by the sedimentary geology research group of the generalitat de catalunya 2014sgr251 we would like to thank andrea ceriani and paola ronchi for their critical and valuable reviews and associated editor piero gianolla for the editorial work

eoalpine and mesoalpine tectonics in the southern alps according to structural and stratigraphic data eoalpine and mesoalpine tectonics can be clearly recognized in the southern alps and distinguished from the better known neoalpine deformation

hydrocarbon provinces in the swiss southern alps a gas geochemistry and basin modelling study abstract in order to evaluate the petroleum potential of southern switzerland south alpine fold and thrust belt gas geochemical investigations including free and adsorbed gases were combined with a basin modelling analysis the palaeotectonic setting and alpine orogenic movements were recognized as main controls in the evolution of the petroleum generation potential three main hydrocarbon provinces are distinguished 1 the arbostora anticline which developed from an early jurassic high has excellent but immature source rocks which probably at no time generated hydrocarbons because of their swallow level in the nappe edifice 2 the stabio anticline south of the arbostora anticline in southernmost switzerland where wet gases are observed at the surface that are likely to have been generated from late cretaceous to present day from triassic source rocks occurring deeper in the nappe pile and 3 the m generoso basin with prevailing petroleum generation in the early jurassic and possible minor generation in marginal areas during cretaceous and tertiary times

golden grove dolomite barbados origin from modified seawater abstract the largest dolomite occurrence on barbados part of a roadcut at golden grove is about 40 m long and 0 5 2 5 m thick dolomite at golden grove constitutes about 10 40 vol of the host limestone an algalforaminiferal facies of late pleistocene age with local patches consisting of up to 100 vol dolomite almost all dolomite is a replacement of matrix and predominantly mg calcite skeletal grains an average of less than 0 1 vol of the rock is fibrous to bladed radial and radiaxial dolomite cements with calcite banding the partially dolomitized algal foraminiferal facies is unconformably overlain by scleractinian coral reef limestones replacive dolomitization appears to have been very localized at the stratigraphic level of golden grove the petrographic data suggest that replacive dolomitization took place after deposition of the algal foraminiferal facies and prior to deposition of the overlying coral reef facies 18o 1 1 to 4 4 pdb values of the replacive dolomites suggest seawater with variable temperature and or slight degrees of evaporation as the principal agent of dolomitization in addition variable and highly negative 13c values of the replacive dolomites 23 5 to 8 913c the main source of this 13c depleted carbonate probably was oxidized methane with a possible but very minor contribution of carbonate derived from bacterial gsulfate reduction methane may have been supplied by bacterial methanogenesis relatively close to the site of dolomitization or by upward seepage of thermogenic methane derived from underlying tertiary hydrocarbon reservoir s it is possible albeit speculative that the localized availability of methane via fractures and or its localized oxidation somehow induced dolomitization at golden grove furthermore the 13c 18o and 87sr 86sr ratios 0 70913 0 70919 of replacive dolomites of golden grove calcites 13c 14 0 to 3 9 pdb 18o 5 0 to 2 2 pdb and of groundwaters from the present coastal mixing zone and inland carbonate aquifers 87sr 86sr 0 70911 0 70924 13c 123 to 5 9 pdb 18o 5 0 to 2 smow effectively role out that replacive dolomitization at golden grove was caused in a typical coastal freshwater seawater mixing zone or that dolomitization was influenced by meteoric waters to any significant degree the small amounts of banded dolomite cements however may have formed in a typical coastal mixing zone

multistage strain localisation and fluid assisted cataclasis in carbonate rocks during the seismic cycle insights from the belluno thrust eastern southern alps italy abstract strain localisation in carbonate rocks impacts upon the nucleation and development of structures within the shallow seismogenic crust studying deformed carbonate rocks is thus a key to the refined understanding of the mechanical behaviour of rock successions with high potential to fail coseismically in response to stress accumulation we studied deformation structures and mechanisms of the miocene belluno thrust from the seismically active eastern southern alps italy the thrust contains several structural facies and features pressure soluted and veined lithons cataclasites s c fabrics principal slip surface which make it possible to define a sequence of deformation events in space and through time during thrusting image analysis of cataclasite particle size distribution and morphology supported by cathodoluminescence imaging indicates corrosive wearing as the main comminuting mechanism during cataclasis and repeated ingress of overpressured aqueous fluids promoting carbonate clast dissolution we propose an evolutionary scenario of multiple episodes of fabric formation and rejuvenation that localised and accommodated increasing shear strain into a progressively narrowing fault core we propose that strain localisation in carbonate rocks can be greatly facilitated by cyclic fluctuations between strain hardening and softening conditions punctuated by transient spikes of coseismic failure accommodated by cataclasis during the ingress of overpressured chemically reactive fluids that control carbonate precipitation and dissolution

dolomite reservoirs porosity evolution and reservoir characteristics systematic analyses of the published record of dolomite reservoirs worldwide reveal that the majority of hydrocarbon producing dolomite reservoirs occurs in 1 peritidal dominated carbonate 2 subtidal carbonate associated with evaporitic tidal flat lagoon 3 subtidal carbonate associated with basinal evaporite and 4 nonevaporitic carbonate sequence associated with topographic high unconformity platform margin buildup or fault fracture reservoir characteristics vary greatly from one dolomite type to another depending upon the original sediment fabric the mechanism by which dolomite was formed and the extent to which early formed dolomite was modified by postdolomitization diagenetic processes e g karstification fracturing and burial corrosion this paper discusses the origin of dolomite porosity and demonstrates the porosity evolution and reservoir characteristics of different dolomite types

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

a jurassic tongue of the ocean infilled with oolitic sands the belluno trough venetian alps italy abstract the belluno trough is a narrow and elongate basin on the northwestern corner of the apulian plate continental margin it acquired topographic identity in early liassic time during the breakup of a widespread upper triassic carbonate shelf at the beginning liassic the belluno trough was a starved depression accumulating euxinic mudstone and bounded by two shallow water carbonate banks trento and friuli platforms this typical bahamian physiography lasted until late liassic time when the shallow water trento platform collapsed tectonically and suddenly drowned tilting northward and breaking along an old tectonic line it became therefore a submerged pelagic plateau in the meantime the western edge of the friuli platform now the windward margin of an oceanic platform turned into a prolific super producing oolite factory quite soon the oolite sands of the friuli margin started to flow down the slope reaching the basin through numerous entry points and gradually building a complex of coalescent deep sea fans which prograding westward infilled the belluno trough the fans terminated westward against the faulted edge of the trento plateau on which above a karst like surface locally encrusted with manganese red nodular ammonitic limestone was slowly accumulating northward where the topographic relief decreased the oolite fans could spill over the escarpment onto the edge of the plateau by the end of middle jurassic time the belluno trough was no longer a submarine depression but a gentle slope connecting the friuli platform to the deep pelagic trento plateau in callovian time probably because of a short drop in sea level large parts of the friuli platform were exposed to subaerial diagenesis during the subsequent oxfordian transgression the resulting rocky bottom became the substratum for an extensive growth of reefal organisms hydrozoans corals rudists which fringed the friuli platform for the whole malm and cretaceous times

3d crustal architecture of the alps apennines join a new view on seismic data abstract seismic data from the alps apennines join have usually been interpreted in the form of 2d cross sections passing either through the western alps or the ligurian alps monferrato apennines however the oblique se nw convergence of adria and europa and superimposed rotations imply a distinct 3d kinematic development around the adriatic indenter ai the westernmost spur of adria in order to develop kinematic models data on motion at the different margins of ai must be coordinated along the northern margin the dextrally transpressive insubric line il was active between 25 and 16 ma insubric helvetic phase of alpine orogeny contemporaneously along the southern margin paleo apenninic phase a complementary sinistral motion took place along the villalvernia varzi line vvl it emplaced the monferrato apennines westward to the north of the ligurian alps by carrying them westward on top of ai between 14 and 6 ma jura lombardic phase of alpine orogeny the lombardic thrust belt developed on the northern margin of ai now largely hidden under the po plain its continuation to the southwest is impeded by older thrust masses along the western alps that consist largely of basement their sediments having been eroded as noted on the deep reflection line crop alpi 1 by earlier investigators this line moreover contains a deep reflection band originating in the autochthonous mesozoic of the apenninic foredeep in order to better visualize this origin and the relation of further elements identified on reflection lines around the northwestern end of the monferrato apennines a 3d fence diagram was constructed it helps in establishing a 3d structural kinematic model of the alps apennines join based on the kinematics of ai this model features an underthrust of ai under the western alps in the paleo apenninic phase in the course of this underthrust the paleo apenninic elements of the monferrato moved under the marginal thrusts of the western alps subsequent neo apenninic thrusting brought both elements together to the surface where they now form the monferrato and turin hills a derivation of the alpine collina di torino from the south instead of from the west as recently proposed meets with serious kinematic difficulties

late pleistocene mixing zone dolomitization southeastern barbados west indies field geochemical and petrographic data for late pleistocene dolomites from southeastern barbados suggest that the dolomite precipitated in the zone of mixing between a coastal meteoric phreatic lens and normal marine waters the dolomite is localized in packstones and wackestones from the algalamphistegina fore reef calcarenite facies stable isotopic evidence suggests that meteoric water dominated the diagenetic fluids responsible for dolomitization carbon isotopes in pure dolomite phases average about 15 0 pdb this light carbon is attributed to the influence of soil gas co2 and precludes substantial mixing with seawater a narrow range of oxygen isotopic compositions coupled with a wide range of carbon compositions attest to the meteoric diagenetic overprint dolomitization likely occurred with as little as a five per cent admixture of seawater strontium compositions of the dolomites indicate probable replacement dolomitization of original unstable mineralogy the dolomite is characterized by low sodium values low concentrations of divalent manganese and iron suggest oxidizing conditions at the time of dolomitization a sequence of petrographic features suggests a progression of diagenetic fluids from more marine to more meteoric early marine diagenesis was followed by replacement dolomitization of skeletal grains and matrix limpid euhedral dolomite cements precipitated in primary intra and interparticle porosity subsequent to replacement dolomitization as waters became progressively less saline dolomite cements alternated with thin bands of syntaxial calcite cement the final diagenetic phase precipitated was a blocky calcite spar cement representing diagenesis in a fresh water lens this sequence of diagenetic features arose as the result of a single fall in eustatic sea level following deposition a stratigraphic eustatic diagenetic model constrains both the timing and rate of dolomitization in southeastern barbados dolomitization initiated as sea level began to fall immediately following the oxygen isotope stage 7 3 high stand some 216 000 yr bp due to the rapidity of late pleistocene glacio eustasy dolomitization locally complete is constrained to have occurred within about 5000 yr

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

reflux stratabound dolostone and hydrothermal volcanism associated dolostone a two stage dolomitization model jurassic lebanon the kesrouane formation which is characterized by pervasive dolomitization has a stratigraphic thickness that exceeds 1000 m it is part of a broad carbonate platform deposited in the levant region and represents 60 of the lebanese jurassic rocks two genetically distinct dolostones are recognized within this unit 1 fine to medium crystalline non planar grey dolostone and 2 coarse crystalline planar beige dolostone the former is stratabound and of early jurassic age 87 sr 86 sr 0ae707455 this dolostone locally exhibits pseudomorphs of evaporite nodules pointing towards seepage reflux dolomitization by hypersaline to marine related fluids exposures of the coarse crystalline dolostone are associated with regional pre cretaceous faults along which late jurassic volcanics also occur sedimentological and diagenetic considerations coupled with microthermometry support a hydrothermal origin for this dolostone with th values of primary inclusions between 50 and 80 c the related dolomitizing fluids are mesosaline 3ae5 12ae0 eq wt nacl and are believed to result from the mixing of evaporative brines and sea water dolomitization is thus believed to have occurred in two stages whereby fluids invaded the host rocks first by seepage reflux explaining the resulting early jurassic stratabound dolostone and later through fracture flow along the faults associated with the late jurassic volcanism explaining the coarse crystalline hydrothemal dolostone

development of a deep karst system within a transpressional structure of the dolomites in north east italy abstract the piani eterni karst system is one of the longest and deepest caves of italy situated in the southern sector of the dolomiti mountain range the area where the cave was formed displays peculiar structural settings confined in a tectonic transpressive corridor between two regional thrusts belluno and valsugana during miocene uplift of the range the inheritance of mesozoic structures led to the formation of a deep and wide upward branching flower or palm tree structure cutting the carbonate sequence and exposing the surrounding surface to karst processes after erosion the relative lowering of the hydrologic base level due both to the uplift of the area and then to the carving of deep glacial valleys in the quaternary allowed the formation of paleo phreatic conduits at subsequently deeper levels interconnected by vadose shafts and canyons this work gives a detailed tectonic interpretation of the transpressive structure and picks out the tectonic features most favorable to the karst development a detailed statistical analysis of the distribution and orientation of the karst conduits was performed using 31 km of 3d surveys showing that the development of the cave was strictly guided by a few favorable surfaces of stratigraphic and tectonic origin these features are known in the literature as inception horizons and tectonic inception features respectively cave levels are usually related to lithologic favorable conditions associated with standings of the paleo water table here we suggest that some tectonic surface geometries could have led to the opening of voids in the active tectonic phase leading to the formation of the original proto conduit network different types of tectonic inception features identified in the cave were described in terms of geometry and kinematics tensional fractures as well as fault plane undulations and flexural slip surfaces between beds are described as the most favorable tectonic surfaces for the development of the conduits finally we discuss why transpressional settings and related flower structures in soluble rocks can enhance the karst process allowing the formation of huge and deep karst systems

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

pangaean climates megamonsoons of the megacontinent the climate for a highly idealized geographic representation of the megacontinent of pangaea corresponding to the period 250 200 m y ago is explored using a low resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth with a provision for sea ice formation and decay soil moisture is included as a predicted variable on the continent because there are large uncertainties about key factors that might influence the pangaean climate sensitivity experiments are used to examine the climate for two different mean elevations 0 and 1000 m two different snowcover prescriptions and two different levels of implied greenhouse heating and solar luminosity modern co2 concentration and modern solar luminosity fivefold increase in modern co2 concentration and a 1 decrease in modern solar luminosity in all of the experiments the large bipolar land masses of laurasia and gondwanaland joined near the equator in the west and separated by the tethys sea in the east exhibit extreme continentality with hot summers cold winters and large scale summer and winter monsoon circulations year round or seasonal aridity is simulated for all but the eastern coastal regions the tropical western coast and the regions poleward of 40 latitude the simulated climate of the idealized pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late permian and triassic however the model results serve mainly to indicate the importance of various climate forming factors geography topography heating detailed comparisons will require new experiments with better models and more accurate geologic boundary conditions

structural controls on polyphase hydrothermal dolomitization in the kinta valley malaysia paragenesis and regional tectono magmatism abstract in the eastern side of the malay peninsula thick successions of limestone formations preserve important records of the mesozoic and cenozoic tectonic events here we investigate the strata and fracture bound hydrothermal dolomites in the palaeozoic carbonates of the kinta valley western peninsular malaysia based on their textural and morphologic characteristics structural relationships with the host rock different facies types and associations with hydrothermal calcite and low grade metamorphic marble we attempt to trace their polyphase origin and relationship with thermo tectonic events of the region a detailed evaluation of the nature of brecciation and crystallization of polyphase dolomites dolomitic limestones limestones and marble under the influences of episodic faulting is associated with the regional structural geology with emphasis on pre existing fault reactivations granitic emplacement and progressive thermal influence supply of mg2 from the host rock for dolomitization limited and episodic influx of circulating fluids and cessation of thermo tectonic evolution with progressive cooling are also inferred correlating the geological events in western peninsular malaysia with regional structural dynamics reveals that the major deformation episodes exerted first order controls on the loci of dolomite occurrences the occurrence geometry and structural relationships of the dolomites were controlled by successive magmatic events whereas the intensity of replacement dolomitization was controlled by host rock texture and varied bulk chemistry together with the nature of circulating fluids

tertiary extension in the southern trento platform southern alps italy the southern trento platform southern alps ne italy was the locus of abundant mafic volcanism associated with paleogene extensional tectonics during the pal eocene and throughout the eocene a nnw sse trending graben the alpone agno graben aag developed in the eastern lessini mountains the graben was filled with basaltic volcaniclastics calcarenites and lava flows the aag is a half graben system probably bounded by rotational listric normal faults most faults in the graben dip towards the wsw paleostress analysis within the aag shows that during the eocene the direction of horizontal extension was ene wsw the volcanic activity continued into the oligocene however the relation between oligocene tectonics and volcanism remains unclear gravimetric and magnetic anomalies in conjunction with the crustal thickness variations suggest a locus of lithospheric thinning slightly off axis from the aag this can be explained by an overall asymmetric extensional geometry dominated by a wsw dipping detachment fault the paleogene geodynamic scenario of the trento platform suggests that the aag developed as a foreland extensional response to the active collisional convergence between the european and adriatic plates neogene compressional tectonics reactivated some of the paleogene normal faults as strike sup faults

fluid inclusions in sedimentary and diagenetic systems abstract some of the major problems in sedimentary geology can be solved by using fluid inclusions in sedimentary and diagenetic minerals important fluids in the sedimentary realm include atmospheric gases fresh water of meteoric origin lake water seawater mixed water evaporated water formation waters deep in basins oil and natural gas preserving a record of the distribution and composition of these fluids from the past should contribute significantly to studies of paleoclimate and global change research is essential for improving understanding of diagenetic systems and provides useful information in petroleum geology applications of fluid inclusions to sedimentary systems are not without their complexities some fluid inclusions exposed to natural conditions of increasing temperature may be altered by thermal reequilibration which results in stretching or leakage and refilling of some fluid inclusions similarly overheating in the laboratory can also cause reequilibration of fluid inclusions so fluid inclusions from the sedimentary realm must be handled carefully and protected from overheating natural overheating of fluid inclusions must be evaluated through analysis of the most finely discriminated events of fluid inclusion entrapment fluid inclusion assemblages fia consistency in homogenization temperatures within a fluid inclusion assemblage consisting of variably sized and shaped inclusions is the hallmark of a data set that has not been altered through thermal reequilibration in contrast fluid inclusion assemblages yielding variable data may have been altered through thermal reequilibration if a fluid inclusion assemblage has not been altered by thermal reequilibration its fluid inclusions may be useful as geothermometers for low and high temperature systems or useful as geobarometers applicable throughout the sedimentary realm if a fluid inclusion assemblage has been altered partially by thermal reequilibration techniques for distinguishing between altered and unaltered fluid inclusions may be applied in studies of global change fluid inclusions can be used as sensitive indicators of paleotemperature of surface environments fluid inclusions also preserve microsamples of ancient seawater and atmosphere the analysis of which could figure prominently into discussions of past changes in chemistry of the atmosphere and oceans in petroleum geology fluid inclusions have proven to be useful indicators of migration pathways of hydrocarbons they can delineate the evolution of the chemistry of hydrocarbons and they remain important in understanding the thermal history of basins and relating fluid migration events to evolution of reservoir systems in studies of diagenesis fluid inclusions can be the most definitive record most diagenetic systems are closely linked to temperature and salinity of the fluid thus fluid inclusions are sensitive indicators of diagenetic environments

an organogenic origin for widespread dolomite in the cambrian eilean dubh formation northwestern scotland abstract dolomite precipitation from seawater is normally inhibited by the presence of sulfate the low activity of the carbonate ion and the high enthalpy of hydration of the magnesium ion however in modern microbial sediments anoxic degradation of cyanobacterial material by sulfate reducing bacteria can significantly alter ambient water chemistry sulfate is removed and enzymatic breakdown of proteins releases ammonia thereby increasing ph and carbonate alkalinity to levels necessary for dolomite formation magnesium may be supplied from complexed ion pairs in solution and from the breakdown of cyanobacterial sheaths and mucilage in the ancient past where benthic microbial communities dominated the depositional environment it is postulated that large scale shallow subsurface modif cation of ambient waters by sulfate reducing bacteria created conditions favorable to widespread dolomite formation early diagenetic cherts from the cambrian eilean dubh formation of northwestern scotland preserve successive stages of the taphonomic history of cyanobacterial biofabrics in sediments of a continuously aggrading shelf depth related sequential degradation of cyanobacterial mat is accompanied by the appearance and increase in abundance of authigenic dolomite culminating in a crystalline dolomitic fabric with only residual organic clots silicified oolitic grainstone fabrics preserve various ooid morphologies these form a diagenetically modified sequence in which progressive degradation of component microbial material together with leaching of the ooid shell is accompanied by the appearance and increase in abundance of intragranular authigenic dolomite total dissolution of ooids re ulted in the release of a package of crystals as sediment similar sequences are observed in peloids and intraclasts ensuing dolomitic rock fabrics bear no clue to their origin except where grains are preserved in early silicified windows these relationships can be explained by biochemical modification of porewaters during organic diagenesis and provide evidence for widespread authigenic dolomite formation in the shelf sediments this organic degradational model may serve as a basis for understanding the origin of thick platformal dolostone sequences of the proterozoic

trophic regimes of benthic foraminiferal assemblages in lower jurassic shallow water carbonates from northeastern italy calcari grigi trento platform venetian prealps abstract benthic foraminiferal distribution patterns in the lower jurassic rotzo member trento platform northeastern italy are analysed in terms of trophic gradients to provide a better understanding of the benthic communities during the time of the initial diversification of lower jurassic large foraminifera in the southern alps the rotzo member deposited on the trento platform records a complex mosaic of distinct shallow water ecosystems the changes in the foraminiferal assemblages of the rotzo member are considered to be primarily a reflection of gradients in trophic resources and oxygen levels the comparative analysis of benthic foraminiferal assemblages characteristic taxa number of species test size reproduction strategy the associated sediments lithofacies and the macrofossil and microfossil content allow three trophic regimes to be identified during the time of deposition of the rotzo member a eutrophic b mesotrophic and c oligotrophic a the eutrophic regime marked by episodically dysaerobic bottom conditions and high organic matter supply occurs stratigraphically below and within the orbitopsella spp assemblage sinemurian pro parte carixian gradual change in the benthic foraminiferal assemblage may have been caused by a combination of reduced nutrient supply and increased bottom water circulation which led to a mesotrophic regime b the latter which has been recognised in the basal and middle part of the rotzo member alternating with the eutrophic assemblage is characterised by a foraminiferal assemblage dominated by orbitopsella sp a major foraminiferal faunal turnover across the carixian domerian boundary corresponding to the disappearance of orbitopsella spp indicates a significant environmental change an oligotrophic regime c became established towards the upper part of the rotzo member new taxa appeared and diversity of the foraminiferal faunas was higher than in the previous ecosystems this part of the member characterised by the maximum lateral and vertical development of large lithiotis bivalve mounds reflects low and more stable nutrient supply which provided optimal conditions for the more specialised benthic communities evolution of these benthic foraminiferal faunas from the late pliensbachian onwards was obliterated by events that led to the drowning of the trento platform which is marked by a regional unconformity

hydrothermal dolomitization in platform and basin carbonate successions during thrusting a hydrocarbon reservoir analogue mesozoic of venetian southern alps italy abstract the early jurassic dolomitized carbonates in the venetian alp represent a surface analogue of the hydrocarbon exploration targets in adriatic offshore and po plain italy dolomitization affected the carbonate platform of monte zugna formation lower jurassic and the neptunian dikes breccia in the pelagic maiolica formation uppermost jurassic lower cretaceous improving the poro perm characteristics petrography stable isotope strontium isotope ratio trace element and fluid inclusion analyses were carried out on samples from the monte grappa anticline which is the direct analogue for subsurface the petrographic analyses showed a first pervasive replacement dolomitization phase d1 followed by volumetrically less important dolomite cement precipitation phases d2 d3 ds the same quite wide range of oxygen isotope 9 to 2 v pdb is observed in all dolomite types the 13 c range is in the positive field of marine derived carbonate from 0 5 to 3 2 pdb the trace element analysis showed a slight enrichment in fe and mn contents in the monte zugna dolostones with respect the original limestone the same dolomite precipitation temperature up to 105 c th was observed in the replacement and cement dolomites suggesting a unique dolomitization event this temperature largely higher than the maximum burial temperature about 50 c supports a hydrothermal origin of the dolomitizing fluids which had a seawater to brackish composition the data collected suggest a hydrothermal dolomitization occurring during to the south alpine thrusting according to the squeegee model the interpretation is consistent with the dolomitization model proposed for similar jurassic successions in the central southern alps this study indicates that the deformed foreland and thrust fold belts carbonates in po plain and adriatic offshore are suitable to be dolomitized and therefore reflect an efficient hydrocarbon exploration play

field geometry petrography and geochemistry of a dolomitization front late jurassic central lebanon this contribution describes the field geometry petrography and geochemistry of a well exposed dolomitization front in upper jurassic carbonates and attempts to highlight the sedimentological structural and relative sea level controls on multiphase dolomitization and related diagenetic events the data presented reflect the superposition of various diagenetic phases which have resulted in a single dolostone body whose dimensions are well defined in the field local microbial intraclastic dolomites of late tithonian age accumulated in a hypersaline lagoon during relative sea level fall these pre date beige hydrothermal dolostones 51 to 55 mol caco3 18o 9 3 to 4 0 v pdb 13c 1 5 to 2 1 v pdb 87sr 86sr 0 70742 matrix porosity 6 klinkenberg permeability 0 5 md whose dolomitizing fluid circulated along faults and invaded the nearby facies first the burrows were dolomitized then the bulk rocks resulting in the investigated tongue shaped dolomite body upon late jurassic early cretaceous uplift near surface water percolated through and altered the underlying beige dolostones this event was followed by a ferroan dolomite cement phase which occurred during further burial this contribution featuring a well defined geometric pattern of a dolomitization front with a large petrographic and geochemical data set may also serve as a case study illustrating the complexity of superimposed diagenetic processes which have to be taken into account in modelling exercises of multiphase hydrothermal dolomitization

seawater normalized ree patterns of dolomites in geshan and panlongdong sections china implications for tracing dolomitization and diagenetic fluids abstract in conventional studies of tracing dolomitization and diagenetic fluids rees of dolomites were widely used as been normalized by paas nasc or chondrite however most dolomites are formed in seawater or seawater derived fluids thus we conduct a new attempt to normalize the rees of dolomite using seawater standard based on case studies on 36 triassic limestone dolomite samples from the geshan section of southeast china and 26 permian triassic dolomite samples from the panlongdong section of northeastern sichuan basin southwest china the geshan seawater normalized sn ree patterns are characterized by notable positive ce sn average ce sn ce 6 823 sd 0 192 and negative pr sn anomalies average pr sn pr 0 310 sd 0 010 and slightly negative gd sn anomalis average gd sn gd 0 864 sd 0 053 with no obvious eu sn anomaly average eu sn eu 1 036 sd 0 094 the signatures of ree patterns barely changed during the dolomitization process for the ree compositions of the panlongdong dolomite it can be found that 1 the recrystallization process can result in varied total ree concentrations between 7 16 ppm and 37 87 ppm but do not alter the ree patterns including consistent positive ce sn anomalies average 4 074 sd 0 27 and lree enrichment average nd sn yb sn 3 164 sd 0 787 2 meteoric incursion can reverse ce anomaly from the strong positive ce anomalies ce sn ce 5 059 to slightly positive ce sn ce 2 459 or even negative ce anomalies and 3 hydrothermal fluid altered ree pattern is complicated by fluctuated distribution curve negative ce anomaly and positive eu anomaly eu sn eu 1 862 these results suggest that the seawater normalized ree patterns of dolomite can serve as an index to study the source of the dolomitization fluids and distinguish complex diagenetic processes providing a complement to previous works

holocene climate variability in antarctica based on 11 ice core isotopic records a comparison is made of the holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east antarctica vostok dome b plateau remote komsomolskaia dome c taylor dome dominion range d47 km105 and law dome and west antarctica byrd with temporal resolution from 20 to 50 yr the long term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations all the records confirm the widespread antarctic early holocene optimum between 11 500 and 9000 yr in the ross sea sector a secondary optimum is identified between 7000 and 5000 yr whereas all eastern antarctic sites show a late optimum between 6000 and 3000 yr superimposed on the long time trend all the records exhibit 9 aperiodic millennial scale oscillations climatic optima show a reduced pacing between warm events typically 800 yr whereas cooler periods are associated with less frequent warm events pacing 1200 yr

from middle jurassic heating to neogene cooling the thermochronological evolution of the southern alps abstract the dolomite region is located in the southern alps which were affected by mesozoic extensional tectonics and by consequent thermal perturbations in this work vitrinite reflectance and apatite fission track analysis are used to estimate the thermal evolution these methodologies have been applied to the permo mesozoic succession which crops out along the transalp seismic profile the regional distribution of the organic matter maturity seems to be mainly controlled by different burials reached during the norian liassic extensional phase in connection with high heat flow values the best solutions obtained from thermal modelling of both vitrinite and fission track data suggest that peak of high heat flow occurred during bajocian bathonian ages when western tethys was characterized by intrusions of gabbros and plagiogranites and extrusion of tholeiite basalts this time coincides with the onset of the drifting phase and related thermal subsidence the following thermal relaxation occurred during continuous sedimentation and the maximum burial does not coincide with peak temperatures cooling history has been carefully analysed through apatite fission track data on samples collected close to the valsugana overthrust which document an important exhumation event at about 10 ma the related erosion has been analysed through the combined use of arenite petrography and fission track analysis on detrital samples of the veneto foredeep succession which represents the storage of detritus during tertiary these data confirm that after serravalian the southalpine domain and related covers were affected by subaerial erosion

chemical study of tectonically controlled hydrothermal dolomitization an example from the lessini mountains italy in the central southern alps feltre verona italy a 750 m thick interval of jurassic and cretaceous pelagic limestones shows post depositional partial brecciation and dolomitization the overlying 500 m thick tertiary sedimentary sequence is unaffected through the paleogene mostly submarine mafic volcanism has been documented in the area small scale extensional features were observed in the limestone near the contact with the dolomitized breccias their orientations measured in the field correspond to the tectonic framework of the area and give evidence for the contemporaneousness of the volcanic activity and the brecciation the distribution and petrologic characteristics of the basalts combined with the orientation of the extensional features observed in the field allow a paleotectonic reconstruction this tectonic scenario can be viewed as a back arc extension an eastward prolongation of the spreading that divided southern france from the sardinia corsica calabria block generating the ligurian balearic basin in the late oligocene

multistage hydrothermal dolomites in the middle devonian givetian carbonates from the guilin area south china pervasive dolomites occur preferentially in the stromatoporoid biostromal or reefal facies in the basal devonian givetian carbonate rocks in the guilin area south china the amount of dolomites however decreases sharply in the overlying frasnian carbonate rocks dolostones are dominated by replacement dolomites with minor dolomite cements replacement dolomites include 1 fine to medium planar e floating dolomite rhombs rd1 2 medium to coarse planar s patchy mosaic dolomites rd2 and 3 medium to very coarse nonplanar anhedral mosaic dolomites rd3 they post date early submarine cements and overlap with stylolites two types of dolomite cements were identified planar coarse euhedral dolomite cements cd1 and non planar saddle dolomite cements cd2 they post date replacement dolomites and predate late stage calcite cements that line mouldic vugs and fractures the replacementdolomiteshaved 18 ovalues from 13ae7to 9ae7 vpdb d 13 cvalues from 2ae 7t o 1 ae5 vpdb and 87 sr 86 sr ratios from 0ae7082 to 0ae7114 fluid inclusiondataofrd3dolomitesyieldhomogenizationtemperatures th of136 149 c and salinities of 7ae2 11ae2 wt nacl equivalent these data suggest that the replacive dolomitization could have occurred from slightly modified sea water and or saline basinal fluids at relatively high temperatures probably relatedtohydrothermalactivitiesduringthelatestgivetian middlefammenian and early carboniferous times compared with replacement dolomites cd2 cements yield lowerd 18 o values 14ae2to 9ae3 vpdb lowerd 13 c values 3ae0 to 0ae7 vpdb higher 87 sr 86 sr ratios 0ae7100 and higher th values 171 209 c whichcorrespondtotrappingtemperatures tr between260and300 c after pressure corrections these data suggest that the dolomite cements precipitated from higher temperature hydrothermal fluids derived from underlying siliciclastic deposits and were associated with more intense hydrothermal events during permian early triassic time when the host dolostones were deeply buried the petrographic similarities between some replacement dolomites and cd2 dolomite cements and the partial overlap in 87 sr 86 sr and d 18 o values suggest neomorphism of early formed replacement dolomites that were exposed to later dolomitizing fluids however the dolomitization was finally stopped through invasion of meteoric water as a result of basin uplift induced by the indosinian orogeny from the early middle triassic as indicated by the decrease in salinities in the dolomite cements in veins 5ae1 0ae4 wt nacl equivalent calcite cements generally yield the lowest d 18 ovalues 18ae5to 14ae3 vpdb variabled 13 cvalues 11ae3to 1ae2 vpdb andhighthvalues 145 170 c andlowsalinities 0 0ae2wt naclequivalent indicating an origin of high temperature dilute fluids recharged by meteoric water in the course of basin uplift during the indosinian orogeny faults were

dolomite characteristics and diagenetic model of the calcari grigi group asiago plateau southern alps italy an example of multiphase dolomitization a multidisciplinary study conducted over the carbonate platform deposits of the liassic calcari grigi group southern alps highlighted how the use of outcrop analogues can contribute to better define the distribution of dolomitic bodies related to fault networks to characterize the petrophysical properties of the dolomitic sequence and unravel a complex diagenetic history this study was carried out in the asiago plateau southernmost part of the eastern southern alps northern italy which provides excellent outcrops of the jurassic calcari grigi group the dolomitization of the jurassic sequence is variable in terms of stratigraphic extension and geographic distribution in the studied localities the dolomitization is generally limited to the mount zugna formation and is characterized by an undulatory front with sub vertical dolomitic chimneys along the major faults within this unit and often associated with faults stacked high porosity and permeability bed parallel dolomitic bodies are developed that show excellent petrophysical properties the dolomitic intervals are characterized by pervasive unimodal and patchy polymodal dolomite crystals thin section cathodoluminescence isotopic and fluid inclusion analyses were used to constrain the paragenetic evolution of the sequence which is similar in all the studied localities the first dolomitization stage is marked by zoned dolomite crystals with a dull luminescent core the porosity is thought to have increased after this stage with dark blue luminescent dolomite accompanied by the corrosion of older crystals the appearance of saddle dolomite marks the onset of the porosity reduction stage ending with the infilling of vugs and the remaining open pores with calcite cement the diagenetic evolution locally stopped at the saddle dolomite stage with the complete occlusion of the remaining pores paragenetic and fluid inclusion data suggest an evolutionary trend of increasing temperatures and decreasing salinity toward brackish fluids responsible for dolomite and calcite precipitation the integration of the available data seem to indicate that the diagenetic evolution of the study area is related to i the interplay between evolving fluids from marine to brackish ii the burial of the sequence increasing temperature and iii the evolution of the hydrogeological system fault and fracture network fluid mixing this complex paragenetic evolution is strongly linked to the evolution of the porosity framework that evolved from a good widespread network in the early stages of the burial history to a confined system in the later stages due to reduction of porosity by the deposition of late calcite and dolomite cements

structurally controlled hydrothermal dolomite reservoir facies an overview structurally controlled hydrothermal dolomite htd reservoir facies and associated productive leached limestones are major hydrocarbon producers in north america and are receiving increased exploration attention globally they include multiple trends in the ordovician locally silurian and devonian of the michigan appalachian and other basins of eastern canada and the united states and in the devonian and mississippian of the western canada sedimentary basin they also occur in jurassic hosts along rifted atlantic margins in the jurassic cretaceous of the arabian gulf region and elsewhere hydrothermal dolomitization is defined as dolomitization occurring under burial conditions commonly at shallow depths by fluids typically very saline with temperature and pressure t and p higher than the ambient t and p of the host formation the latter commonly is limestone proof of a hydrothermal origin for htd reservoir facies requires integration of burial thermal history plots fluid inclusion temperature data and constraints on timing of emplacement hydrothermal dolomite reservoir facies are part of a spectrum of hydrothermal mineral deposits that include sedimentary exhalative lead zinc ore bodies and htd hosted mississippi valley type sulfide deposits all three hydrothermal deposits show a strong structural control by extensional and or strike slip wrench faults with fluid flow typically focused at transtensional and dilational structural sites and in the hanging wall transtensional sags above negative flower structures on wrench faults are favored drilling sites for htd reservoir facies saddle dolomite in both replacive and void filling modes is characteristic of htd facies for many reservoirs matrix replacive dolomite and saddle dolomite appear to have formed near contemporaneously and from the same fluid and temperature conditions the original host facies exerts a major influence on the lateral extent of dolomitization resultant textures pore type and pore volume breccias zebra fabrics shear microfractures and other rock characteristics record short term shear stress and pore fluid pressure transients particularly proximal to active faults high temperature hydrothermal pulses may alter kerogen in host limestones a process designated forced maturation basement highs underlying sandstone and or carbonate aquifers probably overpressured and overlying and internal shale seals and aquitards also may constrain or influence htd emplacement although many questions and uncertainties remain particularly in terms of mg and brine source and mass balance recognition and active exploration of the htd play continues to expand increasing use of three dimensional seismic imagery and seismic anomaly mapping combined with horizontal drilling oblique to linear trends defined by structural sags helps to reduce risk