characterization of dolomitic rocks from the coastal mixing zone of the floridan aquifer florida u s a abstract petrographic xrd sem cathodoluminescence and microprobe analyses were conducted to characterize dolomitic strata from a core penetrating the coastal mixing zone of the floridan aquifer lithologic geochemical and water chemistry data were used to identify diagenetic trends including modern water rock interaction the depositional environment of these middle eocene carbonate sediments of the avon park formation was intertidal to supratidal sabkha conditions caused penecontemporaneous deposition of evaporites and accessory minerals present water chemistry indicates undersaturation for gypsum and its survival is attributed to sluggish groundwater circulation dolomite crystals were commonly found to be compositionally zoned with crystal centers generally calcium rich and less stable than the more stoichiometric crystal rims three stages of dissolution were recognized from sem studies of these crystals 1 initial development of dissolution pits 2 partial dissolution of the unstable crystal center and 3 complete dissolution of the unstable crystal center leaving hollow dolomite present day mixing zone water is saturated with respect to stoichiometric dolomite near stoichiometric dolomite cement may be filling pores in this zone and non stoichiometric dolomite may be dissolving the instability of calcian dolomite in the mixing zone may be related to compositionally modulated crystal lattice defects pervasive dissolved crystal centers in the saline zone are believed to have been highly disordered penecontemporaneous dolomite stoichiometric dolomite does not appear to be precipitating in this zone because of the presence of competing ions stable carbon and oxygen isotopic values for dolomite are comparable to those reported for plio pleistocene dolomites 14 c activity implies some relatively young dolomite exists probably as rims on older crystals

supratidal evaporitic dolomite at ojo de liebre lagoon mineralogical and isotopic arguments for primary crystallization abstract this pair deals with a new site of dolomite formation in supratidal evaporite flats at the southernmost edge of the ojo de liebre evaporitic complex baja california mexico the sedimentary context is mostly siliciclastic except for calcareous outcrops around the flats both chemical and isotopic data on the interstitial solutions demonstrate a mixing between mg2 rich marine derived brines and calcium bicarbonate bearing continental waters which are subjected to concentration by capillary evaporation the lack of any in situ solid caco3 in the sedimentary matrix argues for direct crystallization of dolomite from aqueous solutions this is documented by the oxygen isotope compositions of the dolomite which are consistent with deposition under equilibrium conditions of ambient temperature and 18o of water of the interstitial solutions furthermore the low 13c values of the dolomites and the absence of living plants or organisms in the basin indicate that a fraction of the total dissolved inorganic carbon reservoir is biogenic and is mostly provided by continental groundwaters therefore crystallization of dolomite occurs within the sands infiltrated by solutions whose state of saturation relative to dolomite is mainly governed by the chemistry of continental groundwaters mixing with the inflowing marine brines

mesozoic extension controlling the southern alps thrust front geometry under the po plain italy insights from sandbox models in the southern alps fold and thrust belt east west mesozoic rifting controlled the development of extensional faults the deposition of the sedimentary sequences and the thickness and distribution of the main detachment levels vertical and lateral heterogeneities strongly influenced the structural style of the subsequent north south contractional phase as revealed by surface mapping and by subsurface maps derived from seismic data along the strike of the chain lateral terminations of thrust faults occur at syn rift extensional faults trending normal with respect to the contractional structures from west to east the thrust sheet number decreases and the order of structures and their wavelength changes on a regional scale the effects produced by pre existing heterogeneities on the development of contractional alpine tectonic structures in the external area of the southern alps were evaluated by means of scaled sandbox analogue models modelled lateral heterogeneities produced different wavelength thrust sheets salients and recesses whereas vertical heterogeneities facilitated the development of structures of different orders first order structures detached at the base of the model and second order structures detached at the intermediate relatively weak layers comparison of analogue model results with nature showed good geometrical similarities 2006 elsevier ltd all rights reserved

permian to early triassic magnetostratigraphy from the central european basin in poland implications on regional and worldwide correlations abstract permian early triassic rocks sampled in 15 outcrops 93 hand samples and 11 unoriented boreholes 630 hand samples from the polish part of the central european basin were studied paleomagnetically in spite of extensive remagnetization affecting 50 of samples from the boreholes a magnetic polarity sequence was compiled the polarity pattern is not only common for many sections from the investigated area but also convergent with the global synthetic magnetostratigraphic scale the lower rotliegend early permian rocks contain a reversed polarity record while the upper rotliegend late permian early triassic sediments are characterized by mixed polarity magnetization within the buntsandstein part of that mixed megazone 14 magnetic zones were found buntsandstein sedimentation started with a normal polarity zone which may be compared with that of early griesbachian defined in several places in the world the polarity record noted in the middle buntsandstein sediments could indicate significant stratigraphic gaps or condensations near the middle buntsandstein and rot boundary the comparison of the upper buntsandstein polarity with the early middle triassic magnetostratigraphic data from other basins suggests that the majority or even all the rot sediments should be included in the anisian

chemistry and environments of dolomitization a reappraisal abstract dolomitization of calcium carbonate can best be expressed by mass transfer reactions that allow for volume gain preservation or loss during the replacement process experimental data as well as textures and porosities of natural dolomites indicate that these reactions must include co 3 2 and or hco 3 supplied by the solution to the reaction site since dolomite formation is thermodynamically favoured in solutions of a low ca 2 mg 2 ratios b low ca 2 co 3 2 or ca 2 hco 3 ratios and c high temperatures the thermodynamic stability for the system calcite dolomite water is best represented in a diagram with these three parameters as axes kinetic considerations favour dolomitization under the same conditions and additionally at low as well as at high salinities if thermodynamic and kinetic considerations are combined the following conditions and environments are considered chemically conducive to dolomitization 1 environments of any salinity above thermodynamic and kinetic saturation with respect to dolomite i e freshwater seawater mixing zones normal saline to hypersaline subtidal environments hypersaline supratidal environments schizohaline environments 2 alkaline environments i e those under the influence of bacterial reduction and or fermentation processes or with high input of alkaline continental groundwaters and 3 many environments with temperatures greater than about 50 c subsurface and hydrothermal environments whether or not massive replacive dolostones are formed in these environments depends on a sufficient supply of magnesium and thus on hydrologic parameters most massive dolostones particularly those consisting of shallowing upward cycles and capped by regional unconformities have been interpreted to be formed according to either the freshwater seawater mixing model or the sabkha with reflux model however close examination of natural mixing zones and exposed evaporitic environments reveals that the amounts of dolomite formed are small and texturally different from the massive replacive dolostones commonly inferred to have been formed in these environments many shallowing upward sequences are devoid of dolomite it is therefore suggested that massive replacive dolomitization during exposure is rare if not impossible rather only small quantities of dolomite cement or replacement are formed which may act as nuclei for later subsurface dolomitization alternatively large scale dolomitization may take place in shallow subtidal environments of moderate to strong hypersalinity the integration of stratigraphic petrographic geochemical and hydrological parameters suggests that the only environments capable of forming massive replacive dolostones on a large scale are shallow hypersaline subtidal environments and certain subsurface environments

dolomitization a critical view of some current views the principal models in vogue today for dolomitization are the mixing zone and the sabkha models despite the wide acceptance of these models there has been little critical assessment of their validity such an assessment is the objective of the present paper a close look at the dorag mixing zone model badiozamani 1973 reveals several serious weaknesses 1 the range of freshwater seawater mixtures that meet the dorag requirement for dolomitization shrinks to a small window if the geologically more realistic disordered dolomite is used in the calculations instead of the ordered dolomite on which the model is based 2 in none of the known modern coastal mixing zones in limestone or lime sediments has replacement by dolomite been observed 3 in a number of dolomites interpreted to be of mixing zone origin dolomite has precipitated without dissolution of the calcite substrate evidence that negates the fundamental premise of the dorag model in addition to these weaknesses isotope and trace element data used to identify mixed water dolomite are inadmissible because 1 isotopic fractionation factors for dolomites remain unresolved 2 isotope values uncorrected for temperature for a host of dolomites interpreted to be of different origins overlap 3 nonisomorphous trace elements such as na in dolomite cannot on theoretical grounds be relied on to identify dolomitizing fluids similar overall objections can be brought against folk and land9s 1975 schizohaline version of mixing zone dolomitization in summary mixing zone models have such weak underpinnings that they should be questioned as viable explanations for massive dolomitization contemporaneous dolomite formation in modern sabkhas is well documented but the important question of whether the mechanism of dolomite formation is replacement or direct precipitation remains to be resolved in the well studied sabkha at abu dhabi brine chemistry changes have been used as evidence of a replacement origin for the dolomite but it is shown here that this evidence is far from unequivocal an alternative origin of direct precipitation of dolomite is offered an origin in keeping with dolomite precipitation known from other modern sabkhas and saline lakes and in line with our laboratory experience with dolomite synthesis moreover it is suggested here that in general contemporaneous dolomite will form at low temperatures only by direct precipitation a mechanism that requires special conditions of highly super saturated waters of high mg ca ratio and elevated co 3 hco 3 concentrations this may explain why modern dolomite is mainly restricted to evaporitic environments a bias not shared by ancient dolomites in contrast replacement dolomite appears to require at low temperatures long reaction times or 10 4 yr a requirement that is mainly to be met in large regional groundwater flow systems both marine and nonmarine a third dolomitization model considered here is that of baker and kastner 1981 based on the experimental finding that sulfate ions inhibit or retard dolomitization a number of modern sedimentary dolomites are not in accord with this model in that they are forming from brines with large sulfate concentrations 2 to 70 times that of seawater thus the baker kastner model should be held in abeyance until these serious contradictions are resolved the current emphasis on mixing zone and sabkha dolomitization has diverted attention from other promising avenues of approach to the dolomite problem four of these avenues each of which deemphasizes the special water approach are briefly addressed and are as follows 1 influence of temperature and time 2 mass transfer processes 3 burial diagenesis of epigenetic dolomites 4 fluid inclusion studies at elevated temperatures the dolomite problem essentially disappears ordered dolomite can be made in the laboratory in days at 100 degrees c what is more at temperatures above 60 degrees c ca rich waters become dolomitizing fluids which makes most natural subsurface waters capable of dolomitization at low temperatures time may be the key element so that seawater will become a major dolomitizing fluid only where stable circulation systems such as kohout convention can drive seawater through carbonate platforms for many thousands to millions of years this paper has tried to show that currently favored models of dolomitization carry serious uncertainties enough to warn us to look more critically at the validity of these models and also it is hoped enough to spur new efforts to find new solutions to the problems of dolomitization

thermal convection dolomitization induced by the emeishan large igneous province abstract the mechanism of dolomitization has long been debated due to complex sedimentary and diagenetic conditions large scale dolomite bodies were recently discovered in the permian cisuralian qixia formation 284 273 ma in the northwestern sichuan basin providing an opportunity to understand the dolomitization associated with the emeishan large igneous province elip traditionally the dolomites in the sichuan basin have been interpreted as hydrothermal dolomitization because of the hydrothermal impacts from the elip here we report new petrographic and geochemical data on the permian dolomites which we grouped into two categories matrix dolomites or md1 md3 and cement dolomites or cd that support thermal convection dolomitization the petrographic and geochemical features 13c 18o ree mn sr ratios 87sr 86sr ratios suggest that md1 were formed in penecontemporaneous seawater whereas md2 md3 and cd were formed in fluids resembling permian seawater during shallow burial stage of which both dolomitizing fluids are non hydrothermal high formation temperature inferred from fluid inclusion is consistent with the low 18o values of the md2 md3 and cd suggesting that the elip event may have provided the heat for the dolomitization in the qixia carbonate platform the formation of the widespread dolomite bodies was facilitated by the rapid convection exchange between warm pore seawater in the qixia strata of the platform margin and cold water from outside the slope therefore we demonstrate that the dolomites in the northwestern sichuan basin are mainly due to thermal convection dolomitization in the shallow burial stage this study provides important implications for the mechanism of dolomite formation linked to abnormal geothermal activity

central zagros fold thrust belt iran new insights from seismic data field observation and sandbox modeling 1 we present five generalized cross sections across the central zagros fold and thrust belt iran these sections show that the fold geometry varies significantly both horizontally and vertically the style is closely related to the changes in the mechanical behavior of the lithostratigraphic horizons and in particular to the presence of intermediate decollements within the sedimentary pile restoration of the sections shows amounts of shortening of the same order from one section to the other however it appears to be unequally distributed suggesting variations in basal decollement shear strength analogue modeling has been performed to systematically investigate the effect of an intermediate decollement level at different depths on the style of folding the models demonstrate that the position of intermediate decollements is an important factor controlling both structural style and fold wavelength models with shallow intermediate decollement show regularly and widely spaced anticlines in these models the fold wavelength depends directly on the thickness of the dominant competent layer and short wavelength superficial structures mask broad anticlines at depth models with deep intermediate decollement are characterized by the rapid propagation of deformation with small rate of shortening along this decollement influencing localization of forthcoming anticlines in the upper levels such propagation favors the development of duplexes and multiwavelength folds on this basis fold kinematics in central zagros is discussed using the variation of structural style along different folds as an indicator of the sequence of deformation detachment folding is the main folding style at least for the initial stages of deformation and thrust faults developed only at later stages some of these faults branched on decollement levels express the progression of folding whereas others are linked to late basement faults cutting through early structures in general the decollement levels are activated sequentially from deeper horizons to shallower ones however in one case gachsaran decollement a shallow decollement is activated during the early stages of folding and then abandoned during the subsequent evolution

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

carbonates in upper permian evaporites of the northern calcareous alps austria thin black dolomites occur within the evaporitic alpine haselgebirge formation late permian of the central and eastern northern calcareous alps austria they have been compared with the southalpine bellerophon formation bytollmann 1964 samples obtained from the gypsum anhydrite deposit of wienern am grundlsee styria are mostly unfossiliferous mudstones dolomicrite and dolomicrospar devoid of sedimentary structures only few samples contain a low diversity ostracode fauna electron microprobe and x ray diffraction analysis indicate well ordered and near stoichiometric dolomite 49 9 0 2 mol caco3 the oxygen isotopic composition varies between 3 0 and 5 7 pdb the 13c ratios fall into two distinct groups 0 9 to 1 9 and 3 5 to 6 8 pdb the carbon isotope data of the first group indicate a predominantly marine origin of the carbonates the significantly depleted 13c ratios of the second group are probably due to freshwater influx into the basin and or sulfate reduction sulfur and strontium isotope data from intercalated anhydrite and gypsum preclude an entirely non marine origin of the brines the light 18o ratios are probably due to early diagenetic sulfate reduction and or dolomite recrystallization during moderate burial a detailed interpretation of the depositional environment is rendered impossible because of the pervasive alpine tectonics however northalpine bellerophon carbonates appear to be restricted to areas of major anhydrite deposition and are absent in the halitedominated facies

thrust fault mechanics and origin of a frontal ramp several features of thrust sheets in nonmetamorphic and relatively low grade metamorphic terrains indicate that the modes of faulting included both gradual and stick slip types of motion a first order quantitative analysis is made of the mechanics of this type of faulting in the analysis part of a wedge shaped thrust belt slips forward over a fault area of length l and unit width w producing a strain concentration in subhorizontal strata at the front of the growing thrust where a frontal ramp develops by shear fracturing equations for net slip x and the conditions for ramping are evaluated with limit equilibrium principles and coupled oscillator theory the quantitative analysis takes into account anisotropy resulting from contrasts in competency and facies changes a special case solution for maximum net slip associated with stick slip is lw ki 1 cos ot o 12 1 cos 1t where is the stress drop ki are spring constants of the strata 0 and 1 are natural frequencies of the system and t evaluated from another equation is the time for net slip the spring constants and natural frequencies can be evaluated from seismic and stratigraphic data a preliminary solution for piggy back thrusting indicates that ramp spacing can be systematic and that it depends upon the thickness of the deforming package the elastic parameters of the deforming package the slope of the topographic surface and the stresses along the trailing edge of the package

stable isotope mapping in messinian evaporative carbonates of central sicily mapping stable isotope isolines in both modern and ancient evaporative carbonate formations demonstrates that regional variations of 18 o values exist in the case of the messinian central sicilian basin an ancient evaporite basin the distribution pattern of the 18 o isolines can be related to the paleogeometry and paleohydrology of the basin isolines of equal 13 c values also show large regional variations possibly reflecting the domination of different bacterial processes oxidation sulfate reduction or methanogenesis in different regions the potential application for stable isotope mapping in evaporative carbonate formations deposited in both marine and lacustrine environments lies in its ability to predict the location of depositional centers in ancient evaporite basins

a possible explanation for foreland thrust propagation a common feature of thin skinned fold and thrust belts is the sequential nature of foreland directed thrust systems as a rule younger thrusts develop in the footwalls of older thrusts the whole sequence propagating towards the foreland in the transport direction as each new younger thrust develops the entire sequence is thickened particularly in the frontal region the compressive toe region can be likened to an advancing wave as the mountainous thrust belt advanced the down surface slope stresses drive thrusts ahead of it much like a surfboard rider in an attempt to investigate the stresses in the frontal regions of thrustsheets a numerical method has been devised from the algorithm given by mctigue and mei 1981 the algorithm yields a quickly computed approximate solution of the gravity and tectonic induced stresses of a two dimensional homogeneous elastic half space with an arbitrarily shaped free surface of small slope a comparison of the numerical method with analytical examples shows excellent agreement the numerical method was devised because it greatly facilitates the stress calculations and frees one from using the restrictive simple topographic profiles necessary to obtain an analytical solution the numerical version of the mctigue and mei algorithm shows that there is a region of increased maximum resolved shear stress directly beneath the toe of the overthrust sheet utilizing the mohr coulomb failure criterion predicted fault lines are computed it is shown that they flatten and become horizontal in some portions of this zone of increased thrust sheets are known to advance upon weak decollement zones if there is a coincidence of increased a weak rock layer and a potential fault line parallel to this weak layer we have in place all the elements necessary to initiate a new thrusting event that is this combination acts as a nucleating center to initiate a new thrusting event therefore thrusts develop in sequence towards the foreland as a consequence of the stress concentrating abilities of the toe of the thrust sheet the gravity and tectonic induced stresses due to the surface topography usually ignored in previous analyses of an advancing thrust sheet play a key role in the nature of shallow foreland thrust propagation

crustal scale structural architecture in central chile based on seismicity and surface geology implications for andean mountain building 1 we document a crustal scale structural model for the central chile andes based on seismicity and surface geology which consists in a major east verging ramp detachment structure connecting the subduction zone with the cordillera the ramp rises from the subducting slab at 60 km depth to 15 20 km below the western edge of the cordillera extending eastward as a 10 km depth flat detachment this structure plays a fundamental role in the andean orogenesis because most of the shortening has been accommodated by structures rooted in it and allows the distribution of crustal thickening in a simple shear deformation mode indeed despite shortening distribution being very asymmetric 16 km versus 70 km in the western and eastern side respectively the western side is higher and thicker than what is expected yield strength envelopes show strong rheological control on this structure vp and vp vs variations in the upper mantle and in the deepest limit of the seismogenic interplate contact mark the intersection of the ramp with the slab which coincides with the blueschist eclogite transition therefore subduction processes would control the depth where the major east verging structure may merge with the slab such a ramp flat structure is observed in other parts of the chilean margin hence it seems to be a first order feature in the andean subduction zone this structure delimitates upward the rocks transmitting part of the plate convergence stress from the plate interface and controls mountain building tectonics thus playing a key role in the andean orogeny

regional setting and role of meteoric water in dolomite formation and diagenesis in an evaporite basin studies in the zechstein permian deposits of poland the zechstein basin of poland was an area of widespread cyclical deposition of carbonates and evaporites during late permian time the zechstein shelves along both the northern and the southern margins of the basin were sites of shallow water sedimentation during the formation of the main dolomite and platy dolomite two widespread carbonate units these units consist of oolitic peloidal skeletal micritic and evaporitic carbonates formed in depositional settings ranging from open marine to coastal lagoonal sabkha and salina although originally deposited as limestones the main dolomite and platy dolomite are inferred to have been completely replaced by dolomite through very early stage essentially penecontemporaneous reflux of hypersaline brines the dolomites of the two basin margins however have very different petrographic and isotopic characteristics many northern shelf dolomites show early stage calcitization dedolomitization and even in some cases evidence of a subsequent redolomitization event these northern shelf samples also have a broad range of carbon and oxygen isotopic ratios up to 12 0 for oxygen samples from the southern shelf on the other hand are petrographically much simpler they do not show complex calcitization and redolomitization patterns likewise their isotopic values are much more tightly clustered with only about a 5 0 range of oxygen isotopic ratios the differences between dolomites of the same age from the northern and southern margins are best explained by regional variations in river water influx during episodic exposure events associated with regional or global sea level fluctuations the distribution of clastic terrigenous materials and palaeokarstic features indicate that areas of the northern shelf had extensive river input an influx largely lacking on the southern shelf early formed dolomites appear to have been calcitized during sea level lowstands through the infiltration of meteoric fluids into the evaporitic dolomites created during the previous highstand in some cases redolomitization occurred when meteoric fluids were again replaced by hypersaline brines during subsequent sea level highstands although repeated sea level fluctuations are clearly evident in these strata it is likely that associated climatic changes rainfall variations also played a role in forming these complex diagenetic patterns age equivalent strata from texas and new mexico from sites at much lower palaeolatitudes show no such alteration patterns samples from greenland slightly higher palaeolatitudes show even more intense diagenetic alteration during depositional cycles thus the examination of patterns of diagenesis may be useful in interpreting ancient palaeolatitudinally sensitive climate patterns

higher himalayan shear zone sutlej section structural geology and extrusion mechanism by various combinations of simple shear pure shear and channel flow in shifting modes the higher himalayan shear zone hhsz in the sutlej section reveals 1 top to sw ductile shearing 2 top to ne ductile shearing in the upper and the lower strands of the south tibetan detachment system stdsu stdsl and 3 top to sw brittle shearing corroborated by trapezoid shaped minerals in micro scale in the proposed extrusion model of the hhsz the e1 phase during 25 19 ma is marked by simple shearing of the upper sub channel defined by the upper strand of the main central thrust mctu and the top of stdsu as the lower and the upper boundaries respectively subsequently the e2a pulse during 15 14 ma was characterized by simple shear pure shear and channel flow of the entire hhsz finally the e2b pulse during 14 12 ma observed simple shearing and channel flow of the lower sub channel defined by the lower strand of the main central thrust mctl and the top of the stdsl as the lower and the upper boundaries respectively the model explains the constraints of thicknesses of the stdsu and the stdsl along with spatially variable extrusion rate and the inverted metamorphism of the hhsz the model predicts 1 shear strain after ductile extrusion to be maximum at the boundaries of the hhsz which crudely matches with the existing data the other speculations that cannot be checked are 2 uniform shear strain from the mctu to the top of the hhsz in the e1 phase 3 fastest rates of extrusion of the lower boundaries of the stdsu and the stdsl during the e2a and e2b pulses respectively and 4 variable thickness of the stdsl and rare absence of the stdsu non parabolic shear fabrics of the hhsz possibly indicate heterogeneous strain the top to sw brittle shearing around 12 ma augmented the ductile extruded rocks to arrive a shallower depth the brittle ductile extension leading to boudinage possibly did not enhance the extrusion

the carbon isotope record of dolostones as a stratigraphic tool a case study from the upper cretaceous shelf sequence israel abstract accumulation of evidence on past global changes in carbon isotopes in marine carbonate rocks points to the usefulness of the carbon isotope record as a stratigraphic tool this method will be important in sections with a poor representation of indicative fauna such as dolostones isotope analyses of dolostone sequences from the upper cenomanian turonian sequence of israel suggest that on the average a depletion of 1 1 in 13c ratio can be detected across the boundary the israeli trend agrees with the 13c record across this boundary reported from sections with detailed biostratigraphic records

higher himalayan shear zone zanskar indian himalaya microstructural studies and extrusion mechanism by a combination of simple shear and channel flow thin section studies of the zanskar shear zone zsz rocks reveal a top to sw and subsequent primary and secondary top to ne ductile shearing brittle ductile and brittle extensions top to sw brittle shear steep normal faulting and fracturing in the proposed two phase model of ductile extrusion of the higher himalayan shear zone hhsz a top to sw simple shearing during 22 18 ma was followed by a combination of top to sw simple shear and channel flow at 18 16 ma the second phase simulates a thin zsz characterized by a top to ne shearing the channel flow component ceased around 16 ma the extruding hhsz entered the brittle regime but the top to sw shearing continued until perturbed by faults and fractures variation in the extrusion parameters led to variable thickness of the zsz shear strain after the extrusion is presumably maximum at the boundaries of the hhsz and falls towards the base of the zsz which crudely matches with the existing data the other predictions 1 spatially uniform shear strain after the first stage 2 fastest extrusion rate at the base of the zsz and 3 a lack of continuation of the zsz along the himalayan trend are not possible to validate due to paucity of suitable data non parabolic shear fabrics of the zsz indicate their heterogeneous deformation

selected geochemical factors influencing diagenesis of eocene carbonate rocks peninsular florida u s a abstract the geochemical significance of three selected ions mg2 na and sr2 supports a model of dolomitization by brackish groundwater this groundwater zone contains sufficient quantities of mg2 to facilitate dolomitization mg ca ratios 1 rising and falling of sea level and fluctuations of the phreatic zone related to climatic variations account for the thickness of the dolomite layers and the chemical distributions within these layers sodium concentrations in the calcite are 70 185 ppm indicating formation in brackish water dolomite has sodium concentrations between 50 1400 ppm suggesting formation in waters of similar salinity strontium in calcite ranges from 320 600 ppm suggesting diagenesis in slightly saline waters in an open system dolomite contains 241 ppm sr2 on the average and calcite has 418 ppm sr2 the sr2 concentrations of the dolomite are characteristic of diagenesis in water less saline than sea water average strontium concentrations in the dolomite occur in two distinct groups 260 ppm for dolomite with 39 43 mole mgco3 and 195 ppm for the dolomite with 44 50 mole mgco3 the difference in the sr2 concentrations of the two dolomite groups indicates the higher mole mgco3 dolomite recrystallized in a less saline environment than the lower mole mgco3 dolomite these different environments are attributed to a relatively more saline coastal environment and a less saline inland environment the more nearly stoichiometric dolomite 44 50 mole mgco3 has less scatter when mole mgco3 is plotted against sr2 and na this suggests a greater approach to equilibrium with the dolomitizing fluid than the lower mole mgco3 39 43 dolomite the more saline environment has higher mg ca ratios and promotes more calcium rich dolomite during diagenesis because of the inhibition from competing foreign ions and because it is thermodynamically a more favorable environment which causes more rapid crystallization the less saline waters allow recrystallization to proceed more slowly producing better ordering in the dolomites textural preservation and development of subhedral to euhedral rhombic crystals

ultra high resolution multivariate record and multiscale causal analysis of pridoli late silurian implications for global stratigraphy turnover events and climate biota interactions abstract the upper silurian and especially pridoli epoch is a critical interval for the understanding the evolution of earth s biota since it witnessed series of powerful extinction events global reorganizations of paleocommunities and expansion of new clades which assumed dominance in the subsequent devonian period the stratigraphic record of the eastern part of the silurian baltic basin represents an excellent candidate for the fine scale analysis of paleoecological and paleoceanographic dynamics therefore we presenting here stratigraphic record of the milaiciai 103 core south western lithuania of conodonts brachiopods 13ccarb 18ocarb and a series of various geochemical and geophysical proxies most of which were sampled at a very high resolution 11 ka spanning uppermost ludlow pridoli and the lowermost devonian the analysis revealed that the pridoli was characterized by four distinct long term dynamic states here named i normal pridoli i ii silal negative carbon isotopic excursion and extinction event iii normal pridoli ii and iv klonk positive stable carbon isotopic event and excursion the most significant change in most variables is detected approximately in the middle of the pridoli at the beginning of the delotaxis detorta zone at the recovery after silal event of conodonts and at the onset of collapse of brachiopod communities the analysis of dynamic complexity revealed the strong evidence for the presence of 405 ka metronome milankovitch cycles in the record of 13ccarb which constrains the duration of the pridoli epoch to 4 3 0 2 ma the recurrence plot analyses revealed deterministic coordination between 13ccarband conodont paleocommunity dynamics at all scales finally lead lag analysis using conditional joint recurrence revealed that conodont dynamics as a rule were driven by perturbations in the carbon cycle although silal event interval shown opposite pattern thus confirming the unusual nature of this previously unrecognized coordinated climatic and biotic event

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

carbonate sedimentation and diagenesis associated with mg ca chloride brines the permian san andres formation in the texas panhandle abstract the san andres evaporitic sequence in the palo duro basin includes several thick carbonate units in its lower part and many thin units in its upper part evaporites are concentrated in the northern part of the northern shelf of the midland basin and carbonates predominate to the south within the palo duro basin the carbonates in the lower part of the sequence differ from those in the upper part in containing skeletal lithofacies and in having lower mn fe and terrestrial organic content the br content in halite in the lower part of the sequence is consistently high whereas halite in the upper part is commonly br depleted the sr content in dolomite calcite and anhydrite and 18o values are about the same in the en ire san andres sequence in the palo duro basin depleted 13c values in dolomite and low pristane phytane ratios occur toward the south na cl and k cl ratios attributed to liquid inclusions in almost all carbonates are characteristic of marine brines evaporated beyond halite saturation na in the dolomite lattice is generally low and increases from north to south at the same stratigraphic levels the lower part of the formation was deposited in a broad shelf basin or lagoon sufficiently deep to maintain long periods of steady state circulation during which little halite dissolution and no potash magnesia mineral precipitation occurred the upper part of the formation was deposited in smaller water bodies sensitive to fluctuations in inflow of marine water as well as meteoric water diagenesis of the carbonates occurred in contact with saline mg ca chloride brines evolved through anhydrite and halite precipitation skeletal mold formation anhydrite cementation dolomitization and high sr calcite cementation associated with celestite are all cogenetic products of such a brine rock interaction 18o of dolomite calcite and chert indicates apparent equilibrium relationships with the same solution temperatures have never exceeded 40 to 45 c and imply the 18o of such a solution to be about 3 the somewhat depleted 18 up o composition of the proposed halite saturated brine resulted from the reversal in the dependence of 18o on increased evaporation in highly saline brines the proposed diagenetic model implies that following early diagenetic processes the rock sequence remained as a closed but compacting system unchanged by later fluid introduction low sr values in dolomite are indicative of recrystallization and not fresh water diagenesis

classification and description of dolomitic fabrics of rocks from the floridan aquifer u s a abstract biozones of the lake city formation avon park formation and ocala limestone are characterized by interbedded massive fossiliferous carbonate rocks wackestones to grainstones and thinly bedded peloidal and carbonaceous rocks mudstones and wackestones several horizons have been partly or completely dolomitized a wide range of early to late stages of dolomitic fabrics are recognized the fabrics are classified descriptively as equigranular unimodal or inequigranular multimodal fabrics composed of crystals two processes of dolomitization are suggested a homogeneous dolomitization resulting in a single stage development of microtextured groundmass crystals

dolomitization in a mixing zone of near seawater composition late pleistocene northeastern yucatan peninsula abstract patches of dolomite occur in cores of reefal limestone from the shallow subsurface on the northeastern coast of the yucatan peninsula this limestone accumulated during an interglacial high stand of sea level about 200 000 years ago dolomitization was preceded by freshwater diagenesis including precipitation of sparry calcite cement stabilization of mg calcitic skeletal fragments and partial dissolution of aragonitic components this suggests a predolomitization lowering of sea level with the consequent freshening of pore water the subsequent precipitation of dolomite indicates a return to high sea level with the consequent increase in mg ca ratio of pore water dolomitization took place during a brief high stand of sea level either shortly after deposition about 200 000 yr bp r more likely about 125 000 yr bp dolomite occurs both as microcrystalline replacement dolomite and as cement the cement is part of the following diagenetic sequence 1 limpid euhedral subhedral calcian dolomite crystals 2 zoned dolomite crystals with zones formed by variations of the calcium magnesium ratio in dolomite 3 layers of alternating calcian dolomite and magnesian calcite or calcite and 4 calcite this sequence represents the progressive freshening of ground water during the initial stage of a fall in sea level average cation composition of the limpid dolomite cement is ca57mg43 electron microprobe analysis zoned cement crystals are composed of ca57 59mg43 41 layers and ca62mg38 layers most of the higher calcium dolomite layers are dissolved forming hollow zone crystals in cement with alternating dolomite and calcite zones the calcite is ca99 97mg1 3 low mg calcite and ca96 93mg4 7 mg calcite the dolomite and mg calcite zones are partially to totally leached 18o compositions of yucatecan dolomite and of modern ground water suggest dolomite precipitation from mixed water ranging from about 75 seawater 25 freshwater to nearly all seawater isotope analyses are for the most stable calcian dolomites more soluble calcium rich dolomite presumably is analyzed with calcite and thought to be isotopically lighter than the less soluble dolomite in the cement sequence the most stable dolomite is followed by more soluble dolomite as ground water becomes less saline isotope analyses together with position of dolomite in the cement sequence suggest the most stable calcian dolomite including limpid dolomite precipitated from mixed water with large proportions of seawater and the less stable more calcian dolomite precipitated from fresher mixed water

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

estimating basal friction in accretionary wedges from the geometry and spacing of frontal faults elastic theory applied to the deformation in accretionary wedges is used to calculate the condition for slip along an active frontal fault and the basal decollement the equations for calculating the stresses can be solved for the coefficient of basal friction in the situation of the formation of a new frontal thrust fault this allows us to calculate the efficient coefficient of basal friction which includes the weakening effect of pore fluid pressure from geometric parameters and material properties only the geometric parameters like fault dip and layer thickness can be derived from high resolution seismic cross sections application of our analysis to the makran and the nankai accretionary wedge allows us to estimate the upper limit of the effective coefficient of basal friction wbw0 16 and wbw0 2 in these two areas respectively fl 2001 elsevier science b v all rights reserved

formation of diagenetic dolomite in coastal sabkha along arabian persian gulf aragonitic intertidal sediments are being dolomitized in the subsurface supratidal environment of a sabkha along the south shore of the arabian persian gulf as a result of the percolation of wind driven marine derived brines the development of abundant diagenetic dolomite results from an optimum combination of high mmg mca ratio fluids a rapid flow rate which is related to the flooding frequency and sediment permeability and a shoreline configuration that maintains the proper conditions for a sufficient length of time strongly dolomitized areas are localized along the flanks of remnant channels and in the lee of islands that have been engulfed by the prograding sabkha the dolomitizing process takes about 1 000 to 1 500 years most diagenetic dolomite forms at the expense of primary aragonite according to the reaction mg 2caco3 arag rarr camg co3 2 ca dolomite forms under the following conditions a chloride concentration between 3 25 and 3 75 mcl kg b mmg mca greater than about 6 c ph between 6 3 and 6 9 d minimum pco2 of 10 2 to 10 3 atm e temperature between 25 and 40 c f saturation with respect to gypsum and g reducing environment in association with hydrogen sulfide other recent dolomite occurrences in the bahamas florida and bonaire are significantly different in terms of stratigraphy degree of lithification and evaporite mineral association from those in the arabian gulf

processes affecting interstitial water in the unsaturated zone at the newly exposed shore of the dead sea israel abstract a main process affecting interstitial water and solutes at shallow depths on the newly formed shores of the dead sea ds is evaporation the evaporation rate from the unsaturated zone as calculated based on stable isotope profiles ranges from 0 5 to 36 mm yr 1 the high tritium concentrations 20 40 tu as compared with the main implication of the present study is that the evaporitic sediments can undergo rapid chemical and isotopic changes which later can be found preserved in the sequence thus the isotopic and chemical record of some of the phases found in saline ancient evaporitic sequences may have a freshwater signature

sequence stratigraphy and cyclic development of basal zechstein carbonate evaporite deposits with emphasis on zechstein 2 off platform carbonates upper permian northeast germany abstract although the basal zechstein is classically subdivided into two cycles z1 and z2 lower part it can alternatively be subdivided into three complete third order depositional sequences zs1 zs3 and the associated lowstand systems tract transgressive systems tract of a fourth sequence zs4 third and higher order sea level fluctuations influenced the depositional and diagenetic history of the carbonate evaporite alternations within the basal zechstein the main subject of the present study the zechstein 2 carbonate stassfurt carbonate or ca2 is interpreted to encompass both transgressive predominantly in slope and basinal settings and highstand systems tracts of zechstein sequence zs3 as well as part of the lowstand systems tract of the fourth zechstein sequence zs4 in northeastern germany hydrocarbon reservoirs of the ca2 developed along both northern and southern margins of the southern permian basin on top of the topography of the zechstein 1 cycle z1 this z1 topography resulted from deposition of the werra anhydrite a1 the highstand systems tract of the second zechstein sequence zs2 the northern ca2 carbonate platform is consistently narrow and fringed by coated grain and composite grain bars and shoals it is characterized by a steep fault controlled slope which precluded the formation of in situ shallow water grain dominated carbonates during relative sea level lowstands displaced shallow water coated grain and composite grain packstones wackestones may however occur as slope fan deposits turbidites in contrast the southern carbonate platform is wide tectonically dissected and fringed by grain dominated shallow water carbonates coated grain and composite grain bars and shoals zechstein 2 shallow water carbonates detectable by basal zechstein seismic anomalies also developed on pre existing topographical highs in off platform positions three depositional cycles ca2 cycles i ii and iii most probably reflecting high amplitude fourth order sea level fluctuations can be identified within the stassfurt carbonate our observations suggest that sea level variations possibly reflecting cyclicity in the milankovitch frequency band 0 1 0 4 ma and the pre zechstein topography pronounced during formation of the werra anhydrite were the most important factors in controlling the depositional as well as the diagenetic history of the zechstein 2 carbonate in off platform positions

upper permian carbonates at the northern edge of the zechstein basin utsira high norwegian north sea abstract the first detailed description of zechstein carbonates and their diagenesis along the northern margin of the northern zechstein basin is based on core material from four wells on utsira high in the norwegian sector of the north sea it provides a generic link to the better known southern zechstein basin and northwards to the late permian east greenland basin the zechstein succession consists of shale carbonate cycles and anhydrite only occurs in the uppermost preserved cycle believed to correlate to zechstein 4 the eleven carbonate facies reflect deposition in shallow shelf and arid shoreline environments and resemble zechstein 2 and 3 carbonate facies from the southern zechstein basin the carbonates are pervasively dolomitized by an early texture preserving dolomite characterized by 18o values between 6 and 2 4 similar to dolomites in the southern zechstein basin and 13c values between 0 7 and 5 which is significantly lower than time equivalent dolomites from the southern zechstein basin later subaerial exposure and fresh water infiltration during the late permian or early triassic caused replacement of the upper part of the dolomite by crystalline fabric destructive calcite dedolomite the dedolomitized zone is up to 23 m thick and calcite crystals are characterized by moderately negative 18o values in the range 8 to 5 5 characteristic for meteoric water the utsira high carbonates thus share a depositional history with the classical zechstein carbonates whereas their diagenesis seems to have more in common with the time equivalent succession in east greenland early leaching and dolomitization enhanced porosity whereas subsequent late permian early triassic subaerial exposure and widespread dedolomitization had profound negative impact on reservoir properties of the zechstein carbonates

deformation of accretionary wedges in response to seamount subduction insights from sandbox experiments sandbox experiments using a two dimensional and a three dimensional approach are used to study the deformation of margins in response to seamount subduction successive mechanisms of deformation are activated during the subduction of conical seamounts first reactivation of the frontal thrusts and compaction of the accretionary wedge is observed then back thrusting and conjugate strike slip faulting develops above the leading slope of the subducted seamount the basal d6collement is deflected upward in the wake of the subducting high and a large shadow zone develops behind the seamount trailing slope consequently frontal accretion is inhibited and part of the frontal margin is dragged into the subduction zone when the main d6collement returns to its basal level in the wake of the seamount the margin records a rapid subsidence and a new accretionary wedge develops closing the margin reentrant the sediments underthrusted in the wake of the seamount into the shadow zone are underplated beneath the rear part of the accretionary wedge substantial shortening and thickening of the deformable seaward termination of the upper plate basement associated with basal erosion is observed seamount subduction induces significant material transfer within the accretionary wedge favors large tectonic erosion of the frontal margin and thickening of the rear part of the margin the subduction and underplating of relatively undeformed water ladden sediments associated with fluid expulsion along the fractures affecting the margin could modify the fluid pressure along the basal ddcollement consequently significant variations of the effective basal friction and local mechanical coupling between the two plates could be expected around the subducting seamount

influence of syntectonic sedimentation on thrust wedges in analogue models scaled analogue sandbox models have been used to simulate the growth of coulomb thrust wedges that include syntectonic sedimentation during thrusting increases in the syncontractional sedimentation rate dramatically change the shape of the coulomb thrust wedge decreasing the number of thrust slices the internal shortening and the critical taper of the wedge thrust trajectories change from ramp flat to sigmoidal with increased syncontractional sedimentation the analogue models show many similarities to thrust fault geometries in accretionary prisms and foreland fold and thrust belts in which thrust slices prograded into basins with active sedimentation

formation of 18o depleted dolomite within a marine evaporitic sequence triassic reichenhall formation austria dark grey bituminous dolostones interbedded with marine derived anhydrite horizons occur in the triassic reichenhall formation of western austria fossils are rare and indicate a hostile hypersaline depositional environment the dolomites are finely crystalline fairly stoichiometric well ordered and non ferroan closely spaced samples 94 in total of individual dolomite units have been analysed for their carbon and oxygen isotopic composition the data indicate surprisingly low 18o values 5 7 to 2 1 0 pdb whereas the 13c values are comparable to the contemporary triassic seawater 0 2 to 2 6 0 pdb sedimentological evidence including i lack of any evidence for extensive dissolution ii distinct oxygen and carbon isotope ratios of individual dolomite units iii covariance of carbon and oxygen isotopes within some dolomite layers and iv inclusions of celestite in dolomite indicates a nearly closed system after early diagenesis combining this information with water rock interaction calculations suggests that the lightest oxygen isotope compositions are the result of freshwater influx into the basin during very early dolomite formation a secondary factor may be dolomite recrystallization at elevated temperatures during burial

tracing tectonic deformation using the sedimentary record the study of sediments and sedimentary basins in terms of their tectonic environment requires a multidisciplinary approach and has increasingly drawn both techniques and objectives from fields outside sedimentology the application of different theoretical experimental and empirical resources provided by structural geology geochemistry geophysics scale modelling and field geology complement sedimentological methods with the combined aim of achieving a deeper understanding of the origins evolution and significance of sedimentary sequences in terms of their tectonic history studies presented in this volume range across a wide spectrum from the analysis of sedimentary sequence architecture at basin scale down to the chemical properties of individual grains and include studies from a range of tectonic settings the volume will be of interest to those involved with or contemplating studies involving the linkages between tectonics and sedimentation as well as a wider audience to whom the results of such studies may provide fresh insight

gondolelloid multielement conodont apparatus nicoraella from the middle triassic of yunnan province southwestern china abstract the morphology and position of elements in the apparatus are keys to resolving the taxonomy homology evolutionary relationships structure function and feeding patterns among conodont taxa fused clusters preserving natural associations between elements provide direct information on element morphology the positions of elements within the apparatus and even their original three dimensional arrangement here we report 41 fused conodont clusters from member ii of the guanling formation in luoping county yunnan province southwestern china which provide a basis for inferring the multielement composition of the apparatus of the early middle triassic nicoraella the apparatus is composed of 15 elements a single s0 element two pairs of s1 4 m and p1 2 elements like other apparatuses in gondolellidae i e the genera novispathodus and neogondolella these luoping biota clusters are significant because a they permit a positional homology based comparison of multielement novispathodus with form genera such as cypridodella s1 enantiognathus s2 and hindeodella s3 and s4 b they facilitate a review of apparatus composition within superfamily gondolelloidea c they provide direct insight into apparatus architecture currently interpreted largely in light of distantly related carboniferous polygnathacean ozarkodinins and d these clusters along with collections of discrete conodont elements provide a model for inferring the multielement composition of closely related species known only from discrete element collections

holocene dolomitization of calcium carbonate sediments from the coastal sabkhas of abu dhabi u a e a stable isotope study secondary dolomitization of holocene calcium carbonate sediments occurs beneath the coastal sabkhas of abu dhabi u a e a stable isotope study of the sabhka sediments and brines indicates that the

facies analysis of the trypali carbonate unit upper triassic in central western crete greece an evaporite formation transformed into solution collapse breccias the trypali carbonate unit upper triassic which crops out mainly in central western crete occurs between the parautochthonous series plattenkalk or talea ori ida series e g metamorphic ionian series and the tripolis nappe comprising the tripolis carbonate series and including a basal phyllite quartzite unit it consists of interbedded dolomitic layers represented principally by algally laminated peloidal mudstones foraminiferal peloidal and ooidal grainstones as well as by fine grained detrital carbonate layers in which coarse baroque dolomite crystals and dolomite nodules are dispersed baroque dolomite is present as pseudomorphs after evaporite crystals nodules and rosettes which grew penecontemporaneously by displacement and or replacement of the host sediments sabkha diagenesis however portions of the evaporites show evidence of resedimentation pre existing evaporites predominantly consisted of skeletal halite crystals that formed from fragmentation of pyramidal shaped hoppers as well as of anhydrite nodules and rosettes salt crusts all microfacies are characteristic of peritidal depositional environments such as sabkhas tidal flats shallow hypersaline lagoons tidal bars and or tidal channels along most horizons the trypali unit is strongly brecciated these breccias are of solution collapse origin forming after the removal of evaporite beds evaporite related diagenetic fabrics show that there was extensive dissolution and replacement of pre existing evaporites which resulted in solution collapse of the carbonate beds evaporite replacement fabrics including calcitized and silicified evaporite crystals are present in cements in the carbonate breccias brecciation was a multistage process it started in the triassic but was most active in the tertiary in association with uplift and ground water flow telogenetic alteration during late diagenesis in zones of intense evaporite leaching and brecciation solution collapse breccias were transformed to rauhwackes the trypali carbonate breccias trypali unit are lithologically and texturally similar to the triassic solution collapse breccias of the ionian zone continental greece the evaporites probably represent a major diapiric injection along the base of the parautochthonous series metamorphic ionian series and also along the overthrust surface separating the parautochthonous series from the tripolis nappe phyllite quartzite and tripolis series the injected evaporites were subsequently transformed into solution collapse breccias

gecko global events impacting conodont evolution abstract with a record that spans approximately 300 million years late cambrian through the triassic jurassic transition i e the conodontozoic conodonts witnessed all principal events in the evolution of life on earth from the invasion of the land to the exploration of the air from the explosion of biomineralization in the oceans to the rise of dinosaurs and mammals including three of the major extinction events that occurred in the phanerozoic mainly used for biostratigraphic or geochemical studies the potential of conodonts to help unravel changes perceived to be of global extent rarely has been explored while specialists have identified rapid changes in conodont element morphology throughout their history the conodont animal has often been perceived to have been a static entity in a constantly evolving world when biological equilibrium in the oceans was undergoing profound alteration and faunal recoveries took place in phases that seem to have had recurrent patterns it is now essential that we begin to further investigate how conodonts as biologic entities responded to or were impacted by palaeogeographic changes eustatic and climatic fluctuations shifting redox conditions and major faunal turnovers and reorganizations that took place during the conodontozoic

exceptional basal body preservation in some early triassic conodont elements from oman abstract conodont elements are composed of two main parts the crown and the basal body the basal body of a conodont element is a laminated structure that is less densely mineralized than the crown and as a result is rarely preserved elements with preserved basal bodies are found only in exceptional cases in the fossil record to date no s or m element with preserved basal body has ever been documented for post devonian conodonts which had raised the question of an evolutionary trend towards unmineralized basal bodies in conodonts here we report the discovery in smithian early triassic rocks of oman of neospathodid conodont elements whose basal body is partly preserved we demonstrate the presence of basal body in all elements including s and m elements of novispathodus and most likely of all gondolelloideans thereby suggesting that the absence of basal bodies in post devonian conodonts was due to a preservational bias only we further demonstrate that the morphology and extent of the basal bodies in novispathodus are in agreement with previous predictions and do not contradict a cyclostome like functional model of the apparatus based on a review of the occurrences of basal bodies in the literature we suggest a general pattern for the morphology of the basal bodies in conodont elements that may reflect the mechanical constraints associated with feeding motions

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

origins of co2 in permian carbonate reservoir rocks zechstein ca2 of the nw german basin lower saxony permian carbonate reservoir rocks stassfurt carbonate of the co2 province lower saxony basin nw germany are locally characterised by high amounts of co2 leading to serious problems on exploration in order to receive information on the major co2 sources and co2 migration and accumulation processes mineralogical geochemical and stable isotope analyses c 13 o 18 were carried out on authigenic precipitations within the stassfurt carbonate rocks ca2 these rocks contain early diagenetic e g formed in soft sediment carbonate minerals calcite dolomite and anhydrite in concretions and small cracks in addition large up to 2 cm wide carbonate cemented fractures formed in solid ca2 rocks semi quantitative estimates of the diagenetic mineral content showed variations between the investigated rock cores nine out of 12 ca2 rock cores are derived from wells situated in the area of modem ch4 rich reservoirs and have distinct fracture systems developed in contrast the other three rock cores are from wells characterised by co4 rich reservoirs and lack fractures of similar thickness the assumed relationship between tectonically induced fractures and the gas content of the ca2 reservoir rocks implies co2 degassing of the ca2 rocks at approximately 102 degrees c to similar to 150 degrees c assumed delta 18o pore water variation from 0 parts per thousand to 4 parts per thousand smow ree distribution indicates at least three types of fracture and crack filling carbonates two carbonate generations formed from evolving diagenetic pore waters whereas one type reflects carbonate formation under hydrothermal influence the ages of these cementations derived from rb sr and u pb isotope analyses indicate their fort nation during late stage of or after the inversion of the lower saxony basin in late cretaceous times the stable carbon isotope composition of the authigenic carbonate minerals reflects at least two carbon source endmembers available during diagenesis whereas many early formed carbonates are related to the permian c 13 rich carbon source those carbonates which precipitated or recrystallised during early to late stage diagenesis and or were induced by local tectonic events incorporated c 12 enriched co from organic degradation processes the stable oxygen isotope values of authigenic carbonates probably still reflect low temperatures of mineral formation from permian sea water as it is assumed for non recrystallised carbonates or late stage high temperature up to similar to 150 degrees c precipitation ftoin sea water derived pore waters which may have been locally influenced by o 18 enriched fluids however most of the carbonate samples investigated are recrystallised crystal enlargement of concretionary and fracture carbonate is observed and hence these carbonates are at least partly re equilibrated original o 18 content reduced with surrounding pore waters at elevated temperature similar to the authigenic carbonate at least two sources may explain the concentration carbon isotope relationship of modem co present in the ca 2 reservoir rocks an organic derived co2 endmember source delta c 13 near 20 parts per thousand is present in relatively low concentrations whereas large co concentrations derived from an endmember source with all isotope value near 0 parts per thousand although the latter source is unknown such heavy co sources are most likely attributed to carbonate decomposition processes c 2005 elsevier b v all rights reserved

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

isotope shifts in the late permian of the delaware basin texas precisely timed by varved sediments closely spaced samples 285 in number of varved sediments from the upper permian in delaware basin texas have been analyzed for 13ccarb 13corg 18ocarb corg ccarb and calcite dolomite 13c records a dramatic rise from 2 8 to 5 7 in only 4400 years detected in three sections across the basin extrapolating smoothly through a 600 year interruption by a local west side of the basin fresh water inflow evidenced by low 18o this continuity and low corg within the basin both indicate that the excess net deposition of corg necessary to generate the rise in 13c took place in the ocean external to the delaware basin correlation with similar records from the zechstein basin suggest that the event was world wide although this poses obvious difficulties for the carbon cycle the rate of rise of 13c and its sustained high level must imply conversions of oxidized carbon to reduced carbon that are very large depending on which reservoirs were involved

erosion and exhumation in accretionary orogens experimental and geological approaches 1 this study examines the role of erosion on exhumation and deformation history of accretionary orogens through experimental and geological methods fault propagation kinematics and exhumation rates in an eroded thrust wedge are analyzed through scaled sandbox simulations by testing different parameters friction rheologic layering and sediment input output ratio a model coulomb wedge is submitted to erosion under flux steady state conditions that is the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during shortening results show that the way of exhumation depends on the internal dynamics of thrust wedges and conversely on how this dynamics is modified by erosion in the eroded thrust wedges the diversity of exhumation patterns is controlled by the mode of fault propagation depending on the basal friction high or low the vertical component of exhumation is generally higher for the wedges with high basal friction than for low friction wedges the uplift of material occurs along a cluster of subvertical thrusts in the middle part of the eroded thrust wedge with low basal friction the material is exhumed along a series of inclined 20 50 thrusts in the rear of the high friction wedge the zone of maximum exhumation is generally localized in the middle part of the thrust wedge and migrates toward the backstop with continued shortening the vertical exhumation rate increases with time and the material accreted later is rapidly transferred to the main exhumation zone compared to the material accreted during the early stages the exhumation occurs at rates 2 times faster in the wedges with half the thickness than in full thickness wedges the total quantity of eroded material at the end of convergence constitutes 36 50 of initial model area for the thrust wedges with low basal friction and 20 40 for the high basal friction wedges the extent of basal underplating increases with total shortening the area of basal underplated material constitutes up to 30 and 40 of the eroded thrust wedge area for the models with low and high basal friction respectively presence of decollements in the accreted series allows underplating of thrust units developing an anticlinal stack whose growth and location is favored by erosion our results are compared to different present day active and ancient convergent orogens himalaya taiwan southern alps of new zealand and cascadia orogen allowing the different specific exhumation processes to be characterized

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

dedolomitization review and case study of uncommon mesogenetic formation conditions abstract dedolomitization converts a dolomite into a calcite and conventionally is interpreted to form in an eogenetic or telogenetic diagenetic environment where meteoric water dissolves evaporites to supply excess calcium hydrologic connectivity between a dolostone and the surface water may then lead to a dedolomitized interval often times being a diagnostic indicator for an erosional unconformity subaerial exposure and or karst in contrast to the classic models we present a case study for pervasive burial dedolomitization unrelated to meteoric fluids dedolomitization of the zechstein 2 carbonate ca2 gas reservoir in nw germany is strongly altering reservoir quality on a regional scale the ca2 shows a textbook correlation between reservoir quality and mineralogy petrographic analyses show that approximately 80 of all observed calcite reveal a dedolomite microtexture causing a reduction of average matrix porosity by 5 to 10 compared to the dolomite dedolomite follows initial layering and abundantly forms massive concretions which are surrounded by compaction related curvature of the depositional layering in the dolomite host rock such an early burial timing is supported by a slight burial related shift of 3 18o and 1 13c towards lighter values in the dedolomites compared to dolomite an exceptionally large amount of calcium rich fluids must have been mobilized to account for 50 of the ca2 rock volume to be dedolomitized however core fabrics related to meteoric diagenesis such as karst fabrics or typical fresh water stable isotope signatures have been observed neither in the ca2 nor in over and underlying anhydrite beds instead excess calcium likely comes from gypsum to anhydrite conversion and pressure solution within over and underlying anhydrites an influx of strontium rich waters from the anhydrite beds is indicated by up to 5 times higher strontium contents measured in dedolomite fabrics compared to their dolomite host rock homogenization temperatures between 51 and 56 c measured in some early fluid inclusions in dedolomite textures further exclude a pristine meteoric water input and suggest fluid entrapment in a burial depth range of 900 to 1400 m comparing these results with literature data furthermore indicates that mesogenetic dedolomite is either volumetrically underestimated in other carbonate evaporite settings or formed under unique diagenetic conditions across the southern permian basin during zechstein times

modeling of thrust fronts above ductile and frictional detachments application to structures in the salt range and potwar plateau pakistan series of scaled sandbox models are used to simulate the development of thin skinned simultaneous shortening above adjacent ductile and frictional substrates these models simulate the evolution of the potwar plateau and salt range in pakistan where pale

diagenesis of nearshore carbonate rocks in the sprotbrough member of the cadeby magnesian limestone formation upper permian of eastern england

genesis of evaporite associated platform dolomites case study of the main dolomite zechstein upper permian leba elevation northern poland dolomitization of the zechstein late permian main dolomite carbonates of northern poland was penecontemporaneous and or very early diagenetic well ordered stoichiometric dolomites are associated with the basinal facies the platform dolomitesare relatively poorly ordered and usually non stoichiometric most samples are highly enriched in 13c as in other zechstein carbonates 6 o values show large variations from 5 l to 7 4 there is an isotope zonation of the examined dolomites the isotope signature indicates that dolomites formed from variable solutions of meteoric water seawater and evaporitic brines of possible marine or continental origin once initiated dolomitization proceeded despite the evolution of dolomitizing brines this evolution explains the occurrence of lagoonal dolomites with common evidence for dissolution in the lower part of sections compared with well developed rhombohedra in the upper part crystal zoning suggests the initiation of dolomite growth in hypersaline water and progressive dilution by fresh water there is isotopic evidence for migration of continental waters into the basin presumably following sea level fall at the end of the deposition of the main dolomite influence of fresh water on syndepositional dolomitization well established in the main dolomite strongly suggests that similar relationships may be characteristic for other evaporite associated dolomites as well

episodic accretion and strain partitioning in a model sand wedge we model led thrust wedge accretion and deformation partitioning in a passively layered sand detached and shortened above a smooth rigid decollement the thrust wedge accretes in piggyback style during forward advance of a rear wall the passively layered sand accommodates the shortening penetratively by kinking ramp folding and by imbrication in single layers the style of compression changes with time and or stratigraphic position within the sand prism initial penetrative layer shortening above a slipped zone of decollement is succeeded by formation of monoclinal or conjugate shear bands at temporary terminations of decollement the shear bands subsequently narrow down and lock as thrust ramps the model sand wedge accrets episodically rather than steadily episodicity is controlled by the stick slip mode of decollement propagation and by volume loss and compaction of the wedge material in response to convergence this results in formation of a wedge with a convex upwards cross sectional topography

measurements of friction coefficients and cohesion for faulting and fault reactivation in laboratory models using sand and sand mixtures abstract simple laboratory tests have been made on dry quartz sand and on mixtures of sand and clay and sand and cement tests were made on both low and high density specimens of each mixture as determined by physical handling techniques the tests included measurements of density estimates of the coefficient of internal friction based on fault orientation and estimates of the friction coefficients and cohesion values for fault initiation and reactivation in a shear frame apparatus which was also used to test artificial fault zones made from pure clay glass microspheres and wheat flour the results suggest that density is determined more by handling technique than by composition and that friction coefficients and perhaps cohesion both increase with increasing density the shear testing revealed a consistent drop in cohesion for fault reactivation in all densely packed mixtures tested although small this drop may be significant for some types of laboratory models

influence of syntectonic sedimentation on thrust geometry field examples from the iberian chain spain and analogue modelling abstract steep thrusts are usually interpreted as oblique slip thrusts or inverted normal faults however recent analogical and numerical models have emphasised the influence of surface mass transfer phenomena on the structural evolution of compressive systems this research points to sedimentation and erosion during deformation as an additional explanation for the origin of steeply dipping thrusts the present study uses both field observations and analogue modelling to attempt to isolate critical parameters of syntectonic sedimentation that might control the geometry of the upper part of thrust systems a field study of thrust systems bounding two compressive intermountain tertiary basins of the iberian chain is first briefly presented we describe the surface geometry of thrusts surrounding the montalban basin and the alto tajo syncline at the vicinity of deposits of oligocene early miocene alluvial fans at the footwall of faults field observations suggest that synthrusting sedimentation should influence the structure of thrusts indeed the faults are steeper and splitted at the edge of the syntectonic deposits effects of sedimentation rate on footwall of thrusts and of its change along fault strike are further investigated on two layer brittle ductile analogue models submitted to compression and syntectonic sediment supply two series of experiments were made corresponding to two end members of depositional geometries in the first series the sedimentation was homogeneously distributed on both sides of the relief developed above the thrust front in the second series deposits were localised on a particular area of the footwall of thrust front in all experiments the sedimentation rate controls the number and the dip of faults for low sedimentation rates a single low angle thrust develops whereas for high sedimentation rates a series of steeper dipping thrust is observed in experiments with changing sedimentation rate along fault strike the thrust geometry varies behind the areas with the thickest sediment pile

mixed water and hydrothermal dolomitization of the pliocene shirahama limestone izu peninsula central japan the early pliocene shirahama limestone is a grainstone packstone principally composed of fragments of algae bryozoa and echinoderm and subordinate volcanic rocks the limestone was variously dolomitized and the regional distribution of dolomite is patchy dolomite occurs as isolated crystals filling pores moulds and solution vugs and mosaic aggregates replacing bioclasts calcite occurs as rim and pore filling sparry cements and as calcareous skeletons isotopically the dolomites are classified into a heavy oxygen group 2 to 3 5 0 pdb and a light oxygen group 5 5 to 7 5 0 pdb calcite associated with heavy oxygen dolomite has 18o of 6 5 to 8 5 0 pdb whereas those associated with light oxygen dolomite have a wide range from 7 5 to 14 0 pdb calcite in dolomite free limestone has an oxygen isotopic composition of 2 to 8 5 0 pdb textures chemistry and isotopic evidence indicate that heavy oxygen calcite formed in freshwater and heavy oxygen dolomite in a meteoric marine mixture of 10 30 seawater light oxygen calcite and dolomite precipitated from modified hydrothermal fluids at approximately 30 65 c petrographic features and both isotopic and chemical evidence suggest that the shirahama limestone was exposed to freshwater soon after deposition subsequently blocky calcite precipitated stage i the limestone was locally submerged in the meteoric marine mixture due to gradual subsidence or eustatic movement this led to the precipitation of heavy oxygen zoned dolomite and dolospar stage ii hydrothermal alterations occurred in the area a few myr ago and related hydrothermal fluids and mixed meteoric hydrothermal waters caused dedolomitization of some zoned dolomite partial dissolution of vuggy dolomite precipitation of limpid dolomite and recrystallization of some earlier dolomites stage iii zeolites were also precipitated from these fluids finally the shirahama limestone was exposed again to freshwater and sparry calcite precipitated to plug some of the remaining pores stage iv

hangingwall bed rotation and the development of contractional and extensional structures around a thrust fault geometric and experimental models abstract tectonic inversion of normal faults and development of extensional and contractional structures in the vicinity of thrust faults were studied using two models i a geometric or rigid model and ii an experimental or brittle ductile model the first model is based on simple trigonometric relationships between shortening rotation of layers along a thrust and dip of the thrust the model may be used to understand the structures at upper levels of the earth s crust in a predominant brittle regime the second model is based on a series of experiments performed with clay analogues it simulated the structures forming at a deeper level in a brittle ductile regime and incorporates folding as an essential feature the results of the study reveal that structures near a thrust fault depend on the thrust geometry and dip amount the initial orientation of hangingwall layers and their rheological properties in the absence of frictional effects along a thrust surface the rotation of layers and consequent displacement is directly proportional to the thrust dip since the listric faults are characterized by a decrease of dip with depth the variation in the rotation of layers in a profile section may result in formation of dilation spaces that may serve as potential sites for secondary mineral deposits or oil traps a large rotation of hangingwall layers results in a reverse fault drag and a small rotation caused by frictional effects along the fault produces normal fault drag

fault related folding in sandbox analogue models of thrust wedges abstract the nucleation and growth of thrust fault related folds has been simulated using high resolution sandbox coulomb wedge type analogue models thrust related anticlines grew progressively from initial layerparallel shortening to decollement folding thrust tip folding and eventually thrust ramp folding thrust ramps nucleated in the central sector of the overturned forelimb of decollement folds as a consequence of limb thinning thrust tip folding occurred during outward migration of the ramp tips the fault propagation rate was greater at the lower ramp tip which quickly joined the basal thrust flat while folding continued beyond the upper tip the development of the analogue model thrust fault related folds by progressive changes in kinematics from decollement folding to thrust tip folding and finally thrust ramp folding compares well with analyses of naturally occurring thrust fault related folds

the break up of east gondwana along the northeast coast of oman evidence from the batain basin recent detailed studies on the batain nappes northeast coast of oman which represent a special part of the so called oman exotics have led to a better understanding of the neotethyan geodynamic evolution the batain exotics bear witness to volcanic activity sea level changes tectonic instability rifting and oceanization along the eastern oman margin during late palaeozoic and mesozoic times they allow definition of the batain basin as an aborted permian branch of neotethys this marine basin was created in early permian times extending southward to the east african madagascar region and was linked to the karoo rift system the presented revised classification of the batain nappes considers the batain basin to be no longer a part of the hawasina basin and the neotethyan margin proper we attribute the batain basin to a mozambique somali masirah rift system somoma this system started in early permian times creating a marine basin between arabia and india madagascar rifting in the late triassic and oceanization during late jurassic times led to the separation of east gondwana

kinematic evolution of thrusts wedge and erratic line length balancing insights from deformed sandbox models kinematic evolution of fold thrust structures has been investigated by analogue models that include syntectonic sedimentation different decollement dips and basement thicknesses produced different wedge geometries and propagating characteristics a model with one decollement level was characterized by a closely spaced thrust system during early stages of shortening as compared to the late stages the frequency of fault nucleation was rapid during the early stages of deformation conversely the frequency of fault nucleation was low and thrust spacing was significantly wider in a model with two decollement levels individual faults became locked at steep dips and deformation stepped forward as a new fault nucleated in sequence in front of the older locked structure once the thrust system was established up to 27 overall shortening an overlying bed was introduced to simulate syntectonic deformation model sand wedge did not grow self similarly but rather its length and height increased episodically with deformation restoration of deformed models show that layer parallel shortening accommodated for approximately half of the total model shortening across the multilayers calculated error in apparent layer shortening from the restored layers revealed a direct relation with depth of the layers in the models the experimental results are comparable to a natural example from the northern apennines fold and thrust belts

geochemical evolution of pore waters in the rotliegend early permian of northern germany abstract the distribution of early cements within permian rotliegend sandstones closely resembles cementation patterns within modern playa lake basins the isotopic compositions of eogenetic cements in the thick rotliegend sequence of germany show continental signatures typical of minerals precipitated in such an environment carbon sulphur and strontium isotopic ratios of many rotliegend cements which formed during burial suggest formation from a mixture of rotliegend fluids and waters from the overlying zechstein evaporites a two component mixing model for the evolution of rotliegend pore waters indicates that the isotopic signatures in these cements may result from the introduction of only minor amounts of zechstein fluid

origin of dolomite cement in chesapeake group miocene siliciclastic sediments an alternative model to burial dolomitization abstract ferroan dolomite and calcite cement fossiliferous sandstone unite in the choptank and calvert formations miocene of western maryland and northern virginia the average composition of the dolomite is ca 55mg 43fe 02co3 though nonferroan dolomite is also present the dolomite is generally euhedral and zoned and it may have fluid inclusion rich cores calcite cements are dominantly composed of equant spar though a fine acicular isopachous rim cement may be present calvert formation dolomite is chemically similar to choptank formation dolomite though the former contains both calcite inclusions and hollow centers a relatively simple burial history for ferroan dolomite and calcite cement coupled with petrographic and isotopic evidence indicates that some of the dolomite has a marine origin possibly under the influence of sulfate reducing organisms later recrystallization may have occurred under the influence of alternating marine and meteoric phreatic conditions zoned dolomite rhombs dolomite with calcite cores and clear dolomite rims indicate episodic crystallization possibly due to multiple periods of phreatic conditions most of the calcite cement is demonstrably meteoric in origin dolomite cement is generally confined to permeable sandy intervals bounded on the top and bottom by clays of low permeability when buried this sequence would be similar to dolomite sequences inferred to be of deep burial in origin the timing of dolomite formation in chesapeake bay sediments is significant in that most of the dolomite has derived its magnesium from sources other than the clays as has been suggested in deep burial dolomitization models

stylolite controlled diagenesis of a mudstone carbonate reservoir a case study from the zechstein_2_carbonate central european basin nw germany this study was developed within the framework of dgmk german society for petroleum and coal science and technology project 718 funded by the companies exxonmobil production deutschland gmbh gdf suez e p deutschland gmbh rwe dea ag and wintershall holding gmbh the authors would like to acknowledge exxonmobil production deutschland gmbh that kindly provided core data elliot humphrey thanks the natural environment research council nerc centre for doctoral training cdt in oil gas for a phd grant egr acknowledges agaur agencia de gestio d ajuts universitaris i de recerca for a beatriu de pinos research project additional funding was provided by the generalitat de catalunya government 2017sgr 824 and the spanish government projects cgl2015 66335 c2 1 r cgl2015 69805 p and pgc2018 093903 b c22 we acknowledge theresa straub and simon gast for their assistance during core data collection we would like to thank miroslaw mirek slowakiewicz and an anonymous reviewer for their critical and constructive comments together with the editorial guidance of edoardo perri

mixed evaporative and meteoric water dolomitization isotope study of the zechstein limestone upper permian southwestern poland abstract dolomites of the zechstein limestone in western poland have high 13c values characteristic of the zechstein carbonates and there is some variation in 18o profiles dolomites are mostly stoichiometric and well ordered and are characterized by variable crystal textures the area studied underwent constant burial since the late permian and the isotopic curves despite their complexity show distinct regularities and signals of meteoric water input that in most cases could occur only during the permian moldic porosity interpreted as originated shortly after dolomitization commonly occurs stratigraphic patterns and facies analyses suggest that dolomitization phases occurred at the top of each eustatically controlled subcycle of the zechstein limestone in association to subaerial exposures most of the dolomites therefore originated during the permian a significant proportion of the dolomites originated via meteoric marine mixing during deposition of the zechstein limestone the mixing mechanism was closely related to sea level falls conventionally evaporite related dolomites are believed to have originated in a sabkha environment and or by the reflux mechanism the zechstein limestone case suggests that the mixing of evaporative and meteoric water may be responsible for dolomitization of other evaporate related carbonates

a new explanation for cyclic deposition in marine evaporite basins meteoric water input abstract one of the least discussed processes affecting the deposition of marine evaporites is the role of meteoric water sand and fine grained clastic sediments deposited from river system in a marginal evaporite basin facies the oxygen isotope record in the carbonate minerals mainly dolomites and the br cl ratios of second cycle salts are some of the evidence for influxes of meteoric water important meteoric water influxes are not limited to sabkha and salina evaporites but may also affect deep water evaporite basins one can see in the oxygen isotope record of carbonate minerals an imprint of meteoric water just as the sulfur isotope record reflects the imprint of the marine water sedimentological characteristics of evaporite sequences could be interpreted as variations in the amount of precipitation in the evaporite basin catchment area rather than as a result of changes in sea level for example the varved structures may reflect seasonal flooding of the basin by meteoric water evaporite facies cycles may be the result of longer term weather variation for example the paradox member cycles pennsylvanian utah could reflect periods of increased precipitation which are associated with glacial interglacial cycles