palaeoenvironmental reconstruction of a middle miocene alluvial fan to cyclic shallow lacustrine depositional system in the calatayud basin ne spain the middle miocene sedimentary fill of the calatayud basin in north eastern spain consists of proximal to distal alluvial fan floodplain and shallow lacustrine deposits four main facies groups characteristic of differentsedimentary environments are recognized 1 proximal and medial alluvial fan facies that comprise clast supported gravel and subordinate sandstone and mudstone the latter exhibiting incipient pedogenic features 2 distal alluvial fan facies formed mainly of massive mudstone carbonate rich palaeosols and local carbonate pond deposits 3 lake margin facies which show two distinct lithofacies associations depending on their distribution relative to the alluvial fan system i e front lithofacies a comprising massive siliciclastic mudstone and tabular carbonates or lateral lithofacies b showing laminated and or massive siliciclastic mudstone alternating with tabular and or laminated carbonate beds and 4 mudflat shallow lake facies showing a remarkable cyclical alternation of green grey and or red siliciclastic mudstone units and white dolomitic carbonate beds the cyclic mudflat shallow lake succession as exposed in the orera composite section ocs is dominantly composed of small scale mudstone carbonate dolomite cycles the mudstone intervals of the sedimentary cycles are interpreted as a result of sedimentation from suspension by distal sheet floods the deposits evolving either under subaerial exposure or water saturated conditions depending on their location on the lacustrine mudflat and on climate the dolomite intervals accumulated during lake level highstands with mg rich waters becoming increasingly concentrated lowstand to highstand lake level changes indicated by the mudstone dolomite units of the small scale cycles reflect a climate control from dry to wet conditions on the sedimentation in the area the spatial distribution of the different lithofacies implies that deposition of the small scale cycles took place in a low gradient shallow lake basin located in an interfan zone the development of the basin was constrained by gradual alluvial fan aggradation additional support for the palaeoenvironmental interpretation is derived from the isotopic compositions of carbonates from the various lithofacies that show a wide range of 1 8 o and 1 3 c values varying from 7 9 to 3 0 pdb and from 9 2 to 1 7 pdb respectively more negative 1 8 d and 1 3 c values are from carbonate rich palaeosols and lake margin carbonates which extended in front of the alluvial fan systems whereas more positive values correspond to dolomite beds deposited in the shallow lacustrine environment the results show a clear trend of 1 8 o enrichment in the carbonates from lake margin to the centre of the shallow lake basin thereby also demonstrating that the lake evolved under hydrologically closed conditions

magnesium isotope composition of sabkha porewater and related sub recent stoichiometric dolomites abu dhabi uae abstract earliest marine diagenetic sabkha type dolomites are widespread in earth s geological record potentially these carbonates may act as archives of past seawater magnesium isotope 26mg ratios at present however the fractionation of magnesium isotopes 26mg between seawater here evaporated marine porewater and sabkha dolomite is not constrained in order to explore 26mgdol mg porewater we make use of actualistic sabkha type dolomite precipitation in the gulf region trucial coast united arab emirates this paper documents and discusses the first detailed sabkha 26mg data set of mg bearing solids including stoichiometric dolomites degree of ordering 0 9 mean 26mgdol 0 79 0 41 2 n 17 and related marine pore waters the presence of dolomite crystals with a broad range of ordering in shallow cores is documented using x ray diffraction and scanning electron microscopy but individual crystals are too small

large scale intertidal polygonal features of the abu dhabi coastline this study provides the first quantitative description of modern giant polygons these large scale up to 166 m diameter sedimentological features are described here in detail from the intertidal zone of the arabian gulf near abu dhabi these features form by the displacive carbonate cementation of carbonate sand below a 3 to 5 cm thick cover of unconsolidated sediment the oxygen isotopic composition of cements is consistent with precipitation from evaporated sea water cementation proceeds via a poorly consolidated layer that grades downward into an 8 to 14 cm thick well cemented grainstone the margins of this expanding hardground form the overlapping borders of the polygons tepee structures at the borders of polygons are only occasionally preserved as supporting sediment is removed by strong tidal currents and high energy events such as storms that erode the unsupported tepees these observations have clear implications for the use of tepees in the interpretation of ancient polygons and their associated environments when preserved in the sedimentary record tepee structures are interpreted to indicate lower energy depositional environments than that observed in this study

new insights on subsurface energy resources in the southern north sea barrin area the southern north sea basin area stretching from the uk to the netherlands has a rich hydrocarbon exploration and production history the past present and expected future hydrocarbon and geothermal exploration trends in this area are discussed for eight key lithostratigraphic intervals ranging from the lower carboniferous to cenozoic in the period between 2007 and 2017 a total of 95 new hydrocarbon fields were discovered particularly in upper carboniferous rotliegend and triassic reservoirs nineteen geothermal systems were discovered in the netherlands onshore mainly targeting aquifers in the rotliegend and upper jurassic lower cretaceous formations although the southern north sea basin area is mature in terms of hydrocarbon exploration it is shown that with existing and new geological insights additional energy resources are still being proven in new plays such as the basal upper rotliegend ruby discovery for natural gas and a new chalk play for oil it is predicted that hydrocarbon exploration in the southern north sea basin area will probably experience a slight growth in the coming decade before slowing down as the energy transition further matures geothermal exploration is expected to continue growing in the netherlands onshore as well as gain more momentum in the uk

north sea rift system abstract the mesozoic north sea rift forms an integral part of the arctic north atlantic rift system rifting activity in the north sea commenced during the earliest triassic during the mid jurassic the central north sea underwent a temporary doming stage crustal extension peaked during the late jurassic earliest cretaceous abated subsequently and terminated altogether during the paleocene the saucer shaped cenozoic post rift basin straddles the axis of the viking and central grabens this speaks for the applicability of a depth dependent pure shear model rather than a simple shear model geophysical data indicate an important discrepancy between upper and lower crustal attenuation across the north sea rift suggesting that during rifting processes the mono discontinuity was seriously destabilized this requires a basic modification of currently favoured crustal stretching models

triassic latemar cycle tops subaerial exposure of platform carbonates under tropical arid climate the triassic latemar platform in the dolomites italy is the site of several ongoing controversies perhaps the most interesting debate focuses on apparent cyclic deposition within the latemar platform whose nature and duration are still open to debate further disagreement concerns the lack of meteoric diagenesis related isotope shifts at cycle tops that bear circumstantial petrographic evidence for subaerial emergence here an evaluation of the nature of latemar cycle tops is presented combining evidence from previous work and new field petrographic and geochemical data cycle tops are ranked according to increasing exposure duration and spatial extent type i surfaces lacking unequivocal evidence of prolonged supratidal conditions type ii dolomite caps formed in warm evaporitic intertidal lagoonal waters followed by exposure of perhaps intermediate duration type iii clastic rich red calcareous horizons with some showing platform wide extent representing prolonged supratidal conditions and type iv discontinuities in tepee belts genetically related to type ii and iii surfaces but likely representing shorter lived exposure stages petrographic and geochemical criteria indicate that most diagenesis occurred in the shallow marine and burial domain whilst an extensive meteoric overprint of cycle tops is lacking this is underlined by the scarcity of meteoric diagenetic fabrics such as gravitational cements that where present are here interpreted as marine vadose in origin the scarcity of carbon and oxygen isotope signatures commonly assigned to subaerial exposure stages is best explained in the context of mid triassic climate the low latitude tropical but arid setting of the latemar situated in the western extension of the tethys ocean its isolation from nearby continental areas and overall short term emergence episodes are in agreement with a limited degree of meteoric alteration of most cycle tops high amounts of aeolian clastic material beneath some cycle tops along with high fe and mn elemental abundances argue for intermittent subaerial conditions this study proposes an enhancement of the classical allan and matthews 1982 isotope model for subaerial exposure under strongly arid climates as the subaerial exposure nature of latemar cycle tops and therefore eustasy as the cause for cyclicity have been previously challenged due to the lack of meteoric induced isotopic signatures the outcome of this study is of significance for the ongoing latemar stratigraphic controversy

detailed stratigraphic subdivision and regional correlation of the southern danish triassic succession this paper provides a regional log based lithostratigraphic correlation of the danish triassic deposits with deposits known from the southern north sea basin including the northwest german and dutch onshore areas a new lithostratigraphic nomenclature mainly adapted from the dutch nomenclature is suggested for the danish area south of the ringkobing fyn high replacing the previously used nomenclature the new nomenclature comprises the lower triassic bunter shale and bunter sandstone formations the lower to middle triassic rot and muschelkalk formations and the uppermost middle triassic and upper triassic keuper and sleen formations in total 22 members are also defined from the southern north sea into the southern danish area this main marine southern facies province is separated from a continental northern facies province by the northern flank of the ringkobing fyn high trend units of the southern province only crossed the central and western part of the ringkobing fyn high during the rot and the muschelkalk transgressions whereas the basin north of the eastern part of the high was influenced by the southern facies province during the early to early late triassic

the magnesium isotope δ26mg signature of dolomites abstract dolomite precipitation models and kinetics are debated and complicated due to the complex and temporally fluctuating fluid chemistry and different diagenetic environments using well established isotope systems 18 o 13 c 87 sr 86 sr fluid inclusions and elemental data as well as a detailed sedimentological and petrographic data set we established the precipitation environment and subsequent diagenetic pathways of a series of proterozoic to pleistocene syn depositional marine evaporative sabkha dolomites syn depositional non marine evaporative lacustrine and palustrine dolomites altered marine mixing zone dolomites and late diagenetic hydrothermal dolomites these data form the prerequisite for a systematic investigation of dolomite magnesium isotope ratios 26 mg dol dolomite 26 mg ratios documented here range from 2 49 to 0 45 26 mg mean 1 75 1 08 n 42 the isotopically most depleted end member is represented by earliest diagenetic marine evaporative sabkha dolomites 2 11 0 54 2 n 14 in comparing ancient compositions to modern ones some of the variation is probably due to alteration altered marine 1 41 0 64 2 n 4 and earliest diagenetic lacustrine and palustrine dolomites 1 25 0 86 2 n 14 are less negative than sabkha dolomites but not distinct in composition various hydrothermal dolomites are characterized by a comparatively wide range of 26 mg ratios with values of 1 44 1 33 2 n 10 by using fluid inclusion data and clumped isotope thermometry 47 to represent temperature of precipitation for hydrothermal dolomites there is no correlation between fluid temperature 100 to 180 c and dolomite mg isotope signature r 2 0 14 nor is there a correlation between 26 mg dol and 18 o dol magnesium isotope values of different dolomite types are affected by a complex array of different mg sources and sinks dissolution precipitation and non equilibrium fractionation processes and overprinted during diagenetic resetting further progress on the use of 26 mg dol as a proxy will require new theoretical and experimental data for 26 mg fluid dol that includes dehydration effects of the free mg aquo ion versus fluid temperature in ancient diagenetic systems complex variables must be considered these include fluid chemistry and physical properties mg sources and sinks temporal changes during precipitation and post precipitation processes including open and closed system geochemical exchange with ambient fluids all of these factors complicate the application of 26 mg dol as proxy for their depositional or diagenetic environments nevertheless the data shown here also indicate that 26 mg dol can in principle be interpreted within a detailed framework of understanding

data mining in the dutch oil and gas portal a case study on the reservoir properties of the volpriehausen sandstone interval this paper presents the results of a data mining exercise on core measurements and reports of the triassic lower volpriehausen sandstone member rbmvl in the netherlands the availability of a large accurate online dataset via the dutch oil and gas portal nlog enables the definition of general reservoir property trends on a regional subregional scale accurately defined trends are capable of restricting the uncertainty range of key parameters in exploration studies e g porosity and permeability and thus of reducing risk plotting core porosity v core permeability resulted in a curved data cloud on a log normal plot although porosity permeability relationships are often defined by straight lines the dataset in this study shows that a curved relationship results in a better fit with permeability measurements over the entire porosity range two methods were applied to define a porosity depth relationship for sandstones of the rbmvl the results of both methods confirm and enable quantification of the well known trend of decreasing porosity with depth by assigning grain density attributes to the core measurements the dependency of the porosity depth relationship on sedimentary facies and diagenesis type grade could be determined this case study demonstrates the power of this free online dataset in understanding reservoir quality 2018 the author s

sabkha facies and the preservation of a falling stage systems tract at the sauk ii iii supersequence boundary in the late cambrian eilean dubh formation nw scotland the durness group of northwest scotland represents a nearly one kilometer thick succession of mid cambrian to lower middle ordovician carbonates these rocks crop out in a narrow belt along the foreland of the caledonian orogen and in the moine thrust zone stretching some 170 km from loch eriboll southwestwards to the isle of skye the cambrian parts of the succession represent deposition on a paleo southeast facing low latitude passively subsiding continental margin situated at around 20 s carbonate deposition in scotland formed part of the extensive great american carbonate bank the sauk ii iii supersequence boundary occurs above an interval of thin meter scale shallowing upward peritidal cycles containing intraclast dolorudstones stromatolites tepees siliciclastic sand and surface karst evidence of former evaporites in the succession comprises pseudomorphs of nodular and bedded anhydrite crystal shaped calcite filled vugs representing growth of sulfate dissolution breccias and local halite casts these features represent sabkha facies arranged into cycles that constitute a preserved falling stage systems tract fsst the top of the fsst is marked by a pronounced karst surface of sandstone filled fissures the section preserves a rare snapshot of a seldom preserved environment on the cambrian laurentian margin its preservation during a time of falling relative sea level under slow tectonic subsidence is discussed

detailed 3 d depositional architecture of late jurassic carbonate anhydrite cycles brightling mine weald basin uk abstract quantifying the geometries of evaporite deposits at a 13 c and 18 o isotope analysis the stratigraphic interval contains five facies in stratigraphic order these include supratidal porphyritic nodular evaporite shallow subtidal peloidal packstone with evaporite and two overlying rhythmic sequences of intertidal microbial laminite subtidal shale and subtidal laminar marl capped by nodular anhydrite the interpreted environment of deposition is a supratidal sabkha subject to periodic flooding in which intertidal tidal flat facies and subtidal shallow marine facies laterally passed into the evaporative sabkha the cycles are interpreted as meter scale shoaling upward sequences likely controlled by localized high frequency changes in relative sea level and or sabkha hydrology spatial patterns in the geometries of key stratigraphic surfaces reveal a subtle depression towards the central western region of the mine seam the variation in stratal geometries is interpreted as paleotopography and is a function of individual or composite processes related to dissolution eolian processes and coastal erosion these observations indicate a similar mode of deposition to the modern day sabkha of the persian gulf we conclude that the dynamic process of evaporite deposition led to subtle stratigraphic heterogeneities and changes in bed thicknesses but largely continuous lateral bedding at an interwell scale

mesozoic resource potential in the southern permian basin area the geological key to exploiting remaining hydrocarbons whilst unlocking geothermal potential it is generally accepted that hydrocarbon exploration in northern europe has reached a mature stage a basin s maturity is defined by the underlying number of new discoveries and the declining production rate of mature fields spe 2015 for geoscientists a mature basin has well defined characteristics in terms of for example reservoir presence or trap formation e g byrne 2012 it is interesting therefore to note how much is still unknown about certain stratigraphic intervals in northern europe the mesozoic overburden of the southern permian basin sensu maystrenko et al 2008 doornenbal stevenson 2010 continues to provide fresh insights into the geological history of an area where as the name suggests historical hydrocarbon exploration has focused on the paleozoic the aim of this special publication is to increase knowledge of the mesozoic overburden as a driver for further hydrocarbon exploration production and the development of new geothermal energy sources the succeeding chapters are introduced by tectonic framework overviews that give a context for the papers that follow the remaining articles are organized in approximate stratigraphic order from old to young and include a variety of examples from semi regional to localized field or sub basin studies an overview of the study area for all the following chapters is given in figure 1 it is recognized that the overprinting mesozoic systems have different naming conventions across the study area e g the central european basin system sensu littke et al 2008 maystrenko et al 2008 here we use the title southern permian basin area to emphasize the resource opportunities associated with a region that has at least in large part been associated with hydrocarbon exploration and very large gas fields in the permian rotliegend for our purposes this includes part of the polish trough the highs surrounding the basin e g the ringkobing fyn high and analogous elements of the danish and norwegian offshore in this introduction an overview of the geological history and resource base of the area is presented as a framework for the chapters that follow a description of further prospective resources is then offered oil and gas plus geothermal potential

lithification of peritidal carbonates by continental brines at fisherman bay south australia to form a megapolygon spelean limestone association abstract groundwater springs in the supratidal zone at fisherman bay south australia are the sites of aragonite precipitation and cementation of holocene marine carbonates lithification which commenced less than 3000 years bp and is still active has formed a cavernous limestone containing megapolygons tepees and speleothems including pisoliths floe aragonite and aragonitic pool deposits the emerging waters are from a continental source and have evolved from low alkalinity waters of pleistocene sand and clay coastal plain aquifers which have passed through an underlying tertiary marine carbonate aquifer the resulting waters have high pco2 total carbonate ca and sulphate concentrations they are close to saturation with respect to aragonite and their mmg2 mca2 ratios approach or exceed the critical aragonite precipitation value aragonite is precipitated from these waters when they approach the surface and evolve co2 features which taken together may diagnose ancient examples of this process include 1 primary aragonitic cements with high msr2 mca2 values 2 nonmarine 34s values in associated gypsum 3 two superimposed networks of surface polygons one delineated by extensional boundaries the other by tepees 4 high water vadose zone isopachous grain cements 5 interconnected speleothem lined cavities and 6 the presence of evaporites only in surface sediments possible ancient examples of peritidal carbonate lithification by saline spring waters rising from confined aquifers are recognized in descriptions of carbonates from west texas lombardy and the atlas mountains the areal extent of each of these deposits suggests that the process may be a geologically important feature and its products may be diagnostic of semi arid or arid zone paralic sedimentation

temporal evolution of a carbonate coastal system abu dhabi united arab emirates abstract the southern shore of the persian arabian gulf comprises a low angle carbonate evaporite ramp system that provides a rare recent analogue for ancient epeiric settings including many carbonate petroleum reservoirs during the 1960s several studies documented the distribution of naturally occurring shallow marine facies in the shallow marine environments proximal to abu dhabi island subsequent coastal engineering projects have significantly modified the coastline and sublittoral zone many sedimentary environments have been lost with marine sites now sited beneath buildings parks or roads the data from the earlier studies are used as a pre anthropogenic base line in order to document and assess the temporal changes in the characteristics and distribution of carbonate sedimentary facies as observed today the locations of earlier sample sites were revisited in order to represent the complete range of shallow marine sedimentary environments the shallow subtidal environments adjacent to abu dhabi island continue to be areas of active carbonate sedimentation temporal changes in facies belt geometries and occurrence are assessed changes are recorded for most of the investigated sedimentary settings both in terms of sedimentary environment distribution and sediment composition offshore reefs and their associated back reef lagoons are no longer present ooid shoal and delta complexes are much reduced in their aerial extent now being replaced with shoreface facies or dredged channels significant dredging activity has increased tidal flow to lagoon environments thereby increasing connectivity to open marine conditions however land reclamation has substantially reduced the volume of the area of the lagoon environments despite these changes many facies display surprising resilience to anthropogenic activities with no discernible change in sedimentary facies or biotic distributions understanding these modifications and their associated driving mechanisms allows discrimination between anthropogenic and naturally occurring environmental perturbations this in turn develops our understanding of the temporal evolution of shallow marine carbonate facies under natural and anthropogenic influences

carbonate evaporite sequences of the late jurassic southern and southwestern arabian gulf the carbonate evaporite sequences of the upper jurassic arab and overlying hith formations in the southern and southwestern arabian gulf form many supergiant and giant fields that produce from the arab formation and are excellent examples of a classic reservoir seal relationship the present day sabkha depositional setting that extends along most of the southern and southwestern coasts of the arabian gulf provides an analog to these upper jurassic sedimentary rocks in fact sabkha related diagenesis of original grain supported sediments in the arab and hith formations has resulted in five distinct lithofacies that characterize the reservoir seal relationship 1 oolitic peloidal grainstone 2 dolomitic grainstone 3 dolomitic mudstone 4 dolomitized grainstone an 5 massive anhydrite interparticle porosity in grainstones and dolomitic grainstones and intercrystalline porosity in dolomitized rocks provide the highest porosity in the study area these sediments accumulated in four types of depositional settings 1 supratidal sabkhas 2 intertidal mud flats and stromatolitic flats 3 shallow subtidal lagoons and 4 shallow open marine shelves the diagenetic history of the arab and hith formations in the southern and southwestern arabian gulf suggests that the anhydrite and much of the dolomitization are a result of penecontemporaneous sabkha diagenesis the character and timing of the paragenetic events are responsible for the excellent porosity of the arab formation and the lack of porosity in the massive anhydrites of the hith which together result in the prolific hydrocarbon sequences of these formations

a quantitative analysis of recent arid coastal sedimentary facies from the arabian gulf coastline of abu dhabi united arab emirates abstract this study presents the results of the first quantitative analysis of surface sediments along multiple transects of the arabian gulf shoreline of abu dhabi united arab emirates the natural coastline of this low angle carbonate ramp depositional system is being anthropogenically modified at an unprecedented rate as this system is much employed as a recent analogue for many ancient depositional sequences it is imperative that sedimentological characteristics of natural facies occurrences are accurately recorded for employment in future applications we establish distinct relationships between the geomorphic setting and sediment characteristics siliciclastic grains admixed to this system are naturally sourced from the pliocene ghayathi formation and from aeolian sediment influx during dust storms this natural source of siliciclastic detritus is being increasingly superseded by siliciclastic material derived from anthropogenic activities evaporite minerals are similarly being contributed from anthropogenic sources the occurrence of mud to silt grade sediments is primarily controlled by the presence of a sediment binding microbial mat that prevents the removal of fine material during high energy events similarly the presence of a halite crust in the upper tidal flats and supratidal zone prevents aeolian deflation this study did not establish any clear relationship between coastal geomorphic setting and the bioclastic components present in the sediments this finding has major implications for the application of bioclasts in fine tuning palaeoenvironmental interpretation of ancient carbonate ramp coastal systems

mineralization of soft bodied invertebrates in a jurassic metalliferous deposit the jurassic marine biota of la voulte sur rhone france is characterized by three dimensional preservation of soft bodied animals and their internal organs in contrast to other soft bodied fossils those from la voulte are preserved in an unusual suite of minerals dominated by apatite calcite gypsum barite and pyrite with accessory cu pb and zn sulfides these are thought to be sedimentary in origin fossilization occurred rapidly enough to be influenced by tissue composition and involved a diagenetic sequence apatite calcite gypsum pyrite chalcopyrite galena the la voulte fossils reveal the role of apatite as a template for calcification and pyritization in soft tissue preservation

coastal sabkha and salt pan deposition of the lower clear fork formation permian texas abstract middle permian leonard series evaporites carbonates and red beds of the lower clear fork formation in the texas panhandle display many features common to modern coastal and continental sabkha facies similarities among lithofacies patterns and sequences sedimentary structures and anhydrite halite textures and fabrics of both the lower clear fork formation and modern sabkha facies permit construction of a model of halite deposition in coastal sabkha salt pan environments which may be generally applicable to other ancient sabkha facies in intracratonic basins and around stable or rifted continental margins inferred coastal sabkha and marine inner shelf environments and lithofacies recognized in the lower clear fork formation are largely based upon analogous modern depositional se tings and include the following 1 red siltstone to mudstone deposited in a wadi or desert alluvial eolian plain and inner sabkha mud flats both passing basinward into 2 chaotic mudstone halite of an inner sabkha saline mud flat which flanked 3 inner sabkha salt pans bearing banded to massive halite and laminated anhydrite and 4 nodular nodular mosaic and massive anhydrite and dolomite deposited in marginal sabkha and inner shelf environments salt pans may have formed in the inner sabkha as a result of displacive gypsum anhydrite growth and jacking up of the marginal sabkha surface which impeded seaward drainage of floodwater off the sabkha modern process sediment analogs include alluvial fans saline mud flats and salt pans of the coastal sabkhas in baja mexico the trucial coast and kutch india evaporites and terrigenous clastics in bristol dry lake california exhibit many features analogous with the permian suggesting that this setting though strictly continental serves as a process analog bromide values in lower clear fork halite average 40 ppm which is less than an unaltered marine halite but still within the range of marine halite that has undergone diagenesis upward decreasing values in the lower clear fork upper cycle may indicate a decrease in salinity during deposition or that the younger halite beds suffered more diagenesis than the underlying halite

eustatic controls on carbonate facies in reservoirs and seals associated with mesozoic hydrocaron fields of the arabian gulf and the gulf of mexico abstract abundant subsurface data for mesozoic and cenozoic sections of the us gulf coast and the middle east make it possible to track the relationship of shelf carbonates and evaporites associated with minor amounts of clastics to eustasy our contention is that because the sedimentary deposition for both regions was in part controlled by gentle tectonic subsidence punctuated by eustatic variations the major hydrocarbon fields which occur here can be related to sea level behaviur at the time of deposition of the reservoir sections and their early diagenesis with the exception of chalks most of these carbonate hydrocarbon fields can be related to highstand system tracts and include the following 1 1 keep up reservoirs with sheet like geometry formed when carbonate accumulation matched sea level rise aggrading to form shoaling upward cycles during sea level highstands 2 2 give up and catch up reservoirs with lense like carbonate geometry formed on drowned shelves during and following rapid sea level rises often downslope from carbonate margins give up reservoirs occur when carbonate accumulation was unable to match sea level rise and catch up reservoirs form where carbonate accumulation was initially unable to keep pace with the sea level rise but then aggraded to sea level 3 3 reservoirs with the prograded discontinuous clinoform geometry of the platform margin formed during stillstands by carbonate accumulation that not only kept up with the sea level rise but also advanced in a seaward direction source rocks for these carbonate reservoirs are often formed during rapid sea level rises while the reservoir seals are usually transgressive shales dense transgressive limestones and or highstand evaporites

revisiting the paleogene climate pattern of east asia a synthetic review abstract east asian paleogene climates have long been regarded as controlled by the planetary wind system which might result in a climate pattern with three latitudinally distributed zones two humid zones located separately in the north and south were lithologically designated by coals and oil shales while an arid zone in the middle was represented by red beds and evaporites because the middle arid zone was located along 30 n paleolatitude its presence had been further linked with a then subtropical high however this long standing model has recently been challenged by growing evidence from petrology sedimentology paleontology paleobiogeography paleoclimatology and climate modeling here we review the primary data from these disciplines and reinterpret their climate significances to revisit the east asian climate pattern during the paleogene petrologically while the occurrence of coals and or oil shales is accepted as an indicator for overall humid climates that of red beds and or evaporites is highly equivocal to exclusively indicate perennial arid climates unless their origins are carefully investigated in reality generic red beds merely represent an oxidizing environment not essentially associated with a single specific climate type meanwhile evaporites although typically precipitated in arid environments may be deposited in either perennial dry or seasonal monsoonal climates there is no solid evidence so far to convincingly support that the landscape of the so called middle arid zone was dominated by desert and or steppe under a then subtropical high during most of the paleogene the plant function type study additionally suggests that the middle arid zone appears to be lack of xerophytic vegetation even though some xerophytic or sclerophyllous plant taxa did sporadically occur interestingly paleozoological data show that the paleogene mammalian faunas were somewhat equably distributed over east asia strongly suggesting the evident absence of a critical biogeographical or climatic barrier stretched across the middle arid zone as the planetary wind model implied in contrast to the planetary wind model monsoonal or monsoon like paleogene climates have been broadly reported from the northern middle and southern east asia as well as adjacent regions of russia and kazakhstan if only the indicators for humid climates are considered simply due to the uncertainty of those for perennial arid climates east asia must have had a relatively dry region in the continental interior during the late eocene to oligocene transition likely caused by the continentality and or the rain shadow effect along with the global cooling the monsoonal interpretation is highly in agreement with the evidence from floras faunas basin analyses and modeling experiments and well explicates the paleogene climate distribution and seasonal dynamics of east asia however further studies will be largely needed to verify whether uniformly according to the modern criteria the paleogene climates of the east asia interior can be accurately attributed to the arid category

impact of diagenesis and low grade metamorphosis on isotope δ26mg δ13c δ18o and 87sr 86sr and elemental ca mg mn fe and sr signatures of triassic sabkha dolomites abstract dolomite is a common rock forming mineral in the geological record but its value as archive of ancient seawater 26 mg signatures and their variations in time is at present underexplored unknown factors include the sensitivity of 26 mg ratio to processes in the diagenetic and low grade metamorphic domain this paper documents and discusses the first detailed 26 mg data set from early diagenetic and burial dolomites samples come from the upper triassic hauptdolomit dolomia principale the dolomites italy and include coeval dolomicrites that underwent differential burial diagenesis and low grade metamorphosis in a temperature range between about 100 and more than 350 c magnesium isotope data are complemented by dolomite 13 c 18 o and 87 sr 86 sr isotope ratios as well as ca mg mn fe and sr elemental abundances and data on the dolomite crystal structure as indicated by dolomicrite 87 sr 86 sr ratios and petrographic evidence sabkha calcian d1 dolomites precipitated from evaporated seawater and stabilized at an early marine pore water diagenetic stage to d2 dolomites analysed here with increasing burial temperature dolomite 26 mg ratio scatter in the data set decreases with increasing mg ca ratio and degree of order specifically 26 mg ratio variability is reduced from 0 36 2 at burial temperatures beneath 100 c to about 0 14 2 at temperatures in excess of 350 c respectively with mean 26 mg values ranging constantly near 1 9 this suggests that at least for the rock buffered system investigated here dolomicrite 26 mg proxy data are conservative and preserve near pristine values even at elevated burial temperatures at present the main element of uncertainty is the mg isotope fractionation factor between evaporated seawater and dolomite a possible solution to this problem includes the compilation of data from modern sabkha environments including pore water and calcian dolomite 26 mg isotope signatures

tepees in peritidal carbonates origin via earthquake induced deformation with example from the middle cambrian of western canada abstract tepee structures are common in many ancient carbonate tidal flat successions and because analogues are known from tropical coastal areas they are well established as evidence for synsedimentary lithification of subaerially exposed carbonate sediment existing explanations involving desiccation thermal expansion and contraction fluctuating groundwater pore pressure or diagenetic force of crystallization do not adequately account for the style and degree of deformation seen in some examples such as those in the middle cambrian cathedral formation of the southern rocky mountains western canada these tepees provide evidence for essentially instantaneous events causing brittle failure of decimetre thick crusts of ooidal and pisoidal grainstone followed by their dilation rupturing separation tilting and shingling they can be explained as breccias generated by sporadic episodes of strong ground motion from earthquakes that emanated from a syndepositionally active fault system nearby variably directed tensile and compressive stresses broke crusts shifted them upwards and shuffled them laterally subsequent microbial encrustation and vigorous flushing by seawater in the resulting shelter cavities led to rapid stabilization by cementation recognition of the role of seismically induced deformation in explaining some tepee structures furnishes a proxy for synsedimentary tectonism and adds another member to the family of seismites which reflect a range of rheological properties of unlithified and lithifying sediments

taphonomy of insects in carbonates and amber abstract the major taphonomic processes that control insect preservation in carbonate rocks limestones travertines and nodules are biological insect size and wingspan degree of decomposition presence of microbial mats predation and scavenging environmental water surface tension water temperature density and salinity current activity and diagenetic authigenic mineralisation flattening deformation carbonisation the major taphonomic processes that control the preservation of insects in fossil resins amber and copal are different but can be considered under the same headings biological presence of resin producers size and behaviour of insects environmental latitude climate seasonality resin viscosity effects of storms and fires soil composition and diagenetic resin composition insect dehydration pressure carbonisation thermal maturation reworking oxidation these taphonomic processes are geographically and temporally restricted and generate biases in the fossil record nevertheless where insects occur they may be abundant and very diverse taphonomic processes may impact on phylogenetic and palaeobiogeographic studies in determining the timing of the origin and extinction of insect groups and in identifying radiations and major extinctions taphonomic studies are an essential prerequisite to the reconstruction of fossil insect assemblages to interpreting the sedimentary and environmental conditions where insects lived and died and to the investigation of interactions between insects and other organisms

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

the preservation potential of environmentally diagnostic sedimentary structures from a coastal sabkha abstract the abu dhabi sabkha constitutes the landward portion of the shallow sloping carbonate ramp situated on the northwestern coast of the united arab emirates uae the sabkha in this region is composed of a complex assortment of carbonate organic and evaporitic facies that constitute a regressive sabkha sequence the surface features of the sabkha can be grouped into distinct laterally continuous facies associations that are directly correlatable with elevation above present day sea level previous investigations have suggested the employment of the abu dhabi sabkha as a modern depositional analogue to ancient carbonate evaporite formations however a quantitative analysis of the relationship between sabkha surface and subsurface characteristics has not previously been undertaken this study describes in detail the sedimentary structures and textures seen at the sabkha surface and compares them to the holocene age facies retained in the shallow subsurface of the 36 sedimentary structures observed at the sabkha surface only seven 19 are still identifiable in the early burial realm the majority of the surface structures were lost during early burial as a result of microbial mat decomposition destructive evaporite precipitation and compaction the loss of diagnostic sedimentary features during early burial as a result of fabric destructive processes has considerable implications for the recognition and interpretation of ancient sabkha sequences documenting these processes from a range of modern sedimentary environments will aid in the identification of those diagnostic features that may be reliably employed during paleoenvironmental reconstructions

cool water shell bed taphofacies from miocene pliocene shelf sequences in new zealand utility of taphofacies in sequence stratigraphic analysis

geochemistry of preserved permian aragonitic cements in the tepees of the guadalupe mountains west texas and new mexico u s a abstract tepees are common depositional structures within the shelfal capitanian stage yates and tansill carbonate strata of the permian reef complex of the guadalupe mountains as part of the tepees botryoids of radiating aragonite crystals formed essentially contemporaneously with the host pisolitic strata although most of the cement in the tepees is composed of diagenetic low magnesium calcite x ray diffraction analyses indicate that aragonite constitutes as much as 27 within centimeter size patches back scatter electron microprobe analyses demonstrate a highly irregular pattern of alteration of partly preserved aragonite crystals these patches with the preserved aragonitic fibers have undetectable cathodoluminescence sr concentrations that range up to 3 900 ppm and 87sr 86sr ratios from 0 70689 to 0 70695 which are in agreement with worldwide marine values for the capitanian stage mass balance calculations show that in some samples the diagenetic low mg calcite associated with the preserved aragonite has over 2 300 ppm sr thus the diagenesis to calcite occurred under very low water to rock ratios the least altered of the aragonitic cements have 13c values as high as 7 8 v pdb equivalent to 6 v pdb for calcite and 18o values as low as 5 5 v pdb equivalent to 6 2 v pdb for calcite the high 13c values are consistent with worldwide marine values whereas the very low 18o values probably represent precipitation in hot equatorial shallow marine to tidal flat environments contrary to most diagenetic pathways displayed by marine carbonates increasing alteration has generally resulted in higher 18o values in these relict permian aragonites these analyses demonstrate conclusively that paleozoic aragonitic cements are still preserved in some strata

facies patterns and depositional models of permian sabkha complex red cave formation texas panhandle abstract the red cave formation permian leonard series in the texas panhandle consists of cyclic red bed clastic and carbonate evaporite members that were deposited in an extensive coastal sabkha desert wadi plain and a carbonate inner shelf which bordered the northern midland basin evaporite members were deposited in carbonate evaporite crustal sabkhas and clastic members were deposited in mud rich coastal to continental sabkhas north to south red bed wadi plain facies pass into coastal sabkha facies and inner shelf dolomite facies in a randall county core vertical sequences commonly include slightly fossiliferous faintly laminated to burrowed dolomitic mudstone and pellet wackestone overlain by cross laminated oolitic or pellet packstone to grainstone followed by algal laminated dolomitic mudstone and nodular anhydrite in dolomite matrix a progradational carbonate shoreline is inferred with supratidal or sabkha evaporite to intertidal algal mat and sand flat environments passing seaward into a shallow muddy subtidal inner shelf mud rich sabkha sequences culminate with red to green mudstone and anhydrite above shoreline carbonates carbonate and evaporite facies pinch out generally toward the northwe t and northeast into wadi plain red beds these facies include ripple drift cross laminated siltstone and sandstone deposited in braided fluvial channels adhesion rippled siltstone and red to green mudstone deposited in mud flat and interchannel environments desiccation features intraclasts root zones and paleosol horizons attest to subaerial exposure and probable nonmarine conditions large scale cyclicity of red bed clastic and carbonate evaporite members probably was controlled by the relative supply or fluctuating input of clastics to sabkhas by way of fluvial systems rather than by absolute sea level changes partial modern analogs to red cave sabkha depositional models are the coastal mud flats and alluvial fans in the northwestern gulf of california tidal flats and an ephemeral stream delta wooramel delta in gladstone embayment shark bay australia and the trucial coast sabkhas in the persian gulf each setting has certain facets that are remarkably similar to intepreted paleoenvironments and lithofacies of the red cave formation end of article last page 761

giant polygons in the triassic salt of cheshire england a thermal contraction model for their origin abstract the triassic salt in cheshire england has large polygonal patterns on bedding surfaces the polygons are bounded by deep v shaped fissures the fissures have a banded internal structure made up of individual units of pure secondary salt and clastic rich halite the salt was deposited from shallow brines in an arid environment a thermal contraction model is proposed here for the formation of the polygons calculations of the depth of penetration of thermal waves and the net contraction of salt beds indicate that annual temperature fluctuations would produce fissures of the observed depth and width it is suggested that thermal contraction is the most important factor in the initiation of all polygonal patterns on salt surfaces and that the polygon form that eventually develops is de endent on the thickness of the salt bed and the availability of brines to the salt surface

the hydrological setting occurrence and significance of gypsum in late quaternary salt lakes in south australia well exposed often laminated gypsum sequences occur in many quarternary salt lakes in southern south australia the gypsum in the salt lakes is classified by increasing grain size into gypsite gypsarenite and selenite the salt lakes are classified by age and hydrological setting into coastal salinas which are holocene sea water fed groundwater lakes and continental playas which are late pleistocene endorheic basins a study of the relationships between coastal salina hydrology and the associated gypsum deposition has shown the different types of gypsum form under distinct hydrological regimes as the hydrology above a coastal salina depositional surface changes through time so does the type of gypsum deposited application of a gypsum depositional model derived from a study of the coastal salina gypsum to those portions of a continental playa gypsum unit where deposition is no longer occurring confirms the applicability of the model to non salina gypsum deposits

tepees modern southern australia and ancient permian texas and new mexico a comparison abstract tepee structures are forming today about the edges of a number of holocene groundwater lakes coastal salinas in the coastal zone of south australia tepees form by the groundwater induced deformation of an extensive sheet of fenestral limestone known as a veneer boundstone underlying the veneer boundstone is an extremely porous aquifer known as a boxwork boundstone areas of groundwater resurgence in these salinas are characterized by an association of tepee structures boxwork boundstones and stromatolites the tepees in these salinas are termed groundwater or boxwork tepees to emphasize the importance of resurging groundwater in their formation preliminary studies of tepee structures in the back reef strata of guadalupian age in the guadalupe mountains of west texas and new mexico has shown that these tepees are also groundwater tepees such tepee structures in the guadalupe mountains are often associated with remnants of an underlying boxwork boundstone and or an underlying sandy palaeoaquifer they are tepees which formed in zones of groundwater resurgence at a time when the nearby reef was a subaerially exposed barrier limestone sheets composed of vadose pisolites were deformed coincident with tepee formation this association implies that vadose pisolites like tepees formed in areas of periodic groundwater resurgence characterized by a complex schizohaline hydrological regime

sedimentation distribution and diagenesis of organic matter in a recent carbonate environment abu dhabi u a e abstract in the modern hypersaline carbonate lagoon and sabkha sedimentary environments of abu dhabi united arab emirates three types of organic matter originate respectively from microbial mat avicennia mangrove and halodule lagoonal seagrass the study of recent sedimentary processes and cross sections through the sabkha sediments lead to the definition of organo sedimentary facies based on geochemical and sedimentological criteria this permits the construction of an organo sedimentary sequence which expresses the holocene sedimentary record involving a transgressive and a regressive sequence the various organic facies occur in both sequences heterogeneity within the individual organic facies reflects several factors including sedimentation dynamics mineral matrix oxidation and reduction and selective organic and mineral diagenesis these parameters are discussed in terms of depositional environment and location within the organo sedimentary sequence changes in distribution quantity and preservation potential of the buried organic matter are discussed in terms of sea level changes and sedimentary accretion rates

facies architecture of an isolated carbonate platform tracing the cycles of the latemar middle triassic northern italy the 720 m thick succession of the middle triassic latemar massif dolomites italy was used to reconstruct the lagoonal facies architecture of a small atoll like carbonate platform facies analysis of the lagoonal sediments yields a bathymetric interpretation of the lateral facies variations which reflect a syndepositional palaeorelief based on tracing of lagoonal flooding surfaces the metre scale shallowing upward cycles are interpreted to be of allocyclic origin short term sea level changes led to subaerial exposure of wide parts of the marginal zone resulting in the development of a tepee belt of varying width occasional emergence of the entire lagoon produced lagoon wide decimetre thick red exposure horizons the supratidal tepee belt in the backreef area represented the zone of maximum elevation which circumscribed the sub to peritidal lagoonal interior during most of the platform s development this tepee rim the subtidal reef and a sub to peritidal transition zone in between stabilized the platform margin the asymmetric width of facies belts within individual metre scale cycles was caused by redistribution processes that reflect palaeowinds and storm paths from the present day south and west the overall succession shows stratigraphic changes on a scale of tens of metres from a basal subtidal unit overlain by three tepee rich intervals separated by tepee poor units composed of subtidal to peritidal facies this stacking pattern reflects two third order sequences during the late anisian to early middle ladinian

antecedent aeolian dune topographic control on carbonate and evaporite facies middle jurassic todilto member wanakah formation ghost ranch new mexico usa

carbonate microbialites and hardgrounds from manito lake an alkaline hypersaline lake in the northern great plains of canada abstract manito lake is a large perennial na so 4 dominated saline to hypersaline lake located in the northern great plains of western canada significant water level decrease over the past several decades has led to reduction in volume and surface area as well as an increase in salinity the salinity has increased from 10 ppt to about 50 ppt tds this decrease in water level has exposed large areas of nearshore microbialites these organogenic structures range in size from several cm to over a meter and often form large bioherms several meters high they have various external morphologies vary in mineralogical composition and show a variety of internal fabrics from finely laminated to massive in addition to microbiolities and bioherms the littoral zone of manito lake contains a variety of carbonate hardgrounds pavements and cemented clastic sediments dolomite and aragonite are the most common minerals found in these shoreline structures however calcite after ikaite monohydrocalcite magnesian calcite and hydromagnesite are also present the dolomite is nonstoichiometric and calcium rich the magnesian calcite has about 17 mol mgco 3 ams radiocarbon dating of paired organic matter and endogenic carbonate material confirms little or no reservoir affect although there is abundant evidence for modern carbonate mineral precipitation and microbialite formation most of the larger microbialites formed between about 2300 and 1000 cal bp whereas the hardgrounds cements and laminated crusts formed about 1000 500 cal bp

late quaternary sea level changes of the persian gulf abstract late quaternary reflooding of the persian gulf climaxed with the mid holocene highstand previously variously dated between 6 and 3 4 ka examination of the stratigraphic and paleoenvironmental context of a mid holocene whale beaching allows us to accurately constrain the timing of the transgressive highstand and regressive phases of the mid to late holocene sea level highstand in the persian gulf mid holocene transgression of the gulf surpassed today s sea level by 7100 6890 cal yr bp attaining a highstand of 1 m above current sea level shortly after 5290 4570 cal yr bp before falling back to current levels by 1440 1170 cal yr bp the cetacean beached into an intertidal hardground pond during the transgressive phase 5300 4960 cal yr bp with continued transgression interring the skeleton in shallow subtidal sediments subsequent relative sea level fall produced a forced regression with consequent progradation of the coastal system these new ages refine previously reported timings for the mid to late holocene sea level highstand published for other regions by so doing they allow us to constrain the timing of this correlatable global eustatic event more accurately

a review of the origin and setting of tepees and their associated fabrics carbonate hardgrounds often occur at the surface of shallow subtidal to supratidal lacustrine and subaerial carbonate shelf sediments these are commonly disrupted and brecciated when the surface area of these crusts increases in the subtidal environment megapolygons form when cementation of the matrix causes the surface area of the hardgrounds to expand similar megapolygons form in the supratidal lacustrine and subaerial settings when repeated incremental fracturing and fracture fill by sediment and or cement also causes the area of the hardgrounds to expand the arched up antiform margins of expansion megapolygons are known as tepees the types of tepees found in the geological record include 1 submarine tepees which form in shallow carbonate saturated waters where fractured and bedded marine grainstones are bound by isopachous marine phreatic acicular and micritic cements the surfaces of these brecciated crusts have undergone diagenesis and are bored unlike tepees listed below they contain no vadose pisolites or gravity cements 2 peritidal and lacustrine tepees are formed of crusts characterized by fenestral pisolitic and laminar algal fabrics this similarity in fabric makes these tepees of different origins difficult to separate peritidal tepees occur where the marine phreatic lens is close to the sediment surface and the climate is tropical they are associated with fractured and bedded tidal flat carbonates their fracture fills contain geopetal asymmetric travertines of marine vadose origin and or marine phreatic travertines and or terra rossa sediments the senile form of these peritidal tepees are cut by labyrinthic dissolution cavities filled by the same material lacustrine tepees form in the margins of shallow salinas where periodic groundwater resurgence is common they include groundwater tepees which form over evaporitic boxwork carbonates and extrusion tepees which also form where periodic groundwater resurgence occurs at the margins of shallow salinas but the dominant sediment type is carbonate mud these latter tepee crusts are coated and crosscut by laminated micrite the laminae extend from the fractures downward into the underlying dolomitic micrite below the crust both peritidal and lacustrine tepees form where crusts experience alternating phreatic and vadose conditions in time intervals of days to years cement morphologies reflect this and the crusts often contain gravitational meniscus vadose cements as well as phreatic isopachous cement rinds 3 caliche tepees which are developed within soil profiles in a continental setting they are formed by laminar crusts which contain pisolites and fractures filled by micritic laminae microspar spar and terra rossa most of the cements are gravitational and or meniscoid in ancient carbonates when their cementation and diagenetic fabric can be interpreted tepee structures can be used as environmental indicators they can also be used to trace the evolution of the depositional and hydrological setting

geomorphological changes in the coastal area of farasan al kabir island saudi arabia since mid holocene based on a multi proxy approach abstract the geomorphological evolution of the southeastern coastal area of farasan al kabir island saudi arabia is revealed by the mapping of modern landforms and a multi proxy and high spatial resolution study including grain size particulate organic carbon mineralogy element geochemistry benthic foraminifera analysis and radiocarbon dating of a 3 3 m long sediment core the modern geomorphological features comprise a variety of arid landforms such as plateau cliffs and pediments of pleistocene coral limestones playa depressions located on plateau surfaces alluvial fans butte and sandy beaches the mid holocene evolution of the borehole area is resulted from the detailed analysis of five sedimentary units detected along the core matar 1 and includes three distinct stages a from 5253 223 y cal bp to 3138 223 y cal bp carbonate coarse grained material consisting of coral fragments molluscs calcareous algae and benthic foraminifera are deposited on a shallow marine fringing reefal platform which becomes progressively a nearshore backreef around 3675 215 y cal bp and later around 3138 223 y cal bp a reef ramp b since 3040 220 y cal bp the borehole area obtains the characteristics of a high energy beach that receives increasing inputs of terrigenous material c subsequently a supratidal backshore setting is established influenced mostly by terrestrial processes and occasionally by marine processes as it is indicated by the decreasing and sometimes sporadic presence of benthic foraminifera and recently a sedimentary veneer consisting of terrigenous carbonate and evaporite material is formed by terrestrial mainly wadi and aeolian processes

eocene paleoseismic record of the green river formation fossil basin wyoming u s a implications of synsedimentary deformation structures in lacustrine carbonate mudstones abstract laterally extensive intervals containing sedimentary deformation features are identified in outcrops of lacustrine deposits of the eocene 52 51 ma green river formation in fossil basin southwestern wyoming fossil basin is the smallest of the paleo lakes in the green river system and is located in the sevier fold and thrust belt which was tectonically active during deposition deformation structures include convolute lamination load structures hybrid brittle ductile features sedimentary dikes microfaults fluid escape features such as cusps and pipes oil shale breccias and mass transport deposits in most cases these structures are hosted by finely laminated variably organic rich carbonate mudstones that accumulated in a low energy profundal lacustrine environment deformed intervals range from a few centimeters to 5 m in thickness and are bound above and below by undeformed strata of the same facies which demonstrates the early post depositional timing of deformation the distribution of these features indicates a primary control exerted by sediment rheology resulting from variation in grain size clay and organic content and degree of lithification which in turn were governed by the depositional environment and early diagenesis based on their morphological attributes lateral extent and recurrence at different stratigraphic levels along with their sedimentary environment and the tectonic setting of the basin the deformation structures are interpreted to be seismites i e the result of stresses induced by syndepositional earthquakes and other potential trigger agents are rejected moreover stratigraphic relationships indicate that these small scale deformation features as well as the mass transport deposits formed on a virtually flat lake floor ruling out instability caused by the gravitational regime syndepositional deformation in fossil basin points to tectonic activity along the nearby absaroka and or hogsback thrusts and related fault systems seismites point to possible tectonic forcing as a mechanism for changes in bathymetry and sedimentation in the green river formation and consequently demonstrate their potential for elucidating the tectonic history of other lacustrine and marine basins

reply to the comment on first records of syn diagenetic non tectonic folding in quaternary thermogene travertines caused by hydrothermal incremental veining by billi et alii abstract in our previous paper billi et al 2017 using field geological observations u th dating and stable isotope analyses we studied two deposits of pleistocene thermogene travertines from tuscany in central italy we concluded our study 1 warning that the common stratigraphic concept of travertine being a sedimentary succession with age younging from bottom to top is not always correct 2 demonstrating that caco3 mineralization and veins can develop within the travertines after their formation with this syn diagenetic process being able to modify the continuous bottom up age evolution and 3 showing that this post depositional mineralization veining process can not only modify the temporal succession but also deform and change the initial depositional travertine structure and its petrophysical properties these conclusions could potentially make the interpretation of a travertine series more difficult than commonly thought alcicek et alii questioned our conclusions claiming that the travertine structures that we observed in tuscany and interpreted as post depositional features should have been interpreted in analogy to similar structures from travertines elsewhere as primary structures although we recognize as already thoroughly stated in billi et al 2017 that the travertine depositional post depositional processes generally require further studies we reaffirm the validity of our original interpretation at least for the structures analyzed in our previous paper we therefore counter all criticisms by alcicek et alii and conclude by indicating the way forward to further explore the depositional and post depositional processes of thermogene travertines

structural and depositional controls on the distribution of the upper jurassic shallow marine sandstones in the fife and angus fields area quadrants 31 39 uk central north sea abstract an integrated evaluation of the tectonic and depositional history of the upper jurassic of the fife and angus area of uk quadrants 31 and 39 has been carried out through 3d seismic interpretation and a range of geological studies sedimentological and petrological data indicate that the upper jurassic sands in the study area are the lateral equivalents of the fulmar formation they can be divided into three groups of sandstones deposited by different processes during an interval of almost 10 million years i open shelf group 1 sandstones comprise sands dominated by storm wave activity which accumulated in fault bounded mini basins embayments ii group 2 sandstones possibly deposited by storm induced flows and iii group 3 sandstones which may represent subaqueous dunes deposited in a tidally influenced shallow marine environment sedimentological and heavy mineral studies suggest that the sands in the study area were sourced from the adjacent mid north sea high and were transported along the shelf probably by wave storm and tide generated currents biostratigraphic dating indicates that the upper jurassic sands in the fife angus area were deposited during late kimmeridgian to upper middle volgian an earlier depositional period with a possible callovian age is also inferred deposition of jurassic sediments in the study area occurred during two transgression periods callovian and upper late jurassic separated by an erosional non depositional phase oxfordian to middle kimmeridgian the accumulation of late jurassic sands started in the fife embayment and progressed northwards it was confined however to the eastern side of the embayments possibly due to the hydrodynamic conditions of the area

giant polygons in the realmonte mine agrigento sicily evidence for the desiccation of a messinian halite basin abstract the messinian realmonte salt deposit consists of a 400 600 m thick halite succession that can be divided into four main lith ologic units base to top a cumulates of plates settled out from a stratified water column b plate cumulates in a shallowing upward sequence containing six kainite layers near the top of the unit c cu mulates of skeletal hoppers with chevron overgrowths precipitated from a nonstratified water body and d skeletal halite and anhydrite spectacular vertical fissures cut through the upper part of unit b at its boundary with salt unit c these fissures are spaced at intervals of up to 5 m apart extend down to a depth of 6 m and are filled by red mud the salt beds affected by the fissures are commonly upturned buckled and are truncated and onlapped by the succeeding flat lying halite beds of unit c additionally the upturned layers are cut by vertical dissolution pipes that extend down to as much as a depth of 4 m below the fissured surface to explain the observed superimposed structures we propose two mechanisms both induced by the desiccation of the evaporite basin 1 when the salt surface was exposed the halite layers were buck led broke into polygonal crusts and formed tepee structures the buckling was caused by a net volume increase due to thermal expan sion and what is more important precipitation of new halite induced by evaporative pumping of brines moving up from the groundwater table the buckled salt layers were then affected by meteoric dissolu tion which created vertical pipes 2 the tepee structures and the associated zone of dissolution pipes are further crosscut by a new network of large polygons these new polygonal sets are outlined by deep fissures in which red silt collected blown by the wind or carried by episodes of surface flooding this type of deep contraction crack is known to be produced by volumetric changes induced by annual temperature fluctuations the documentation of contraction polygons and other exposure fea tures represents the first report of desiccation events during the de position of the sicilian salt no geological data are yet available to settle the questions if the salt of sicily is correlatable with the halite present beneath the floor of the mediterranean and if the desiccation of the realmonte salt basin could have been induced by a local tectonic causes uplift of the basin floor by thrust activity b simple evaporitic drawdown c basinwide drop of the mediterranean sea level or d complex interaction among these factors

modern and late holocene dolomite formation manito lake saskatchewan canada abstract major advances have occurred in our understanding of modern dolomite formation and penecontemporaneous dolomitization over the past several decades manito lake located in west central saskatchewan canada is a large 65 km 2 deep z max 22 m perennial saline 45 ppt tds lake in which modern and late holocene dolomite coexists with other endogenic and authigenic carbonate precipitates including aragonite monohydrocalcite calcite and mg calcite like many other lacustrine dolomites manito lake dolomite is microcrystalline less than 1 m to 5 m ca rich and poor to moderately ordered it occurs as relatively pure hardgrounds and as a component of nearshore microbialites it also forms isopachous cements in consolidated siliciclastic shoreline sediments manito lake dolomite is most likely forming by mainly biomediated precipitation at or near the sediment water interface i in pore spaces of coarse siliciclastic sediments i e beachrock ii as fine laminae associated with microbialites and iii as a major component of mudstone hardgrounds and pavements

taphonomy of the insects from the insect bed bembridge marls late eocene isle of wight england the environmental setting and taphonomy of the insect fauna of the insect bed bembridge marls late eocene 36 ma of the isle of wight is described cluster analysis of taxonomic data on the insect fauna of a diversity of modern tropical environments together with that of the bembridge marls shows that the insects of the latter are characteristic of a primary sub tropical tropical forest subject to significant seasonal rainfall a similar approach indicates that the sample of taxa preserved in the insect bed is biased toward insects from leaf litter and lower herbage microhabitats external ornamentation of the cuticle is preserved on a micron scale and the individual microfibrils of the procuticle can be distinguished the insects of the bembridge marls are remarkable in preserving cuticle and mineralized internal tissues in a largely uncompacted state chemical analysis py gc ms reveals that the cuticle is composed of an aliphatic polymer possibly due to polymerization of cuticular waxes during diagenesis no chitin was detected the soft tissues which include sarcolemma and muscle fibres are preserved through replacement in calcite

holocene coastal carbonates and evaporites of the southern arabian gulf and their ancient analogues abstract the holocene sediments of the coast of the united arab emirates in the southeastern arabian gulf are frequently cited in the literature as type examples for analogous assemblages of carbonates evaporites and siliciclastics throughout the geologic record this paper is intended as a convenient single source for the description of sediments of this region providing information on how to reach the classic localities and some of the analogs the holocene sediments of the region accumulate over an area that is 500 km long and up to 60 km wide the sediments collecting offshore are predominantly pelecypod sands mixed with lime and argillaceous mud with these latter fine sediments increasing as the water deepens the pelecypod rich sediments also collect east of abu dhabi island both in the deeper tidal channels between the barrier island lagoons and in deeper portions of the protected lagoons west of abu dhabi island the shallow water margin is the site of coral reefs and coralgal sands whereas to the east oolites accumulate on the tidal deltas of channels located between barrier islands grapestones accumulate to the lee of the reefs and the oolite shoals where cementation becomes more common they are particularly common on the less protected shallow water margins of the lagoons west of abu dhabi island pelleted lime muds accumulate in the lagoons in the lee of the barrier islands of the eastern abu dhabi lining the inner shores of the protected lagoons of abu dhabi and on other islands to the west are cyano bacterial mats and mangrove swamps landward of these a prograding north facing shoreline is formed by supratidal salt flats sabkhas in which evaporite minerals are accumulating this paper describes the localities associated with 1 the mangrove swamps of the west side of the al dhabaiya peninsula 2 the indurated cemented carbonate crusts cyanobacterial flats and sabkha evaporites on the shore of the khor al bazam south of qanatir island 3 the reef and oolitic sand flats on the coast just east of jebel dhana and 4 the marine travertine and aragonite coats associated with the beach sediments in a small bay south of jebel dhana and 5 the sabkha mutti between jebel barakah and al sila similar sedimentological associations of carbonate and evaporites to those of the holocene of the united arab emirates are to be found in the tertiary and mesozoic sedimentary rocks of the immediate subsurface in the arabian gulf other analogs to this setting include the paleozoic carbonates of the western usa europe and asia mesozoic carbonates of the gulf of mexico europe and middle east and tertiary sedimentary rocks in the middle east

revision and update of the stratigraphic nomenclature of netherlands in 1991 the geological survey of the netherlands started a project for revision and updating of the pre quaternary lithostratigraphy of netherlands this had not been done systematically since 1980 main objective of the study are 1 to bring the lithostratigraphic ideas into agreement with new findings and increased knowledge of dutch subsurface geology lithostratigraphy was extended into the lower carboniferous and devonian 2 expansion and standardization of the definitions and descriptions of existing lithostratigraphic units 3 application of modern concepts e g sequence stratigraphy in order to describe better the distribution of reservoir prone sediments and 4 to reach consensus on a number of stratigraphy related subjects such as a chronological time frame application of biozonations and the designation of the behavior of main structural elements through time eight working groups were formed each working on a specific aspect or stratigraphic interval under the supervision of a steering committee both working groups and steering committee were composed of persons from the geological survey several leading oil companies and in some cases universities several working groups have completed their tasks and updates of these stratigraphic intervals are available at the conference posters will display stratigraphic updates of lithostratigraphy for the carboniferous zechstein lower triassic more and upper jurassic lower cretaceous less

dolomite formation within microbial mats in the coastal sabkha of abu dhabi united arab emirates microbial mediation is the only demonstrated mechanism to precipitate dolomite under earth surface conditions a link between microbial activity and dolomite formation in the sabkha of abu dhabi has until now not been evaluated even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences such an evaluation is the purpose of this study which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of abu dhabi along a transect from the intertidal to the supratidal zone this investigation revealed a close association between microbial mats and dolomite suggesting that microbes are involved in the mineralization process observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats in current models microbial dolomite precipitation is linked to an active microbial activity that sustains high ph and alkalinity and decreased sulphate concentrations in pore waters such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone by contrast these models cannot be applied to the supratidal zone where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity as no abiotic mechanism is known to form dolomite at earth surface conditions two different hypotheses can reconcile this result in a first scenario all of the dolomite present in the supratidal zone formed in the past when the mats were active at the surface in a second scenario dolomite formation continues within the buried and inactive mats in order to explain dolomite formation in the absence of active microbial metabolisms a revised microbial model is proposed in which the mineral template properties of exopolymeric substances play a crucial role

the hydrological significance of holocene tepees stromatolites and boxwork limestones in coastal salinas in south australia abstract holocene groundwater lakes salinas are common in the coastal zone of south australia they usually contain an evaporitic carbonate sequence that surrounds a central gypsum unit to form a bull s eye pattern of sediment distribution in the salina the evaporitic carbonates can be subdivided into three units a boxwork boundstone unit a veneer boundstone unit and an algal boundstone unit these units contain many interesting structures including tepees stromatolites and mound springs all of which show a megapolygonal outcrop pattern the salina carbonates have formed under a hydrological regime that has changed little since its inception some 6000 years ago consequently it has been possible to interpret the hydrological significance of the salina carbonates the salinas are fil ed by schizohaline surface waters whose water levels and salinities fluctuate seasonally all of the salina carbonates form where marine derived groundwater resurges from a surrounding dune aquifer into the margin of the salina tepee structures form in the veneer boundstone as a response to groundwater induced seasonal changes in the pore pressures of the underlying boxwork sediments the recognition of such groundwater tepees or other groundwater controlled structures in ancient carbonate sequences could aid paleohydrological interpretation of the ancient basin

some buried tertiary dykes of britain and surrounding waters deduced by magnetic modelling and seismic reflection methods dykes of tertiary age have been identified by modelling offshore marine and aeromagnetic data and onshore aeromagnetic data dykes have been found in the north sea off ne england and in the irish sea published aeromagnetic maps have also been used to locate non outcropping tertiary dykes in the scottish borders many of the offshore anomalies are caused by multiple dykes that cannot be separately resolved all dykes retain the dominant nw se trend of the known tertiary dykes although this trend approaches e w near the east coast of england under the north sea the trend swings back and becomes increasingly southerly trending the dykes may be the result of nw se compressional or ne sw tensional stress with deep crustal weaknesses causing changes in trend

neoarchaean c 2 58 ga halite casts implications for palaeoceanic chemistry possibly the most extensive and best preserved archaean halite casts yet discovered occur in the c 2 58 ga upper black reef and basal oaktree formations transvaal supergroup in mpumalanga province south africa halite casts are isolated on bedding planes range in size from c 1 mm to 20 mm and have cubic dumbbell and triangular shapes as well as hopper like pyramidal hollows on cube faces some of the casts display distinct hopper shapes characteristic of halite crystals the halite cast bearing pavements are developed within silicified mudstone interbedded with siltstone or stromatolitic dolomite associated sedimentary structures pointing to subaerial exposure include adhesion ripples and warts desiccation and prism cracks rill marks and tepee structures halite cast bearing beds are interpreted as supratidal flat or sabkha deposits the presence of isolated casts and hopper shaped crystals suggests that halite resulted from displacive growth within the sediment from supersaturated residual brines after mudstone deposition absence of any indication of the former presence of gypsum or anhydrite supports previous contentions that the neoarchaean ocean was deficient in sulphate or contained a high bicarbonate to calcium ratio such that with progressive evaporation most calcium was consumed before the gypsum stability field was reached the association of halite and carbonate in the upper black reef and basal oaktree formations constrains the palaeolatitude of the transvaal basin at 2 58 ga to subequatorial 10 30

holocene marine hardground formation in the arabian gulf shoreline stabilisation sea level and early diagenesis in the coastal sabkha of abu dhabi abstract this study provides the first comparison between a seaward and a landward section of the same diachronous hardground surface observed in the coastal sabkha of abu dhabi this hardground is described here in terms of its mode of formation its diagenetic environment and its impact on shoreline stabilisation during transgression the hardground is exposed in the intertidal zone and buried by a late holocene prograding succession of carbonates evaporites and microbial sediments in the supratidal zone the hardground itself is composed of bioclastic grains primarily of aragonitic composition that originate from intertidal depositional environments aeolian silt to sand sized quartz grains are also observed lithification occurred through the precipitation of pore filling aragonite high mg calcite and dolomite cements from sea and interstitial water that was marked by high salinities and temperatures as confirmed by stable isotope analyses high mg calcite and non stoichiometric dolomite are also observed as secondary recrystallisation products the formation of these two mineral phases as recrystallisation products was possibly microbially mediated lithification progressed in two phases the older phase of which is marked by higher amounts of non stoichiometric dolomite and high magnesium calcite as compared to the younger phase transgressive reworking of precursor siliciclastic sands was inhibited by the development of transgressive pore filling gypsum cements in the supratidal zone

facies and sedimentary environment of the permian carbonates khuff formation in the united arab emirates abstract the late permian to early triassic khuff formation of the united arab emirates is a 625 970 m thick sequence of shallow water carbonates dolomites limestones and dolomitic limestones with subordinate anhydrite it can be subdivided into ten facies units distinguished on the basis of their depositional textures that represent an overall regressive carbonate evaporite sequence based on the paleoecology sedimentary structures and lithology four distinct depositional settings can be recognized supratidal sabkha lagoon shoal and shallow shelf the khuff formation has both primary interparticle and secondary dissolution vugs and intercrystalline porosities

the role of decay and mineralization in the preservation of soft bodied fossils abstract fossil deposits that preserve soft bodied organisms provide critical evidence of the history of life usually only more decay resistant materials e g cuticles survive as organic remains as a result of selective preservation and subsequent diagenesis to more resistant biopolymers permineralization the permeation of tissues by mineralizing fluids may preserve remarkable detail particularly of plants however evidence of more labile tissues e g muscle normally requires the replication of their morphology by rapid in situ growth of minerals i e authigenic mineralization this process relies on the steep geochemical gradients generated by decay microbes the minerals involved and the level of detail preserved which may be subcellular depend on a number of factors including the nature of microbial activity and amount of decay availability of ions and the type of organism that is fossilized understanding these controls is essential to determining the conditions that favor exce

late holocene to recent aragonite cemented transgressive lag deposits in the abu dhabi lagoon and intertidal sabkha modern cemented intervals beachrock firmgrounds to hardgrounds and concretionary layers form in the lagoon and intertidal sabkha of abu dhabi seafloor lithification actively occurs in open current swept channels in lowlying areas between ooid shoals in the intertidal zone of the middle lagoon some centimetres beneath the inner lagoonal seafloor i e within the sediment column and at the sediment surface the intertidal sabkha the concept of concretionary sub hardgrounds i e laminar cementation of sediments formed within the sediment column beneath the shallow redox boundary is introduced and discussed based on calibrated radiocarbon ages seafloor lithification commenced during the middle to late holocene ca 9000 cal yr bp and proceeds to the present day lithification occurs in the context of the actualistic relative sea level rise shifting the coastline landward across the extremely low angle carbonate ramp the cemented intervals are interpreted as parasequence boundaries in the sense of marine flooding surfaces but in most cases the sedimentary cover overlying the transgressive surface has not yet been deposited aragonite micritic calcite and less commonly gypsum cements lithify the firmground hardground intervals cements are described and placed into context with their depositional and marine diagenetic environments and characterized by means of scanning electron microscope petrography cathodoluminescence microscopy and raman spectroscopy the morphology of aragonitic cements changes from needleshaped forms in lithified decapod burrows of the outer lagoon ooidal shoals to complex columnar lath and platy crystals in the inner lagoon precipitation experiments provide first tentative evidence for the parameters that induce changes in aragonite cement morphology data shown here shed light on ancient formerly aragonite cemented seafloors now altered to diagenetic calcites but also document the complexity of highly dynamic near coastal depositional environments

ages and stratigraphical architecture of late miocene deposits in the lorca basin betics se spain new insights for the salinity crisis in marginal basins unlike most neogene basins of the betic cordillera where the salinity crisis is dated to the messinian a contradictory tortonian dating was proposed for evaporites of the lorca basin as a consequence complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites in order to integrate the lorca basin into the geological context of the western mediterranean domain during the late miocene new sedimentological and stratigraphical studies coupled with new dating were performed which allow us to propose a messinian age for both diatomite bearing deposits and evaporites of the lorca basin these new ages challenge the idea of a tortonian salinity crisis in the lorca basin three main events of base level drop were evidenced during the messinian each event is correlated with successive steps of basin restriction shallow salina evaporites were deposited after a base level fall during the messinian before a final base level drop which led to the entire exposure of the basin this last exposure is interpreted as coeval with the deposition of first evaporites and halite in the deep mediterranean basins the reflooding which allowed the deposition of brackish deposits and a short lived marine incursion occurred at the end of the messinian base level drops occurred during eustatic falls amplified by the gradual uplift of the betic cordillera the exhumation of the tercia ridge along the strike slip alhama de murcia fault system during the messinian probably favoured the gradual restriction of the basin a discussion on correlations of main unconformities between several neogene basins of the betics is proposed suggesting a similar structural evolution at the regional scale