alluvial fan carbonate facies with evaporites eocene guarga formation southern pyrenees spain continental carbonates of the basal part of the guarga formation upper eocene have been studied in the field and in the laboratory both geographic pattern and vertical sequences served as a basis for sedimentary models the pattern reveals that carbonate deposition was greater in the western part of the tremp graus basin than in the eastern part studies of slabs and thin sections suggest high energy deposition in the eastern part of the basin and low energy deposition in the western part gross lithology petrography and faunal floral associations indicate sedimentary environments which include calcimorphic palaeosoils caliche nodule zones solid caliche nodule zones caliche crusts fluvial carbonates paludal carbonates and pond lake carbonates distribution pattern of the carbonate bodies and lithologies seem to be controlled by alluvial fan processes they are typical fining upward sequences in the sense of collinson 1978 which furthermore can be assigned to a channel bound group and a succession independent of fluvial channels referring to fan physiography the sequences can be subdivided into fluvial proximal interchannel fluvial distal interchannel lacustrine distal interchannel nearshore lacustrine paludine and lacustrine offshore carbonate facies the two last categories are distal alluvial plain and or fan edge associations the presence of especially charophyte oogonia adjacent to pseudomorphs of lenticular gypsum in the lacustrine carbonates of the western tremp graus basin indicates that their depositional environment was that of shallow lakes with alternating salinities diagenetic alterations consist of three major phenomena a general cementation of the carbonates by low mg calcite b pseudomorphs of lenticular gypsum and c silification the relationship of gypsum and silica diagenesis to the regional distribution of lacustrine carbonates suggests early diagenetic processes for their formation gypsum pseudomorphs are small and are found to be replaced by fe calcite throughout the whole area or are large and replaced preferentially by silica in the west only there is experimental evidence cody 1979 that distribution of gypsum morphology and crystal sizes can be related to increased salinities and increased organic production in the west chert gypsum fabrics from that area resemble the silex nectique of cayeux 1929 the occurrence of this noteworthy type of chert together with length slow chalcedony is an indication of relatively early silification of the gypsum it is suggested that the sediments containing the silicified lenticular gypsum hosted brines of partly marine origin which alternately became brackish or fresh an attempt was made to check the influence of evaporation during carbonate deposition by determining the stable isotope composition of the carbonates and of the chert the data show no distinct variations with respect to the presumed palaeoenvironments the ranges in the carbonates 13c 5 0 to 7 9 18 o 4 5 to 7 7 fit among the data given in the literature the values derived from chert 18o 26 9 to 31 smow support a concept of alternating salinities distribution of carbonate lithofacies indicate a systematic change in sedimentation from fluvial ephemeral to permanent lacustrine from east to west diagenetic alterations suggest an increase of salinities of pore waters in the same direction in addition the lacustrine limestones in the west were due to frequent changes in pore water salinity similar sequences lacking subtidal and or lagoonal fossil associations but including pseudomorphs of carbonate and chert after lenticular gypsum were described from the lower purbeckian of dorset west 1964 1975 1979 and from the tertiary of the paris basin fontes 1968 guarga limestone environments of especially the western tremp graus basin probably resembled the modern semi arid ephemeral saline lakes in australia burne bauld de dekker 1980 gypsum precipitation in these environments can be compared to the one in modern sabkhas from the mediterranean coast of egypt west ali hilmy 1979 ali west hilmy 1980

palustrine carbonates and the florida everglades towards an exposure index for the fresh water environment abstract palustrine carbonates are shallow fresh water deposits showing evidence of subaqueous deposition and subaerial exposure these facies are common in the geological record the intensity of modification is highly variable depending on the climate and the length of emergence palustrine limestones have previously been interpreted as marginal lacustrine deposits from fluctuating low salinity carbonate lakes but several problems remain with existing facies models 1 palustrine carbonates possess a lacustrine biota but commonly display fabrics similar to those of calcretes and peritidal carbonates 2 the co occurrence of calcrete horizons and karst like cavities is somewhat unusual and appears to indicate contemporaneous carbonate precipitation and dissolution in the vadose zone 3 the dominance of gray colors indicates water saturation apparently inconsistent with the evidence for strong desiccation overprint 4 profundal lake deposits are generally absent from palustrine sequences and sublittoral facies commonly make up only a small proportion of total thicknesses 5 no good modern analogue has been identified for the palustrine environment analogy with the florida everglades suggests a re interpretation of palustrine limestones not as pedogenically modified lake margin facies but as the deposits of extensive very shallow carbonate marshes the distribution of environments in the everglades is determined by the local hydrology reflecting the control of seasonal water level fluctuations and topography climate and topography were the main controls on deposition of ancient palustrine carbonates as in peritidal sequences aggradational cycles are capped by a range of lithologies evaporites desiccation and microkarst breccias calcretes lignite or coal horizons etc permitting interpretation of the climate careful analysis of lateral facies variations may permit reconstruction of subtle topography consideration of the florida everglades as a modern analogue for the palustrine environment has suggested the development of an exposure index for fresh water carbonates

pedostratigraphic models for alluvial fan deposits a tool for interpreting ancient sequences this paper reviews the scattered literature on quaternary arid type alluvial fan soil sequences and presents a series of model stratigraphies these are primarily influenced by the degree of entrenchment and by climatic controls these models are used to interpret well exposed miocene fan deposits from the madrid basin central spain

palaeontological and sedimentological observations on nonmarine lameta formation upper cretaceous of maharashtra india their palaeoecological and palaeoenvironmental significance abstract the lameta formation upper cretaceous is exposed in parts of central and western india as detached outcrops and covers an area of nearly 5000 km 2 it generally rests on precambrian and gondwana rocks and is invariably capped by deccan trap volcanic flows in the nand and dongargaon areas of the chandrapur and nagpur districts of maharashtra the lameta formation covers more than 400 km 2 attains a thickness of 20 m and is richly fossiliferous the palaeontological and sedimentological observations strongly indicate alluvial limnic environment for the deposition of the lameta sediments under semi arid conditions different lithofacies representing channel overbank paludal and lacustrine subenvironments have been identified the biota represents terrestrial semiaquatic and aquatic communities and is represented by dinosaurs fishes crocodiles chelonia gastropods ostracodes charophytes coniferales and angiosperms the biota appears to be mainly controlled by the different lithofacies thereby suggesting strong palaeoecological and taphonomical control over their occurrence records of mass death of clupeids have been observed in many layers within the lacustrine clays a nesting site of sauropods has been found near pavna along with evidence of site fidelity a clutch with small oblong shaped eggs of avian like affinity has been also unearthed from this nesting site the lameta sediments were deposited in a freshwater environment that provided the preferred ecological niche for large scale breeding and nesting of sauropods

lacustrine carbonates and pedogenesis sedimentology and origin of palustrine deposits from the early cretaceous rupelo formation w cameros basin n spain the berriasian rupelo formation of the w cameros basin consists of a 2 200 m thickness of marginal and open lacustrine carbonate and associated deposits open lacustrine facies contain a non marine biota with abundant charophytes both stems and gyrogonites ostracods gastropods and rare vertebrates carbonate production was mainly biogenic the associated marginal lacustrine palustrine facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history the succession was laid down in a low gradient shallow lake complex characterized by wide fluctuations of the shoreline carbon and oxygen stable isotope analyses from the carbonates show non marine values with ranges of 13 from 7 to 11 and 18 from 3 to 7 5 differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake analyses from the entire sample suite plot on a linear trend isotopic compositions become lighter with increasing evidence of pedogenic modification this suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil derived co2 the stable isotope data thus support evidence from petrography and facies relations that palustrine limestones form through pedogenic modification of lake carbonates

sedimentology of ancient coastal wetlands insights from a cretaceous multifaceted depositional system coastal wetlands are prominent modern environments widely studied in geomorphology and ecology but the term coastal wetland is still barely used for the sedimentological classification of ancient deposits the depositional system studied here leza formation cameros basin early cretaceous n spain includes diverse carbonate and clastic facies deposited at the sea land transition and is an illustrative example of the wide array of sedimentary environments that may occur in coastal wetlands systems the studied system was composed mainly of carbonate water bodies whose salinity ranged from fresh to brackish and near marine and which had variable input of clastic material due to their lateral connection with alluvial fans in addition the system also included carbonate water bodies with stronger marine influence tide influenced oolitic areas and relatively restricted evaporative settings the deposits of all these environments occur alternating with each other throughout a unit 30 280 m thick and they range from continental to marine conditions in a relatively small area approximately 10 km 3 30 km thus this sedimentological study of the leza fm provides an ideal opportunity to investigate challenging ancient deposits with both continental and marine features comparison with other modern and ancient coastal settings allows the conclusion that coastal wetland may be the most accurate sedimentological classification for the leza fm since it was not part of a major coastal system e g delta or estuary a series of general sedimentological characteristics of coastal wetland deposits are gathered from the cretaceous case study and from the modern and ancient examples examined these characteristics include predominance of shallow water facies common subaerial exposure and edaphic features great variety of interrelated continental transitional and marine environments with contrasting hydrodynamic and hydrochemical conditions and low diversity biotic communities including both continental and marine fossils as well as fossils of ambiguous affinities

carbonates associated with alluvial fans an example from the messinian colombacci formation of the pietrarubbia basin northern marche italy abstract the carbonates known as colombacci of a terrestrial series deposited within an upper messinian basin in marche italy have been examined by means of stable isotope analyses aas analyses study of thin sections and sem observations the results of the analyses attest to the in situ production of the carbonates in shallow ponds induced by biological activity as well as to the considerable influence of meteoric waters on late messinian sedimentation the carbonates were compared to coeval limestones from neighbouring basins the composition of the latter is indicative of precipitation out of meteoric water as well minor differences reflect the distinct settings of the separate marginal basins of the messinian mediterranean

sedimentology and geochemistry of carbonates from lacustrine sequences in the madrid basin central spain abstract lacustrine and alluvial carbonate facies have been investigated in middle miocene successions of the western side of the madrid basin in order to evaluate paleoenvironments in which carbonates formed carbonate facies are varied and include 1 calcrete and dolocrete 2 pond deposits 3 lake margin dolostone 4 mudflat carbonate and 5 open lake carbonate facies the dominant mineralogy of these is dolomite and or low mg calcite no high mg calcite or aragonite have been detected in any sample 18 o and 13 c values range from 8 20 to 1 80 pdb and 10 25 to 0 70 pbd respectively more negative 18 o and 13 c values correspond to predominantly calcite calcretes and to carbonate deposited in ponds at the foot of arkosic alluvium higher 18 o values are from both lacustrine carbonate and dolocrete this latter lithofacies has strong geochemical similarities to dolostones deposited in a lake margin environment mudflat carbonate deposited on shallow platforms subject to lake water oscillation shows great heterogeneity in both stable isotope value and trace element content the mineralogy of these carbonates is dominated by calcite and the limestones contain molds of gypsum occurrence of calcitized dolomite textures in these facies suggests the influence of fresher water during expanding lacustrine cycles or further interaction with less saline groundwater trace element contents are considered to be potential indicators of the different carbonate facies types thus aiding the paleoenvironmental interpretation however discrimination among carbonate facies on the basis of trace element contents appears to be dependent on the statistical method utilized for treatment of data more information is needed to ascertain their use as paleoenvironmental indicators

carbonate production within the orcadian basin northern scotland a petrographic and geochemical study a number of primary phases and textures are described for the debonian lacustrine carbonates of the orcadian basin textural and mineralogical variations record changes in the original lake water chemistry stable isotopic and trace element studies of the primary carbonate phases support the conclusion that the orcadian basin was the site of a lacustrine system that fluctuated between two end member conditions 1 one or a number of shallow evaporative playa lacustrine systems and 2 a deep probably stratified freshwater lake or lakes the basin was receiving 18o depleted meteoric groundwaters derived from the adjacent caledonian mountains from relatively fresh waters with a 18o composition of 7 or less primary precipitates of low mg calcite or pure calcite are preserved as calcite at times of low lake stand with a water composition of 3 or greater high mg calcite aragonite or protodolomite was precipitated and dolomitized sodium contents of the carbonates generally increase with dolomite content and the grain size of primary calcite precipitates was greater at higher lake levels

palaeoclimate control on sequence stratigraphic patterns in the late jurassic to mid cretaceous with a case study from eastern england abstract sediment supply is a fundamental control on the architecture of sedimentary sequences in clastic depositional environments the volume of sediment being transported into the basin of deposition is strongly dependent on both the nature of the weathering regime in the hinterlands and on runoff during arid low sea level phases in the late jurassic and early mid cretacwous clastic supply was reduced and long hiatuses became common at sequence boundaries or during maximum flooding these hiatuses amalgamated where sediment starvation produced strongly condensed super condensed sections in intervening humid higher sea level phases clastic supply was more abundant hence thick sediment packages separate sequence boundaries downlnpping surfaces should be apparent on seismic sections and condensed sections become rare where carbonate deposition dominates over clastic sediment formation is largely intrabasinal and the effects of palaeoclimate on sequence stratigraphy are less obvious knowledge of palaeoclimates may lead us to search for certain sequence stratigraphic patterns connected to changes in sediment supply

rapid identification of dolomite using a fourier transform infrared spectrophotometer ftir a fast method for identifying heinrich events in iodp site u1308 this study demonstrates that fourier transform infrared spectrophotometry ftir provides a quick and relatively inexpensive method for identifying and quantifying dolomite in deep marine sediments ftir is used to determine concentrations of dolomite in the top 29 m of sediments recovered at iodp site u1308 some of these dolomite peaks can be reliably correlated with heinrich events h1 through h6 thus ftir appears to provide a fast and reliable method for identifying heinrich events in deep sea sediments

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

seasonal wetland carbonate sequences and dynamic catenas a re appraisal of palustrine limestones abstract palustrine carbonate cyclothems are compared directly to well documented peritidal carbonate cyclothems in the case of the latter the trend of increasing degree of exposure seen vertically through a cyclothem has been interpreted as due to the aggradation of the sediment surface relative to the semi diurnal tidal regime palustrine cyclothems also show similar increases in the degree of exposure and this is interpreted as the effect of sediment aggradation in a seasonal wetland regime the resulting changes in the drainage characteristic revealed in a palustrinc cyclothem reflect a type of seasonally variable catenary relationship referred to here as a dynamic catena this model explains the key features of palustrine cyclothems and suggests the importance of seasonal wetland environments in ancient continental settings

black pebble occurrence and genesis in holocene carbonate sediments florida keys bahamas and tunisia abstract black carbonate lithoclasts along with blackened peloids ooids skeletal fragments and entire limestone beds are found in the shallow subtidal intertidal and supratidal zones of modern and ancient carbonate environments they are often associated with pedogenic features such as root traces or caliche the blackening is due to impregnation of the sediment by dissolved colloidal or finely particulate organic substances in an anoxic and alkaline environment or microenvironment the organic matter is derived from decayed algae and or decayed or burnt higher terrestrial plants iron sulfides contribute to the blackening especially in samples containing algal matter a complex interplay of adsorption of organic matter on carbonate crystal surfaces neomorphism and microcrystalline cementation in the vadose or freshwater phreatic zones is thought to fix the organic matter and make the black coloration relatively resistant to oxidation black pebbles form through reworking of the preferentially cemented and blackened sediment by coastal erosion they are mostly relics because the less consolidated host sediment is washed away black pebbles may thus be valuable indicators of ancient coastal and terrestrial environments

continental humid and arid zones during the jurassic and cretaceous abstract the global distribution of climatically significant criteria is surveyed for six successive time intervals hettangian toarcian aalenian callovian oxfordian tithonian berriasian barremian aptian cenomanian and turonian maastrichtian the criteria are primarily mineralogical evaporites coals bauxites ironstones and kaolinite but include sedimentological and palaeontological aspects of facies e g aeolian sands fossil ferns and xerophytes fresh water invertebrates in early and mid jurassic times an arid zone can be distinguished in low to mid latitudes in western pangaea with humid zones elsewhere in the late jurassic this arid zone spread northwards to embrace much of southern eurasia there followed in the early cretaceous a sharp reversal to more humid conditions over a large area extending from the eastern margin of north america to the middle east a major consequence of which was the widespread replacement of carbonates by coarse siliciclastic facies by late cretaceous times humid conditions were well established also in north america and the south atlantic margins and the tropical arid zone had contracted to a minimum the 87 sr 86 sr ratio of marine carbonates provides an independent monitor of continental runoff which is related to a area and b extent of aridity changes in the ratio confirm that taking sea level stand into account the late cretaceous was appreciably more humid than the late jurassic these climatic changes are related primarily to the progressive breakup of pangaea in the late jurassic and cretaceous which together with sea level rise in the mid to late cretaceous caused a significant increase in maritime influence this implies that monsoonal winds probably had a major role in promoting higher precipitation rates a puzzle remains as to why there was a spread of aridity in the late jurassic finally some implications for terrestrial plant evolution are noted

geochemical evaluation of fenghuoshan group lacustrine carbonates north central tibet implications for the paleoaltimetry of the eocene tibetan plateau abstract a sedimentologic petrologic and geochemical evaluation of lacustrine carbonates from the eocene oligocene fenghuoshan group of north central tibet provides insight into the paleoenvironmental and paleolimnological setting of the hoh xil basin during the mid tertiary fenghuoshan lacustrine rocks consist primarily of carbonate mudstones and wackestones these carbonates are generally less than 3 m in thickness and are intercalated with siliciclastic lacustrine and fluvial alluvial plain deposits individual limestone beds coarsen and contain increasing amounts of siliciclastic material upward fenghuoshan carbonates also contain abundant ostracode bivalve and charaphyte fossils sedimentologic evidence suggests that carbonate deposition occurred in shallow relatively short lived lacustrine systems that were subsequently filled by alluvial deposits of coeval fluvial systems stable c and o isotopic analysis of fenghuoshan carbonates show 18o values ranging from 11 7 to 10 3 vienna pee de

evolution of the adriatic carbonate platform palaeogeography main events and depositional dynamics abstract the adriatic carbonate platform adcp is one of the largest mesozoic carbonate platforms of the perimediterranean region its deposits comprise a major part of the entire carbonate succession of the croatian karst external or outer dinarides which is very thick in places more than 8000 m and ranges in age from the middle permian or even upper carboniferous to the eocene however only deposits ranging from the top of the lower jurassic toarcian to the top of the cretaceous can be attributed to the adcp defined as an isolated palaeogeographical entity although the entire carbonate succession of the karst dinarides was deposited within carbonate platform environments there were different types of carbonate platforms located in different palaeogeographical settings carboniferous to middle triassic mixed siliciclastic carbonate deposits were accumulated along the gondwanian margin on a spacious epeiric carbonate platform after tectonic activity culminating by regional middle triassic volcanism recorded throughout adria the african promontory a huge isolated carbonate southern tethyan megaplatform abbreviated as stm was formed with the area of the future adcp located in its inner part tectonic disintegration of the megaplatform during the middle to late early jurassic resulted in the establishment of several carbonate platforms including the adriatic apenninic and apulian separated by newly drowned deeper marine areas including the adriatic basin as a connection between the ionian and belluno basins lagonero basin and the area of the slovenian and bosnian troughs the adcp was characterised by predominantly shallow marine deposition although short or long periods of emergence were numerous as a consequence of the interaction of synsedimentary tectonics and eustatic changes also several events of temporary platform drowning were recorded especially in the late cretaceous when synsedimentary tectonics became stronger leading up to the final disintegration of the adcp the thickness of deposits formed during the 125 my of the adcp s existence is variable between 3500 and 5000 m the end of adcp deposition was marked by regional emergence between the cretaceous and the palaeogene deposition during the palaeogene was mainly controlled by intense synsedimentary tectonic deformation of the former platform area some carbonates mostly eocene in age were deposited on irregular ramp type carbonate platforms surrounding newly formed flysch basins and the final uplift of the dinarides reached its maximum in the oligocene miocene the adriatic carbonate platform represents a part although a relatively large and well preserved one of the broader shallow water carbonate platform that extended from ne italy to turkey although its continuity is somewhat debatable in the area near albanian greece boundary this large carbonate body which was deformed mostly in the cenozoic including a significant reduction of its width needs a specific name and the central mediterranean carbonate platform is proposed abbreviated to cmcp although the local names such as adcp for its nw part should be kept to enable easier communication and to facilitate description of local differences in platform evolution

continental brackish and marine carbonates from the lower cretaceous of kolone barbariga istria croatia stratigraphy sedimentology and geochemistry abstract during the early cretaceous wide areas of the dinaric adriatic carbonate platform emerged for long periods the hauterivian barremian carbonates from kolone barbariga show a few typical examples of lacustrine facies with dinosaur bones and brackish palustrine facies the sequence of the platform is made for the most part by subtidal and intertidal limestones the bone levels are located in a large depression few meters deep in the uppermost hauterivian marine limestones the filling facies of this depression are made by oncolitic rudstones and algal boundstones which represent marginal lacustrine facies and by laminated limestones thin stromatolitic levels and distal fringes of rudstones which represent relatively open lacustrine facies the fossil content is characterized by rare charophyte stems ostracods gastropods and plant remains while typical marine fauna is absent at the hauterivian barremian boundary a major emersion event has been observed then a slow transgressive phase occurred the transgressive facies are primarily made by mudstones with ostracods charophytes and spirillina brackish and probably freshwater facies wackestones with ophtalmidiidae and rare dasyclad algae storm layers with gastropods and miliolids and breccia like dinoturbated beds wackstones packstones and very rich in dasyclad grainstones outcrop at the top of the section representing the maximum of the transgression trace elements content carbon and oxygen stable isotope analyses have been performed to aid the palaeoenvironmental interpretation in this geological setting barium seems to discriminate between brackish and freshwater facies the isotopic values of the marine carbonates appear to depend on early diagenetic processes meanwhile lacustrine facies seem to show a weak signal of the depositional environment

palustrine sedimentation and associated features grainification and pseudo microkarst in the middle miocene intermediate unit of the madrid basin spain abstract a rather thick sequence 50 75 m of lacustrine limestones forms the uppermost part of the intermediate unit middle miocene in the ne part of the madrid basin central spain a gradual change from distal alluvial to open lake facies is recorded in this area red mudstones passing vertically to strongly mottled limestones are typical of the transition from distal alluvial to marginal lake deposits a wide variety of facies occur in the marginal lacustrine facies association all of them showing pedogenic features e g root traces alveolar septal structures pseudo microkarst micrites and biomicrites are interpreted as open lacustrine deposits although not as strongly pedogenically modified as the marginal lacustrine facies they still show evidence of subaerial exposure the carbonate sequence was deposited in a low gradient shallow lake system in which slight fluctuations in the water level caused extensive emergence pedogenic processes affected most of the lake deposits but modification was more intense in the marginal facies biogenic activity and mechanical reworking at lake margins led to the formation of pedogenic diagenetic pseudo microkarst and peloidal and or intraclastic limestones