drowning of algal mounds records from the upper carboniferous lower pseudoschwagerina limestone carnic alps austria abstract anthracoporella algal mounds up to 22 m thick occur within the cyclic sequences of the lower pseudoschwagerina limestone uppermost carboniferous carnic alps austria their depositional environment lay between the wave base and the base of the photic zone the algal mounds are overlain by dark well bedded cherty wackestones and packstones the cherty limestones contain cephalopods thick shelled brachiopods and sponge spicules and lack anthracoporella in growth position they are typical deeper water sediments deposited below the photic zone this sequence records drowning episodes the shallow water algal mounds were drowned by relative rise of sea level as sea bottom production shut down below the photic zone the sedimentological and paleontological evidence of drowning are supported by geochemical data of two measured sections the mean sulfur content of the well oxygenated algal limestones is 0 02 for both sections the toc values are 0 17 for the section ai and 0 10 for the section ar the s contents of the cherty limestones are approximately twice as high with values of 0 48 and 0 05 for the respective sections toc values of the cherty limestones are also significantly higher with 0 30 and 0 51 contents for the respective sections the cherty limestones document the termination of the mounds and the demise of reef building algae in each cycle this interval is therefore termed shroud facies the rapid sea level rise reported is a further proof for high magnitude sea level fluctuations in intervals of glacio eustasy the documented drowning mode is novel through the definable interval of drowning the repeated events during a short time interval the full record of pre syn and post drowning deposits and the unequivocal attribution to glacio eustatic sea level rise this mode seems to be characteristic of an icehouse period and clearly differs from the drowning mode in greenhouse periods which is often gradual lacks an unequivocal cause and is often preceded by subaerial exposure

oh defect contents in quartz in a granitic system at 1 5 kbar quartz is able to incorporate trace elements e g h li al b depending on the formation conditions p t and chemical system consequently quartz can be used as a tracer for petrogenetic information of silicic plutonic bodies in this experimental study we provide the first data set on the oh defect incorporation in quartz from granites over a pressure temperature range realistic for the emplacement of granitic melts in the upper crust piston cylinder and internally heated pressure vessel synthesis experiments were performed in a water saturated granitic system at 1 5 kbar and 700 950 c crystals from successful runs were analysed by secondary ion mass spectrometry sims and fourier transform infrared ftir spectroscopy and their homogeneity was verified by ftir imaging ir absorption bands can be assigned to specific oh defects and analysed qualitatively and quantitatively and reveal that 1 the aloh band triplet at 3310 3378 and 3430 cm 1 is the dominating absorption feature in all spectra 2 no simple trend of total oh defect incorporation with pressure can be observed 3 the lioh defect band at 3470 3480 cm 1 increases strongly in a narrow pressure interval from 4 kbar 220 g g h2o to 4 5 kbar 500 g g h2o and declines equally strong towards 5 kbar 180 g g h2o proton incorporation is charge balanced according to the equation h a p5 m3 b3 with a alkali ions and m3 trivalent metal ions

dynamics of tethyan carbonate platforms tethyan carbonate platforms are relatively short lived depositional systems which were born developed died and sometime resurrected in a tectonically active area in contrast with pericratonic platforms which are generally huge in size hundreds of kilometers across and show wide facies belts very gentle slopes ramps and transitional boundaries tethyan carbonate platforms are smaller tens of kilometers and have steep slopes generally faulted boundaries and abrupt facies changes it appears clear that the overall control on these two contrasting systems is the geodynamic milieu relatively stable in the first case where eustatic oscillations and long term subsidence are probably the main dictators quite dynamic and aggressive in the second one where carbonate platforms developed through the entire geodynamic spectrum rifting transtension transpression and collision of the wilson cycle primary controls on tethyan carbonate platforms appear to be tectonics most important and eustatic sea level oscillations which determine their emplacement growth and decay their overall shape and architecture are a function of these factors secondary factors affecting tethyan carbonate platform evolution are physiography oceanographic conditions and biology as a function of geologic time especially across the mesozoic tertiary boundary facies and facies distribution and to a lesser extent their shape are controlled by thesemore variables less

platform drowning leading to cool water carbonate deposition evolution of a late ordovician turinian chatfieldian mixed sediment platform within the taconic orogen long point group newfoundland appalachians late ordovician turinian chatfieldian drowning of a mixed carbonate siliciclastic platform within the taconic orogen newfoundland appalachians is recorded by net deepening of an initial warm shallow water platform succession lourdes formation culminating in a metre scale thick condensed interval that characterizes a drowning succession punctuated by storm deposits composition of transported material suggests that seaward drowning was coupled with back stepping of a high energy carbonate factory related to hinterland uplift and erosion that would eventually lead to drowning of the outer platform beneath marine transported siliciclastic sediments winterhouse formation in the new offshore shelf setting a sparse reciprocal stratigraphy of fine to very coarse grained phosphatic carbonate and mixed sediment is interpreted to document gravity flow deposition downgradient from either a sustained or episodically developed high energy cool water carbonate source along the inner shelf transported carbo

facies associations and evolution of pelagic carbonate platform basin systems examples from the italian jurassic abstract during the structural and sedimentological evolution of rifted continental margins in carbonate dominated settings a characteristic stage is commonly reached when pelagic carbonate sedimentation occurs in association with complex fault block systems an integrated study of the ammonite biostratigraphy and sedimentology of jurassic pelagic rocks in the umbria marche apennines central italy and in the sila mountains north east calabria southern italy has revealed three distinctive facies associations which can be related to specific structural and depositional settings the condensed pelagic facies association is the constituent of condensed usually discontinuous sequences with numerous hiatal surfaces the normal and resedimented pelagic facies association is typical of thicker sequences comprising gravity flow and rockfall deposits the composite pelagic facies association is one in which rockfall deposits are found associated with condensed sequences containing minor or no gravity flow deposits palaeotopographical highs are dominated by the condensed pelagic facies association and constitute the pelagic carbonate platform pcp structurally the pcp can be coincident with the top of a horst or central high block or the crestal area of a tilted block in the latter case the sediment surface of the pcp slopes gently maximum of 1 3 in this the shallowest area of a pelagic carbonate ramp pcps can have erosional bypass rare and depositional margins stepped margins also exist as subparallel rows of erosional and bypass margins trends from erosional to depositional margins are usually seen as a response to basin filling and burial of submarine tectonic escarpments by pelagic deposits in late synrift or early post rift times this is apparent from progradation of pcp facies deposits beyond the structural boundaries of the pcp palaeoenvironmental analysis in pelagic carbonate platform deposits of the umbria marche apennines suggests that drowning of ancestral peritidal carbonate platforms in pliensbachian time was followed first by a moderate deepening and then by shallowing in the tithonian

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

reconstruction of a lost carbonate platform on the shelf of fennosarmatia evidence from visean polymictic debrites holy cross mountains poland

accumulation rates of carbonate platforms the growth potential of carbonate platforms i e the maximum rate at which they can aggrade vertically is difficult to assess to estimate the growth potential from the conservative side and search for variations with time we have compiled published accumulation rates from the phanerozoic accumulation rates vary in a pattern with maximum rates up to 200 m ma or more not corrected for compaction in the late devonian permian late triassic late jurassic and mid cretaceous separated by intervals of reduced rates e g carboniferous early jurassic and late cretaceous the most dramatic drop occurs at the permo triassic boundary after which there is no documented platform growth this pattern resembles the evolutionary rhythm of bloom and demise of reefs and reef builders the observed maximum accumulation rate of 200 m ma over 10 6 10 7 yr is probably imposed by the maximum rate of long term relative sea level rise on passive margins the most favorable site for carbonate platform deve

the drowning of a carbonate platform an example from the devonian carboniferous of the southwestern holy cross mountains poland the broad middle devonian carbonate platform of the holy cross mountains was fragmented during the frasnian and afterwards submerged as isolated blocks and transformed into a topographic depression the section exposed in the ostrowka quarry illustrates a well documented drowning of the last small fragment seamount of this carbonate platform which submerged during late devonian and early carboniferous times the recognized facies succession reflects a progressive stepwise lowering of the sediment surface through time from a peritidal lagoonal environment to a deep water anoxic basin the frasnian shallow water carbonate platform is represented by lagoonal facies with peritidal sediments small scale deepening upward cycles punctuated with emersion surfaces are a feature of this stage they resulted from a combination and continuous balance between carbonate production subsidence and low order eustatic sea level fluctuations the carbonate platform aggraded at rates around 100 125 m ma the shallow water peritidal carbonates are separated from the post platform deposits by an unconformity surface developed during subaerial exposure the flooding of the faulted block of galezice in the pre late marginifera time and the subsequent initial drowning resulted primarily from a rapid sea level rise small dimension of the seamount and its cemented upper surface were the most important factors that facilitated the sediment removal and thus suppressed the sediment accumulation a condensed section was deposited on the top of the seamount its stratigraphic succession and rare cephalopod storm beds account for a model of redistribution of sediment over the swell disintegrated by small scale faulting during drowning the seamount traversed down through the photic zone at an average rate not higher than 20 25 m ma transformation of the swell into a basin accelerated in the late tournaisian anchoralis zone it is manifested by an increase of deposition rate and by a lithology of alternating limestones and clays with participation of fine grained calciturbidites the associated tephra deposits and syndepositional ferruginous hydrothermal mineralization were the result of extensional tectonics on the facies evolution the drowning was completed in the visean with deposition of black siliceous shales in the starved basin the death of the devonian carbonate platform in the galezice area illustrates well the famed paradox of drowned platforms as the subsidence rate was much slower during the drowning than during the phase of the platform aggradation

reply to narkiewicz 2017 comment on thermal evolution of paleozoic successions of the holy cross mountains poland abstract in this paper we reply to the criticisms advanced by narkiewicz 2017 on the paper by schito et al 2017 we clarify the issues related to the stratigraphic and thermal maturity constraints used for reconstructing burial and thermal models of the two blocks of the holy cross mountains we also show how geological evidences brought by narkiewicz 2017 as a proof of elevated variscan heat flow are not conclusive or at least suggest the occurence of a localized thermal anomaly only along the area of the holy cross fault in the end we performed new burial and thermal models in the kielce region demonstrating that stratigraphic thickness variations between schito et al 2017 and narkiewicz et al 2010 produce only negligible differences in levels of thermal maturity of paleozoic rocks in addition we outline that levels of thermal maturity for silurian rocks can be matched only by using constant heat flow values through the paleozoic and point to a decisive role for the absence of regional high variscan heat flow in the area

depositional evolution of a lower paleozoic portion of the southalpine domain the mt pizzul area carnic alps italy the carnic alps represent the best exposed paleozoic succession within the alpine domain being fossiliferous mostly non metamorphic and largely complete this study focuses on the area around mt pizzul because the bedrocks record well the basin dynamics and most of the units are conodont bearing our aims were to contribute to the procedure of formalization of the lithostratigraphic units and to understand the depositional and deformation history of the study area the area has been mapped tectonic overprint constrained and the successions described measured and dated as a second order aim we discuss these data to infer the relations with other parts of the carnic basin and to recognize the global controls on sedimentation the depositional evolution can be sketched as follows pre hirnantian ramp type margin hirnantian glacioeustatic related deposits and unconformity pelagic deposition in a ramp type margin p idoli eifelian slope formation and differentiation in buildup foreslope and pelagic environments eifelian frasnian transgression and reef drowning frasnian visean probable subaerial exposures likely during in uppermost famennian and visean times and turbidite deposition visean global controls or deposits suggesting a global control are documented including the boda event the hirnantian glaciation the middle devonian reef growth the kacak event and the high frequency sea level fluctuations around the devonian carboniferous boundary the drowning of the buildups here and elsewhere in the carnic alps started during the frasnian unlike observed globally this suggests that local tectonics lead to progressive deepening up to the transition to turbidite deposition

non annual laminations and expansion of anoxic basin floor conditions in santa monica basin california borderland over the past four centuries sediments from box cores in the deep portion of santa monica basin have been examined by x radiography and the upper 10 20 cm are characterized by laminations 1 5 mm in thickness age dating of 9 cores by 210pb analysis has shown that accumulation rates on the central basin floor have been remarkably constant during the past century averaging 16 0 0 4 mg cm2 yr densitometer analysis of the x radiography films from 7 cores and spectral analysis of the resulting time series indicates that most lamination couplets have a periodicity in the 3 7 year range a range matching that of the el nino southern oscillation periodicity the median periodicity appears to have decreased slightly during the past 3 centuries from 7 0 years during 200 300 yrs b p to 5 2 yrs during 0 100 yrs b p this trend could be due to a decreasing sedimentation rate an increasing forcing frequency or an increasingly faithful response of the basin in more recent years multiple processes have contributed to creation of the laminations in santa monica basin the principal factors appear to be 1 variations in porosity due to the relative abundance of organic filaments probably formed by beggiatoa mats and 2 compositional variations that reflect variations in carbonate lithogenous ratios and in grain size both of these are expected to respond to enso events the presence of near anoxic bottom waters has prevented bioturbation permitting laminations to be preserved basin bottom waters became nearly anoxic about 350 years ago at the onset of warming as the little ice age waned expansion of the near anoxic area during the past century may have been augmented by 20th century anthropogenic effects the style of these non annual laminations in santa monica basin matches that of the annual laminations in the adjacent santa barbara basin and demonstrates the need for caution in interpreting all laminations as representing annual varves

erosion on an anaerobic seafloor significance of reworked pyrite deposits from the devonian of new york state abstract several devonian black shale units in new york state display conspicuous basal discontinuities marked by accumulations of exhumed and reworked pyrite nodules tubes and fossil steinkerns this coarse debris is overlain by and or interlayered with black laminated shale the most important level is the leicester pyrite member which occurs along a regional unconformity flooring black shale deposits of the basal genesee formation the detrital pyrite occurs in discontinuous lenses both on and slightly above this surface basal genesee beds geneseo shale member record westward overlap of basinal anoxic muds during a major marine transgression taghanic onlap the reworked pyrite deposit is regionally diachronous as indicated by conodont data and shingling of lenses with basal genesee beds which are successively younger from east to west pyrite chemically unstable in aerobic bottom settings was exhumed and concentrated on the sea floor during brief erosion episodes in a normally anaerobic environment lenses contain istinctive diagenetic pyrite structures e g fossil steinkerns burrow tubes derived from muds underlying the discontinuities erosional reworking of pyrite on the sea floor is shown by mechanical breakage of pyrite grains reorientation of geopetal stalactitic pyrite and compactional features plus alignment of pyritic tubes by bottom currents general absence of carbonate allochems in lenses is believed to reflect dissolution of carbonate following its exhumation episodic deep storm generated turbulence was probably important in exhuming and transporting pyrite however shoaling internal waves impinging the sediment starved basin margin slope may also have been important in scouring the bottom a model of internal wave erosion during the taghanic transgression is presented herein we feel that such erosion concentrated at or near the base of the pycnocline during a period of relative sea level rise offers a particularly good explanation for the observed juxtaposition of geneseo and other similar black shale deposits on erosional discontinuities the diachronous character of leicester lenses and associated black genesee muds above the unconformity suggests a transient rather than fixed basin axis allowing for progressive westward burial of the unconformity and assiciated remanie deposits by onlapping black muds older and younger occurrences of resedimented pyrite are briefly described from other devonian basinal units and are shown to have formed in about the same manner as the leicester reworked pyrite is believed to be common although seldom recognized in phanerozoic sediment starved basinal settings moreover detrital pyrite analogous to that described herein probably awaits discovery in certain modern marine basins

comparing optical and raman spectroscopic investigations of phytoclasts and sporomorphs for thermal maturity assessment the case study of hettangian continental facies in the holy cross mts central poland abstract thermal maturity of six organic rich samples from jurassic continental successions cropping out in the holy cross mountains in central poland has been characterized by classic thermal maturity indicators micro raman spectroscopy and palynomorph darkness index in order to create a multi method workflow for complex palynofacies thermal maturity assessment transmitted light observations on dispersed organic matter define a hettangian lacustrine depositional environment characterized by periods of reducing oxidizing conditions and variable sedimentation rates thermal maturity detected by classical maturity indicators and pdi indicates an early maturation stage of hydrocarbon generation and is in agreement with spectroscopic analyses performed on phytoclast groups moreover raman parameters in the sporomorph group indicate a systematic shift toward a lower degree of aromatization compared to the phytoclast group finally the multivariate statistical analysis performed on raman spectra is found to be a promising tool to define and predict the heterogeneity of dispersed organic matter in sediments

pelagic carbonate platforms in the geologic record their classification and sedimentary and paleotectonic evolution drastic differences in thickness and abrupt lateral facies changes in synrift and postrift pelagic sequences usually indicate structural control over deposition although the highs and the basins in pelagic carbonate systems have long been recognized in ancient rifted continental margins relatively little detailed information has been available on facies transitions between the two and on the geometries of pelagic sediment bodies outcrops in the umbria marche apennines central italy provide new constraints for jurassic paleogeographic reconstructions allowing for the development of models for these depositional systems pelagic carbonate platforms pcps are submarine highs that are drowned fragments of an ancestor regional peritidal carbonate platform pcps can be horsts or crests of rotated blocks the extensional regime and drowning history exert a major control over the pcp type and over the composition of sediment which fills inter pcp basins given the very low rates of pelagic sedimentation a few mm 1000 yr the effects of faulting on submarine topography are drastic block tilting is of great importance creating pelagic carbonate ramps that are the source area of most of the gravity flow deposits in half grabens excessively rapid tilts cause nondeposition in horst and graben settings on the other hand basins are sediment starved and there are comparatively only minor gravity flows ma s transport there is mostly in the form of collapse of platform margins the margins of pcps are erosional during most of pcp history becoming depositional when adjacent basins are filled stepped margins develop through fault induced reduction of the pcp area back stepping

deciphering the message of early cretaceous drowning surfaces from the helvetic alps what can be learnt from platform to basin correlations drowning unconformities are a frequent feature of carbonate platforms and generally express the incapacity of shallow marine ecosystems to adapt to abrupt sea level rise and or palaeoenvironmental change during the late hauterivian and early barremian the helvetic carbonate platform experienced a major drowning phase documented by the phosphate and glauconite rich altmann member it has been shown that a drowning unconformity in the form of a hardground at the base of the altmann member on the pilatus summit central switzerland results from a complex polyphased diagenetic history that includes two main phases of phosphogenesis using carbon isotope stratigraphy biostratigraphy and sequence stratigraphy the correlation of this drowning unconformity from the helvetic domain with more distal and more complete sedimentary archives allows reconstruction of the sequence stratigraphic context of the drowning surface and also an estimation of the amount of time represented by the episodes of condensation unconformities associated with the altmann member drowning phase developed during transgressive episodes when strong currents arrived onto the previously subaerially exposed platform and periods of phosphogenesis may have lasted up to 2 8 myr variations in trophic levels and hitherto less well known intervening emersion phases played an essential triggering role for the altmann drowning phase high resolution studies of drowning unconformities unravel the diversity of palaeoenvironmental parameters involved in the unfolding of such crises during the evolution of carbonate platforms

facies patterns and depositional environments of palaeozoic cephalopod limestones abstract in the eastern anti atlas morocco a platform and basin topography was established during the late devonian probably as a result of early variscan tensional tectonics cephalopod limestones were deposited on shallow pelagic platforms platform slopes and shallow slowly subsiding basins on the platform a transition from land areas into nearshore quartzose brachiopod coquinas crinoidal limestones condensed cephalopod limestones and finally into nodular limestones is observed the latter often become disintegrated into incipient debris flows which pass into nodular limestone marl alternations of a shallow basin deeper basins with shale sedimentation lack cephalopod limestones similar facies types also occur in the late devonian of the montagne noire france rheinisches schiefergebirge west germany moravian karst czechoslovakia holy cross mountains poland and in the early carboniferous of the cantabrian mountains spain due to strong late variscan compressional tectonics and limited outcrops detailed facies patterns could not be mapped in these regions but the same facies types as in the eastern anti atlas suggest similar coast platform slope and shallow basin topographies during cephalopod limestone deposition water depth on the platforms was in the order of several tens to about one hundred metres as is inferred from repeated subaerial exposures and distinctive depositional and faunal floral features water depth in the adjacent shallow basins might have reached several hundreds of metres cephalopod limestones represent a typical stage in the evolution of geosynclines characterized by extremely low sedimentation rates 1 5 m m y 1 this stage is preceded by deposition of thick neritic clastics and or carbonates and is succeeded by deposition of deep water clastics or flysch

solar modulation of cosmogenic nuclide production over the last millennium comparison between 14c and 10be records for about the last 30 years it has been recognized that the high frequency component of the tree rings 14c 12c record is dominated by the modulation of the cosmic ray flux by the solar wind in particular it has been demonstrated that the three most recent periods of low sunspot occurrence were characterized by high values of atmospheric 14c 12c during the last millennium other periods of high 14c 12c values were observed but their solar origin is still debatable in the present work we compare these fluctuations with an independent record of cosmogenic 10be measured in ice from the south pole to check the solar origin of the observed 14c 12c variations in order to compare quantitatively the results obtained on 10be and 14c it is necessary to take into account the different behaviour of these two cosmogenic isotopes and especially the damping effect of the carbon cycle in the case of 14c as an input to a 12 box numerical model we used the relative fluctuations of the 10be concentrations record measured in south pole ice and converted it into a synthetic 14c record we took into account the fact that 10be modulation is enhanced in polar regions due to the orientation of the geomagnetic field as expected the fluctuations of the modelled 14c record are much smaller a factor of 20 than those observed for the raw 10be record in addition the variations are smoother and shifted in time by a few decades the 10be based 14c variations closely resemble the 14c measurements obtained on tree rings r 0 81 in particular it is easy to identify periods of maximal 14c 12c which correspond to solar activity minima centred at about 1060 1320 wolf 1500 sporer 1690 maunder and 1820 dalton yr a d cross correlation calculations suggest that there is no significant lag between the 10be based 14c and the tree ring 14c records our study strongly suggests the dominance of the solar modulation on the cosmonuclide production variations during the last millennium

organic rich radioactive marine shale a case study of a shallow water condensed section cretaceous shaftesbury formation alberta canada abstract organic rich radioactive shales are a common regional feature resting on cretaceous transgressive surfaces in western canada the basal shale in the shaftesbury formation late albian from the peace river area of northern alberta is characterized by high gamma ray high resistivity and low neutron wireline log signatures three facies in ascending order are present within the basal shaftesbury formation 1 a brackish water estuarine shale 2 a restricted marginal marine shale which is radioactive and 3 an open marine normal salinity shale the radioactive shale contains an abundance of large lenticular algal cysts cf lancettopsis lanceolata madler 1963 which are rare in overlying and underlying shale the algal cysts and high organic content may be the locus of th radioactivity the total organic carbon content 6 and sulphur content 3 4 of the radioactive shale also are higher than the shale above and below with a different mineralogy as well the radioactive portion of the basal shaftesbury shale has the characteristics of a condensed section it is directly above a ravinement surface and transgressive lag deposit which in turn locally overlie estuarine sediments deposited within an incised valley other characteristics include evidence of low oxygen values low concentrations of benthonic foraminifera and evidence of a slow sedimentation rate palynological micropaleontological and geochemical results indicate that the radioactive s ale was deposited in restricted marginal marine conditions and that overlying shale shows a progressive deepening to nearshore open marine conditions this radioactive shale does not represent the deepest water sediments of the transgression but is a condensed section deposited in relatively shallow water

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

deciphering the history of climate and sea level in the kimmeridgian deposits of bure eastern paris basin abstract an integrated stratigraphic study was conducted on a kimmeridgian succession of 3rd order cycles including marls and limestones in a shelf context at bure paris basin the study was possible due to the exceptional opportunity provided by well boring activities related to the construction of an underground laboratory of the french national agency for radioactive waste management andra studies of macrofossils microfossils sedimentology clay mineralogy isotopic composition c o of shells and organic molecular geochemistry lead to a detailed description of the stratigraphic column which allows us to address the history of sea level and climate changes six transgressive regressive cycles are recognised in the studied kimmeridgian succession in these 3rd order cycles the deepest environments are systematically represented by marls and organic rich sediments whilst the shallowest are represented by limestones these cycles do not correspond to changes in temperatures or carbonate production rates at a regional or global scale on the contrary long term palaeontological sedimentological and geochemical changes during the early kimmeridgian are interpreted as climatically induced these climatic changes are considered as responsible for bringing significant granular carbonate production to an end in contrast to carbonate mud that was deposited in alternation with marls throughout the late kimmeridgian

defining the nature and location of a late devonian early mississippian pycnocline in eastern kentucky the pycnocline the intermediate layer in a tripartite density stratified water column is an important element in recent explanations of the origin of anaerobic sediments dysaerobic sediments deposited where the pycnocline intersects the bottom are distinct from overlying aerobic and underlying anaerobic sediments and were used to define the position of the paleopycnocline on a late devonian early mississippian sea bottom in eastern kentucky surface and subsurface mapping of the bedford berea sequence and equivalent parts of the new albany and chattanooga shales reveals approximately coeval aerobic dysaerobic and anaerobic facies that permitted mapping of the paleopycnocline apparently the first time the actual sea bottom position of a paleopycnocline has been defined the bedford berea devonian mississippian sequence is situated between the black ohio shale devonian below and the black sunbury shale mississippian above the black shales reflect deposition in a deepening transgressive sea where anaerobic conditions were easily established and maintained the intervening bedford berea sequence however represents deposition in aerobic and dysaerobic environments during a shallowing regressive episode as deltas prograded to the south and west in eastern kentucky the gray sandstones siltstones and shales of the bedford berea sequence have been interpreted as pinching out between the black shales above and below in east central kentucky each of the above units however has a distinctive signature on gamma ray logs comparison of gamma ray logs and radioactivity profiles with corresponding cores drillers9 logs and exposures indicates that black shale equivalents are present beyond the point where the gray bedford shale pinches out this also is supported by limited biostratigraphic data this transition from gray bedford shales to black shale equivalents marks the approximate position of the ancient pycnocline and has been mapped in the subsurface and on the outcrop in eastern kentucky the ancient pycnocline closely parallels the bedford berea delta front suggesting major control by the delta the continued influx of oxygen rich sediment laden waters from the delta apparently prevented the northward and eastward migration of the pycnocline up the delta front the introduced oxygen and sediment however were effective only in breaking up the pycnocline over a distance of 25 to 40 km from the active delta fronts stratigraphic paleontologic and geographic constraints indicate that the paleopycnocline was not horizontal but sloped northeastward from shallower waters near the cincinnati arch to deeper waters off the delta fronts