palaeomagnetism and magnetostiatigraphy of triassic strata in the sangre de cristo mountains and tucumcari basin new mexico usa summary we report palaeomagnetic data and a composite magnetic polarity sequence for middle and upper triassic rocks assigned to the anton chico member of the moenkopi formation and chinle group respectively exposed along the eastern flank of the sangre de cristo mountains and in the tucumcari basin of eastern and northeastern new mexico thermal demagnetization isolates a well defined dual polarity characteristic magnetization carried in most cases by haematite and interpreted as an early acquired chemical remanent magnetization crm characteristic magnetizations from 74 palaeomagnetic sites one site one bed are used to define a magnetic polarity sequence which we correlate with previously published triassic data obtained from both marine and non marine rocks preliminary correlation suggests that the resolution of magnetostratigraphic data derived from continental strata is not necessarily of lesser quality than that from marine rocks on the basis of the magnetostratigraphic data a profound unconformity is believed to separate lower middle norian and upper norian rhaetian strata of the chinle group palaeomagnetic poles derived from selected sites in steeply dipping 85 strata for the middle triassic anisian 240 ma 50 n 121 e n 8 late carman early norian 225 ma 53 n 104 e n 16 and late norian rhaetian 208 ma 59 n 77 e n 8 are in relatively good agreement with previously published data for the moenkopi formation and chinle group and related strata in southwest north america none the less comparison with palaeomagnetic poles obtained from gently dipping or flat lying triassic strata from this study anisian 46 n 112 e n 13 late carnian 54 n 87 e n 12 and previously published triassic poles in southwest north america suggest that a modest apparent rotation not greater than about 5 affects declinations from steeply dipping rocks the distribution of palaeomagnetic poles indicates 25 angular distance of apparent polar wander between about 240 and 208 ma

outcrop analog for mixed siliciclastic carbonate ramp reservoirs stratigraphic hierarchy facies architecture and geologic heterogeneity grayburg formation permian basin u s a abstract the grayburg formation late permian guadalupian is a shallow marine succession flanking the delaware and midland basins of texas and new mexico u s a the grayburg exemplifies the facies heterogeneity imparted by cyclic interbedding of siliciclastic and carbonate rocks from lithologically diverse inner ramp to outer ramp facies assemblages high resolution correlation and mapping of laterally continuous grayburg strata exposed in the brokeoff mountains new mexico allow the stratigraphic architecture facies distribution and lateral variability to be characterized in detail this study provides an outcrop analog for stratigraphically equivalent subsurface reservoirs and comparable carbonate ramp reservoirs that accumulated during periods of low amplitude sea level fluctuations vertical and lateral facies successions in the grayburg record four hierarchical scales of cyclicity the entire grayburg is a composite sequence that initiated with transgression of the san andres platform and culminated with subaerial exposure followed by a major basinward shift in deposition this third order cycle contains four high frequency sequences defined by transgressive outer ramp facies overlain by aggradational ramp crest to inner ramp facies capped by an unconformity each high frequency sequence contains several composite cycles intermediate scale cyclic successions the high frequency fifth order cycles constitute the smallest scale upward shoaling facies successions that can be recognized and mapped comprising the basic correlation entity to delineate lithofacies bodies lateral heterogeneity in the grayburg reflects both systematic facies transitions and interwell scale meters to hundreds of meters variability due to geologic complexity larger scale systematic facies changes that reflect primary environmental and or depositional controls e g water depth platform position accommodation trends can be characterized using well and or seismic data abetted by appropriate depositional models interwell heterogeneity due to geologic complexity however is difficult to recognize from subsurface datasets appropriate outcrop analogs provide information on lateral facies dimensions and heterogeneity architecture that is essential for constructing more realistic three dimensional reservoir models rather than oversimplified models based on lithofacies correlations forced between wells by linear interpolation an understanding of geologic heterogeneity exhibited in outcrop analogs is crucial for geoscientists involved with characterizing and modeling subsurface heterogeneity

sedimentary architecture of a prograding oolitic siliciclastic wedge response to changes in wave base oscillation kimmeridgian iberian basin abstract a detailed facies and sequential architectural analysis has been carried out along the wedge shaped shallow marine cross bedded oolitic siliciclastic ricla member kimmeridgian northern iberian basin the obtained results are based on fieldwork along the 4 1 km continuous outcrops with the use of high resolution photomosaics and drone made videos which have led to a precise and extensive facies reconstruction three main facies that are laterally related a to b to c in down dip direction have been differentiated which correspond to the topset foreset and bottomset parts of a sloping depositional surface sedimentation was controlled by sweeping drift and downwelling storm induced currents causing avalanching processes with the deep action of oscillatory currents the sedimentary architecture consists in 5 successive units composed by several sub units arranged according to different stacking patterns which reflect the sedimentary response to wave base oscillations superimposed to the regressive part of a third order transgressive regressive cycle the sedimentological features indicate that this unit which has been previously interpreted as a dune complex fit with an infralittoral prograding wedge model as it is observed in geographically close and stratigraphically similar units the ricla member is therefore regarded as an example of a well exposed grain supported unit with broad potential application to other prograding grain dominated lithosomes that do not conform to the traditional sand shoal model

volcanism on mercury evidence from the first messenger flyby for extrusive and explosive activity and the volcanic origin of plains the first messenger flyby of mercury obtained images of 21 of the surface not seen by mariner 10 including the center and western half of the caloris basin and regions near the terminator that show details of the nature of smooth and intercrater plains these new data have helped to address and resolve a series of longstanding questions on the existence and nature of volcanism on mercury and the distribution of volcanic materials data from the mercury dual imaging system mdis on the messenger spacecraft have shown the following 1 numerous volcanic vents in the form of irregularly shaped rimless depressions are concentrated around the interior edge of the caloris basin 2 these vents appear to be sources for effusive volcanism that in one case built a shield in excess of 100 km in diameter and in some cases formed bright haloes around the vents that are interpreted to represent pyroclastic eruptions 3 lobate margins of plains units seen previously in mariner 10 data are documented in messenger images with more clarity and are often distinctive in morphology and color properties supporting the interpretation that these features are the edges of lava flow units 4 the interior of the caloris basin is filled with plains units spectrally distinctive from the rim deposits and comparison with the lunar imbrium basin and superposed impact crater stratigraphy provide evidence that these units are volcanic in origin detailed differences in the mineralogy of lava flow units so prominent in imbrium are not seen in the caloris interior 5 some of the smooth plains surrounding the exterior of the caloris basin show distinct differences in color and morphological properties supporting a volcanic origin 6 some smooth and intercrater plains units distant from the caloris basin show evidence of flooding and embayment relations unrelated to caloris ejecta emplacement local and regional geological and color relationships support a volcanic origin for these plains 7 large impact craters show a sequence of embayment of interior floor and exterior ejecta deposits that supports a volcanic origin for the embayment and filling processes 8 crater embayment and flooding relationships in selected areas suggest volcanic plains thicknesses of many hundreds of meters and local thicknesses inside impact craters of up to several kilometers 9 impact crater size frequency distributions for caloris exterior deposits including the facies of the caloris group and relatively high and low albedo smooth plains show that they are younger than plains interior to caloris and thus must be dominantly the product of post caloris volcanism these new data provide evidence that supports and confirms earlier hypotheses from mariner 10 data that volcanism was important in shaping the surface of mercury the emerging picture of the volcanic style of mercury is similar to that of the moon the other small one plate planetary body there are no major shield volcanoes e g comparable to tharsis montes on mars shallow magma reservoirs are rare and there is little evidence for surface deformation or long lived volcanic sources related to sites of upwelling mantle the close association of volcanic plains and surface deformation features suggests that future observations and analyses can help document the relation between the volcanic flux and the evolving state and magnitude of stress in the lithosphere of mercury

carnian norian biomagnetostratigraphy at silicka brezova slovakia correlation to other tethyan sections and to the newark basin correlations of upper triassic magnetic stratigraphies from tethyan sections have been hampered by difficulties with conodont biostratigraphy and taxonomy and discontinuous sedimentation particularly in the hallstatt limestones of turkey and austria the magnetic stratigraphy and conodont biostratigraphy from the upper carnian to upper norian limestones exposed at silickabrezova slovakia can be correlated to other tethyan sections and to the continental succession in the newark basin the resulting correlations help to resolve some of the apparent discrepancies in existing conodont zonations and result in a revised correlation to north american terrestrial vertebrate and palynological zones the correlations imply that the norian rhaetian boundary lies within newark polarity zone e17r at v207 ma the carnian norian boundary lies close to the base of newark polarity zone e7r at v226 ma this implies durations for the norian and rhaetian stages of 19 myr and 7 myr respectively 2002 elsevier science b v all rights reserved

anatomy of a late quaternary carbonate island constraints on timing and magnitude of sea level fluctuations west caicos turks and caicos islands bwi abstract the data set of the island of west caicos consists of a combination of high resolution lidar and digital imagery radiometric data and amino acid racemization aar d l values as well as extraordinary preservation of sedimentary and bio constructed deposits on the island together with a well established regional stratigraphic framework from the neighboring bahamian island chain and detailed field mapping the west caicos data set provides an opportunity to advance our understanding of the link between carbonate stratigraphy and the controlling parameters of sea level sediment supply tectonics and climate the exceptionally well preserved stratigraphic record of the mid late pleistocene from west caicos allows recognition of marine isotope stages mis 9 11 5e and holocene the west coast of the island provides a continuous 8 4 km exposure of the mis 5e record that enhances our understanding of the intra mis 5e bipartite succession in this region and supports a sea level lowering that occurred during the last interglacial lig west caicos accreted as a series of eolian foreshore shoreface barrier reef and fringing reef facies shoreline positions for all but the mis 7 and mis 5a c deposits are now captured in the sub meter geodetic quality topobathy lidar survey the star town unit of mis 9 11 age forms the southern margin of the island as well as the central karst modified spine with uranium thorium u th coral ages of between 368 and 365 thousand years ago ka and a d l glu average of 0 60 early mis 5e strata include the railroad ridge unit in the center of the island which was previously identified as one of the older units the railroad ridge unit is a north south linear dune ridge that has a d l glu average of 0 52 and indicates the onset of sediment sources from the east associated with a flooded central caicos platform approximately synchronously the early mis 5e south reef unit 3 75 4 m sea level elevation nucleated on the western coast of west caicos attached to the middle pleistocene star town unit the south reef corals yield an average coral u th age of 126 5 ka with an average d l glu from skeletal matrix of 0 46 this transitional barrier fringing reef is unconformably overlain by the late mis 5e boat cove unit corals in the basal transgressive phase of this upper mis 5e boat cove unit yield an average 120 6 ka u th and average d l glu of 0 45 shallow marine foreshore and eolian facies of the late mis 5e rest on a wave cut terrace that cuts the early mis 5e south reef unit by as much as 3 m down to a 0 5 m above present sea level elevation the upper mis 5e boat cove unit displays a maximum of 4 5 m elevation above present day sea level measured from the middle of the foreshore this estimate may be a minimum value as the exposures on the west coast are part of a forced regressive foreshore sequence last stages of the upper mis 5e deposition are seen in a series of regressive dune beach ridge deposits referred to as the northeast ridges unit with sea level positions ranging from 4 5 m early in the central part of west caicos to 0 5 m on the far northeast coast eventually building down below present day sea level this sea level history fits well with previously documented records in the bahamas and globally and the extensive erosion supports a short lived between 126 and 120 ka intra mis 5e relative sea level fall holocene deposition on west caicos is restricted to northern and eastern margins of the island as a combination of strandplain and dune ridge mixed skeletal oolitic units using the high resolution digital elevation model dem and linked digital geologic map makes it possible to compare areas of the different pleistocene and holocene units quantitatively and to constrain volumetric assessments and accumulation rates on the island for different units the peak sediment volume production accumulation rate between 6 5 and 8 106 m3 or between 2 2 and 2 7 106 m3 per ka is observed in the upper mis 5e unit this rate is 5 times greater than the 0 5 106 m3 per ka estimated for the holocene ooid dune ridge strandplain complex suggesting that the combination of higher sea level greater wave and wind energy and warmer ocean temperatures may have fostered the higher rate of chemically precipitated sediment supply

integrated upper carnian to lower norian biochronology and implications for the upper triassic magnetic polarity time scale abstract we summarize the ammonoid conodont and halobiid biochronology of the upper carnian to lower norian based on a discussion of data in the alps sicily balkans turkey himalayas and timor with this integrated biostratigraphic scale the pizzo mondello section sicily can be recalibrated and the carnian norian boundary more precisely located there as a result the magnetostratigraphy of this section is now in good agreement with previous results from turkey although the latter series are more condensed cross correlation of available magnetostratigraphic data from marine tethyan sections allow us to construct a composite upper carnian to upper norian geomagnetic polarity time scale gpts this gpts leads us to question previously proposed magnetobiostratigraphic and chronostratigraphic correlations within the upper triassic newark non marine sedimentary sequence

holocene oolitic marine sand complexes of the bahamas abstract although the general factors influencing the occurrence and distribution of oolitic systems are well known details of their landscape scale patterns and formative processes are less systematically explored by reviewing published studies and presenting new data and insights this review systematically examines a suite of holocene systems from the bahamas in which patterns and processes are characterized and explicitly linked with the goal of providing more realistic and accurate models for variability heterogeneity and predictability in these systems and their ancient analogs sedimentological geomorphic and hydrodynamical data document that each ooid shoal is unique in detail yet shoals share common elements within bar forms systematic trends in grain size type and sorting are related to spatial and temporal variability in wave tide and current energy these trends are driven by connections among sedimentology hydrodynamics and geomorphic forms as they shape and concomitantly are shaped by each other similarly due to feedbacks a limited number of bar forms occur among shoals including tidal sand ridges parabolic bars transverse shoulder bars tidal deltas and sand flats the dominant bar form broadly corresponds with flow velocities within and among shoals among bahamian tidal shoals the mean grain size of ooids maximum bar heights and the width of the oolitic facies belts are all positively correlated collectively these results illustrate the mode and magnitude of variability in shapes orientations and sedimentology of holocene oolitic bodies interpreted to be driven by self organization and autogenic processes these perspectives provide testable qualitative and quantitative insights that can be used to understand and predict the character of ancient analogs

new magnetobiostratigraphic results from the ladinian of the dolomites and implications for the triassic geomagnetic polarity timescale abstract we investigated for magnetostratigraphy the rio nigra and rio frommer stratigraphic sections from alpe di siusi seiser alm dolomites northern italy in order to improve the calibration of the triassic time scale both sections are characterized by ammonoid and conodont associations typical of longobardian late ladinian middle triassic age moreover the rio nigra section is constrained by a u pb zircon date of 237 77 0 05 ma building on the recently verified newark hartford astrochronological polarity timescale for the late carnian rhaetian plus the hettangian and through magnetostratigraphic correlations of an updated inventory of tethyan marine stratigraphic sections from the literature some of which are provided with u pb zircon age constraints we propose a revised geomagnetic polarity time scale for the entire triassic

controls on links between geomorphical and surface sedimentological variability aitutaki and maupiti atolls south pacific ocean abstract isolated carbonate platforms and atolls occur throughout the geologic record from archean to present although the roles of sea level change tectonics and sediment supply on large scale changes in stratigraphical architecture of these systems are relatively well understood the details of the nature and controls on sedimentological variability between and within individual geomorphic elements on platforms and atolls are less well constrained the purposes of this study are 1 to describe compare and contrast geomorphological and sedimentological characteristics of surficial holocene sediments from two south pacific atolls aitutaki and maupiti representing different physical and chemical oceanographic settings and 2 to explore possible causes for sedimentological heterogeneity by contrasting the patterns with those present on other platforms and regions both atolls include annular shelf edge reef systems with a red algal rim and reef flat flanked lagoonward by reef sand aprons up to 1 500 m wide these aprons consist of moderately sorted coarse sand and gravel with an abundance of halimeda coral and red algal fragments broadly sediments become finer and better rounded away from margins water depths increase abruptly inboard of these reef sand aprons into platform interiors with depths up to 25 m maupiti and 9 m aitutaki although patch reefs dot these lagoons sediment is commonly poorly sorted with bimodal and polymodal size distributions and includes a mix of whole and fragmented skeletal grains peloids and ooids mud and fine sand are abundant up to 80 on maupiti 85 on aitutaki the occurrence of peloids fine ooid sand and oolitically laminated skeletal grains on maupiti atoll as previously documented on aitutaki is consistent with interpretations of the impact of elevated regional ocean total alkalinity ta and ph levels in this part of the pacific on these wave dominated atolls open ocean waves impinging on the platform margins generate currents that transport sediment from the reef across the sand apron and towards the platform interior unlike the tide dominated platforms of the bahamas however weak tides preclude strong daily agitation and circulation so ooids do not grow large and mud and fine sand transported into the atoll interiors is sequestered there in the interiors both sediment produced in situ and fine allochthonous sediment are more influenced by biological processes than by physical transport processes so bioturbated muddy sand is most common collectively the comparative analysis provides actualistic process based conceptual models for the nature and controls on variability of shelf margin reef and reef apron systems and platform interiors within and among atolls

carbonate slopes and gravity deposits in this special volume a series of papers are presented that concentrate on sedimentation patterns observed on the slopes and within the basins surrounding shallow water carbonate depositional systems four papers discuss depositional patterns on the slope to basin transect of the cainozoic sedimentary system of the bahamas four other papers examine gravity deposits of jurassic and cretaceous carbonate depositional systems

high energy carbonate sand accumulation the quicksands southwest florida keys abstract high resolution seismic reflection profiles of the quicksands located along a broad ridge on the platform shelf west of key west florida indicate a significant deposit of non oolitic carbonate sand occurs in a belt 47 km long by 28 km wide the surface of the belt is ornamented by large 5 m migrating tidal bars oriented in a north south direction on which sand waves oriented in an east west direction are superimposed some of the sand waves are awash at low tide the sand waves are formed by strong reversing tidal currents flowing between the gulf of mexico and the straits of florida the waves migrate directly over pleistocene bedrock to the east but the deposit thickens to the west and sand waves there overlie non oolitic holocene accumulations as thick as 12 m westward ipping accretionary bedding indicates that net migration of the sands is to the west despite north south movement of tidal currents the westward edge of the accumulation has accreted over deeper muddier deposits although tidal currents and resultant bedforms appear identical to those of active ooid deposits in the bahamas and elsewhere no oolitically coated grains were found in this study thin section analyses show the principal component average 48 of the sands is fragmented plates of species of the green alga halimeda followed by particulate coral average 17 which increases off the flanks of the main sand body short vibracores confirm the presence of cross bedding

shear sense criteria in the antalya and alanya thrust system southwestern turkey evidence for a southward emplacement abstract a northern as opposed to a southern origin of the antalya and alanya nappes in turkey has been a contentious issue among geologists the two hypotheses are essentially supported by contrasting geometrical and sedimentary arguments to introduce new information into the debate we have been analyzing for shear sense criteria in thrust contacts these data give clear evidence for a south directed vergence these results suggest that both the antalya and alanya nappes were derived from the same oceanic basin and continental margin as the other tauric nappes whose northern origin has long been recognized

new constraints on the end triassic upper norian rhaetian magnetostratigraphy abstract the end triassic was marked by one of the five important phanerozoic global mass extinctions the construction of a detailed magnetic polarity time scale for this period that would integrate data from marine and terrestrial realms is thus of particular interest we report new magnetostratigraphic data from the oyuklu section located in southwestern turkey which allow one to propose a complete late upper norian sevatian 2 to rhaetian magnetic polarity sequence two correlations are discussed between the new tethyan marine sequence and the continental magnetic polarity record previously determined from the newark basin in eastern north america both options suggest that the rhaetian is at least partly missing in the newark basin which would reconcile most late triassic magnetostratigraphic results and biotic features obtained from marine and continental environments following our preferred correlation the rhaetian would have a duration as short as 2 myr and 4 5 myr if the sevatian 2 zone is included as part of the rhaetian

the late triassic timescale age and correlation of the carnian norian boundary the late triassic timescale is poorly constrained due largely to the dearth of reliable radio isotopic ages that can be related precisely to biostratigraphy combined with evident contradictions between bio stratigraphic and magnetostratigraphic correlations these problems are most apparent with regard to the age and correlation of the carnian norian boundary base of the norian stage we review the available age data pertaining to the carnian norian boundary and conclude that the long norian in current use by many workers which places the carnian norian boundary at 228 ma is incorrect the evidence supports a norian stage that is much shorter than proposed by these workers so the carnian norian boundary is considerably younger than this close to 220 ma in age critical to this conclusion is the correlation of the carnian norian boundary in nonmarine strata of europe and north america and its integration with existing radioisotopic ages and magnet ostratigraphy three bio stratigraphic datasets palynomorphs conchostracans and tetra pods reliably identify the same position for the carnian norian boundary within normal limits of bio stratigraphic resolution in nonmarine strata of the chinle group american southwest newark supergroup eastern usa canada and the german keuper these biostratigraphic datasets place the carnian norian boundary at the base of the warford member of the lower passaic formation in the newark basin and as was widely accepted prior to 2002 this correlates the base of the norian to a horizon within newark magnet ozone e13n in recent years a correlation based solely on magnetostratigraphy has been proposed between the pizzo mondello section in sicily and the newark section this correlation which ignores robust biostrati graphic data places the norian base much too low in the newark basin section at the base of the lockatong formation correlative to a horizon near the base of newark magnet ozone e8 despite the fact that this correlation is falsifiable on the basis of the bio stratigraphic data it still became the primary justification for placing the carnian norian boundary at 228 ma based on newark cyclo stratigraphy the long norian created thereby is unsupported by either bio stratigraphic or reliable radioisotopic data and therefore must be abandoned while few data can be presented to support a carnian norian boundary as old as 228 ma existing radio isotopic age data are consistent with a norian base at 220 ma although this date is approximately correct more reliable and precise radio isotopic ages still are needed to firmly assign a precise age to the carnian norian boundary

norian magnetostratigraphy from the scheiblkogel section austria constraint on the origin of the antalya nappes turkey abstract late triassic magnetostratigraphic investigations in southwestern turkey have suggested that parts of the antalya nappes are constituted of a melange of blocks originally deposited either in the vicinity of the northern tip of arabia or more surprisingly directly north of india in the southern hemisphere in order to ascertain this result more clearly we have correlated the turkish series with austrian sections of corresponding age from the northern calcareous alps for which the hemisphere of deposition is beyond doubt the new magnetostratigraphic results obtained from the scheiblkogel section austria confirm the previously suggested middle to late norian magnetic polarity sequence and support the heterogeneous character of the antalya nappes

middle triassic magnetostratigraphy and biostratigraphy from the dolomites and greece abstract magnetostratigrapic and biostratigraphic data across the anisian ladinian middle triassic boundary were obtained from the frotschbach seceda section from the dolomites region of northern italy and the vlichos section from the greek island of hydra where the aghia triada published section was also resampled the frotschbach seceda section includes two radiometrically dated u pb tuff levels and covers two of the three chief candidates for the position of the base of the ladinian namely at the base of the secedensis zone or the subsequent curionii zone the aghia triada section yields biochronological evidence for the base of the secedensis zone whose significance is however critically discussed in the light of the magnetostratigraphic correlation with frotschbach seceda the vlichos section can be correlated with aghia triada and frotschbach seceda by means of magnetic polarity stratigraphy and sparse fossil occurrences the satisfactory correlation of the magnetozones allows us to construct a composite geomagnetic polarity sequence tied to tethyan ammonoid and conodont biostratigraphy for about a 2 4 myr interval across the anisian ladinian boundary

regional quaternary submarine geomorphology in the florida keys high quality seismic reflection profiles fill a major gap in geophysical data along the south florida shelf allowing updated interpretations of the history of the quaternary coral reef system incorporation of the new and existing data sets provides the basis for detailed color maps of the pleistocene surface and thickness of overlying holocene accretions the maps cover the florida keys to a margin wide upper slope terrace 30 to 40 m deep and extend from the elbow reef north key largo to rebecca shoal gulf of mexico the data indicate that pleistocene bedrock is several meters deeper to the southwest than to the north east yet in general holocene sediments are 3 to 4 m thick shelf wide the pleistocene map demonstrates the significance of a westward dipping bedrock surface to holocene flooding history and coral reef evolution seismic facies show evidence for two possible holocene stillstands aerial photographs provide information on the seabed surface much of which is below seismic resolution the photographs define a prominent regional nearshore rock ledge that extends 2 5 km seaward from the keys9 shoreline they show that bands of rock ridges exist along the outer shelf and on the upper slope terrace the photographs also reveal four tracts of outlier reefs on the terrace one more than had been documented seismically seismic and photographic data indicate the tracts are 200 km long nearly four times longer than previously thought new interpretations provide insights into a youngest possible terrace age ca 175 ka and the likelihood that precise ages of oxygen isotope substage 5e ooid tidal bar and coral reef components may differ the tidal bar reef complex forms the florida keys

growth dynamics of pennsylvanian carbonate mounds from a mixed terrigenous carbonate ramp in the puebla de lillo area cantabrian mountains northern spain abstract carbonate mounds are widespread in many places around the world and are especially well exposed in the cantabrian mountains northern spain this study focuses on the composition and growth dynamics of two large mound complexes well exposed near the village of puebla de lillo 70 km northeast of leon and evaluates the impact of sea level accommodation and siliciclastic input on mound growth the mound substrate consists of bedded dark skeletal bindstone the core facies exhibits patchy growth forms of alternating massive microbial algal boundstone and skeletal and nonskeletal wackestone reflecting the overall mound internal composition of smaller coalescent bodies microbial activity as inferred from the volumetrically important clotted peloids appears to be the main factor leading to the high accumulation rate in the cores the steeply dipping flanks presumably resulted from early cementation and subsequent lithification and stabilization induced mainly by microbial activity in the intermound strata carbonate beds and small mounds alternate with fine grained sandstone siltstone and shales the intermound carbonates consist of skeletal and intraclastic mudstone to wackestone whereas algal microbial boundstone is a minor component overall facies transition from the mound core towards the flanks or the mound capping beds is gradual however the volume of bioclasts and intraclasts increases towards the flank and capping facies inversely to amount of clotted peloids or micrite the substrate and the cores of the two mound complexes likely formed in the photic zone as inferred from the common calcareous algae carbonate precipitation favored by microbial activity and algal growth along with gain in accommodation space led to mound core accretion the growth of the small mound complexes was most likely stopped by recurrent sea level fall and siliciclastic input the large high relief mound complex actually kept growing until reaching shallow water and high energy conditions unlike many late paleozoic counterparts these mounds were not subaerially exposed during growth the great thickness and the aggradational mound growth are indicative of a high subsidence rate at a later stage however siliciclastic input also buried the large mound complex rapid subsidence sea level fluctuations and siliciclastic input were thus decisive factors controlling carbonate production this study reveals that mound complexes nucleated and grew on preexisting paleohighs maintaining consistent growth in these specific settings paleohighs recurrent sea level fluctuations presumably linked to glacio eustasy and episodic siliciclastic input are the principal factors that controlled the shape size and growth evolution furthermore the internal architecture as a mosaic of juxtaposed small bodies composing the complexes represents an important finding for better understanding of mound growth and thus for better constraining reservoir heterogeneity particularly for upper paleozoic deposits

relations between geomorphic form and sedimentologic stratigraphic variability holocene ooid sand shoal lily bank bahamas although the linkages among surface sediments geomorphic forms and hydrodynamics in holocene ooid tidal sand shoals have been evaluated recently how these factors are reflected in the geomorphic evolution and stratigraphic record of shoals is less constrained yet such understanding is essential to developing meaningful predictive conceptual models of three dimensional architecture of ancient reservoir analogs integrating remote sensing imagery high frequency seismic data and core characterization from lily bank a modern tidally dominated bahamian ooid shoal in which sedimentologic processes are well documented reveals the stratigraphic record of geomorphic change an irregular gently dipping rocky surface interpreted as the top pleistocene with no pronounced topographic high underlies the holocene oolitic succession a 6 m 20 ft thick poorly sorted gravelly muddy sand with few ooids overlies this basal surface this lower interval is overlain by sand with an upward increase in proportion of ooids sorting and grain size the uppermost unit present only under active bar forms is well sorted oolitic medium sand with accretionary foresets sediments vary stratigraphically and geomorphically the lower unit is finer and less well sorted than the upper units and in the oolitic upper unit sediment size and sorting on bar crests are distinct from bar flanks collectively these results suggest that a marked antecedent bump is not necessary for occurrence of ooid shoals and that the stratigraphic record of analogous ooid shoal systems may preserve clues of geomorphic position as well as geobody size and orientation

magnetostratigraphy of the kavur tepe section southwestern turkey a magnetic polarity time scale for the norian we present the magnetostratigraphy of the late triassic pelagic kavur tepe section from the taurides southwestern turkey the section investigated is about 30 m thick and consists of fine grained whitish limestones the biostratigraphy based on the conodont zonation gives an age from the lacian 2 zone lower norian to the sevatian 2 zone upper norian the paleomagnetic analyses indicate very favourable behaviour with two magnetic components which can be isolated both by thermal and af demagnetization the magnetization is carried by magnetite and goethite which are clearly evident in irm experiments the first component of normal magnetic polarity has roughly the direction of the present day field the high unblocking temperature component shows directions of both polarities in total fifteen magnetic polarity intervals are observed within the kavur tepe section the characteristic calculated fisherian mean direction is particularly tightly grouped d 220 2 and i 32 1 with k 40 9 95 1 7 and nsamp 179 after bedding correction polarity correlations with two other sections in turkey and in austria northern calcareous alps show that the kavur tepe sediments were deposited in the southern hemisphere by combining the magnetostratigraphic results from the bolucektasi tepe 1 and the kavur tepe sections an almost complete norian magnetic polarity sequence is established showing 30 magnetic intervals that are well calibrated with the conodont and ammonoid zonations a magnetic reversal frequency close to about 2 7 reversals myr is derived for the norian this medium frequency is in agreement with the hypothesis of a long time constant 150 200 myr in the changes of the magnetic reversal frequency since the kiaman reversed superchron

tide effects on wave attenuation and wave set up on a caribbean coral reef abstract the effects of tides on wave attenuation and wave set up were investigated at great pond bay a caribbean reef located in st croix u s virgin islands measurements of wave pressure fluctuations were made at three stations across the reef profile total wave set up was measured between the forereef and the reef crest or backreef lagoon wave spectra indicate significant filtering of energy at the peak frequencies as waves traveled across the reef the energy dissipation calculations imply an average energy reduction of 62 between the forereef and reef crest mean energy reduction between the forereef and lagoon was 90 energy dissipation between the forereef and reef crest increased 15 between high and low tide and 6 between forereef and lagoon tidal reduction of water depth at the reef crest intensified wave breaking and this condition increased energy dissipation measurements of wave set up ranged from 0 8 to 1 5 cm calculations of wave set up using tait s 1972 model showed good agreement with observations

geology of the caloris basin mercury a view from messenger the caloris basin the youngest known large impact basin on mercury is revealed in messenger images to be modified by volcanism and deformation in a manner distinct from that of lunar impact basins the morphology and spatial distribution of basin materials themselves closely match lunar counterparts evidence for a volcanic origin of the basin s interior plains includes embayed craters on the basin floor and diffuse deposits surrounding rimless depressions interpreted to be of pyroclastic origin unlike lunar maria the volcanic plains in caloris are higher in albedo than surrounding basin materials and lack spectral evidence for ferrous iron bearing silicates tectonic landforms contractional wrinkle ridges and extensional troughs have distributions and age relations different from their counterparts in and around lunar basins indicating a different stress history

magnetostratigraphic dating of the proposed rhaetian gssp at steinbergkogel upper triassic austria implications for the late triassic time scale the global stratotype section and point gssp for the rhaetian stage has recently been proposed at steinbergkogel in austria we re sampled the steinbergkogel sections stk a and stk b c in high resolution to establish a robust magnetostratigraphy that allows global correlation the palaeomagnetic signal at steinbergkogel is composed of three components which can be separated by thermal demagnetization the highest temperature component revealed between 280 300 and maximum 600 c is of dual polarity and is interpreted as primary rock magnetic experiments showed that the signal is carried by magnetite our results allow correlation between the two individual steinbergkogel outcrops subsequently we correlate the two key biostratigraphic horizons for the base of the rhaetian the fo of m hernsteini and the fad of m post hernsteini to other sections of the tethys domain the correlation to the astronomically dated continental successions of the newark basin indicates that these positions for the base of the rhaetian are most likely determined in chrons e16n and e16r respectively this correlation is confirmed by cyclostratigraphic control on the marine pizzo mondello italy section where a combination of long period milankovitch cycles 175 myr and short eccentricity cycles 100 kyr provide additional correlation constraints respectively supporting a long duration of the rhaetian our study implies that the norian and rhaetian stages have durations of 17 and 9 myr

improving the upper triassic numerical time scale from cross correlation between tethyan marine sections and the continental newark basin sequence abstract magnetostratigraphic cross correlations between biochronologically well dated tethyan marine sections and the astronomically tuned sedimentary sequence from the continental newark basin eastern north america help to improve the upper triassic time scale we show here that the most recent radiometric results constraining the age of the base and top of the upper triassic 237 and 200 ma respectively strengthen the chronostratigraphic calibration of the newark sedimentary sequence proposed by krystyn et al earth planet sci lett 203 2002 343 351 these results allow one to reconcile the milankovitch based cyclostratigraphy from the newark sequence the magnetostratigraphic data from both marine and continental environments and upper triassic biostratigraphy including data on tethyan marine faunas and on terrestrial vertebrates according to this calibration the successive upper triassic stages would have very different durations 10 myr for the carnian 237 227 ma 25 myr for the norian 227 202 ma and 2 myr for the rhaetian 202 200 ma but only if the entire rhaetian is recorded in the newark sequence we further show that the biozone durations in the upper triassic would have been highly variable and as a whole would have lasted much longer than in the lower and middle triassic

geomorphic and sedimentologic heterogeneity along a holocene shelf margin caicos platform abstract reef rimmed margins on isolated carbonate platforms are heterogeneous and studying holocene platforms provides a valuable means for characterizing the spectrum of facies variability and understanding the processes behind facies changes in this study insights from petrographic data granulometric measurements bottom observations and remote sensing and subbottom profiler data from the northwestern part of caicos platform make this one of the more intensely studied shallow marine carbonate systems in the caribbean collectively analyses of the thicknesses and heterogeneity of shallow water holocene carbonates and the platform margin reveal details of the considerable geomorphic variability present on this part of the margin on which the orientation changes markedly in this area the shelf margin arcs from northwest to north to northeast facing accompanied by changes in morphology as well as the distribution thickness and type of sediments the nw facing margin has discontinuous reefs near the margin flanked platformward by coarse sands in poorly developed aprons that transition to a deeper rocky bottom interpreted as pleistocene with patches of sand to fine gravel sized sediment locally lobate to arcuate shoals with medium sands 500 m mean size form a reef apron that is continuous along strike and over 1000 m wide because the interpreted top pleistocene surface is gently dipping seaward holocene sediment thicknesses vary with changes in bathymetry and generally thin away from the reefs sediments in most areas are between 1 5 and 3 m thick but can reach over 6 m locally although the interpretation of the base of the holocene can be ambiguous under shelf margin reefs subbottom profiles illustrate that backreef shelf patch reefs do not necessarily nucleate on pleistocene bedrock highs facies trends are interpreted to reflect a combination of physical oceanographic sedimentologic and biologic processes acting within the framework of pleistocene bedrock configuration the ne facing margin with the continuous reef and expansive sand apron is interpreted to be more wave dominated influenced by swells from the open atlantic and by locally derived wind waves comparison with bahamian platforms suggests that this trend is not unique margins facing open atlantic swells from the north northeast have the best developed reefs not east facing windward margins in contrast the beaches and tidal deltas on the nw facing margin suggest tidal currents and longshore transport are more pronounced here consistent with the nature of geomorphic changes through time the enhanced tidal influence reflects the inlets open to the open bank interior a factor which also may discourage growth of reefs on this part of the margin nonetheless other bahamian platforms with fewer tidal passes have comparable discontinuous reefs suggesting that island continuity is not the most influential parameter on leeward reef development collectively these results illustrate the nature scale and causes of along strike heterogeneity and provide a conceptual model for ancient carbonate platform margins some of which may be equally complex in their facies architecture

interactions between tidal flows and ooid shoals northern bahamas abstract oolitic strata are common through the geologic record ooids generally form in high energy environments but it remains unclear how ooids remain in such systems and form geomorphic features such as bars and shoals integrating remote sensing hydrodynamic bathymetric granulometric and field observations of modern tidal systems in the bahamas provides insight into this fundamental question oolitic tidal sands in the northern abacos display a geomorphic pattern in which bedrock islands restrict and focus tidal flow down a main channel within the channel a shallow shoal separates an ebb dominated subchannel from a flood dominated subchannel tidal velocities in these subchannels can exceed 1 m s enough to transport the oolitic sediments hydrodynamics and bathymetry in these subchannels produce a net circular hydrodynamic pattern around the shoal the spin cycle allowing the sands to remain in motion without being transported out of the ooid factory this general pattern is apparent in several other ooid shoal complexes this concept provides integrated insights into the physical influences impacting the formation suspension transport and deposition of ooids and the resulting geomorphic forms these results represent first steps toward developing more comprehensive and predictive analogs of spatial heterogeneity in ancient tidally dominated oolitic shoals

unravelling the influence of water depth and wave energy on the facies diversity of shelf carbonates carbonate sequence stratigraphy is founded on the principle that changes in relative sea level are recorded in the rock record by the accumulation of sediment with relative water depth dependent attributes while at the scale of a shelf to basin transect facies clearly arrange by water depth the relation blurs for depths 40 m the most vigorous zone of carbonate production the reason for this change in behaviour is two fold firstly in shallow water the intrinsic processes of storm and wave reworking influence the seabed through submarine erosion and sediment redistribution secondly facies diversity tends to be greater in shallow water than deep water because of a greater diversity in grain producers remote sensing imagery field observations and hydrodynamic models for two reef rimmed shore attached carbonate platforms in the red sea show neither water depth nor energy regime to be reliable indicators of facies type when considered in isolation considered together however the predictive power of the two variables rises significantly the results demonstrate it to be an oversimplification to assume a direct link between palaeo water depth and depositional diversity of subtidal lithofacies while highlighting the importance of hydrodynamics in directing the accumulation of carbonate sediments in the shallow photic zone while the size distributions of facies extents in the two focus areas follow power laws no direct relation between the lateral continuity of the facies belts and water depth or wave height is reported the work is relevant for the interpretation of metre scale subtidal carbonate cycles throughout the geological record by demonstrating how caution must be applied when inferring palaeowater depths from depositional facies

gruithuisen domes region a candidate for an extended nonmare volcanism unit on the moon small lunar areas known as red spots are thought to represent good candidates for nonmare volcanic units predating or contemporaneous with the period of mare volcanism in this study we present imaging telescopic and orbital clementine multispectral surveys of the gruithuisen region located in the northwestern border of mare imbrium which contains imbrian age domical features of likely viscous volcanic origin with spectral characteristics of red spot areas a rather spectrally homogeneous unit having typical characteristics of red spots is found to coincide with the material within the morphological boundaries of the gruithuisen delta gamma and northwest domes an extended dome like unit is identified spectrally and surrounds and extends to the west and the north of the domes this unit shows spectral characteristics close to those of the domes suggesting the presence of a significant amount of dome material extending many kilometers away from the domes themselves both the spectral characteristics of the dome and the dome like unit are clearly different from those of highlands and the surrounding mare basalts the spectral identification of a widespread dome like unit suggests that the specific style of eruption that is inferred for the formation of the domes i e viscous flows of possible more silicic composition might have occurred on a regional scale in this part of the moon prior to the iridum event about 3 8 gyr ago this volcanic style appears to be more widespread in the early part of lunar history than previously thought

wave set up on coral reefs 1 set up and wave generated flow on an idealised two dimensional horizontal reef wave set up may be significant in determining water levels on coral reefs particularly in microtidal environments and hence is an important factor for the design of reef top structures and for the stability of reef top islands laboratory experiments have been made on a two dimensional model of an idealised horizontal reef under two different conditions corresponding to a fringing reef or closed lagoon situation and a platform reef or open lagoon situation both wave set up on the reef top and the wave generated flow across the reef were measured and related to wave and tide level conditions all other factors being the same wave set up is greatest at low tide levels whereas wave generated flow is greater at higher tide levels the magnitude of the set up on a platform reef with a wave generated flow is less than on a fringing reef without any net flow by an amount equal to the velocity head of the flow across the reef dimensionless parameters ghrt o and q gho3 are found to be functions of relative submergence parameters hrho or r hr ho for values of ghr hr ho 1 waves break on the reef top and radiation stress theory can be used to calculate set up for ghr hr ho 0 7 waves break on the reef face and set up is determined by broadcrested weir control at the reef edge the symbols are defined as follows g is gravitational acceleration hr is still water depth over horizontal reef top ho is offreef wave height equivalent deep water value q is discharge per unit length of reef edge t is wave period and ghr is maximum wave set up on reef top

controls on platform scale patterns of surface sediments shallow holocene platforms bahamas isolated carbonate platforms occur throughout geological history and commonly exhibit considerable spatial variability to evaluate the controls on the nature of sediment accumulation across the expansive shallow platform tops this study systematically compares and contrasts patterns in surface sediments from several shallow 10 m holocene bahamian examples remote sensing data field observations petrographic characterization and quantitative grain size analyses reveal the spatial patterns of sediment accumulation on crooked acklins platform and the berry islands bank integration of these data with synoptic observations of waves tides and currents along with regional geochemical data provides a means to explore the factors that influence platform scale sedimentary patterns these data illustrate that the platform interiors of both crooked acklins platform and berry islands bank are blanketed with medium to coarse sand size sediment peloids are most common in the interior of crooked acklins platform whereas the berry islands bank includes more abundant composite grains in both areas very little mud is present with surface sediments averaging 2 mud comparison of these results with published data from little bahama bank great bahama bank and caicos platform suggest that contrary to previous interpretations the presence of open margins and or brisk winds are not necessary for the occurrence of a platform top with little mud although the muddy sediment fraction of the interior can be suspended by elevated wave energy wind generated current speeds in protected platform interiors are relatively low instead in parts of the platform interiors transport and winnowing of fines is enhanced greatly by tidal currents which carry suspended sediments off the shallow platforms even if shielded by islands beyond physical influences however regional geochemical compilations suggest that the bahamian tides supply highly supersaturated waters rich in dissolved oxygen to these platform interiors this exchange is interpreted to facilitate favourable conditions for calcium carbonate precipitation in the form of ooids marine cements and hardened peloids across vast expanses of the platform interiors such fundamental controls on holocene platform scale sediment dynamics are likely to have influenced carbonate systems through the geological record

tethyan magnetostratigraphy from pizzo mondello sicily and correlation to the late triassic newark astrochronological polarity time scale we present the magnetostratigraphy and stable isotope stratigraphy from an expanded 430 m thick upper triassic marine limestone section at pizzo mondello sicily and review published biostratigraphic information that can be used to defi ne the location of the conodont carnian norian and norianrhaetian boundaries in this section pizzo mondello offers good potential for magnetostratigraphic correlation of marine biostratigraphic and chemostratigraphic data with the continental newark astrochronological polarity time scale apts for development of an integrated late triassic time scale the relatively stable average values of 18 o centered on 0 are a strong indication that the cherty limestone at pizzo mondello suffered very little diagenetic overprinting the conodont carnian norian boundary is located 12 5 m above a positive shift of 13 c a statistical approach was applied to evaluate various pizzo mondello to newark magnetostratigraphic correlations two correlation options have the highest correlation coeffi cients in option 1 the base of pizzo mondello correlates with the middle part of the newark apts whereas in option 2 the base of pizzo mondello starts toward the early part of the newark apts we prefer option 2 in which the carnian norian boundary based on conodonts as well as its closely associated positive 13 c shift correspond to newark magnetozone e7 at ca 228 227 ma adopting newark astrochronology implying a long norian with a duration of 20 m y and a rhaetian of 6 m y duration these ages are in fact not inconsistent with the few high quality radiometric dates that are available for late triassic time scale calibration based on its good exposure accessibility stratigraphic thickness and continuity and multiple chronostratigraphic correlation possibilities we propose pizzo mondello as global stratigraphic section and point for the base of the norian

relation between stratigraphic architecture and multi scale heterogeneities in carbonate platforms the barremian lower aptian of the monts de vaucluse se france abstract understanding the relationship between multi scale sedimentary heterogeneities and the stratigraphic architectures of carbonate platforms improves the interpretation of paleoenvironmental evolution in time and space such an approach improves the prediction of the spatial distribution of reservoir properties within carbonate stratigraphic units the reservoir scale stratigraphic anatomy and the growth history of a barremian aptian carbonate platform monts de vaucluse se france was based on 1 high resolution measured sections on outcrops 2 detailed microfacies analyses 3 paleoenvironmental interpretations 4 biostratigraphy using rudist bivalves foraminifera calcareous algae and locally echinoderm and ammonites and 5 sequence stratigraphic interpretations with a special focus on the identification of discontinuity surfaces with a significant stratigraphic correlation potential and critical environmental meaning the platform succession consists of subtidal mainly infralittoral with rare inter to supratidal deposits thirty types of elementary facies grouped in 12 facies associations have been defined the vertical and lateral changes in paleoenvironments together with the development of remarkable stratigraphic surfaces such as subaerial exposures marine erosional surfaces and drowning surfaces allow the definition of five stratigraphic sequences ranging from the late barremian to the earliest aptian these depositional sequences can be grouped into two distinct carbonate sedimentary systems characterized by specific sedimentary profiles and skeletal and non skeletal components 1 a carbonate platform with stronger hydrodynamic gradients rimmed by a narrow belt of high energy deposits with corals and rudistid rudstone facies and 2 a carbonate ramp dominated by orbitolinids fine grained facies including an elongated high energy oolitic shoal the two dimension architecture of the depositional sequences dimensioned geometries thickness and facies variations and the morphology of the shelf reflect a strong interaction between tectonic differential subsidence sediment production and global environmental conditions at the km scale the gorges de la nesque stratigraphic motif could represent a nested stratigraphic structure within the large scale model which could be implemented for up scaling petrophysical properties from the well to a full field model the association of coral facies to the rudist dominated system in the provence platform is a very clear proxy of the polarity of the carbonate platform and is critical for subsurface facies property modeling based on well data finally at the global scale the stratigraphic architecture and the step wise drowning events of the provence platform confirm and document the precursor events associated with environmental perturbations that affected the carbonate factory prior the oceanic anoxic event 1a oae1a

seascape metrics of shelf margin reefs and reef sand aprons of holocene carbonate platforms shelf margin reefs and reef sand aprons are important geomorphic and facies elements associated with many isolated platforms today and in the stratigraphic record although it is generally appreciated that shelf margin reefs and reef sand aprons have formed at or near breaks in slope at the rims of platforms throughout geologic time possible environmental causes for variation in their sizes are not well understood to provide better constraints for assessing possible reasons for such variability in ancient systems this study relates local regional and global patterns of variation in the seascape attributes of holocene shelf margin reef and reef sand apron systems to a suite of potential environmental controls landsat data from more than 60 isolated carbonate platforms and atolls from the caribbean sea indian ocean south pacific ocean central pacific ocean south china sea and indonesian seas were investigated by digitization and spatial analysis of facies belts and compared with regional environmental parameters the results of this analysis suggest that 1 reefs cover from 1 to 55 of the spatial extent of lithotopes on platforms mean 20 whereas reef sand aprons represent between 0 and 65 mean 20 2 the spatial extent of reefs is inversely related to platform size but reef sand aprons show no comparable trend 3 widths of reefs and reef sand aprons are variable within and among platforms but widths from all platforms and from platforms within different regions are characterized by log normal size frequency distributions 4 widths of these facies belts vary as a function of environmental factors such as swell period swell height tidal amplitude latitude and margin orientation relative to direction of wind and wave approach these data indicate the presence of trends in widths of facies belts within different regions that correlate with regional oceanographic patterns nonetheless marked variability is evident on individual platforms among platforms within each region and globally these variations are not related to any of the parameterized environmental variables this observation are interpreted to reflect the influences of unknown and in some cases unknowable spatial and historical contingencies such as the depth to bedrock character of earlier holocene sea level change or changes in physical oceanographic state waves or tides the collective influence of these parameters each of which individually may have the potential to invoke a deterministic response may be reflected in reef and sand aprons with log normal width frequency distributions interpreted to reflect multiplicative random effects collectively however these results suggest that accurate a priori prediction of the details of the sizes of analogous facies bodies in the stratigraphic record may be impossible especially in the deep geologic past where biologic and physical controls are even less well constrained

magnetostratigraphy of the kavaalani section southwestern turkey consequence for the origin of the antalya calcareous nappes turkey and for the norian late triassic magnetic polarity timescale a magnetostratigraphic study of the kavaalani section of uppermost carnian to upper norian age located in the antalya calcareous nappes southwestern turkey reveals nineteen polarity intervals this pattern correlates very well with two other polarity sequences obtained from the same nappe system bolucektasi tepe and kavur tepe if these sections were deposited in the same northern hemisphere this new interpretation changes our previous conclusions regarding the southern hemisphere origin of the magnetic remanence of the kavur tepe section the paleomagnetic data obtained from the kavur tepe and the kavaalani sections therefore reflect large 180 internal rotations within the antalya nappes these nappes were likely formed close to the northern tip of the arabian promontory we propose a revised yet still preliminary version of the norian magnetic polarity sequence

quantified rates of geomorphic change on a modern carbonate tidal flat bahamas comparison of aerial photographs and ultrahigh resolution remote sensing data reveals changes in the geomorphology of a modern carbonate tidal flat in the 58 yr between acquisition of the two data sets several tidal channels have extended headward more than 100 m channel bars have stabilized the shoreline has eroded as much as 50 m the inland algal marsh locally has prograded as much as 90 m and many mangrove ponds have increased in size these changes over the known time interval allow quantification of the rates of these geomorphic processes and suggest rates of migration of landforms to several meters per year some observed rates appear to be different than rates averaged over the past several thousand years however possibly because of changes in storm activity or circulation patterns these data illustrate the dynamic nature of the entire coastal tidal flat system not just the shoreline and reflect the system9s response to factors including relative rises in sea level

magnetostratigraphy of the mayerling section austria and erenkolu mezarlik turkey section improvement of the carnian late triassic magnetic polarity time scale abstract we present a magnetostratigraphic study of two carnian late triassic pelagic limestone sections from the northern calcareous alps mayerling section and southwestern turkey erenkolu mezarlik section biostratigraphic control is based on conodont zonation for the mayerling section and both on conodonts and ammonoids for the erenkolu mezarlik section in both sections the characteristic magnetization is essentially carried by a mineral of the magnetite family eight magnetic intervals are obtained from the mayerling section and fourteen from erenkolu mezarlik when these results are compared to the carnian magnetostratigraphic sequence obtained from the bolucektasi tepe section satisfactory correlations are observed and a composite carnian magnetic polarity time scale containing 24 intervals can be proposed by combining all these results the lower part of the upper carnian is however missing tuvalian 1 zone and lower part of the tuvalian 2 zone no clear correlation is observed between our composite sequence and the other published magnetostratigraphic data of carnian age the satisfactory correlation observed between the mayerling and the bolucektasi tepe sections indicates that both sections were deposited in the northern hemisphere thus providing constraints on the origin of the antalya nappes

pervasive palaeogene remagnetization of the central taurides fold and thrust belt southern turkey and implications for rotations in the isparta angle the turkish anatolide tauride block rifted away from the northern margin of gondwana in the triassic which gave way to the opening of the southern neo tethys by the late palaeocene to eocene it collided with the southern eurasian margin leading to the closure of the northern neo tethys ocean to determine the position of the anatolide tauride block with respect to the african and eurasian margin we carried out a palaeomagnetic study in the central taurides belt which constitutes the eastern limb of the isparta angle the sampled sections comprise carboniferous to palaeocene rocks mainly limestones our data suggest that all sampled rocks are remagnetized during the late palaeocene to eocene phase of folding and thrusting event related to the collision of the anatolide tauride block with eurasia to further test the possibility of remagnetization we use a novel end member modelling approach on 174 acquired isothermal remanent magnetization irm curves we argue that the preferred three end member model confirms the proposed remagnetization of the rocks comparing our data to the post eocene declination pattern in the central tauride belt we conclude that our clockwise rotations are in agreement with data from other studies after combining our results with previously published data from the isparta angle that includes our study area we have reasons to cast doubt on the spatial and temporal extent of an earlier reported early to middle miocene remagnetization event we argue that the earlier reported remagnetized directions from triassic rocks in tilt corrected coordinates from the southwestern antalya nappes western taurides are in good agreement with other studies from the area that show a primary origin of their characteristic remanent magnetization this implies that we document a clockwise rotation for the southwestern antalya nappes since the triassic that is remarkably similar to the post eocene 40 rotation of the central taurides for the previously published results that are clearly remagnetized we argue that their remagnetization has occurred in the palaeocene to eocene

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

impact induced thermal effects in the lunar and mercurian regoliths while the moon and mercury are similar objects in a geomorphologic sense they also possess important differences particularly in the context of small scale impact phenomena not only is the surface of mercury notably hotter than that of the moon but the impact flux is also more intense at mercury due to higher impact velocities and a greater spatial density of micrometeoroids by extrapolating the terrestrial micrometeoroid flux to the moon and mercury it is found that the impact rate at mercury is 5 5 times greater and the mean impact velocity more than 60 percent higher than at the moon a model of impact melting and vaporization applied to the lunar and mercurian environments indicates that almost 14 times more impact melt and over 20 times more vapor are generated per unit time in the mercurian regolith although the surface temperature plays a role in determining the melt and vapor volumes the difference in impact velocity appears to be markedly more important average craters formed by identical projectiles under the two velocity distributions on the two planets should be very similar in size because differences in the kinetic energy of the average impactors will be offset by the differences in gravitational acceleration as a result variations in regolith mixing should depend more on the actual impact rates than on disparities in excavated volumes each average impact on mercury however will produce more than twice as much impact melt as its lunar counterpart introducing more glass into the mercurian regolith although substantial quantities of impact vapor are produced on both planets mixing of the regolith should occur quickly enough in each case to spread the deposited vapor over large surface areas the resulting vapor coatings should be negligibly small for most purposes a much larger agglutinate population should exist on mercury and individual agglutinates should be similar to those of the lunar highlands reflectance spectra and visual albedos indicate that the mercurian crust possesses relatively small quantities of fe perhaps similar to those of apollo 16 light and dark matrix breccias laboratory studies have demonstrated that as the magnetic fractions which are correlated with agglutinate abundances of soils derived from these breccias increase the differences in 0 565 mm visible light reflectivity between the soils diminish should the regional variations in fe content of the mercurian crust be similar to those of these apollo 16 samples then the intense agglutination environment could account for the lack of optical contrast across the mercurian surface at the same time the very large fraction of impact glass in the regolith would imply that most pyroxenes have been fused and incorporated into these glasses seriously attenuating the fe2 crystal field absorption near 0 9 mm supporting this picture are the most recently published spectral observations of mercury which provide little or no evidence of such an absorption feature

physical oceanographic influences on sedimentology of reef sand aprons holocene of aranuka atoll kiribati equatorial pacific abstract depositional facies are the net product of a complex set of processes that impact sediment supply and transport in geomorphic systems although the general facies motifs of many isolated platforms throughout the geologic record are well documented the details of geomorphological and sedimentological patterns and the physical oceanographical processes that can impact sedimentological differentiation are less well constrained on these platforms accumulations of reef associated debris in platform top reef sand aprons can form expansive geomorphic elements hosting prolific hydrocarbon reserves in geologic analogs to better understand the nature and scale of reef sand apron accumulations this project integrates remote sensing field petrographical and granulometrical characterization of surficial holocene sediments with physical oceanographical observations and modeling of aranuka atoll republic of kiribati in the western equatorial pacific results illustrate trends in hydrodynamics geomorphology and sedimentology from the platform margin to the platform interior current meter data and modeling illustrate how the tides 2 5 m spring tide amplitude modulate wave energy open ocean annual average swell height of 2 m distal swell can be larger to produce dominant on platform flow speeds up to 90 cm s on the northern reef sand apron the strongest currents there appear to be impacted by southward propagating waves related to fronts that pass thousands of kilometers north of the atoll not local wind generated waves these hydrodynamical influences are interpreted to have led to the development of the expansive northern reef sand apron 2000 m wide the southeastern apron with currents that reverse with the tides includes a distinct narrower sand apron 1500 m wide concomitantly the hydrodynamical patterns and platformward decrease in energy across the reef sand apron coupled with changes in biota are interpreted to control variability in sedimentary structures bottom types and sediment attributes sediment near the margin on the reef sand apron contains coral and red algal rich coarse sand and gravel passing to foraminifera rich medium to coarse sand toward the lagoon the lagoon includes even finer sediment chiefly fine and very fine sand and patch reefs collectively the results of this study illustrate that selective winnowing differentiation of sediment size type and sorting and nature and size of geomorphic elements ultimately are linked to the hydrodynamical patterns across the platform the sedimentological depositional porosity and permeability and geomorphic facies bodies variability and the processes active on this reef sand apron provide a general conceptual model that may be applicable to predict trends in ancient reservoir analogs

karst and early fracture networks in carbonates turks and caicos islands british west indies abstract historically studies of quaternary carbonates have not adequately addressed the influence of early fracture networks on diagenesis because of this lack of detail understanding and predicting fracture related diagenetic heterogeneities and preferential fluid flow pathways in ancient carbonate successions is particularly challenging the pleistocene oolitic grainstones of the caicos platform provide an excellent opportunity to evaluate the relative importance of fractures on early diagenetic alteration styles and are a suitable analog for subsurface carbonate reservoirs detailed analyses of fractures e g orientation aperture spacing fill material from caicos outcrops combined with high resolution three dimensional ground penetrating radar 3d gpr assisted in exploring the causality and distribution of fractures and relationship to karst four models were evaluated to explain the observed distribution of dolines 1 gravitational fractured margin controlled 2 tectonic fracture controlled 3 antecedent topography controlled and 4 a hybrid model based on observations of numerous fractures n 306 on the western caicos platform early fractures are abundant and dominantly margin parallel these fracture networks are well established in limestones prior to mineralogical stabilization thereby indicating that diagenetic heterogeneities evolve very early in carbonate diagenesis the spatial distribution of dolines on providenciales is likely the result of a complex interplay between the antecedent topography margin parallel fracture systems and meteoric fluids resultant diagenetic alteration is far more complicated than simple unconfined meteoric lenses associated with topographic highs any attempts to model early diagenesis in carbonates should not dismiss the role of fractures as diagenetic facilitators and diagenetic anisotropy templates

paleolatitudes of late triassic radiolarian cherts from argolis greece insights on the paleogeography of the western tethys the hellenides fold and thrust range comprises two subparallel ophiolite belts of triassic to jurassic age the external ophiolite belt e g mirdita pindos argolis in the west and the internal ophiolite belt in the east broadly separated by the continental crust units of the korabi pelagonian zone it is still a matter of debate whether these ophiolites derived from a single ocean meliata maliac vardar or mark the suture of two distinct oceanic seaways pindos and meliata maliac vardar we contribute to the resolution of this controversy by studying the migdalitsa ophiolitic complex in argolis greece which contains triassic oceanic basalts and pertains to the external western ophiolite belt three key areas were mapped and several sites were targeted for structural biostratigraphic and paleomagnetic analyses radiolarian cherts in primary or tectonic contact with oceanic basalts were dated to the late triassic carnian norian using radiolarians and provided paleomagnetic directions of primary origin carried by magnetite and hematite the derived mean direction was corrected for sedimentary inclination shallowing and yielded a paleolatitude of 22 n that was placed in a broader paleogeographic context by reconstructing pangea at 225 5 ma using a recent apparent polar wander path corrected for sedimentary inclination shallowing the late triassic paleogeography of the tethys ocean was constrained using additional paleolatitude estimates from the literature which we checked and corrected when possible for sedimentary inclination shallowing according to our reconstruction the meliata maliac vardar ocean between adria the promontory of africa and europe represents the locus of origin of the late triassic argolis ophiolitic rocks of the external ophiolite belt presently resting in tectonic contact on the pindos subpelagonian zones which represent a deep water trough with no substantial evidence of in situ oceanization in the triassic