tidal modeling of an ancient tide dominated seaway part 1 model validation and application to global early cretaceous aptian tides abstract the utility of deep time global paleotidal modeling is evaluated with a series of modeling experiments focused on the early cretaceous aptian the results from a series of paleobathymetry sensitivity experiments indicate that despite paleogeographic and paleobathymetric uncertainty appropriate use of global paleotidal models complements and enhances stratigraphic and sedimentological methods before being applied to global paleotidal modeling the imperial college ocean model icom is validated for the computation of modern global tides the icom results only deviate slightly from a state of the art published model and were achieved with considerably less computational expense and without data assimilation the results from global paleotidal modeling of the early cretaceous aptian were assessed by comparison with the published geological record icom predicts high mesotidal to macrotidal ranges on the arabian platform around india especially to the north and west along the pacific coast between north and south america northeast of australia and around southeast asia the model predicts low microtidal ranges in the proto south atlantic ocean and weddell sea a further validation test assessed the ability of the model to predict the dominant tidal constituents diurnal or semidiurnal in the aptian lower greensand seaway of southeastern england and northern france during the aptian this region was connected to the boreal proto atlantic and neotethys oceans and now preserves superbly documented tidal deposits the model predicts low microtidal ranges in the proto central atlantic ocean and boreal ocean suggesting that they had little impact on tides in the lower greensand seaway higher tidal amplitudes especially of diurnal once daily tides are predicted in the northwestern neotethys ocean suggesting that this ocean was an important source of tidal energy to the lower greensand seaway sensitivity tests to paleogeographic and paleobathymetric uncertainty indicate that the model predictions are robust the prediction of predominantly diurnal tides is supported by published analyses of large dune scale deposits in the lower greensand of southeast england

time space modeling of the dynamics of santorini volcano greece during the 2011 2012 unrest the 2011 2012 unrest of santorini thera volcano aegean sea greece was associated with microseismicity confined to the kameni line kl a major tectonovolcanic lineament and has been regarded as a single magmatic episode produced by a spherical source derived from inversion of gps data however such a source is a few kilometers away from the kl and cannot explain observed microseismicity for this reason we divided the unrest episode into five periods based on the fluctuations of seismicity and deformation rates and investigated the connection between seismicity and two spherical magmatic point sources for each period based on a new inversion algorithm and consistent gps data we recognized during the volcano unrest episode an unstable pattern of intrusions correlating with both the kl and columbo line cl a second major tectonovolcanic lineament intrusions correlating with cl appear relatively persistent aseismic small and shallow which is consistent with marine geophysical evidence for arrested shallow dykes and geodetic evidence from a previous inflation episode during the two periods of intense seismicity sources close to the kl explaining seismicity were obtained this unstable pattern of intrusions explains both the well observed location and timing of seismicity as well as ground deformation and is consistent with results of an okada type inversion for a sill and a dyke the stress interactions between the two sources agree with coulomb failure stress models santorini appears to be affected by concurrent offset magma pulses and only recent activity from a magma pulse below the kl produced microseismic swarms

three dimensional to two dimensional cross strata transition in the lower pleistocene catanzaro tidal strait transgressive succession southern italy sandstone tidal cross strata are the predominant sedimentary feature of strait fill stratigraphic successions however although widely described in numerous studies tidal strait fill two dimensional and three dimensional cross strata have rarely been reported to occur in discrete intervals which are laterally adjacent or vertically stacked and the meaning of this stratigraphic architecture has not yet been fully investigated understanding of the processes responsible for changes in the internal features of modern and ancient tidal bedforms is essential in order to predict lateral and vertical heterogeneities in analogous reservoir strata this facies based study aims to interpret the three dimensional to two dimensional cross strata transition observed in the lower pleistocene mixed siliciclastic bioclastic sandstone filling the catanzaro strait in southern italy during a continuous phase of tectonically driven marine transgression tidal cross strata disappear in the uppermost interval of the studied succession where mudstone strata prevail this stratigraphic trend is interpreted as the evidence of an important change in the tidal strait hydrodynamics due to a phase of relative sea level rise at the beginning of the transgression three dimensional tidal dunes migrated throughout the ca 3 to 4 km wide and ca 30 km long wnw ese oriented catanzaro strait due to strong tidal currents amplified through the seaway and flowing in semi diurnal phase opposition as the intermediate phase of transgression enlarged the seaway width the tidal current strength decreased as tidal water exchange occurred over a larger cross sectional area the progressive reduction of the bed shear stress modified three dimensional tidal dunes into an extensive two dimensional bedform field at the end of the transgression the further widening of the catanzaro strait into a ca 10 to 12 km wide marine passageway changed the tidally dominated strait into a non tidal open shelf the results of this research suggest the presence of a critical cross sectional area in the narrowest strait centre zone which controls the activation and deactivation of tidal current amplification along a marine seaway

numerical simulations of tidal and wind driven circulation in the cretaceous interior seaway of north america twenty two numerical experiments using a multi layer numerical model of turbulent flow in shallow seas better define fluid circulation and sediment transport paths in the cretaceous interior seaway of north america each experiment consists of a different combination of paleogeography paleobathymetry coriolis acceleration boundary tidal amplitudes wind stresses and bed friction the paleogeographies and paleobathymetries represent three seaway configurations a seaway of intermediate size and depth 200 m during a transgressive peak t5 in late albian time a seaway of maximum size and depth 400 m during peak transgression t6 in early turonian time and a seaway of minimum size and depth 100 m during a peak regression r8 in the campanian values for the other key model parameters are m 2 co oscillating boundary tides of 0 1 to 0 2 m range at the arctic ocean boundary and 0 5 to 1 m range at the proto gulf of mexico boundary coriolis accelerations corresponding to 30 n 45 n and 60 n latitude chezy friction factors ranging from 31 to 70 m s 1 and average winter winds and two winter storms computed by the community climate model at the national center for atmospheric research for paleogeographic conditions during the late albian results of the numerical experiments and comparison of these results with geologic observations allow the following conclusions 1 circulation in the seaway was generally storm dominated 2 typical winter storms crossing the seaway from west to east generated 0 3 m s 1 shore parallel geostrophic currents on the shelves north of arizona at first flowing weakly to the north but later during the storm flowing strongly to the south 3 extreme storms could have produced 0 8 m s 1 currents over the shelves and 0 3 m s 1 currents in 200 m of water 4 co oscillating tides propagated into the seaway as progressive kelvin waves and therefore tidal ranges in the seaway were mesotidal to macrofdal along the southeastern margin but microtidal everywhere else 5 significant deep water wave heights and periods of the fully developed wave field are predicted to have been 5 to 6 m high and 10 s respectively the northwestern shore of the seaway would have experienced these storm waves approaching from the north and thus net sediment drift should have been to the south limited available field data support these conclusions

a nonhydrostatic finite element model for three dimensional stratified oceanic flows part ii model validation a three dimensional nonhydrostatic ocean model that utilizes finite element discretizations on structured or unstructured meshes has been formulated in the current part of this work a first step in the validation of this model is performed due to the inherent strengths of the modeling approach in being able to fully simulate three dimensional flows in arbitrary domains it has been decided here to focus attention on a single well studied collection of problems as such the flow of stratified fluid past an isolated gaussian seamount is considered it is shown that at moderate resolutions the model is relatively insensitive to the use of an increasingly fine mesh in addition qualitative as well as rough quantitative comparisons are made between results from the current model and previous studies carried out using alternate numerical models close agreement is demonstrated both in the eddy shedding and flow trapping structure of the flow as well as in the generation of internal trapped lee waves finally time periodic forced flow is examined where resonantly generated trapped waves on the seamount are shown to be produced the current model predicts resonant interactions occurring at parameter values consistent with previous numerical as well as linearized analytical studies

use of tidal circulation modeling in paleogeographical studies an example from the tertiary of the alpine perimeter tidal conditions in ancient shallow marine basins as revealed by preserved sedimentary deposits reflect the strong influence of the paleobathymetry use of a tidal circulation model can test existing paleobathymetric reconstructions meso and macrotidal conditions are believed to have existed throughout most of the miocene molasse france and switzerland seaway tidal simulations using external tidal ranges of 2 and 4 m entering from the south mediterranean fail to generate mesotidal conditions in the majority of the seaway because of a narrow constriction in the present alpes du dauphine and drome areas meso tidal conditions are simulated in the rhone alp part of the seaway only after the postulated paleobathymetry is widened in the alpes du dauphine area this change allows tidal penetration from the mediterranean despite this widening the new simulations fail to generate mesotidal conditions in the swiss part of the seaway mesotidal conditions are simulated in switzerland with the addition of a second tidal input from eastern switzerland favoring an interpretation that the swiss part of the seaway was connected with either the eastern mediterranean or the indo pacific ocean the revised paleobathymetry brackets uplift events that affected the basin margin

tidal modeling of an ancient tide dominated seaway part 2 the aptian lower greensand seaway of northwest europe abstract the cretaceous lower greensand deposits of southeastern england and northern france contain abundant evidence of diurnal once daily paleotides with tidal influence increasing into the late aptian the imperial college ocean model icom is used herein to determine the amplitude origin astronomical or co oscillating and characteristics diurnal or semidiurnal of the tides in the shallow marine lower greensand seaway where these sediments were deposited a global ocean paleotidal model of the aptian predicts very low tidal ranges microtidal in the proto central atlantic ocean and boreal ocean with higher tidal amplitudes especially of the diurnal constituents predicted in the northwestern neotethys ocean this suggests that the neotethys ocean was the only significant source of oceanic tides to the lower greensand seaway herein the results of the global ocean paleotidal model are used to supply boundary conditions to a higher resolution regional paleotidal model of the lower greensand seaway the regional paleotidal model shows that the tidal range of the lower greensand seaway is largely controlled by the width of the connections to the open ocean as sea levels rose during the aptian the oceanic connections widened resulting in reduced frictional damping of the oceanic tidal wave coupled with funneling shoaling and coriolis effects this led to tidal amplification sensitivity tests using a variety of paleogeography and paleobathymetry scenarios suggest that the model predictions are robust the global to regional scale paleotidal modeling presented here strongly suggests that there was a connection through france in the aube region of the paris basin from the neotethys ocean to southeastern england however there are no time equivalent deposits in this region to validate this suggestion it is herein argued that that this is due either to postdepositional erosion or to low sediment supply coupled with strong tidal currents sweeping the seafloor to exposed bedrock

tidal circulation in an ancient epicontinental sea the early jurassic laurasian seaway we model tides and associated bed shear stress in the early jurassic laurasian seaway of northwest europe sensitivity tests with different water depths highlight those regions that are least affected by paleobathymetric uncertainty results show that although the vast seaway was largely microtidal the tides were still capable of affecting sediment transport more than 2000 km from the open ocean flow constriction associated with shallow platforms and straits produced elevated bed shear stresses a direct proxy for the entrainment and transport of sediment that were decoupled from tidal range and were capable of transporting sand areas of increased bed shear stress broadly correlate with published geological data varying the water depth in the basin provides an insight into the effects of an idealized transgression increasing the water level leads to a net reduction in the bed shear stress at the shelf edge but promotes further penetration of tidal energy into the basin interior although it is still focused into areas of flow constriction further drowning of the seaway eventually widens the straits to the point that they fail to constrict the flow and bed shear stress is reduced increasing water level counterintuitively leads to an increase in bed shear stress in a small number of locations

neoproterozoic earth moon dynamics rework of the 900 ma big cottonwood canyon tidal laminae the tidal rhythmites in the proterozoic big cottonwood formation bcc of utah the neoproterozoic elatina formation of the flinders range of southern australia and the lower pennsylvanian mansfield formation of indiana indicate that the rate of retreat of the lunar orbit has been approximately constant since the late precambrian and closely matches the present epoch value determined from apollo lasers examination of a new bcc core leads to a slightly revised length of day lod and modified values for other earth moon dynamical parameters thus implying the length of day 900 million years ago reported earlier by sonett et al 1996 should be modified to 18 9 hrs

spatial and temporal evolution of coastal depositional systems and regional depositional process regimes campanian western interior seaway u s a abstract this paper provides a critical review and regional synthesis of late cretaceous shallow marine deposits along part of the western margin of the western interior seaway of north america which contains the most extensively documented outcrop based studies of siliciclastic coastal depositional systems in the world the results of this synthesis are presented in the form of paleogeographic maps covering present day new mexico utah colorado and wyoming usa for five timeslices in the campanian these maps are used to evaluate the spatial and temporal evolution of regional depositional process regimes along a large 1000 m stretch of coastline the evolution of regional depositional process regimes is linked to tectonic and paleoceanographic controls on the western interior seaway which enables the results of this synthesis to be applied to prediction of depositional process regimes in other less intensively studied basins six gross depositional environments have been mapped for each timeslice 1 alluvial to coastal plain sandstones 2 coastal plain coals mudstones and sandstones 3 shoreline sandstones 4 marine mudstones 5 gravity flow siltstones and sandstones and 6 marine marls and chalk shoreline sandstones in each timeslice are interpreted in further detail using documented evidence for the three principal classes of depositional process wave tidal and fluvial and published reconstructions of coastal morphology which is widely considered to reflect depositional process regime based on these interpretations shoreline sandstones are assigned to five categories of depositional process regime 1 regressive wave dominated shorefaces and delta fronts 2 regressive river dominated delta fronts 3 regressive mixed tide and wave influenced delta fronts 4 regressive tide dominated delta fronts and 5 transgressive barrier islands back barrier lagoons and estuaries the accuracy of and uncertainty in classification of depositional process regime are critically evaluated additionally stratal thickness and sediment routing pathways have been interpreted in order to assess the impact of tectonic and paleoceanographic controls on spatial and temporal changes in all of the evaluated shallow marine successions thin tide influenced intervals were deposited in back barrier and lagoon systems associated with net transgressive shorefaces and estuaries however it is notable that all preserved tide dominated and tide influenced regressive deltaic systems are located along the northern margin of the utah bight a tectonically related embayment that had a pronounced expression during the middle campanian the southern margin of the embayment and coastlines to the north are conspicuously more wave dominated which supports their exposure to a larger wave fetch in contrast the northern margin of the embayment was relatively wave protected it is concluded that tidal range was amplified due to resonance of the principal semidiurnal tide in the strongly embayed geometry of the middle campanian utah bight

a three dimensional model of diurnal and semidiurnal tides on the european shelf a three dimensional hydrodynamic model of the continental shelf is used to examine the sensitivity of computed diurnal k1 and o1 and semidiurnal m2 s2 and n2 tidal elevations and currents to changes in eddy viscosity profile friction coefficient and water depth the influence of the tide generating potential is also considered the model uses a standard finite difference grid in the horizontal with a functional approach in the vertical thereby giving a continuous tidal current profile from sea surface to seabed the magnitude of the vertical eddy viscosity depends upon the flow field comparisons are made between model computed profiles and harmonic analyses of 278 current time series at a range of locations in varying water depths with particular emphasis on locations where there are current measurements at a number of points in the vertical a detailed examination of these comparisons shows that frictional effects in the near bed region are particularly important in determining near bed shear and that an accurate specification of water depth is critical for tidal current magnitude the spatial distribution of computed current ellipses shows that the semidiurnal currents are strongest in shallow water with the diurnal currents exhibiting an intensification in the shelf edge region the inclusion of the equilibrium tide is particularly important for the correct determination of the magnitude of the k1 tidal current as well as k1 elevations in the north sea the detailed comparisons show that the magnitude of the tidal currents is correctly determined to within 5 cm s 1 at 220 locations with the model accurately to within 2 cm s 1 reproducing the vertical variation the most sensitive test of a three dimensional model of the tidal current at most locations

early to mid cretaceous tectonics and unconformities of the wessex basin southern england sediment distribution patterns time subsidence plots seismic data and outcrop analysis of the lower cretaceous ryazanian albian of the wessex basin southern england suggest that a number of unconformable horizons exist and that there is no single late cimmerian unconformity surface a tectonic change from areally restricted deposition in the weald and channel sub basins to extensive sedimentation across the whole of southern england began in the mid aptian this change ended with transgression of basement highs in the early albian of the dorset area and later albian of the devon and london platform basin margin areas its onset can be linked to the austrian tectonic phase of europe the onset of marine deposition in the aptian is coincident with periodic transgression of the margins of the wessex basin throughout the aptian albian mid late aptian and early mid aibian transgressions were preceded by periods of erosion the aptian albian lower greensand is characterized by transgressive regressive phases suggesting a short term controlling process third order eustatic changes or intra plate mechanisms tectonic changes in the mid aptian include uplift followed by widespread subsidence this change coincides with a time of plate reorganization in the european and north atlantic areas

earth s variable rotation recent improvements in geodetic data and practical meteorology have advanced research on fluctuations in the earth9s rotation theinterpretation of these fluctuations is inextricably linked with studies of the dynamics of the earth moon system and dynamical processes in the liquid metallic core of the earth where the geomagnetic field originates other parts of the earth9s interior and the hydrosphere and atmosphere fluctuations in the length of the day occurring on decadal time scales have implications for the topography of the core mantle boundary and the electrical magnetic and other properties of the core and lower mantle investigations of more rapid fluctuations bear on meteorological studies of interannual seasonal and intraseasonal variations in the general circulation of the atmosphere and the response of the oceans to such variations

the structural evolution of the english channel area the structural evolution of the english channel area is controlled by structure and particularly by the pre existing cadomian and variscan crustal discontinuities which have been reactivated repeatedly in post variscan times they controlled the crustal subsidence that produced basin development in the mesozoic prior to the sea floor spreading in the north atlantic region they were then reactivated during the cenozoic compression and basin inversion the english channel development is ascribed to mid tertiary differential uplift oligocene to miocene during late tertiary to quaternary times the channel displays characteristics of a tectonically controlled fluvial basin periodically invaded by the sea at the lithospheric scale the channel can be considered as an active intraplate area influenced by the nw se alpine push the nw se atlantic ridge push and glacial rebound stresses copyright 2003 john wiley sons ltd

the role of tidal velocity asymmetries in the deposition of silty tidal rhythmites carboniferous eastern interior coal basin u s a abstract laminated to thin bedded siltstones directly overlie carboniferous coals at several localities in the eastern interior coal basin because lamina thicknesses show cyclical variations the siltstones have been termed tidal rhythmites the rhythmites commonly show a repetitive thick thin pairing of the laminae and these two lamina rhythmites have been interpreted as the result of the asymmetry of flood and ebb velocities that affected sedimentation in a diurnal paleotidal system alternatively the pairing has been interpreted to be related to a pronounced difference in height between successive high tides in a semidiurnal system this explanation suggests deposition in a mixed predominately semidiurnal system with a marked diurnal inequality in addition to the two lamina rhythmite described originally subsequent examination of drill cores indicates the occurrence of relatively rare more complex three and four lamina rhythmites a variety of mathematical techniques are used herein to analyze lamina thickness data extracted from these rhythmites processing techniques include 1 comparing the linear relationship between the thicknesses of the thinner and thicker laminae and comparing these relationships to modern tidal systems 2 analyses of thickness periodicities and comparison with modern neap spring tidal cycles and 3 extraction of lamina thickness inequalities and comparison to the diurnal inequalities that occur in semidiurnal tidal systems these tests indicate that reasonable conclusions can be made for the type of originating paleotidal system for the cases analyzed herein the paleotidal signature suggests a mixed predominantly semidiurnal system with a marked diurnal inequality

deep marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons abstract submarine canyons provide a unique setting for tidal processes to operate from shallow marine to deep marine environments in modern canyons current meter measurements at varying water depths 46 4200 m show a close correlation between the timing of up and down canyon currents and the timing of semi diurnal tides these tidal bottom currents in submarine canyons commonly attain maximum velocities of 25 50 cm s based on core and outcrop studies of modern and ancient deep marine deposits it is proposed here that sand mud rhythmites double mud layers climbing ripples mud draped ripples alternation of parallel and cross laminae sigmoidal cross bedding with mud drapes internal erosional surfaces lenticular bedding and flaser bedding can be used to interpret deposits of deep marine tidal currents this approach is an alternative to the conventional approach in which most deep water traction structures e g climbing ripples and cross bedding would be attributed to deposition from turbidity currents underwater photographs show active mass flows i e slides slumps grain flows and debris flows in modern canyons box cores taken from modern submarine canyons e g la jolla california and conventional cores and outcrops of ancient canyon fill facies oua iboe pliocene nigeria and the annot sandstone eocene oligocene se france contain deposits of both tidal processes and mass flows this facies association in the rock record can be used as a criterion for recognizing submarine canyon settings in a channel mouth environment deep marine tidal deposits are likely to develop elongate bars that are aligned parallel to the channel axis within the channel whereas turbidites are more likely to develop depositional lobes that are aligned perpendicular to channel axis turbidite depositional lobes are much larger than the channel width whereas tidal sand bars are much smaller than the channel width therefore the wrong use of a turbidite lobe model with sheet geometry in lieu of a tidal bar model with bar geometry will result in an unrealistic overestimation of sandstone reservoirs in deep water exploration

the miocene sommieres basin se france bioclastic carbonates in a tide dominated depositional system abstract the miocene sommieres basin in se france is a semi enclosed depression that was connected to the mediterranean sea by a flooded paleo incised valley and then filled by a suite of sediments comprising carbonate grains coming from temperate factories that were largely deposited in tidal dominated paleoenvironments the strata are partitioned into two sequences that reflect repeated flooding of the incised valley system one of several similar situations in this region of france the carbonate grains are mostly bioclasts namely from barnacles bryozoans coralline algae encrusting branching and rhodoliths echinoids and benthic foraminifers large and small with ostracods sponge spicules and planktic foraminifers prominent in muddy facies particles were produced by shallow water carbonate factories on hard substrates valley walls in particular associated with subaqueous dunes and in deeper water basinal settings each depositional sequence is underlain by an eroded and bored hard surface that is progressively overlain by tst subaqueous tidal dunes or storm deposits that grade up in one case into hst marls the hst of the upper sequence has been removed by erosion the lower sequence is ebb tide dominated whereas the upper sequence is flood tide dominated the succession is interpreted to represent a tst whose tidal currents were focused by the narrow valley and a hst that reflected flooding of the overbanks this stratigraphic and depositional motif is comparable to that in other spatially separated neogene paleovalleys that are filled with tide dominated clastic carbonates in the region together with other recently documented similar systems these limestones constitute an important new group of carbonate sand bodies in the carbonate depositional realm

lower cretaceous stage durations combining radiometric data and orbital chronology towards a more stable relative time scale abstract we propose an alternative calibration of lower cretaceous stage durations constrained by direct absolute dating of each stage combined with orbital chronology ten glauconitic horizons sampled in the vocontian basin se france from the base of the lower hauterivian to upper albian yielded k ar ages from 123 3 1 7 ma to 96 9 1 4 ma respectively the relative duration of each stage has been derived by cyclostratigraphy previously obtained in the south east france and central and south italy basins using the gl o standard from the albian cenomanian boundary at 95 3 ma as the anchor point a cyclostratigraphic age for each stage boundaries has been extrapolated and thus compared with the k ar ages this shows a very well defined linear correlation which demonstrates the robustness of the proposed durations of the lower cretaceous stages the estimated durations are 5 3 0 4 my 5 1 0 3 my 6 8 0 4 my and 11 6 0 2 my for the hauterivian barremian aptian and albian stages respectively it also shows that glauconite minerals are powerful radiochronometric tools when precisely stratigraphically defined and carefully selected moreover the large discrepancy of the estimated aptian duration of more than 6 my between the most recent published time scale and this study highlights the problem of the radiometric calibration of the m 0 magnetic chron finally the stage durations and boundary ages proposed here bring strong constraints towards the calibration of the lower cretaceous time scale such accurate temporal calibration is required before any relationship between major biological crises and magmatic emplacement for instance could be further investigated

modelling tidal current induced bed shear stress and palaeocirculation in an epicontinental seaway the bohemian cretaceous basin central europe lower to middle turonian deposits within the bohemian cretaceous basin central europe consist of coarse grained deltaic sandstones passing distally into fine grained offshore sediments dune scale cross beds superimposed on delta front clinoforms indicate a vigorous basinal palaeocirculation capable of transporting coarse grained sand across the entire depth range of the clinoforms ca 35 m bi directional alongshore oriented trough cross set axes silt drapes and reactivation surfaces indicate tidal activity however the bohemian cretaceous basin at this time was over a thousand kilometres from the shelf break and separated from the open ocean by a series of small islands the presence of tidally influenced deposits in a setting where co oscillating tides are likely to have been damped down by seabed friction and blocked by emergent land masses is problematic the imperial college ocean model a fully hydrodynamic unstructured mesh finite element model is used to test the hypothesis that tidal circulation in this isolated region was capable of generating the observed grain size distributions bedform types and palaeocurrent orientations the model is first validated for the prediction of bed shear stress magnitudes and sediment transport pathways against the present day north european shelf seas that surround the british isles the model predicts a microtidal to mesotidal regime for the bohemian cretaceous basin across a range of sensitivity tests with elevated tidal ranges in local embayments funnelling associated with straits increases tidal current velocities generating bed shear stresses that were capable of forming the sedimentary structures observed in the field the model also predicts instantaneous bi directional currents with orientations comparable with those measured in the field overall the imperial college ocean model predicts a vigorous tide driven palaeocirculation within the bohemian cretaceous basin that would indisputably have influenced sediment dispersal and facies distributions palaeocurrent vectors and sediment transport pathways however vary markedly in the different sensitivity tests accurate modelling of these parameters in this instance requires greater palaeogeographic certainty than can be extracted from the available rock record

passive seismic imaging using microearthquakes we have developed a method of processing seismic signals generated by microearthquakes to image local subsurface structure beneath a recording station this technique uses the autocorrelation of the vertically traveling earthquake signals to generate pseudoreflection seismograms that can be interpreted for subsurface structure processed pseudoreflection data from microearthquakes recorded in the island of hawaii show consistent reflectivity patterns that are interpreted as near surface horizontal features forward modeling of the pseudoreflection data results in a p wave velocity model that shows reasonable agreement with the velocity model derived from a refraction study in the region usable signal to noise ratio is obtained down to 2 s a shear wave velocity model was also generated by applying this technique to horizontal component data

evolution and hydrocarbon prospectivity of the brittany basin western approaches trough offshore north west france abstract the faulted preservation of a complete jurassic cretaceous succession in the brittany basin is primarily the result of early cretaceous rifting throughout the western approaches trough jurassic and cenozoic strike slip deformation has also contributed to the distribution of sedimentary successions now observed consequently the brittany basin has a different burial uplift history to the adjacent basins of the western approaches making the lias lower jurassic a mature source rock reservoir rocks are present but the unique deformation history has resulted in the late formation and possible breaching of structural traps the sedimentary record from the brittany basin allows us to observe the depositional effects of tectonic events occurring elsewhere in the western approaches trough these suggest middle jurassic early cretaceous late cretaceous and cenozoic uplift events each have different structural effects the origin of the most prominent intra mesozoic unconformity throughout the western approaches trough the early mid cretaceous is discussed with reference to causes of juxtaposed uplift and renewed rifting

sequence stratigraphic analysis of the aptian albian lower greensand in southern england abstract facies analysis and its use in sequence stratigraphy is described using the lower greensand of southern england as an example and the resulting interpretations are outlined this work forms an independent test of sequence stratigraphic techniques and the exxon cycle chart sequence stratigraphy is a very powerful tool in the analysis of problematic successions although some modification is made here in emphasizing the use of the transgressive surface changing palaeoenvironmental conditions and the effect that palaeoceanography has on the recognition of sequence boundaries are also discussed broad agreement is found between these results and the cycle chart although changing tidal conditions alter the criteria available for analysis of the aptian albian lower greensand succession comparison between this study and sequence stratigraphic analyses conducted in the more condensed type sections of england and france shows that further sequence boundaries are recognizable

a three dimensional model of the northwest european continental shelf with application to the m4 tide abstract the solution of the fully nonlinear three dimensional hydrodynamic equations in polar coordinates for tides is developed using a finite difference grid in the horizontal and the galerkin method in the vertical using this method a three dimensional model of the northwest european continental shelf is used to investigate the spatial distribution of the m4 tidal elevations and currants over the shelf computed m4 currents are compared with observations and found to he in good agreement in the celtic sea although there are significant errors in the north sea the reasons for these discrepancies and the spatial and depth variations in the m4 currants are discussed in detail

a two dimensional tidal model for the mediterranean sea the tidal propagation in the mediterranean sea is described through a high resolution two dimensional hydrodynamic model forced by the equilibrium tide and the incoming tide at the strait of gibraltar the four most significant constituents m2 s2 k1 and o1 are included in the model good agreement with a set of 63 coastal gauges is achieved the significance of the equilibrium tide and the forcing at the open boundary is investigated the incoming wave from the strait of gibraltar is important in tuning the tides in the whole of the mediterranean for the north aegean sea the solution without the forcing at gibraltar results in a doubling of the amplitudes of the semidiurnal tides the estimated energy dissipation due to bottom friction is 8 8 108 w the major area of dissipation is the gulf of gabes energy fluxes through the major straits are calculated

lower cretaceous tides revealed by cross bedding with mud drapes the sand dominated folkestone beds widely exposed around the weald of south east england are of upper aptian to lower albian lower cretaceous age and range in thickness up to 84 m refs 1 3 their content of ammonites bivalves and sponges indicates a marine origin while their relative coarseness and the incorporation of drifted timber point to a shallow water deposition near land one striking sedimentary facies is formed by medium to coarse grained cross bedded sands in which several foreset and or bottomset surfaces support mud drapes although it was suggested4 that this facies may have been formed by the storm induced movement of sand waves i now consider that the facies is best explained by the migration of sand waves under the influence of strongly asymmetrical tides and that the mud drapes are formed at slack water a model of this process has been described elsewhere5 and i now describe measurements of a section which supports my earlier conjecture6that the separation of the mud drapes is systematically related to the phase of the spring neap tidal cycle at the time of deposition although criteria for recognizing tidal deposits have long been available it has not previously been possible to analyse a series of ancient sediments with a view to characterizing the tidal regime

mid cretaceous onlap history of the market weighton structural high northeast england the mid cretaceous sediments of northeast england were deposited at the western margin of the southern north sea basin with sedimentation occurring in a range of tectonic settings detailed analysis of the areal distribution and sedimentary facies of aptian to earliest cenomanian sediments has allowed the pattern of onlap onto the market weighton structural high and changes in relative sea level to be documented successive onlap episodes during the early aptian late aptian and early albian culminated in the final flooding of the structure during the late albian varicosum subzone sea level curves generated from coastal onlap patterns are difficult to relate to published global sea level curves due to the high frequency of the fluctuations in relative sea level observed despite this detailed correlation and analysis of sedimentological events suggest that even the most expanded basinal succession is relatively incomplete this study has also shown that the change from dominantly syn tectonic to dominantly post tectonic sedimentation style occurred in the late early albian

precambrian length of day and the validity of tidal rhythmite paleotidal values paleotidal records obtained from sedimentary tidal rhythmites may be systematically abbreviated and so may give incorrect paleotidal and paleorotational values the validity of determined values including past length of day l o d can be assessed by testing for internal self consistency through application of the laws of celestial mechanics three independent values obtained from the 620 ma elatina reynella rhythmites in south australia 14 1 sidereal months year 401 sidereal days year and 19 5 years for the lunar nodal period when employed in different equations that make allowance for lunar and solar tidal effects each give a lunar semimajor axis in the range of 96 5 96 9 of the present figure such self consistency strongly supports the validity of the derived l o d of 21 9 hours at 620 ma the validity of the estimated l o d of 20 9 hours at 900 ma revised value big cottonwood rhythmites utah and of 17 1 18 9 hours at 2 5 ga weeli wolli rhythmites western australia cannot be assessed in that way because each data set has only one directly determined value the derived mean rate of lunar retreat of 2 16 cm year since 620 ma averts a close approach of the moon at least since 3 ga and a lower rate of retreat seems likely during the proterozoic

a three dimensional model of the principal tides on the european shelf abstract a three dimensional hydrodynamic model of the continental shelf is used to examine the spatial distribution both elevations and currents of 28 of the major tides in the region tidal constituents in the diurnal and semi diurnal band together with higher harmonics and long period tides are used to illustrate the magnitude and spatial variability of the tides over the shelf comparisons are made between model computed profiles and harmonic analyses of 278 current time series at a range of locations in varying water depths with particular emphasis on locations where there are current measurements at a number of points in the vertical observed and computed tidal elevation amplitudes and phases are also compared at up to 257 shore based and off shore tide gauges these detailed comparisons are used to determine any bias in the model and the accuracy of predicted elevations and currents derived with the model results of these comparisons show that although the diurnal and semi diurnal tidal elevations and currents can be accurately reproduced using a 12 km grid the error in the higher harmonics is significantly larger the fact that the model contains all the non linear terms advection quadratic friction wave drift time varying viscosity necessary to generate these harmonics together with a full set of tidal harmonics in order to have the correct level of friction suggests that potentially it should reproduce these constituents however a rigorous comparison was found to be very difficult because of the rapid variation of the higher harmonics in shallow water which cannot be adequately resolved in the model and possible inaccuracy in the measurements of the small currents associated with the higher harmonics

shelf sheet sand reservoir of the lower cretaceous greensand north celtic sea basin offshore ireland core and log data show that the marine early to middle albian a sand of the aptian to lower cenomanian greensand gault interval north celtic sea basin offshore ireland was deposited as an approximately tabular sand body in shelf water depths the a sand is the major reservoir interval at kinsale head and ballycotton gas fields the reservoir sandstone is bioturbated variably glauconitic shell rich and least muddy toward its provenance in a local area of the irish massif and finer grained southeastward into the basin thickness and coarseness of the a sand are related in part to distance from a narrow area of the paleoshore bathymetric control of sand thickness was superimposed on proximal distal trends specifically thick intervals are inferred to have be n deposited in shelf lows and thin zones were deposited over bathymetric highs the a sand was not deposited as a ridge sand and positive relief on the depositional sand body appears to have been minor deposition of the greensand occurred during thermal subsidence of the north celtic sea basin following early cretaceous rifting overall late early cretaceous to late cretaceous transgression was interrupted by progradation of the a sand probably caused by a relative drop in sea level forced regression the a sand sheet consists of several units within the central depositional basin three slightly coarsening upward units up to 15 m thick probably are the consequence of high frequency fluctuations in sea level during progradation the top of the a sand consists of a several m ter thick very glauconitic muddy sandstone to sandy mudstone the upper unit accumulated in deepening water following the maximum lowstand

late proterozoic and paleozoic tides retreat of the moon and rotation of the earth the tidal rhythmites in the proterozoic big cottonwood formation utah united states the neoproterozoic elatina formation of the flinders range southern australia and the lower pennsylvanian pottsville formation alabama united states and mansfield formation indiana united states indicate that the rate of retreat of the lunar orbit is dxi dt approximately k2 sin 2delta where xi is the earth moon radius vector k2 is the tidal love number and delta is the tidal lag angle and that this rate has been approximately constant since the late precambrian when the contribution to tidal friction from the sun is taken into account these data imply that the length of the terrestrial day 900 million years ago was approximately18 hours

large sea small tides the late carboniferous seaway of nw europe debate surrounds the extent of tidal influence in palaeozoic shallow epi continental seas in the absence of analogical reasoning numerical modelling provides a quantitative means of investigating tidality in the geological record herein a new finite element model tested for accuracy on the present day mediterranean is used to predict an exceedingly low tidal range cm in the epi continental seaway that covered much of nw europe during the late carboniferous this small bulge may have been amplified to c 1 m in estuaries leading to the localized deposition of cyclic rhythmites agreeing with geological observations extremely low tidal ranges in ancient epi continental seas may be one mechanism to prevent water body mixing enhancing stratification and promoting anoxia

european cretaceous shorelines stage by stage abstract inferred shorelines are presented for the twelve cretaceous stages for the area of europe and adjacent seas contained between approximately 35 and 65 n and between 15 w and 25 e there is a brief stage by stage commentary and a bibliography of source materials

palaeotidal speeds and ranges estimated from cross bedding sets with mud drapes tidally formed cross bedding sets in which mud drapes are spaced out among sandy foresets occur in cretaceous1 4 eocene5 and holocene6 sands deposited subtidally by strongly asymmetrical sand waves a striking feature of some sets4 6 is that the horizontal drape spacing measured in the direction of sand wave advance varies cyclically on a time scale related to the spring neap tidal cycle as indicated by the numbers of drapes each drape forms part of a distinctive lithological couplet consisting of a group of sandy foresets recording avalanching on the steeper side of the sand wave followed by the drape itself typically divided into upper and lower parts by a centrally placed silt sand parting the drapes have been assigned to slack water but the groups of sandy foresets to episodes of vigorous flow the combination suggesting a quantitative model based on the tide here i show how the peak speeds and ranges of ancient tides can be estimated by combining an empirical bedload transport function with appropriate measurements from such cross bedding sets

recognition and documentation of depositional sequences from outcrop an example from the aptian and albian on the eastern margin of the wessex basin stratigraphic data relating to the aptian and albian sediments around folkestone in southeast england on the eastern margin of the wessex basin are plotted graphically to illustrate biostratigraphic gaps and condensed intervals these are then used to suggest candidate sequence boundaries notated lg1 4 and gl 3 which are named after the lower greensand and gault the biostratigraphic subzones apparently unrepresented in the area are lg1 obsoletus and bodei lg2 gracite and debile lg3 schrammeni gl bulliensis candidate sequence boundaries g2 cristatum subzone and g3 auritus subzone are erosion surfaces correlating with probable biostratigraphic gaps elsewhere in the basin the age of lg4 is uncertain but must lie within the mammillatum superzone all candidate sequence boundaries correspond closely to those predicted by recent global sea level cycle charts and additionally there is a close match between predicted maximum flooding surfaces and the occurrence of condensed intervals most of the candidate sequence boundaries could have been formed as a result of rapid and at least regionally extensive relative sea level falls but the sedimentological contexts of lg3 and gl suggest that these may have been generated by transgression related sediment condensation the minor sequence boundary in the loricatus zone intermedius subzone illustrated in the cycle charts cannot be unambiguously recognized at outcrop in the folkestone area additional sequence boundaries not shown in the cycle charts may also be present in the wessex basin

firmgrounds key surfaces in the recognition of parasequences in the aptian lower greensand group isle of wight southern england aptian lower greensand group exposures in the cliffs of the isle of wight southern england display a consistent coarsening up cyclicity on the scale of centimetres to tens of metres that reflects the bed bed set parasequence parasequence set and sequence hierarchy these coarsening up cycles are most commonly recognized at the scale of parasequences 20 cm to 10 m thick genetically related groups of which form parasequence sets both parasequences and parasequence sets contain the succession of biofacies that culminate in firmground development numerous episodes of erosion deposition and colonization are recorded reflecting multiple erosion bypass events the increase in mean grain size through each cycle is reflected by changes in physical sedimentary structures ichnofauna or bioturbational fabric fossil fauna and diagenesis interbedded mudstones siltstones and sandstones in the lower beds of each cycle display a variety of structures ranging from low angle hummocky or tabular cross strata sandstone filled erosional gutters and planar lamination the cleaner sandstones found in the upper parts to each cycle are often completely bioturbated with only rare stratification and pebble plant debris filled scours preserved bioturbational fabrics change upward through each cycle from small subhorizontal mud or sandstone filled burrows to large branching clay filled or cemented burrow systems the top surface of each cycle is marked by a fossil epifauna indicative of firm to hard substrate conditions concentrations of bivalves brachiopods bryozoa crinoids and corals are preferentially cemented by iron oxide carbonate or phosphate such cements were early and thus utilized by firm or hard substrate dwellers this fossiliferous cemented sandstone is overlain by a flooding surface marked by the mudstone and silt rich sandstones at the base of the next cycle together the fauna and ichnofauna in each cycle represent the gradual development of firm substrate conditions culminating in the diverse firmground fauna preserved at the top of each cycle the fauna and changing substrate conditions reflect the hiatuses developed during successive episodes of marine flooding high species diversity is matched by complex patterns of taphonomic feedback in the mature firmground faunas that mark major flooding surfaces increasing faunal maturity allows recognition of a hierarchy of hiatuses this hierarchy is analogous to the parasequence parasequence set division the stratigraphic condensation of firmgrounds can be used to empirically define the condensed section the thickness of sediment between firmgrounds being a function of sediment supply and water depth accommodation space

variscan structure and its influence on post carboniferous basin development western approaches basin sw uk continental shelf reflection seismic records from the western approaches basin sw uk continental shelf reveal sse dipping reflection packages within the variscan basement these have been mapped and are believed to originate from variscan thrusts orthogonal transfer faults are apparent as nnw trending zones of discontinuity structural trends in the permian mesozoic western approaches basin parallel those of the underlying basement an end variscan structural high in the northern part of the basin was progressively onlapped from the south during permian times this high may have been formed by thrust driven tectonic thickening of the crust during late jurassic early cretaceous times variscan thrusts were reactivated in the western part of the basin melville basin to form a half graben however in the east st mary9s basin the basin is more symmetrical and mesozoic reactivation of variscan thrusts cannot be unequivocally demonstrated

transgressive changes from tidal estuarine to marine embayment depositional systems the lower cretaceous woburn sands of southern england and comparison with holocene analogs the lower cretaceous woburn sands lower greensand group in southern england constitutes one of the most intensively studied tidal sandstone outcrops for sedimentological and reservoir analog studies most recent workers have interpreted the whole 30 60 m 100 200 ft thick succession around leighton buzzard as representing an ancient tide dominated estuary however unequivocal estuary characteristics are limited to the lowermost part about 15 20 m 50 66 ft we suggest that a significant portion of the woburn sands and most of the middle part was formed in a tide dominated marine embayment hence the vertical facies change from the lower to middle part of the woburn sands is interpreted as a change from 1 a narrow estuary to 2 a broad marine embayment the wash embayment in eastern england is a striking modern analog it receives most of its sediments and waters from marine sources and is largely filled with nondiluted seawater moreover the holocene transgressive history of the wash is remarkably similar to the transgressive evolution of the woburn sands early estuarine sequence models predict landward translation of facies zones along the valley thalweg during transgression but eventual facies translation in the strike direction has not been fully documented or discussed an embayment facies that is not commonly confined in the early incised valley can occur vertically between the estuarine valley fill and marine shelf deposits and is probably underrepresented in current models however this segment of the transgression comprising along strike bay expansion and the development of a broad marine embayment may be more important than previously thought

between scylla and charybdis part 2 the sedimentary dynamics of the ancient early pleistocene messina strait central mediterranean based on its modern analogue abstract the 3 km wide messina strait divides sicily from the italian peninsula representing one of the most impressive examples of tide dominated marine passageway of the central mediterranean sea the tidal hydrodynamics governing the strait results from a semi diurnal phase inversion between two interlinked wider basins i e the tyrrhenian sea to the north and the ionian sea to the south due to the presence of a nodal tidal point in the centre of the strait this condition associated with coastal narrowing causes continuous water exchanges and a local phenomenon of tidal amplification producing collinear tidal currents up to 3 m s 1 in velocity in the point of tidal maxima of the strait centre currents follow bi directional patterns across the strait decelerating towards either opposite peripheries because of the progressive enlargement of the cross sectional areas tides exert a relevant influence on the strait bottom shaping characteristic erosional features governing the main sediment transport routes and promoting the migration of distinctive bedforms the textural and dimensional attributes of these bottom features vary according to the current velocity trends and main directions indicating a specific partition of the strait in individual sedimentary zones in the early pleistocene analogous conditions established across the same area and huge quantities of siliciclastic and bioclastic deposits accumulated in the ancient messina strait under a similar tidal hydrodynamics the 250 m thick strait fill succession which is magnificently exposed across the two opposite margins i e scylla and charybdis of the modern passageway represents a crucial correlative element in supporting the reconstruction of the sedimentary dynamics of the past strait based on the observation of the modern system in this work which represents the second part of a first article focused on the modern messina strait previous stratigraphic data are reviewed and integrated with new sedimentological observations carried out in both onshore and offshore key areas in particular outcrop analysis allows distinguishing a number of facies associations which are described and interpreted by taking into account the correspondent modern depositional strait setting the results of this study highlight a mutual correlation between the depositional zones detected in the modern messina strait and the individual facies associations recognised in the onshore margins the strait centre zone represented a bedload parting sector in the ancient system this zone which is one of the most difficult environment to detect in ancient straits due to a condensed sedimentary record is suggested to coincide with a structural palaeo high exposed in the southern sector of the investigated onshore area and continuing offshore in the modern strait this tectonic horst symmetrically separated two opposite highly depositional zones to the north and to the south hosting gravel and sand size siliciclastic and bioclastic deposits exhibiting diffuse motifs of large scale tidal cross stratification and a specific vertical facies stacking these characteristic tidal deposits which are believed to record the migration of several generations of tidal dunes forming extensive bedform fields in the strait reflect a tidal asymmetry between flood and ebb currents tidal asymmetry is referable to the oceanographic setting observable nowadays in the messina strait and deriving from a marked density driven water mass stratification between the two opposite flows in the ancient system tidal dunes transited down current to highly bioturbated fines including sporadic small scale tidal cross strata representing the distal periphery of the early pleistocene strait here bedforms followed migration pathways not always reflecting mutually evasive net gross sediment transport routes due to local conditions of current rotation occurring during each tidal phase inversion during these stages similar to slack water periods currents were weak enough to allow fine sediments to be settled from suspension reproducing a signature typical of other tide dominated coastal systems e g estuaries tidal flats etc these sedimentary zones of the ancient messina strait were laterally bounded by tectonically active margins where fan deltas clastic aprons and carbonate wedges developed under the constant interplay between mass transport processes and tidal currents the resulting architectural and sedimentary features observable in outcrop reveal impressive similarities with the morpho bathymetric features nowadays documented in the correspondent strait margin modern environments these considerations allow deciphering a general palaeo environmental reconstruction of the ancient strait which although suffering of limitations due to a partial preservation of the whole rock record discloses sedimentary processes and depositional environments of the ancient messina strait the process based analysis of this field based case study is crucial in predicting long term environmental changes and facies migration pathways and improves the state of knowledge on tidal straits which are the less understood among the most common tidal depositional systems

record of latest barremian cenomanian environmental change in tectonically controlled depressions from the jura burgundy threshold jura mountains eastern france and western switzerland abstract the area of the western jura mountains constitutes the former jura burgundy threshold between the tethys ocean and the epicontinental paris basin sea during the barremian the area was covered by a shallow water urgonian carbonate platform tectonic processes influenced the architecture of the urgonian platform and were notably responsible for the formation of fault related depressions on top of the urgonian series which were subsequently transformed into incised valleys and then to marine depocenters their sedimentary infills are mostly represented by the perte du rhone formation and record stepwise environmental change on the innermost platform which was strongly influenced by the nearby landmass from the latest barremian onward sedimentation progressively changed from i predominantly oncoidal and detrital charophyte rich marly limestones to ii heterozoan marly limestones and marls followed by iii detrital sediments interspersed with numerous phosphatic conglomerates these changes are linked with the onset of the latest barremian taxy episode and with the following oceanic anoxic episodes oae s 1a to d in the neighbouring basins the sedimentary changes are associated with sedimentary sequences which formed during 2nd order transgressions and which express the effect of sea level fall followed by drowning events the presence of a rich ammonite fauna allowed a precise biostratigraphical dating of these events during the latest barremian to cenomanian time interval

present day crustal stress field in greece inferred from regional scale damped inversion of earthquake focal mechanisms in this study we utilize regional and teleseismic earthquake moment tensor solutions in order to infer the contemporary crustal stress in the greek region we focus on crustal earthquakes and select only solutions with good waveform fits and well resolved nodal planes a data set of 1614 focal mechanisms is used as input to a regional scale damped stress inversion algorithm over a grid whose node spacing is 0 35 several resolution and sensitivity tests are performed in order to ascertain the robustness of our results our findings show that for most of the greek region the largest principal stress 1 is vertically oriented and that the minimum principal stress axis 3 are subhorizontal with a predominant n s orientation in the sw peloponnese the orientation of 3 axes rotates clockwise and in se aegean counterclockwise these results are in agreement with the generally accepted model that slab rollback combined with gravitational spreading of the aegean lithosphere are the main causes of the extension transitions between different faulting types in nw greece or in the aegean occur within narrow zones in the order of tens of kilometers a visual comparison of the principal horizontal stress axes and the principal strain axes derived from gps observations shows good agreement suggesting that the crust in the greek region behaves largely in an elastic manner