bryozoans as carbonate sediment producers on the cool water lacepede shelf southern australia abstract modern sediments on the lacepede shelf and adjacent slope are typical mid latitude cool water palimpsest deposits dominated by bryozoan mollusc and quartz particles bryozoan bioclasts form autochthonous and to a lesser extent allochthonous accumulations across the grain size spectrum from mud to boulder size the bryozoan skeletons are grouped on the basis of architecture and style of disarticulation fragmentation into nine morphotypes erect rigid forms comprise 1 fenestrate 2 foliose 3 flat robust branching and 4 delicate branching morphotypes large adeona sp skeletons are recognised as a separate type of fenestrate form because of their distinctive shape mineralogy and restricted environment erect flexible forms are either 5 articulated branching or 6 articulated zooidal other important morphotypes are 7 encrusting 8 nodular arborescent and 9 vagrant differences in skeletal architecture result in distinct particle types encrusting morphotypes on soft organic substrates and the wide variety of erect rigid forms are broken into fragments erect flexible forms disintegrate upon death into definitive sand and silt size grains encrusting morphotypes on hard substrates nodular arborescent and vagrant forms remain whole and when large accumulate in place morphotypes are mineralogically distinct and so bryozoan sediment composition is environmentally controlled shallow water

middle miocene serravallian temperate carbonates in a seaway connecting the atlantic ocean and the mediterranean sea north betic strait s spain abstract miocene deposits in the contact area between the prebetic and subbetic domains betic cordillera s spain record the last stages of marine deposition on the southern iberian margin and the final closure of the north betic strait in the early tortonian late miocene serravallian middle miocene shallow water carbonates and mixed carbonate siliciclastics formed on a platform at the southern margin of the north betic strait these shallow water deposits informally termed the la escalera formation onlap an erosion surface carved into underlying miocene and older rocks carbonate components are mainly bryozoans coralline red algae molluscs and benthic and planktonic foraminifers typical of heterozoan lithofacies several facies types can be distinguished based on different grain sizes and sedimentary structures large scale geometries and stratigraphic facies relationships indicate that the la escalera formation was deposited on a homoclinal ramp attached to a deeply eroded emergent relief to the south a beach system developed at the southern margin with backshore lagoons and local incursions of coarse terrigenous sediments seawards of the beach system was a submarine dune belt that extended over several square kilometres at the northeastern end of the la escalera formation longshore currents shifted submarine dunes to the northeast maximum production of carbonate skeletons took place seawards of the dune field from this factory area skeletal debris was moved landwards and incorporated into the dunes and beaches whereas other skeletal particles were transported downslope by storms and fed a facies belt with hummocky and swaley cross stratified sediments the finest grained particles accumulated below a storm wave base along with significant planktic debris carbonate deposits change laterally westwards to terrigenous sediments formed in similar facies belts terrigenous influx limited carbonate production on the western part of the ramp by disturbing the growth of coralline algae and bryozoans vertical variations of facies within the formation depict a major transgressive regressive cycle modulated by up to 10 higher frequency cycles despite its location in an atlantic linked basin the sedimentary model of the la escalera formation shows similarities to the models proposed for neogene mediterranean temperate carbonates which imply a relatively low energy regime on the ramp in comparison with the open ocean platforms this relatively low energy regime can be explained by the position of the north betic strait at the eastern end of the guadalquivir basin however hummocky and swaley cross stratified deposits are significantly more developed in la escalera deposits than in known examples of neogene mediterranean carbonates

origin of late pleistocene bryozoan reef mounds great australian bight bryozoan rich biogenic mounds grew periodically on the prograding carbonate slope of the central great australian bight throughout pliocene pleistocene time cores from three odp leg 182 drill sites provide a record of mound growth during the last 300 000 years over a stratigraphic thickness of similar to 150 m these mounds the first such structures described from the modern ocean grew between paleodepths of 100 and 240 m we infer that the upper limit of growth was established by swell wave base and the lower boundary was fixed by an oligotrophic water mass detailed chronostratigraphy based on radiometric and u series dating benthic foraminifer stable isotope stratigraphy and planktonic foraminifer abundance ratios confirms that buildups flourished during glacial lowstands even numbered marine isotope stages but were largely moribund during interglacial highstands and are not extant today mound floatstones are compositionally a mixture of in situ bryozoans comprising 96 genera and characterized by fenestrate flat robust branching encrusting nodular arborescent and delicate branching growth forms the packstone matrix comprises autochthonous and allochthonous sand size bryozoans benthic and planktonic foraminifers serpulids coralline algae sponge spicules peloids and variable glauconite and quartz grains together with mud size ostracods tunicate spicules bioeroded sponge chips and coccoliths intermound allochthonous packstone and local grainstone contain similar particles but they are conspicuously worn abraded blackened and bioeroded an integrated model of mound accretion during sea level lowstands begins with delicate branching bryozoan floatstone that increases in bryozoan abundance and diversity upward over a thickness of 5 10 m culminating in thin intervals of grainstone characterized by reduced diversity and locally abraded fossils mound accumulation was relatively rapid 30 67 cm ky and locally punctuated by rudstones and firmgrounds intermound highstand deposition was comparatively slow 17 25 cm ky and typified by meter scale fining upward packages of packstone and grainstone or burrowed packstone with local firmgrounds overlain by characteristically abraded particles mound growth during glacial periods is interpreted to have resulted from increased nutrient supply and enhanced primary productivity such elevated trophic resources were both regional and local and thought to be focused in this area by cessation of leeuwin current flow together with northward movement of the subtropical convergence and related dynamic mixing

mound forming cold water corals and bryozoans in the early palaeocene of denmark the faxe quarry in south east denmark offers excellent exposures of early palaeocene danian deep water intercalated coral and bryozoan mounds that form complexes at least 40 m thick and a few kilometres wide along and over submarine highs the co existing coral and bryozoan mounds represent two different biogenic carbonate factories with a highly dynamic interplay during growth the sedimentary facies mound geometries and the density diversity and palaeoecology of the associated benthic invertebrates and nannofossils allow recognition of six successive growth units unit 1 represents an outer shelf bryozoan mound belt characterized by an oligotrophic cool water nannofossil assemblage unit 2 comprises a mixed faunal assemblage of bryozoans and octocorals with an initial sparse colonization of hexacorals the nannofossil assemblage records a decrease in diversity and an increase in warm water forms unit 3 marks the onset of dense colonization of the scleractinian coral dendrophyllia candelabrum with associated low diversity macrofauna and nannofossil assemblages unit 4 represents the main coral build up phase with frame building hexacorals of dendrophyllia and faxephyllia associated with a high diversity invertebrate fauna and relatively low diversity nannofossil assemblages unit 5 represents the late coral mound phase showing extensive lateral distribution and finally death and erosion of the coral mounds this event was contemporaneous with a warming trend in the pelagic environment the succeeding unit 6 marks the burial and overgrowth of the coral mound complex by bryozoan rich sediments the coral mound complex in the faxe quarry initiated and terminated in global nannofossil zone np3 and regional nannofossil zones nntp2g 3 suggesting a mound growth duration of approximately 300 kyr and a mean vertical accretion of the coral mound of 13 cm kyr the mound complex probably serves as the best exposed analogue to modern deep and cold water coral mounds in the north atlantic this article is protected by copyright all rights reserved

palaeoecology and survival strategies of an impoverished benthic chalk community in a mid danian deep shelf setting abstract upper cretaceous chalk is characterized by a rich and diverse benthic fauna followed by a poor benthic fauna in the lowermost danian immediately after the k pg extinction event in the early to mid danian diversity increased and rich bryozoan and cold water coral mound ecosystems were established in localized areas in the contemporary mid danian dalbyover deep shelf chalk the benthic fauna is markedly impoverished the danian macrofauna from bulk samples at dalbyover comprises 22 species and several bryozoan morphogroups and is of low diversity and density compared to latest maastrichtian and mid danian shelf faunas average fischer alpha index is 2 34 and shannon index 1 38 with minor stratigraphic variations guild analysis of the macrofauna indicates that the vast majority of species show special adaptations to survival at and in the uppermost few centimetres of the soft substrate with dominance of root attached species attaching to small substrates and free lying suspension feeders further the morphology of the serpulid tubes and the occurrence of crinoids in situ reflect a stable substrate with little overturning by the infauna the benthic foraminiferal assemblages are dominated by low trochospiral and planispiral epifaunal morphogroups whereas elongated forms with an infaunal mode of life are rare the combined macrofauna and foraminiferal data indicate deposition in a relatively stable environment where food was a limiting factor for the macrofauna it is evident that species occurring in small numbers are long ranging and also known from the cretaceous whereas species occurring in high numbers are known solely from the danian evidently the mesozoic survivors had the strategy to survive in this special chalk environment where only few danian species were successful

further investigations of geomagnetic diurnal variations associated with the 2011 off the pacific coast of tohoku earthquake mw 9 0 abstract as one of the most promising candidates for short term earthquake forecasting the seismo electromagnetic phenomena have been intensively studied for several decades recently xu et al 2013 have reported unusual behaviors of geomagnetic diurnal variations in the vertical component prior to the 2011 off the pacific coast of tohoku earthquake mw 9 0 to validate this result further investigations have been applied in this study geomagnetic data of 16 years long term observation have been analyzed using the same method in xu et al 2013 ratios of diurnal variation range between the target station esashi esa which is about 130 km from the epicenter and the remote reference station kakioka kak about 300 km distant to the epicenter have been computed after removing seasonal variations revealed by wavelet transform analysis the 15 day mean values of the ratios in the vertical component shows a clear anomaly exceeding the statistical threshold about 2 months before the mega event this anomaly is unique over a 16 year long background and further discussions indicate that this anomaly is unlikely caused by strong geomagnetic storms or a statistical fluke therefore this study has provided a strong support to the previous results in xu et al 2013

contourite drifts moats and channels in the upper cretaceous chalk of the danish basin during the late cretaceous high global sea level meant that most of the nw european craton was flooded by the deep epeiric chalk sea the classical paradigm for chalk deposition envisages a quiet rain of minute skeletal debris of coccolithophorid algae and other pelagic organisms deposited as horizontal flat lying pelagic oozes with local redeposition by slumps slides and debris flows along faults and other structural features seismic data from the danish basin and elsewhere necessitate a revision of this paradigm these demonstrate that the chalk sea floor had a considerable relief commonly of more than a hundred metres amplitude comprising moats drifts mounds and channels seismic sections from the kattegat sea illustrate the development in the maastrichtian of a deep moat adjacent to a topographic ridge formed over the inverted nw se trending sorgenfrei tornquist zone the moat was up to 120 m deeper than its sw flank which was formed by an internally complex elongate drift up to 20 km wide with an estimated length of ca 200 km smaller mound like features channels and clinoform beds are superimposed on the large scale relief the sea floor relief is interpreted to have formed in response to persistent bottom currents flowing parallel to bathymetric contours the initial build up of the broad gently convex up sheeted drift was controlled by relatively low velocity bottom currents the region of highest current velocity was gradually shifted ne wards towards the inversion zone ridge resulting in the formation of the deep moat flanked by the elongate drift the current is interpreted to have flowed from the se towards nw on the basis of the internal architecture of the elongate drift and the nw ward branching and decrease in moat relief the architecture and morphology of the moat drift and other features of the chalk sea floor are in all aspects similar to contourite systems of modern continental margins it is accordingly proposed that the fundamental physical oceanographic concept contour currents and their resulting contourite drifts is extended to include the deep epeiric seas which covered nw europe during the late cretaceous

benthic palaeoecology of danian deep shelf bryozoan mounds in the danish basin abstract early danian cool water bryozoan mounds exposed in the coastal cliff stevns klint in denmark were formed shortly after the cretaceous tertiary mass extinction they represent a relatively deep water highly diverse benthic ecosystem within the epeiric seaway that covered the danish basin the mounds are 50 110 m long and reached a height of about 5 10 m above the seafloor they are asymmetrical with a steep southern and a gentle northern flank and were dominated by small suspension feeders the benthic elements generally occur as fragments set in a carbonate mud matrix the main skeletal contributors are delicate branching bryozoans with minor contributions of bryozoan sheets and nodular arborescent bryozoans locally abundant octocorals occur on the mound crests and upper parts of the steep flanks echinoids are present in minor amounts but are locally abundant serpulids crinoids asteroids brachiopods bivalves massive calcareous sponges and benthic foraminifers are generally minor contributors to the benthic mound fauna influx of planktonic foraminifers coccoliths and other planktonic organisms was high and was probably a major source of nutrient supply to the mainly suspension feeding benthic fauna the faunal association reflects a relatively low energy environment with a high possibly seasonal influx of particulate nutrients the best growth conditions with respect to nutrient influx were on the mound crest and upper steep flank reflected by the diverse and relatively largest benthic faunal elements periodic reworking and winnowing occurred across the entire mound structure but most prominent on the gentle northern flanks limiting the benthic growth and notably the colony density and size of delicate branching bryozoans vagile benthic faunas were also adapted to different areas on the mound irregular echinoids preferred the intermound areas within fine grained wackestone packstone facies where they ploughed through the sediment whereas regular echinoids were epifaunal and preferred the upper parts of the mounds possibly feeding mainly on bryozoans skeletons of both groups became concentrated at the toe of the steep flanks and in the intermound areas by physical reworking during major storms changes in faunal composition on the mound crests occurred rhythmically on both small and large scale during mound growth rhythmically recurring faunal assemblages reflect alternating hydrodynamic conditions on the seafloor with respect to nutrient influx and energy which probably were linked to short term seasonal and long term climatic variations the long term alternation may be within the milankovitch frequency band blooming events of bryozoan sheets resulted from relatively short periods with large amounts of available food and suitable substrate successful colonisation by octocorals on the other hand reflected longer term favourable conditions on the mounds possibly associated with overall higher energy levels a possible pleistocene analogue to the bryozoan dominated danian mounds occurs at the shelf slope break of the great australian bight both of these cool water mound systems deviate from most other biogenic mounds known from the fossil record in their non cemented nature regular geometry and a lack of core and flank facies

the tectonic evolution of the fennoscandian border zone in denmark abstract the fennoscandian border zone is a complex tectonic zone defining the border between the stable fennoscandian baltic shield and the metastable danish basin and polish trough it forms the northwestern part of the tornquist teisseyre lineament one of the major european tectonic sutures intricate tectonic movements took place within the fennoscandian border zone from early paleozoic to recent time it is postulated that its evolution was dominated during the early palaeozoic by tensional tectonics and during the late paleozoic by dextral wrench movements the latter led to the development of curvilinear faults and the subsidence of pull apart basins transtensional stresses governing the triassic to early cretaceous evolution of the fennoscandian border zone induced the differential subsidence of rift basins during the late cretaceous and early cenozoic dextral transpressional stresses induced the partial inversion of mesozoic basins associated with the fennoscandian border zone this is reflected by the uplift of a major anticlinorium over which cretaceous strata became progressively truncated whilst adjacent areas developed into late cretaceous early tertiary depocentres basin inversion diminishes to the northwest along the fennoscandian border zone and disappears in the skagerrak area

carbonate mounds from paradox to world heritage the recent marine carbonate world comprises two major compartments 1 the surface domain of the photozoan carbonates confined in space by water depth and by the penetration of light and 2 a deep domain where heterozoan mound builder guilds directly forage on fluxes of nutrients which primarily percolate from the photic zone and or are generated by in situ benthic processes locally giant cold water coral mounds tower up to heights of 150 to 250 m above the sea floor in general between 500 and 1300 m water depth and within sharply delineated provinces some 15 years of research on these giant mound provinces conveys a picture of their distribution in space and possibly sheds light on controls acting in concert globally there is no counterpart for the prolific north atlantic mound basin namb a chemical control is seen by an overlay of the mound provinces on a map of the aragonite saturation horizon ash an external physical control is inferred fromthe position of themound provinces girdling a vigorous north atlantic subtropical gyre systemand clustering close to the roof of the intermediate to deep water masses of a dynamically stratified ocean on the eastern boundary of the namb nutrient fluxes are enhanced by mixing processes driven either by internal waves between galicia and the shetlands or by the vast and heterogeneous eastern boundary upwelling system along the iberian african margins down to 10 n early diagenesis by carbonate dissolution and re precipitation driven by convecting or advecting internal fluids can contribute to stabilize such constructions facilitating an exuberant vertical accretion it is speculated that in thenorth atlantic ocean the deep water carbonate factory outclasses in size the shallow water coral reefs giant mound formation is a recurrent play of life since the dawn of the metazoans nama group upper neoproterozoic however with actors and plots varying from act to act remarkably literature reports only three occurrences of deep water mounds in the phanerozoic the modern ocean possibly the danian and the carboniferous some striking parallelisms in the development of the atlantic and the paleo tethys oceans combined with the developing insights in the controls on deep watermounds in the present ocean invite for a comparative study this has the potential to eventually shed light on the full circulation pattern of the paleo tethys ocean surface and deep comparative studies will build upon 1 modeling of ocean circulation constrained by the record of deep water carbonate systems and supported by advances in tracer and proxy tools and 2 field studies on representative and accessible continental locations the mound route that develops in morocco under the auspices of ioc unesco will provide tomulti disciplinary teams with marine and continental experience opportunities for confronting observations from the modern ocean and on key records of past oceanic basins it has the potential to eventually qualify for a unesco recognition as world heritage

a giant 5 3 107 m3 middle miocene c 15 ma sediment mound m1 above the siri canyon norwegian danish basin origin and significance abstract a large scale enigmatic mound structure m1 has been discovered in middle miocene strata of the norwegian danish basin c 10 km east and updip of the central graben it is located about 1 km beneath the seabed and clearly resolved by a 3d seismic data set focused on the deeper remobilised sand filled siri canyon m1 comprises two culminations up to 80 m high and up to 1400 m long constituting a sediment volume of some 5 3 10 7 m 3 it is characterized by a hard reflection at the top a soft reflection at the base differential compaction relative to the surrounding sediments and 10 ms twt velocity pull up of underlying reflections indicating a relatively fast mound fill attributed to the presence of sand within the mound internal seismic reflections are arranged in an asymmetric concentric pattern suggesting a progressive aggradation to the nw downstream to a mid miocene contour current system numerous elongated pockmarks occur in the upper miocene succession close to the mound and indicate that the study area was influenced by gas expulsion in the mid and late miocene the reflection configuration velocity dimensions regional setting and isolated location can best be explained by interpreting the mound as a giant sand volcano extruded 1 km upward from the siri canyon during the middle miocene c 15 ma the likely causes of this remarkable structure include gas charge and lateral pressure transfer from the central graben along the siri canyon reservoir while this is the first such structure described from this part of the north sea similar aged sand extrudites have recently been inferred from seismic observations in the north viking graben thus suggesting that the mid miocene was a time of widespread and intense sediment remobilization and fluid expulsion in the north sea

magnetic and electric fields associated with changes in high pore pressure in fault zones application to the loma prieta ulf emissions we determined the electric and magnetic fields generated during failure of faults containing sealed compartments with pore pressures ranging from hydrostatic to lithostatic levels exhumed fault studies and strain measurement data limit the possible size of these compartments to less than 1 km in extent rupture of seals between compartments produces rapid pore pressure changes and fluid flow and may create fractures that propagate away from the high pressure compartment along the fault face nonuniform fluid flow results from pressure decrease in the fracture from crack generated dilatancy partial blockage by silica deposition and clearing as pressure increases a direct consequence of this unsteady fluid flow may be associated transient magnetic signals caused by electrokinetic piezomagnetic and magnetohydrodynamic effects models of these processes for fault geometries with 1 km high pressure compartments show that electrokinetic effects are several orders of magnitude larger than the other mechanisms the electrokinetic signals produced by this unsteady flow are comparable in magnitude and frequency to the magnetic signals observed prior to the ml 7 1 loma prieta earthquake of october 18 1989 provided fracture lengths are less than 200 m

multiple seismo anomalies associated with the m6 1 ludian earthquake on august 3 2014 abstract multiple geophysical parameters including groundwater level water temperature water radon crustal deformation electromagnetic waves and total electron contents tec in the ionosphere are examined together to investigate pre earthquake anomalous phenomena associated with the mw6 1 ludian earthquake on august 3 2014 cross parameter comparison eliminates anomalies that are detected in one parameter only and examine earthquake related phenomena in various fields simultaneously retrieved anomalies show that abnormal decreases of water temperature and radon concentration related to anomalous uplift of groundwater levels appeared about 1 8 days before the earthquake even without contributions from rain significant step like changes are observed from data recorded by strainmeters on july 31 and are consistent with water related anomalies in timing no significant anomalies can be found from electromagnetic data through the preliminary observation in contrast tec appeared positive anomalies 1 3 days before the ludian earthquake although causal mechanisms of the tec anomalies from stressed rocks are not fully understood multiple parameter examination can increase credibility of determination regarding pre earthquake phenomena

adaptive morphologies of the brachiopod fauna from danian coral mounds at faxe denmark abstract only few of the brachiopod species that lived in the late cretaceous chalk sea of northern europe survived the mass extinction at the cretaceous paleogene boundary however a rich brachiopod fauna rapidly evolved from the survivors and most of the vacant niches were filled in by the middle danian when a large cool water subphotic coral bryozoan mound complex was developed at faxe in the eastern part of the danish basin the brachiopod fauna of the complex comprises 17 species dominated by micromorphic species of similar types as those known from the upper cretaceous maastrichtian chalk from the same region all species are found in the coral mound facies and six of the species are restricted to this facies large sized species are rare both in terms of species numbers and abundance one species is adapted to a life between the branches of the cool water hexacorals dendrophyllia candelabrum and oculina becki secondarily free living species are close to absent this is in contrast to the maastrichtian chalk fauna where this group includes 10 species 24 of the total brachiopod fauna the otherwise great similarity in morphological adaptations in the brachiopods from the maastrichtian chalk and the danian coral mounds is remarkable and somewhat surprising as the latter almost lacks soft substrates the danian brachiopod fauna essentially represents a continuation of the maastrichtian fauna but in a very different habitat the similarity between the two faunas is explained by the abundance of small hard substrates notably bryozoans in both environments the brachiopods from faxe are one of the very few ancient examples of a rich brachiopod fauna from a coral mound environment

pre seismic geomagnetic anomaly and earthquake location article i nfo many researchers studied the relationships between appearances of geomagnetic anomalies and their distances to earthquake epicenters or faults yet occasionally some magnetometer stations located nearby earthquake epicenters and or faults do not observe geomagnetic anomalies in this paper a new hybrid system which simultaneously takes the hypocenter and fault plane solution into account is constructed to examine 38 earthquakes interpreted to be associated with geomagnetic anomalies during the period 1988 2001 in taiwan the surface magnetic anomaly reference tip smart of the new system is used instead of the epicenter or the fault to investigate statistically the distance relationship between the anomalies and the earthquake parameters results show that the anomalies gather along the fault and in the belt zone to the smart possible mechanisms causing the anomalies in the two zones are proposed and discussed characteristics of the anomaly might shed some light on locations of faults before earthquake occurrences

groundwater strain coupling before the 1999 mw 7 6 taiwan chi chi earthquake summary the coupling of pre earthquake anomalous phenomena between long term groundwater levels recorded at 42 monitoring stations and time varying surface strain derived from 16 gps stations was found in the choshuichi alluvial fan before the 1999 m w 7 6 chi chi earthquake in taiwan the noise free groundwater level anomalies consistently comprised by a sequence of decrease rise and flat phases which agree very well with changes in strain rates computed from the gps stations these coupling agreements show that in addition to compression tension can be generated before a thrust earthquake occurrence as well this case demonstrates that short term surface deformation as signals against noise and accuracy of pre earthquake anomalous phenomena can be simultaneously examined by using multiple parameter crosscheck for significantly reducing the uncertainty of earthquake precursory evaluation

statistical analysis of ulf seismomagnetic phenomena at kakioka japan during 2001 2010 to clarify and verify the ultralow frequency ulf seismomagnetic phenomena we have performed statistical studies on the geomagnetic data observed at the kakioka kak station japan during 2001 2010 we investigated the energy of ulf geomagnetic signals of the frequency around 0 01 hz using wavelet transform analysis to minimize the influences of artificial noises and global geomagnetic perturbations we used only the geomagnetic data observed at nighttime lt 2 30 a m to 4 00 a m and utilized observations from a remote station kanoya as a reference statistical results of superposed epoch analysis have indicated that ulf magnetic anomalies are more likely to appear before sizable earthquake events es 108 rather than after them especially 6 15 days before the events further statistical investigations show clearly that the ulf geomagnetic anomalies at kak station are more sensitive to larger and closer events finally we have evaluated the precursory information of ulf geomagnetic signals for local sizable earthquakes using molchan s error diagram the probability gain is around 1 6 against a poisson model the above results have indicated that the ulf seismomagnetic phenomena at kak clearly contain precursory information and have a possibility of improving the forecasting of large earthquakes

impact of horizontal resolution 1 12 to 1 50 on gulf stream separation penetration and variability abstractthe impact of horizontal resolution 1 12 to 1 50 6 to 1 5 km at midlatitudes on gulf stream separation penetration and variability is quantified in a series of identical north atlantic experiments the questions the authors seek to address are twofold 1 is the realism of the modeled solution increased as resolution is increased 2 how robust is the modeled mesoscale and submesoscale eddy activity as a function of grid spacing and how representative is it of interior quasigeostrophic qg or surface quasigeostrophic sqg turbulence this study shows that i the representation of gulf stream penetration and associated recirculating gyres shifts from unrealistic to realistic when the resolution is increased to 1 50 and when the nonlinear effects of the submesoscale eddies intensifies the midlatitude jet and increases its penetration eastward ii the penetration into the deep ocean drastically increases with resolution and closely resembles the observations and iii surface power spec

anomalous behaviors of geomagnetic diurnal variations prior to the 2011 off the pacific coast of tohoku earthquake mw9 0 there have been many reports on ultra low frequency ulf electromagnetic phenomena associated with earthquakes in a very wide frequency range in this study unusual behaviors of geomagnetic diurnal variations prior to the 2011 off the pacific coast of tohoku earthquake mw9 0 have been reported ratios of diurnal variation range between the target station esashi esa which is about 135 km from the epicenter and the remote reference station kakioka kak about 302 km distant to the epicenter have been computed the results of 10 day running mean of the ratios showed a clear anomaly exceeding the statistical threshold in the vertical component about 2 months before the mega event this anomaly is unique over a 3 year background and the further stochastic test indicates that this anomaly is unlikely a random anomaly which is highly suggestive of correlation with the mega event the original records of geomagnetic fields of the esa station also exhibit continuous anomalous behaviors for about 10 days in the vertical component approximate 2 months prior to the mw9 0 earthquake

temporal and spatial precursors in the ionospheric global positioning system gps total electron content observed before the 26 december 2004 m9 3 sumatra andaman earthquake 1 we report seismo ionospheric precursors of anomalous decreases in the total electron content tec appearing day 5 prior to an m9 3 earthquake the largest one in the last five decades which occurred in sumatra andaman indonesia on 26 december 2004 sequences of global ionosphere maps of the tec derived from worldwide ground based receivers of the global positioning system gps are used to statistically study the temporal and spatial precursors of the earthquake it was found that the temporal precursor of the gps tec around the epicenter was significantly reduced during the afternoon period on d 5 before the earthquake the spatial precursors prominently persistently and simultaneously appear around the epicenter and its conjugate areas of the sumatra andaman earthquake

observation of surface displacements from gps analyses before and after the jiashian earthquake m 6 4 in taiwan abstract a blind thrust fault with a unique strike which is orthogonal to the strike of most tectonic structures in taiwan triggered the jiashian earthquake on march 4 2010 m 6 4 22 96 n 120 70 e this study utilizes 100 global positioning system stations to examine changes of surface displacements during the jiashian earthquake we mitigate effects of short term noise and long term plate movements from surface displacement data using a frequency dependent filter via the hilbert huang transform and compute the horizontal azimuth i e gps azimuth using residual data at the ns component relative to residual data at the ew component analytical results show that orientations of horizontal azimuths were aligned and orthogonal to the strike of the blind thrust fault meanwhile inverse orientations are observed before and after the earthquake that agrees well with the seismic rebound theory as stress disturbed on strata a few days before the earthquake an impeded region can be clearly identified by disordered orientations of horizontal azimuths for anticipating the mainshock these results provide an additional view to explore stress disturbance associated with earthquakes and offer more information to examine diverse models of tectonic evolution in this region

a revised classification of limestones abstract the most widely used classifications of limestones are now thirty years old and our appreciation of the diagenetic effects on limestone textures is now much greater a revision of the classifications of dunham 1962 and embry and klovan 1971 is offered and new diagenetic categories are proposed the confusing term lime mudstone is replaced by calcimudstone two categories of diagenetic textures are recognized non obliterative and obliterative the former contains limestones which are almost wholly composed of diagenetic cement cementstones and those whose fabric is the result of intergranular pressure solution condensed and fitted grainstones obliterative categories include limestones and dolomites whose original fabric has been destroyed sub categories include sparstones or dolosparstones crystals 10 m in size and microsparstones dolomicrosparstones crystals 4 10 m in size and dolomicrostones crystals m in size many diagenetic processes can produce fabrics which mimic depositional ones and these are reviewed

danian cool water bryozoan mounds at stevns klint denmark a new class of non cemented skeletal mounds abstract a laterally extensive danian early paleogene bryozoan mound complex is well exposed in 14 km of nearly continuous outcrop in the coastal cliff stevns klint in eastern denmark a nw se oriented seaway covered the danish basin in danian time it widened towards the nw where it passed into the deeper north sea basin and narrowed towards the se where it was connected with the polish trough the exposed mound succession is up to 20 m thick individual mounds are oval in plan view internally asymmetrical 5 11 m high 45 110 m long in nne ssw oriented dip sections parallel to the direction of mound migration and 50 300 m in strike sections the southern flanks are steep and dip 15 30 mainly towards the ssw whereas northern flanks have gentle dips of 0 15 towards the nne four facies associations are distinguished 1 the initial mound association consisting mainly of bryozoan packstone rudstone 2 the steep flank mound crest association consisting of bryozoan rudstone with subsidiary octocoral and encrusting bryozoan rudstone and bryozoan grainstone 3 the gentle flank association characterized by bryozoan packstone and incipient to fully developed hardgrounds and 4 the intermound association consisting of echinoid rudstone packstone and minor occurrences of bioclastic grainstone and argillaceous wackestone packstone beds and laminae facies analysis and mesoscale mapping indicate that the bryozoan mound complexes were formed in relatively deep cool water below the photic zone and swell wave base deposition was influenced by along slope currents with prominent seasonal and long term variations mound growth was governed by primarily in place benthic carbonate production of mainly delicate branching bryozoans which baffled and trapped pelagic and detrital benthic carbonate mud gentle currents rich in particulate nutrients flowing towards the wnw deflected by the coriolis force and possibly a tidally or wind induced upslope component towards the nne resulted in mound growth mainly towards the ssw high production in the surface waters combined with an effective tidally induced mixing of the water column was important for transporting particulate nutrients to the bottom waters periodic intensification of the mean wnw ward flowing bottom current system combined with a storm associated downslope component towards the ssw resulted in winnowing and erosion of the northern mound flanks long term periodic waning or cessation of bottom currents and possibly stratification of the water column resulted in very limited benthic carbonate production and mound growth associated with formation of extensive thalassinoides burrow galleries mirrored by the rhythmic occurrences of flint nodule bands mound development thus reflects the delicate balance between biogenic growth towards particulate nutrient carrying currents current winnowing and erosion the lack of framework buildup and the poorly cemented nature of the mounds is remarkable in this respect they deviate from most other mound types known from the geological record and may possibly together with the sub recent analogues on the great australian bight represent a new class of noncemented skeletal mounds

low frequency magnetic field measurements near the epicenter of the ms 7 1 loma prieta earthquake the authors report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the m sub s 7 1 loma prieta earthquake of 17 october 1989 their measurements cover 25 narrow frequency bands in the more than six decade frequency range 0 01 hz 32 khz with a time resolution varying from a half hour in the ulf range 0 01 10 hz to one second in the elf vlf range 10 hz 32 khz the ulf system is located near corralitos about 7 km from the epicenter the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf data has revealed no precursor activity that they can identify at this time however the ulf data have some distinctive and anomalous features first a narrow band signal appeared in the range 0 05 0 2 hz around september 12 and persisted until the appearance of the second anomalous feature which consisted of a substantial increase in the noise background starting on 5 october and covering almost the entire frequency range of the ulf system third there was an anomalousmore dip in the noise background in the range 0 2 5 hz starting one day ahead of the earthquake finally and perhaps most compelling there was an increase to an exceptionally high level of activity in the range 0 01 0 5 hz starting approximately three hours before the earthquake there do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase further while the systems are sensitive to motion seismic measurements indicate that there were no significant shocks preceding the quake thus the various anomalous features in the data and in particular the large amplitude increase in activity starting three hours before the quake may have been magnetic precursors less

benthic extinction and recovery patterns at the k t boundary in shallow water carbonates denmark abstract benthic extinction at the k t boundary in the danish basin is abrupt and indistinguishable from the termination of maastrichtian white chalk deposition the danian benthic fauna already fully established in the earliest danian nannoplankton zone np1 is essentially an impoverished maastrichtian fauna established through direct survival or limited evolution within well established clades already present in the maastrichtian of the danish basin however recovery of the early danian community is initially retarded the transition is illustrated in some detail for the locality nye klov here the lower 2 3 m of danian strata corresponding largely to the lower np1 subzone contains an extremely impoverished highly unusual dead zone community dominated by bourgueticrinid crinoids associated with other presumed soft ground specialists and devoid of such important faunal elements as cyclostome bryozoans brachiopods calcitic bivalves etc over the next metres the dead zone fauna is gradually replaced by more ordinary faunas and about 6 m above the boundary the characteristic early danian bryozoan limestone community is fully established

the cretaceous palaeogene boundary at stevns klint denmark inversion tectonics or sea floor topography the cretaceous palaeogene boundary interval is exposed over 12 km in the coastal cliff stevns klint denmark an important lowermost danian hardground has been interpreted as an originally horizontal marine abrasion surface its present elevation varies from a few metres below to about 35 m above sea level this relief has traditionally been considered as resulting from late or post danian laramide folding new seismic profiles offshore stevns klint show however that the base chalk reflector is not folded is remarkably planar and has a gentle northward dip thus the folding hypothesis cannot be upheld seismic stratigraphic analysis of the chalk group necessitates a fundamental revision of general ideas of chalk deposition a highly irregular sea floor topography was formed at many levels and includes broad valleys ridges channels drifts and mounds a system of major wnw ese oriented valleys and ridges can be traced into the succession exposed in stevns klint and further inland where it corresponds to the relief of the cretaceous palaeogene boundary the marked topographic elements of the chalk sea floor are elongate with a wnw orientation roughly parallel to the axis of the danish basin and to the sorgenfrei tornquist zone forming the ne border of the basin the sea floor relief undoubtedly reflects the influence of strong contour parallel bottom currents the cretaceous palaeogene boundary succession at stevns klint was thus developed on an underlying sea floor topographic relief of about 40 m recognition of the highly irregular current influenced topography of the late cretaceous sea floor stands in marked contrast to the conventional picture of quiet pelagic deposition of the chalk

three dimensional architecture and development of danian bryozoan mounds at limhamn south west sweden using ground penetrating radar bryozoan mounds from the middle danian lower palaeocene of the danish basin represent a possibly new class of non cemented skeletal mounds the sedimentology and palaeoecology of the mounds have recently been studied in detail three dimensional images of middle danian bryozoan mound structures in the limhamn limestone quarry south west sweden obtained from combined reflected ground penetrating radar signals and outcrop analysis provide new information about the architecture and growth development of such mounds the mounds are composed of bryozoan limestone and dark grey to black flint bands which outline mound geometries ground penetrating radar data sections are collected over a 120 m by 60 m grid of data lines with trace spacing of 0 25 m providing a depth penetration of 7 to 12 m and a vertical resolution of ca 0 30 m the ground penetrating radar images outline the geometry of the internal layering of the mounds which typically have widths and lengths of 30 to 60 m and heights of 5 to 10 m mound architecture and growth show great variability in the ground penetrating radar images small scale mound structures with a palaeorelief of only a few metres may constitute the basis for growth of larger mounds the outermost beds of the individual mounds are commonly characterized by sub parallel to parallel reflections which have a circular to slightly oval appearance in map view the mounds are mainly aggrading and do not show clear signs of pronounced lateral migration during growth although some mound structures indicate a preferential growth direction towards the south growth patterns interpreted from the ground penetrating radar images suggest that the palaeocurrents in the study area may have shown great variability even on a small scale this observation is in contrast to results from studies of extensive slightly older early danian mound complexes exposed in coastal cliffs at stevns klint and karlby klint located 50 and 200 km away from the study area respectively at these locations the mounds show a remarkably uniform development and typically are asymmetrical clearly showing migration directions towards the south these differences in mound geometry may be the result of differences in the current systems and water depths that existed during formation of the early and middle danian mounds respectively the mounds at limhamn were located closer to the basin margin in shallower water than those at stevns klint and karlby klint in addition the difference in mound architecture may be due to the occurrence of non layered irregular coral mounds intercalated with the bryozoan mounds at limhamn

danian cool water coral reefs in southern scandinavia localised over seafloor highs abstract danian paleocene reefs formed by ahermatypic scleractinian corals in relatively deep water are known in a few localities in southern scandinavia reflection and shallow seismic profiles and samples from drilling and scuba diving in bridge pier excavations in oresund the strait between denmark and sweden for the first time allow interpretation of the factors that controlled the localisation of the reefs after the mass extinction at the k t boundary reef building scleractinian corals were absent in the boreal early danian in the danish basin faunal evolution after the biotic crisis and a rise in relative sea level are interpreted to have favoured formation of deep water coral reefs in the oresund region in mid danian time the reefs were 6 20 m high and 20 200 m long on the seafloor and have a patchy distribution within a bryozoan mound dominated setting in an area of about 10 km 2 they are composed of the framework building ahermatypic scleractinian coral dendrophyllia candelabrum with minor occurrences of bryozoans echinoderms gastropods and bivalves it has been suspected that the reefs were located over contemporaneous seafloor highs but this notion was only based on comparison with similar modern deep water reefs offshore norway the data from oresund indicate that the danian reef complex was formed over a late maastrichtian palaeo seafloor high the saltholm malmo high supporting this interpretation and thus adding fundamentally to the understanding of the factors controlling the formation and localisation of these deep and cool water coral reefs individual reefs were initiated and grew on eroded crests and steep south dipping flanks of bryozoan mounds and were predominantly situated on the southern part of the high and are interpreted as growing towards nw flowing bottom currents rich in particulate nutrients

marine macrofossil communities in the uppermost maastrichtian chalk of stevns klint denmark abstract three successive marine habitats and their benthic macrofossil communities have been recognised and assessed in the uppermost maastrichtian chalk of stevns klint denmark the mound bedded lower sigerslev member was deposited below the photic zone under the influence of persistent non erosive bottom currents it is draped by the upper sigerslev member which was laid down in deeper water than any other chalk known from onshore denmark deposition took place under quiet conditions apparently not influenced by bottom currents the sparse level bottom community lived on a seafloor with low nutrient supply it was characterised by recumbent brachiopods and bivalves sponges and some spatulate long spined echinoids which were able to traverse the soft substrate the top part of the maastrichtian assigned to the hojerup member consists of low biogenic chalk mounds formed mainly by profuse growth of small sized bryozoans governed by nutrient rich currents from the south the macrofauna of this member is of very high density and richness yet species composition is similar to that of the mound bedded lower sigerslev member the bryozoan thickets of the two members are accompanied by a rich fauna of bivalves echinoids polychaetes gastropods and brachiopods attached forms were dependent on hard mainly small substrates provided largely by dead bryozoans and on a steady nutrient supply the bivalve fauna is richer and occurs in slightly higher densities in the hojerup member than in the similarly mound bedded lower sigerslev member the number of polychaete species is also greater in the hojerup member the faunal differences reflect the shallower water setting and a higher influx of food during deposition of the latter unit the final maastrichtian benthic macrofossil community at stevns klint represented by the hojerup member thus shows the greatest faunal richness and density in the upper cretaceous chalk in the danish basin there is no evidence of faunal impoverishment at the end of the cretaceous in the stevns klint succession which is complete across the cretaceous paleogene boundary and the study thereby corroborates the increasingly dominant view of a very abrupt faunal turnover at the k pg boundary

late maastrichtian chalk mounds stevns klint denmark combined physical and biogenic structures abstract upper maastrichtian chalk exposed at the sigerslev quarry stevns klint denmark is characterized by wavy and mound like bedding geometries outlined by bands of black flint nodules four morphological elements are recognized although bedding geometries are highly variable southward migrating mounds eastward migrating mounds chalk waves and evenly bedded chalk the mounds are interpreted as having been formed by currents carrying fine grained suspended sediment which was primarily deposited on the up current mound flanks bryozoans were prolific on the up current flanks and mound summits which stabilized the mounds increased bed roughness and the overall accumulation rate however accumulation thicknesses do not correlate consistently with bryozoan density the bryozoans were therefore important for the formation of the mounds but the distribution of bryozoans did not solely determine depositional thickness across a mound and thus mound growth pattern relatively long wavelength wavy bedded chalk show gentle convex up geometries and would probably be described as sediment waves if recognized in seismic sections the chalk waves were deposited under weaker current velocities than those active during mound formation the exposed succession is topped by more evenly bedded chalk which was deposited by quiet pelagic fall out of fine grained material the whole succession was deposited on the upper part of the northern flank of a large wnw ese trending 3 km wide depositional ridge with an amplitude of 35 40 m formed by contour parallel wnw ward flowing bottom currents the mounds may have been deposited by regional bottom currents or by spill over currents from the valley south of the large ridge the succession was deposited during varying bottom current intensities and the depositional architecture indicates a complex and dynamic environment the depositional style seems to be controlled by the interplay and relative importance of two end member processes those that were purely physical and related to the interaction between available grain sizes and hydrodynamics and those that were largely biological and associated with benthic growth and sediment trapping of mainly bryozoans examples of end member conditions are known from haute normandy france and the lower danian of stevns klint the structures described here adds to the considerable complexity of depositional styles in chalk

the enigma of the arthur s pass new zealand earthquake 2 the aftershock distribution and its relation to regional and induced stress fields the aftershock distribution of the 1994 arthur s pass earthquake mw6 7 is unusual for a reverse faulting event in that it extends 12 km nnw and 30 km sse of the actual fault plane which strikes ne sw we have used several methods to infer the regional stress field in the region including geodetic results earthquake mechanisms and inversion of p wave polarity data for the stress tensor orientation the inversion method is new and does not require the focal mechanisms of the events used it also incorporates the coulomb failure criterion all results point to a stress field favoring strike slip faulting not thrusting with near horizontal 1 and 3 principal axes striking at 298 and 28 using dislocation theory we calculate the stress induced by the arthur s pass earthquake and its largest aftershock a strike slip event and add this to the regional field there is a fair correspondence between the hypocenters of aftershocks away from the mainshock fault plane and regions of high induced coulomb failure stress cfs on optimally oriented fault planes however there are regions of high induced cfs that are devoid of aftershocks it appears that earthquake slip in this region of oblique 19 plate convergence is as observed elsewhere partitioned into components parallel and perpendicular to the plate margin most of the slip is parallel as occurs on the nearby dextral alpine fault the boundary between the pacific and australian plates however occasional reverse events such as the arthur s pass earthquake account for at least some of the perpendicular component of slip and the uplift that produced the southern alps

a search in strainmeter data for slow slip associated with triggered and ambient tremor near parkfield california 1 we test the hypothesis that as in subduction zones slow slip facilitates triggered and ambient tremor in the transform boundary setting of california our study builds on the study of peng et al 2009 of triggered and ambient tremor near parkfield california during time intervals surrounding 31 potentially triggering m 7 5 teleseismic earthquakes waves from 10 of these triggered tremor and 29 occurred in periods of ambient tremor activity we look for transient slow slip during 3 month windows that include 11 of these triggering and nontriggering teleseisms using continuous strain data recorded on two borehole gladwin tensor strainmeters gtsm located within the distribution of tremor epicenters we model the gtsm data assuming only tidal and drift signals are present and find no detectable slow slip either ongoing when the teleseismic waves passed or triggered by them we infer a conservative detection threshold of about 5 nanostrain for abrupt changes and about twice this for slowly evolving signals this could be lowered slightly by adding analyses of other data types modeled slow slip signals and gtsm data calibration detection of slow slip also depends on the slipping fault s location and size which we describe in terms of equivalent earthquake moment magnitude m in the best case of the gtsm above a very shallow slipping fault detectable slip events must exceed m 2 and if the slow slip is beneath the seismogenic zone below 15 km depth even m 5 events are likely to remain hidden

integrated seismic analysis of the chalk group in eastern denmark implications for estimates of maximum palaeo burial in southwest scandinavia abstract the origin of the topography of southwest scandinavia is subject to discussion analysis of borehole seismic velocity has formed the basis for interpretation of several hundred metres of neogene uplift in parts of denmark here refraction seismic data constrain a 7 5 km long p wave velocity model of the chalk group below the stevns peninsula eastern part of the danish basin the model contains four layers in the 860 m thick chalk group with mean velocities of 2 2 km s 2 4 km s 3 1 km s and 3 9 4 3 km s sonic and gamma wireline log data from two cored boreholes represent the upper 450 m of the chalk group the sonic velocities are consistent with the overall seismic layering although they show additional fine scale layering integration of gamma and sonic log with porosity data shows that seismic velocity is sensitive to clay content in intervals near boundaries of the refraction model moderate increases in clay content correlate with reduction of porosity and increase in velocity higher clay contents do not further increase velocity the reduction of porosity and increase in velocity are interpreted as clay causing increased pressure dissolution and cementation the interpreted velocities are systematically higher than values of a chalk velocity curve determined in previous studies and it is estimated that a significant part of the velocity anomaly may be explained by the presence of clay the remaining velocity anomaly can be explained by 450 500 m palaeo burial of the chalk group the burial anomaly will be over estimated by 150 200 m if the analysis is based on the average chalk group velocity and clay content is disregarded burial anomaly values of 450 600 m result if the strongest velocity contrast at 600 650 m depth is interpreted to be a result of diagenetic effects consistent with the clay corrected estimates within uncertainty

sediment waves with a biogenic twist in pleistocene cool water carbonates great australian bight abstract sediment waves composed of fine grained carbonate ooze with in place bryozoans are a characteristic element of the pleistocene of the great australian bight gab the low amplitude and strongly elongate sediment waves are up to 10 km long 1 km wide 40 m high and oriented sub parallel to contours immediately off the shelf slope break they are asymmetrical showing up slope migration and mainly occur in trains the sediment waves were drilled during odp leg 182 in 1998 and were interpreted as biogenic reef mounds new high quality seismic and multibeam bathymetry data were acquired on the galathea 3 expedition in 2006 allowing description of the morphology and internal architecture of the sediment waves in unprecedented detail leading to an alternative interpretation of their formation most sediment waves were initiated by preferential deposition on the landward side of irregular erosion surfaces sediment wave accretion took place under the influence of density driven currents which decelerated up the landward dipping flanks and accelerated down the seaward dipping flanks of the sediment waves the currents are interpreted as dense water cascades formed by summer evaporation and strong winter cooling by analogy with oceanographic processes in the present day gab the lithological composition varied with climate and sea level but sediment wave formation did not sediment waves formed and accreted during both glacials and interglacials in contrast to the previous interpretations which involved growth in glacial periods only bryozoans influenced the depositional environment by adding sediment trapping fine grained particles and stabilizing the muddy sea floor this caused the sediment waves to gain a more prominent sea floor relief than most muddy siliciclastic sediment waves formed by similar depositional processes the interpretation of the sediment waves as purely biogenic build ups is rejected and the sediment waves are most appropriately described as biogenically influenced sediment waves

quaternary bryozoan reef mounds in cool water upper slope environments great australian bight bryozoan reef mounds are common features in the geological record occurring within mid ramp slope paleoenvironments especially in paleozoic carbonate successions but until now have not been recorded from the modern ocean recent scientific drilling in the great australian bight ocean drilling program leg 182 has confirmed the existence of shallow subsurface bryozoan reef mounds in modern water depths of 200 350 m these structures have as much as 65 m of synoptic relief and occur both as single mounds and as mound complexes they are unlithified have a floatstone texture and are rich in delicate branching encrusting and or nodular arborescent flat robust branching fenestrate and articulated zooidal bryozoan growth forms the muddy matrix is composed of foraminifers serpulids fecal pellets irregular bioclasts sponge spicules and calcareous nannofossils the 14c accelerator mass spectrometry dates of 26 6 35 1 ka indicate that the most recent mounds the tops of which are 7 10 m below the modern seafloor flourished during the last glacial lowstand but perished during transgressive sea level rise this history reflects changing oceanographic current patterns strong upwelling during lowstands and reduced upwelling and lowered trophic resources during highstands large specimens of benthic foraminifers restricted to the mounds confirm overall mesotrophic growth conditions the mounds are similar in geometry scale general composition and paleoenvironments to older structures but lack obvious microbial influence and extensive synsedimentary cementation such differences reflect either short term local conditions or long term temporal changes in ocean chemistry and biology

deep onshore reflection seismic imaging of the chalk group strata using a 45 kg accelerated weight drop and combined recording systems with dense receiver spacing the chalk group forms important hydrocarbon reservoirs offshore and water aquifers onshore denmark within a day of fieldwork a 450 m long reflection seismic profile was acquired onshore in an are