remagnetization in southeast china and the collision and suturing of the huanan and yangtze blocks abstract nearly all paleomagnetic studies in south china have encountered problems with remagnetization the region underwent widespread tectonic deformation during the mesozoic and the warm humid climate causes rapid weathering of surficial sediments paleomagnetic results from three carboniferous formations from three provinces in southeast china reveal two possible overprinting ages one is probably a post folding cretaceous remagnetization and the other appears to be a jurassic overprint which may be associated with the collision and suturing of the yangtze and the huanan or north china blocks the jurassic overprint is found in sediments with both magnetite and hematite as primary magnetic remanence carriers the remagnetization pre dates deformation in at least one of the formations further constraining the overprint to the jurassic or late triassic

spatangoid produced ichnofabrics bateig limestone miocene spain and the preservation of spatangoid trace fossils a spatangoid produced ichnofabric is described from the miocene bateig limestone se spain this ichnofabric is characterized by the dominant presence of large meniscate burrows bichordites produced by irregular echinoids this constitutes an unusual mode of occurrence for spatangoid bioturbation as their traces are most typically preserved in bases and tops of sandstone event beds in fact despite their important role as burrowers in modern settings that can be extended back to the early cretaceous based on their body fossil record spatangoid trace fossils scolicia and bichordites are comparatively rare several factors play an important role in their preservation mechanism of burrowing sediment characteristics early diagenesis and presence absence of deep tier burrowers spatangoid produced ichnofabrics such as those from the bateig limestone characterize depositional settings with intermittent deposition of event beds where there is an absence of deeper tier bioturbation

the calcarenite di gravina formation in matera southern italy new insights for coarse grained large scale cross bedded bodies encased in offshore deposits excellent outcrops of the upper pliocene lower pleistocene calcarenite di gravina around matera southern italy provide continuous exposure of coarse grained clastic basin margin shoreline to offshore facies among these facies the most conspicuous and volumetrically important are the transition slope deposits that form large scale high angle cross bedded lithosomes these are laterally extensive parallel with the paleoshoreline and show seaward progradation we interpret them to represent avalanches of sediment swept out onto a depositional slope below wave base from the shoreface zone by storm waves and wind driven currents three types of building blocks are recognized based on bedding patterns and facies architecture embryonic parasequences mature parasequences and simple sequences parasequences formed during stillstands of sea level and simple sequences during high frequency cycles of relative change of sea level these building blocks are stacked in a backstepping configuration and onlap onto cretaceous limestone substrate backstepping is believed to be due to a tectonically forced transgression that is punctuated by high frequency cycles of sea level modern analogs for these building blocks are the holocene prograding prisms detected in high resolution seismic lines of the mediterranean shelves the reflection patterns of these seismic units resemble the bedding architecture of the matera simple sequences and parasequences and show similarities of shape size position and orientation of coastal setting and direction of progradation comparison of the holocene prisms and the pliocene pleistocene accretional units in matera indicates that they may represent the same begin page 662 genetic process progradation of clastic prisms below the wave base level the matera accretional units also show similarities with other examples of laterally extensive large scale cross bedded sand bodies encased in offshore deposits such as some sandbanks differentiating between these laterally extensive and seaward prograding cross bedded sand bodies and some coarse grained gilbert type deltas is difficult however if interpretations are based only on two dimensional 2 d outcrops in dip section without high resolution data it is also difficult to distinguish between transition slope and prograding shoreface lithosomes this difficulty may be acute where only seismic or well log data are available however certain other architectural characteristics such as stacking and preservation of facies belts and position of bounding surfaces as well as differences in associated sedimentary structures and fossil content may be used for interpretation the matera example provides a mechanism for emplacement in offshore settings of elongate and strandline parallel sand and gravel deposits that prograde seaward and that preserve a coarsening upward internal succession this article offers an interpretation for other ancient examples of large scale cross bedded lithosomes encased in offshore deposits

evolution model of progressive failure of landslides an evolution model considering rheologic effects is proposed to describe the progressive failure process of soil slopes the proposed method is illustrated using previously published examples and analyses some of the results obtained are impossible in conventional methods of stability analyses to obtain a visual understanding of the mechanical mechanism of progressive failure and the evolutionary process of the local failure of slopes a numerical simulation is presented for the whole failure process in this way the whole evolution process is clearly shown from slopes of local failures near the toe through the appearance of tensional cracks at the top to the final landslide this understanding of the failure mechanism is very helpful for the prediction and prevention of landslides

intertropical latitudes and precessional and half precessional cycles a mcintyre and b molfino in their report about the forcing of atlantic equatorial and subpolar millennial cycles by precession suggest that climatic changes in high polar latitudes which are related to heinrich iceberg surges may be caused by events that occur in low latitudes 1 1 this

palaeomagnetic constraints on the collision and rotation of north and south china the eastern half of china is dominated by the north china block ncb and south china block scb separated by a complex fold system that trends roughly east west interpretation of the geology of this fold belt has led to a variety of estimates of the age of amalgamation of these two blocks1 7 palaeomagnetic results are few and have also been subject to conflicting interpretations8 11 here we present our own palaeomagnetic results for late permian rocks for both the scb and ncb and summarize other relevant palaeomagnetic data by reinterpreting the polarity given in some previous studies we are able to synthesize the results for the widespread emeishan basalts of the scb and to suggest a new model for the collision and relative rotation of the two blocks

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

ecologic interpretation of deep sea trace fossil communities abstract trace fossil types and their vertical arrangement tiering are closely related to the biotope and hence can provide information on ecological conditions especially on oxygenation benthic food content sedimentation rate and substrate consistency however to use the full potential of trace fossils for environmental analyses various ichnologic criteria are necessary in addition to trace fossil taxonomy based on a taxonomically oriented ichnologic evaluation of modern deep sea environments six ichnologic aspects to ecologic changes have been found to be of major importance 1 1 penetration depth of burrows is influenced by oxygenation benthic food availability and substrate consistency 2 2 the number and vertical extension of tiers varies due to environmental changes a decrease in the vertical extension of tiers telescoping indicates a decrease in oxygenation benthic food content and or sedimentation rate if shallow penetrating traces disappear oxygen may be depleted and if the deepest tiers disappear the benthic food content may be lowered 3 3 the size diameter of specific trace fossils can indicate oxygen and benthic food availability 4 4 degree of bioturbation is related to sedimentation rate and benthic food content and the diversity of the whole ichnocoenoses or within a specific tier is affected by oxygenation benthic food content sedimentation rate and substrate consistency 5 5 the type of burrow wall unlined mucus lined pellet lined mainly refers to substrate consistency and subordinately to pore water oxygenation 6 6 the type of sediment displacement by body appendages used for excavation ingestion sideward pressing or outside pumping is related to substrate consistency and grain size

new paleomagnetic results from the ediacaran doushantuo formation in south china and their paleogeographic implications abstract a new paleomagnetic pole is obtained from the top of member 3 of the doushantuo formation in the jiulongwan section of the yangtze gorges area in south china a total of 191 samples from 23 sites were collected and subjected to stepwise alternating field af and thermal demagnetization after the removal of a soft component sc of viscous magnetic remanence acquired in present geomagnetic field a high temperature component hc likely carried by magnetite was isolated the hc includes vectors from 147 samples using principal component analysis and arc constraints from 44 samples using remagnetization great circle analysis both the vectors only and the combined vectors and arc constraints of the hc passed a reversal test this is the first ediacaran paleomagnetic remanence from the south china block scb that passes a reversal test and it is interpreted as a primary remanence the hc vectors were thus used to calculate the paleomagnetic pole and in combination with arc constraints were used for polarity interpretation the vectors give a mean direction of d 75 2 i 41 0 95 2 5 n 147 after bedding correction and a corresponding paleomagnetic pole at 23 9 n 187 0 e dm dp 3 0 1 8 this pole differs significantly from previously published results of the doushantuo formation which may have been subjected to paleozoic remagnetization our results provide a 23 5 1 8 n paleolatitude for the yangtze gorges area of the scb and suggest several alternative paleogeographic options for the ediacaran cambrian amalgamation of east gondwana depending on chronostratigraphic correlations

ichnology of a glacially influenced continental shelf and slope the late cenozoic gulf of alaska yakataga formation abstract the study of trace fossils in glaciomarine strata is important because of the low preservation potential of fauna but glaciomarine settings have received little attention from ichnologists widespread biological activity is recorded by ichnofossil assemblages in glaciomarine strata of the late cenozoic 6 ma to present yakataga formation alaska glacial sedimentation began in the gulf of alaska in the miocene along a deep water active margin basin dominated by turbidity currents and debris flows later strata record progradation of the continental slope by mass flow processes and the establishment of a broad shelf influenced by repeated glaciation ice rafting of coarse debris changes in water depth and salinity storms earthquakes and high sedimentation rates yakataga formation strata show overall a limited ichnological diversity and low degree of bioturbation in relation to comparable non glacial settings although certain beds are highly bioturbated twenty four ichnotaxa are identified and grouped into nine assemblages characteristic of different depositional settings and substrate types ichnogenera and body fossil evidence shows that polychaetes arthropods molluscs and echinoderms were the dominant infaunal benthic organisms with deposit feeding being the predominant feeding strategy poorly consolidated muddy sediments excluded suspension feeders and limited the development of the skolithos ichnofacies typical of non glacial shelves characterized by clean shifting sand substrates evidence of rapid sedimentation is given by escape structures fugichnia the presence of diplocraterion and by the mass mortality of bivalves firm ground burrows typical of the glossifungites ichnofacies are associated with erosional surfaces boulder pavements and coquinas diminutive feeding traces may reflect salinities lowered by glacial meltwater inputs the downslope transport of food by turbidity currents and mass flows may explain the development of a diverse cruziana ichnofacies in water depths where in non glacial settings the nereites ichnofacies is found an ichnological summary is presented for the late cenozoic gulf of alaska continental margin similar ecological conditions obtain in the modern setting and provide valuable supportive data ichnofacies identified from the yakataga formation are probably widespread in late paleozoic and late cenozoic glacially influenced marine strata

bottom current controlled sand deposits a review of modern shallow to deep water environments abstract different examples of modern marine sand accumulations generated or strongly influenced by the action of bottom currents are here presented they are drawn from a variety of tectonic and morphological settings and grouped into three water depth zones deep water 2000 m mid water 300 2000 m and outer shelf upper slope 50 300 m deposits in the first two of these depth zones are normal contourites according to their original definition heezen and hollister 1971 being those sediments that have been transported and deposited by contour currents in deep water environments those deposited at shallower depths under the influence of surficial geostrophic currents combined with other hydrodynamic factors shelf currents induced by wind tide and waves gyres internal waves etc are more properly referred to as outer shelf upper slope bottom current sands or shallow water bottom current sands we have elaborated a facies model for each bathymetric zone deep water sandy contourites are relatively rare thin and very thin bedded highly bioturbated and mainly of bioclastic composition they are interbedded with muddy contourites and pelagites or in some areas with turbidites in the latter case thin bottom current reworked sandy tops of turbidites provide a different and distinct facies mid water sandy contourites are more common ranging up to a metre in thickness and may form extensive sandy sheets in a variety of slope bank and channel settings they are mainly of mixed siliciclastic bioclastic composition typically bioturbated and associated with muddy silty contourites in coarsening up fining up complete or truncated sequences shallow water bottom current sands occur in particular outer shelf upper slope settings where they may develop relatively thick 1 20 m laterally extensive sheets covered by fields of sandwaves megaripples and ribbons internal structures may be preserved along with much bioturbation their composition varies from mainly siliciclastic to bioclastic and they may be interbedded with both inner shelf facies and slope hemipelagites the principal factors that control the deposition of sandy contourites and shallow water bottom current sands are the hydrodynamic regime of the basin the availability of coarse grained sandy sediments and the physiographic context of the area swept by the currents the greater the depth the finer and rarer the bottom current or sandy contourite deposits global sea level and climatic changes and the time involved in the depositional history play an ultimate role in the development of important sand accumulations of this sort by controlling the ocean circulation pattern and its long term persistence from the present analysis we conclude that mid depth sandy contourites are the most commonly found in modern environments and that shallow water bottom current sands constitute the most significant potential oil reservoirs to be found in the geological record

temporal constraints on the paleoproterozoic lomagundi jatuli carbon isotopic event the paleoproterozoic lomagundi jatuli positive 13c excursion in sedimentary carbonates represents an event whose magnitude and duration is unique in earth history although precise absolute chronology of this event remains poorly constrained in northeastern fennoscandia an 1300 m thick sedimentary volcanic succession of the pechenga greenstone belt records decline of this isotopic excursion zircons from sedimentary rocks that occur within the decline have yielded 207pb 206pb dates at 2058 2 ma 6 ma including u decay constant uncertainties and provide the first maximum age constraint on the termination of the lomagundi jatuli event combined with existing constraints these data indicate an 140 m y interval characterized by 13c rich carbonate accumulation

lithostratigraphy and deep water setting of the upper nanaimo group upper cretaceous outer gulf islands of southwestern british columbia the upper cretaceous nanaimo group consists of extensive shaly units and lenticular bodies of sandstone and conglomerate deposited in neritic to bathyal marine paleoenvironments single sandstone and conglomerate lenses cannot be traced throughout the basin but instead tend to concentrate at particular stratigraphic levels defining crudely sheet like composite units of coarse grained rocks many of the lenticular coarse grained units rest in major channels as deep as about 550 m sand and gravel were generally transported to the west and northwest by sediment gravity flows through these channels into the basin centre recognition of widespread channeling is critical to the definition of formal lithostratigraphic units four formations and two informal members are defined here for the upper nanaimo group the top of the nanaimo group is probably truncated by a major unconformity with local relief of at least 2 km the effect of the unconformity can only be seen by mapping the orientation of offshore rid

deformed cross stratified deposits in the early pleistocene tidally dominated catanzaro strait fill succession calabrian arc southern italy triggering mechanisms and environmental significance abstract the early pleistocene catanzaro strait fill succession consists of large scale tidal sets accumulated in a tectonically confined basin during a phase of rapid relative sea level rise it crops out mainly in the present day catanzaro trough where numerous field sections supported the characterization of the vertical and lateral facies variations and the documentation of a variety of soft sediment deformation structures exposed throughout their vertical and lateral extents the soft sediment deformation structures ssds are the result of liquefaction and fluidization processes that deformed cross laminations and other primary structures into folds fluid escape structures and structureless expanses three different groups of ssds have been documented in the cross stratified deposits of the catanzaro strait the detailed description of these soft sediment deformation structures in a depositional context established by facies analysis enables interpretation in terms of possible trigger mechanisms consistent relationships between the occurrence of distinctive ssds and specific tidally dominated facies have been established indicating a probable autogenic origin for the soft sediment deformations liquefaction and fluidization features are interpreted as the result of increases in water pore pressure induced by overloading in particular two types of overloading agents are hypothesized which affect the lee and stoss sides of the migrating dunes in distinct events and inducing the deformation of foreset laminae or sets of cross strata respectively

a facies based depositional model for ancient and modern tectonically confined tidal straits modern and ancient tidal straits are the least well understood of all tide dominated depositional systems to provide an increased understanding of these systems a facies based depositional model is assessed by comparing multibeam surveys of three present day tidally dominated seaways with a number of superbly exposed neogene to quaternary strait fill successions of calabria south italy the model points out the existence of four depositional zones laterally adjacent from the narrowest strait centre to its terminations distributed along symmetrical or asymmetrical seaways these zones whose signature is recorded in four facies associations in the calabrian tidal straits are as follows i the strait centre zone associated with the tidal current maxima and where sediments are scarce or absent ii the dune bedded zone where sediments form dune complexes due to tidal flow expansion iii the strait end zone where currents decelerate accumulating thinly bedded fine grained deposits and iv the strait margin zone where sediment massflows descend tectonically active steep margins towards the strait axis in ancient tectonically confined narrow seaways these facies generate a distinctive deepening upward vertical succession where tidal currents are the dominant process in the sediment distribution

bedform distribution and inferred sand transport on georges bank united states atlantic continental shelf four bedform provinces have been identified on georges bank using sidescan sonar and echo sounding techniques large sand waves superimposed on sand ridges small sand waves megaripples and featureless seafloor the large sand waves and sand ridges are found on the bank crest where the surface tidal currents are strongest areas of small sand waves and megaripples formed where tidal currents are moderate in strength border the area of large sand waves to the north and south featureless seafloor is found farthest from the bank crest where surface tidal currents are weakest sand wave asymmetry and surface sediment texture have been used to infer bedload transport paths on georges bank in the large sand wave area bedforms indicate a clockwise transport around each of the linear north west striking sand ridges with slight convergence of the sand waves on the ridge crests this transport pattern implies erosion from the troughs and accumulation on the sand ridges the asymmetry of the small sand waves along the south side of georges bank indicates that sand is also transported southward away from the linear sand ridges on top of the bank although the asymmetry of megaripples could not be determined the occurrence of megaripples between the small sand wave province and areas of featureless seafloor suggests a decreasing effectiveness of sand transport away from the bank crest this sand dispersal pattern is further supported by the surface sediments which become progessively finer to the north and sw away from the crest of georges bank

structural and geomorphological constraints on active normal faulting and landscape evolution in calabria italy calabria is one of the fastest uplifting and most seismically active regions in the mediterranean yet the time averaged c 10 6 years rates of normal faulting remain poorly constrained here we use digital elevation model analysis geological cross sections and a compilation of published data to quantify systematically along strike the fault throws and time averaged throw rates of the serre cittanova armo east crati and west crati faults we show that regional uplift has uplifted both their hanging wall and footwall blocks by c 200 400 m and the aspromonte massif by up to c 1150 1300 m we find that these faults have throws between c 640 and 1430 m and throw rates between c 0 6 and 1 4 mm a 1 their footwall ranges have variable proportions of inherited relief up to c 300 800 m the channels draining these ranges reflect the active normal faulting and relief in their steepness indices becoming c 5 8 m 0 9 steeper for each 0 1 mm a 1 throw rate increment and each 100 m relief increase finally the presence of knickpoints suggests that these channels are transiently responding to changes in relative base level which could be due to fault linkage or regional strain rate increases for the southern calabrian faults and to regional uplift acceleration in the case of the crati faults supplementary material topographic profiles of the marine terraces and long profiles of rivers are available at https doi org 10 6084 m9 figshare c 3689464

present day kinematics of the plate boundary zone between africa and europe from the azores to the aegean anticlockwise rotation of africa relative to europe around an euler pole in the eastern atlantic causes plate convergence in the central mediterranean towards n20 w at rate considered a priori to be 5 10 mm yr 1 however previous summaries of the present day deformation sense in the central mediterranean are inconsistent with observations in southern italy recent investigations of italy and adjacent parts of north africa enable local deformation sense observed to be reconciled with sense predicted from relative plate motions suggested angular velocity of the african plate relative to europe is 0 07 myr 1 around a pole near 21 n 21 w this predicts 2 6 mm yr 1 maximum extension rate towards n64 e near the azores consistent with the minimum local accretion of new oceanic crust in the past few millions of years and 4 3 mm yr 1 plate convergence towards n20 w in the central mediterranean at 13 e further east the northern margin of the african plate can be regarded as the gargano seismic zone in the central adriatic sea the northern adriatic sea is a microplate rotating anticlockwise relative to europe at 0 3 myr 1 around a pole in northwestern italy causing northeastward shortening in yugoslavia and up to 4 mm yr 1 extension in central and northern italy the african plate is deforming internally in tunisia and northern libya extending obliquely in direction e10 s at rate up to 5 5 mm yr 1 the resultant velocity relative to europe in the ionian and southern adriatic seas 5 mm yr 1 towards n50 e explains the observed relative velocity across southern italy kinematic consistency requires present day shortening rate east of calabria associated with subduction on the tyrrhenian sea benioff zone and tyrrhenian sea extension rate to be both zero or equal to within 1 mm yr 1

absolute paleointensity from hawaiian lavas younger than 35 ka abstract paleointensity studies have been conducted in air and in argon atmosphere on nine lava flows with radiocarbon ages distributed between 3 3 and 28 2 ka from the mauna loa volcano in the big island of hawaii determinations of paleointensity obtained at eight sites depict the same overall pattern as the previous results for the same period in hawaii although the overall average field intensity appears to be lower since the present results were determined at higher temperatures than in the previous studies this discrepancy raises questions regarding the selection of low versus high temperature segments that are usually made for absolute paleointensity the virtual dipole moments are similar to those displayed by the worldwide data set obtained from dated lava flows when averaged within finite time intervals the worldwide values match nicely the variations of the sint 200 synthetic record of relative paleointensity and confirm the overall decrease of the dipole field intensity during most of this period the convergence between the existing records at hawaii and the rest of the world does not favour the presence of persistent strong non dipole components beneath hawaii for this period

fossil contourites a critical review abstract despite three decades of study there is still great controversy over the recognition and interpretation of fossil contourites exposed in ancient series on land in order to best examine this problem we briefly review the evidence from modern systems including the many examples of cenozoic contourites that have been recovered from dsdp odp drilling on major drifts in the present day oceans the range of contourite facies described from both deep water 2000 m and mid water 300 2000 m drifts are mostly fine grained bioturbated and homogeneous often with a distinct bedding cyclicity and with some coarser grained sandy contourites developed under higher energy bottom currents there are also a number of current controlled sediment bodies that have formed in outer shelf upper slope settings 50 300 m under the influence of counter currents underflows and major surface currents these are not considered contourites sensu stricto but may be mistaken as such in ancient examples the most commonly described fossil contourites in the literature have been interpreted by the authors concerned as bottom current reworked turbidites however a critical review suggests that these are the facies most subject to misinterpretation and many of the sediments claimed as fossil contourites are almost certainly fine grained turbidites whereas others were more likely formed under outer shelf upper slope current systems there remain very few ancient examples that are more closely comparable to modern contourites these include the cretaceous talme yafe formation in israel the ordovician jiuxi drift in china and parts of the paleogene lefkara formation cyprus and the neogene misaki formation in japan we present a set of possible criteria for the recognition of fossil contourites and bottom current reworked turbidites

an ichnofabric approach to the depositional interpretation of the intensely burrowed bateig limestone miocene se spain abstract the foraminiferal rich pelagic bateig limestone forms several varieties of the important building stones quarried at bateig hill in southeastern spain three principal ichnofabrics bichordites mottled palaeophycus and mottled ophiomorpha are recognized which are present in at least two possibly up to four repeated successions cycles each succession begins with an erosional event the bichordites ichnofabric represents a new type of facies formed as thin turbidity grain flow stratiform units derived from sediment slips off a fault into deep water each slipped unit became almost completely bioturbated by infaunal echinoids colonizing by lateral migration because of the thinness of the units successive colonizations tended to truncate the underlying burrows giving rise to a pseudo stratification as the bichordites ichnofabric accumulated on the fault apron thus reducing the effective height of the fault scarp the substrate gradually came under the influence of currents traversing the shelf this led to a change in hydraulic regime and to the mottled palaeophycus and mottled ophiomorpha ichnofabrics in sediment deposited under bed load transport and associated with laminar and cross stratified beds and local muddy intervals reactivation of the fault triggered erosion and channeling and a return to grain flow sedimentation and to the bichordites ichnofabric of the succeeding cycle the highest unit of the bateig limestone is formed entirely of cross stratified calcarenites with occasional ophiomorpha ophiomorpha primary lamination ichnofabric and is similar to many shallow marine facies but they still bear a significant content of pelagic foraminifera the sedimentary setting bears resemblance with that described for the pleistocene monte torre paleostrait and the modern strait of messina italy where the narrow morphology of the depositional area enhanced tidal currents and allowed for high energy sandy deposition in relatively deep areas more data on the miocene paleogeography of the bateig area should provide further testing for this hypothesis the ichnofacies and stacking of the bateig limestone differ from the classic seilacherian model in that they reflect changes in hydraulic process and are associated with faulting and subsidence and changes in sediment supply recognition of the unusual ichnofabrics and their relationships provides a clear indication of the overall dynamic setting

incompatible ediacaran paleomagnetic directions suggest an equatorial geomagnetic dipole hypothesis abstract paleomagnetic results obtained from rocks of ediacaran age in several localities in laurentia and baltica persistently display co existence of two magnetization components one shallowly and the other steeply inclined both components pass criteria for a primary magnetization while geological considerations and radiometric age dating indicate that these magnetizations are surprisingly close in age the conventional interpretation of these results translating the inclination into paleolatitudes using the geocentric axial dipole hypothesis would imply that rocks acquired magnetizations in positions switching back and forth between equatorial and near polar latitudes in a geographic reference frame such large scale and fast 45 cm yr migrations of a continent have been rejected as dynamically implausible neither plate tectonics nor true polar wander are thought to be able to attain the required velocities a highly irregular behavior of the geomagnetic field during the ediacaran possibly an alternation of the geomagnetic dipole axis between a co axial and an equatorial alignment remains the only viable explanation for the paleomagnetic data such a behavior entails specific outer core conditions which in turn impose strong constraints on the possible models for the thermal evolution of the earth s interior

sub milankovitch cycles in periplatform carbonates from the early pliocene great bahama bank high resolution bulk sediment magnetic susceptibility and aragonite content and 18o records from two different planktonic foraminifera species were analyzed in an early pliocene core interval from the straits of florida ocean drilling program site 1006 the 18o record of the shallow dwelling foraminifera g sacculifer and the aragonite content are dominated by sub milankovitch variability in contrast magnetic susceptibility and the 18o record of the deeper dwelling foraminifera g menardii show precession cycles the relationship between the aragonite and the paleoproxy data suggests that the export of sediment from the adjacent great bahama bank was triggered directly by atmospheric processes rather than by sea level change we propose a climate mechanism that bears similarities with the semiannual cycle component of eastern equatorial pacific sea surface temperatures under present day conditions

widespread syn eruptive volcaniclastic deposits in the pleistocenic basins of south western calabria abstract since late tortonian depositional sequences developed along the southern calabrian forearc inside the half graben depressions of the mesima gioia tauro and reggio calabria basins in these basins volcaniclastic sedimentation took place during lower to middle pleistocene volcaniclastic deposits consist of isolated pumice swarms ash layers and thick successions of lapilli and ash in this paper we describe and discuss the depositional characteristics of these volcanogenic sediments and the morphology mineralogy and chemistry of pumices shards lithics and crystal fragments these deposits all have the characteristics of a proximal tephra fall deposit from a plinian plume which has been reworked in a shore environment in the mesima basin the deposits reach 6 m in thickness and in the gioia tauro plain 21 m of pumiceous sediments have been cored in a drill hole the compositional homogeneity of fragments and the absence of non volcanic detritus as well as of soil or organic matter suggest that the deposits were quickly reworked after their primary emplacements all the tephra deposits exhibit calc alkaline affinity and dacitic to rhyolitic composition the mineralogical assemblage including orthopyroxene as phenocryst indicates provenance from magmatic arc volcanism icp ms and la icp ms analyses of crystals and glass point to a common origin probably from a single eruption this makes these volcaniclastic layers a very useful tool for stratighaphic reconstructions at a regional scale the geological setting of the deposits their petrological and geochemical signature and the occurrence of large size clasts suggest a provenance from explosive eruptions preceding the emplacement of the 50 ka dacitic lava dome of the island of panarea aeolian archipelago however a provenance from a different calc alkaline volcanic system cannot be excluded these deposits can therefore represent the only evidence of a large explosive eruption in the southern tyrrhenian sea whose very proximal equivalent is not preserved

detrital modes of the ionian forearc basin fill oligocene quaternary reflect the tectonic evolution of the calabria peloritani terrane southern italy abstract during oligocene neogene time the calabria peloritani terrane cpt a small block of continental lithosphere rifted from the southern margin of the eurasian continent and drifted southeastward to collide with the african continent along the leading edge of the cpt a late oligocene to quaternary mostly siliciclastic succession 2 000 meters thick was deposited in the ionian forearc basin the detritus forming the succession was derived directly from the erosion of the nearby cpt composed of hercynian plutons intruding metasedimentary host rocks contrary to most modern and ancient forearc basins penecontemporaneous volcanic detritus is virtually absent this results from rift related topographic barriers which separated the forearc basin from the associated volcanic arc in spite of an overall quartzofeldspathic continental block provenance the analysis of a large sandstone and conglomerate petrological dataset 228 samples points to three discrete detrital inputs of aphanitic lithic fragments in i late oligocene early miocene ii late messinian and iii quaternary times these petrological variations can be linked to independently determined tectonic events in the western mediterranean which likely modified the lithologic composition of the sediment source terranes input i documents the progressive widespread unroofing of the continental basement of the southern european margin when northwestward subduction of the remnants of the ligurian ocean began input ii is related to widespread intra messinian tectonism possibly due to out of sequence thrusting induced by isostatic readjustments of the perimediterranean orogenic wedges following the messinian drawdown input iii reflects the rapid vertical uplift experienced by the cpt since mid pleistocene time possibly the result of slab detachment along the ionian subduction zone this study indicates that detailed statistical analysis of the detrital modes of ancient terrigenous deposits can be used to identify the tectonic events affecting somewhat petrologically monotonous sediment source areas within small lithospheric terranes

uranium and molybdenum isotope evidence for an episode of widespread ocean oxygenation during the late ediacaran period abstract to improve estimates of the extent of ocean oxygenation during the late ediacaran period we measured the u and mo isotope compositions of euxinic anoxic and sulfidic organic rich mudrocks orm of member iv upper doushantuo formation south china the average 238 u of most samples is 0 24 0 16 2sd relative to standard crm145 which is slightly higher than the average 238 u of 0 02 0 12 for restricted black sea deep water unit i euxinic sediments and is similar to a modeled 238 u value of 0 2 for open ocean euxinic sediments in the modern well oxygenated oceans because 238 u is preferentially removed to euxinic sediments compared to 235 u expanded ocean anoxia will deplete seawater of 238 u relative to 235 u ultimately leading to deposition of orm with low 238 u hence the high 238 u of member iv orm points to a common occurrence of extensive ocean oxygenation ca 560 to 551 myr ago the mo isotope composition of sediments deposited from strongly euxinic bottom waters h 2 s aq 11 m either directly records the global seawater mo isotope composition if mo removal from deep waters is quantitative or represents a minimum value for seawater if mo removal is not quantitative near the top of member iv 98 mo approaches the modern seawater value of 2 34 0 10 high 98 mo points to widespread ocean oxygenation because the preferential removal of isotopically light mo to sediments occurs to a greater extent in o 2 rich compared to o 2 deficient marine environments however the 98 mo value for most member iv orm is near 0 relative to standard nist srm 3134 0 25 suggesting extensive anoxia the low 98 mo is at odds with the high mo concentrations of member iv orm which suggest a large seawater mo inventory in well oxygenated oceans and the high 238 u hence we propose that the low 98 mo of most member iv orm was fractionated from contemporaneous seawater possible mechanisms driving this isotope fractionation include 1 inadequate dissolved sulfide for quantitative thiomolybdate formation and capture of a seawater like 98 mo signature in sediments or 2 delivery of isotopically light mo to sediments via a particulate fe mn oxyhydroxide shuttle a compilation of mo isotope data from euxinic orm suggests that there were transient episodes of extensive ocean oxygenation that break up intervals of less oxygenated oceans during late neoproterozoic and early paleozoic time hence member iv does not capture irreversible deep ocean oxygenation instead complex ocean redox variations likely marked the transition from o 2 deficient proterozoic oceans to widely oxygenated later phanerozoic oceans

factors controlling shelf sediment dispersal along the southeast african continental margin abstract four major factors control sediment dispersal along the southeast african continental margin 1 morphology of the upper continental margin 2 wave regime and wind driven circulation 3 influence of the agulhas current and 4 sediment supply these factors interact on various scales to produce a unique regional sediment dispersal pattern the continental shelf is very narrow and the adjacent slope extremely steep the shelf platform is interrupted by a number of structural offsets and locally the shelf break is dissected by numerous submarine canyons the nearshore zone down to about 60 m waterdepth is dominated by a high energy swell regime and in most places is underlain by a thin wedge of sandy sediment this wedge appears to have achieved dynamic equilibrium with the prevailing energy regime and additional sediment is rapidly dispersed and fed into a sandstream situated on the central shelf where the agulhas current dominates sediment transport along some parts of the coast the sediment wedge is dammed behind a drowned coastal dune ridge within the sandstream sediment is transported alongshelf until a structural offset is reached where sediment spills over the shelf break four major localities for off shelf transport are recognized between maputo and port elizabeth most of the suspended load appears to be expelled from the system without being deposited on the shelf in the lee of each offset a clockwise gyre is developed which produces return flow currents capable of moving sediment northward thereby creating bedload partings in the vicinity of these partings depositional features are observed that are similar to those normally associated with tidal regimes e g bedforms migrating in opposite directions most of the bedload sediment entering the system is eventually deposited in well defined sinks situated in the lee of structural offsets this model applies only to inter glacial high sea level situations accompanied by strong western boundary flow of the agulhas current

relationships between fault controlled subsidence and preservation of shallow marine small scale cycles example from the lower pliocene of the crotone basin southern italy abstract the northern part of the crotone basin southern italy was characterized by the activity of pliocene growth faults bounding half graben sub basins the thickest unit deposited during growth fault activity is the lower pliocene belvedere formation up to 450 m thick which shows a small scale highly regular rhythmic cyclicity this sandstone unit was deposited in a shallow marine environment and its accumulation was mostly influenced by storm processes and locally by flows in tectonically confined areas the meter scale cycles are represented by rhythmic alternations between shell rich intervals characterized by storm structures or large scale cross sets and shell poor sandy intervals that are commonly burrowed and poorly stratified the better preserved cycles commonly show a fining upward trend with minor progradation in their upper part and may be bounded at the base by a shell lag the deposition of large scale cross sets is thought to be the consequence of the creation of fault scarps which led to tectonic confinement in the half graben basins in the tectonically confined areas tidal currents were enhanced and large subaqueous dunes migrated the evidence suggests that the observed cyclicity was generated by sea level and climatic variations that controlled the sediment input into the basin the relationship between large scale cross sets and tectonic confinement demonstrates that local extensional tectonics significantly influenced the sedimentation the excellent preservation of the observed small scale cycles is thought to be the consequence of deposition in the highly subsiding half graben sub basins on the structural highs this cyclicity is amalgamate and less appreciable the data presented may be significant for a better understanding of the role of subsidence in preserving sedimentary successions in these growth faulted settings

paleoecology of the marine endobenthos endobenthic animals which reside within the sea bottom include stationary suspension feeders mobile deposit feeders and both stationary and mobile carnivores their activities especially with regard to dwelling feeding walking crawling and resting nesting are recorded as trace fossils abundance diversity and density of some kinds of trace fossils allow interpretation of the population strategies of the trace makers in terms of opportunistic r selected and equilibrium k selected strategies opportunistic ichnotaxa tend to be faciesbreaking traces which are highly localized in low diversity high density trace fossil associations in rocks representing environmental extremes e g variable salinities harsh temperatures low oxygen levels or shifting substrates equilibrium ichnotaxa usually are restricted to particular sedimentary facies and are characteristic of high diversity low dominance trace fossil associations in sediments reflecting stable predictable environmental conditions the most important environmental factors influencing the composition of trace fossil assemblages in marine settings are bathymetry substrate oxygen and hydrodynamic energy the four factors are closely interrelated because as water depth increases there is a general decrease in sediment grain size and hydrodynamic energy of the depositional environment as depth below the water sediment interface increases the firmness of the sediment due to compaction and dewatering increases and the oxygen content of interstitial waters drops drastically marine ichnofacies are largely substrate controlled soupgrounds are water saturated incompetent substrates typified by highly compressed and usually unidentifiable burrows softgrounds commonly contain numerous distinctive burrows and are zoned bathymetrically by the skolithos cruziana zoophycos and nereites ichnofacies firmgrounds are characterized by stiff compacted sediments in which traces of the glossifungites ichnofacies are excavated hardgrounds are cemented substrates in which bioerosion traces of the trypanites ichnofacies are bored woodgrounds are woody materials that have been exposed to the sea and bored by bivalves which produce characteristic traces of the teredolites ichnofacies tiering of endobenthic communities is common and is related to substrate preference of the burrowers and oxygen stratification of interstitial waters

high resolution estimate for the depositional duration of the triassic latemar platform a new magnetostratigraphy and magnetic susceptibility cyclostratigraphy from basinal sediments at rio sacuz italy 1 a new magnetostratigraphy and magnetic susceptibility cyclostratigraphy from middle triassic basinal sediments at rio sacuz northern italy suggests a depositional duration of 1 myr for most of the 670 m carbonate latemar platform giving a high resolution estimate for the duration for the latemar s deposition the new magnetostratigraphy from rio sacuz clarifies the ambiguities in a previous magnetostratigraphic study of the latemar caused by lightning strike remagnetizations our rio sacuz study was unaffected by lightning using thermal demagnetization we show a normal reversed normal reversed sequence at the latemar correlated locality of rio sacuz with a polarity interval duration of 0 25 0 5 myr for the middle triassic this gives a depositional duration of 1 2 myr rock magnetic experiments show that the magnetic carrier is magnetite suggesting a primary depositional age remanence measurement of magnetic susceptibility at 1 m intervals from rio sacuz reveals eight short eccentricity cycles 95 125 kyr bundled into slightly more than two 405 kyr long eccentricity cycles indicating a more precise duration for the rio sacuz section of 0 8 to 1 myr the shorter depositional duration required by this study forces a sub milankovitch time scale of 1 2 kyr for the latemar platform s meter scale rhythmic bedding and provides strong evidence for nonorbitally driven climate change in the middle triassic

integrated ediacaran sinian chronostratigraphy of south china abstract the ediacaran period was a critical time in the history of life and earth understanding the complex interactions between geological and biological events during this interval requires high resolution chronostratigraphy thanks to its uniquely favorable palaeogeographic setting south china is an ideal region for constructing a framework for global chronostratigraphic correlation of ediacaran strata here continuous ediacaran successions contain both siliciclastic and carbonate rocks that range from shallow to deep marine and contain rich fossil assemblages showing a variety of preservation styles as part of the present study 62 reference sections distributed throughout the yangtze platform were investigated analyses of the sedimentary facies and sequence stratigraphy of more than 40 sections revealed four major sequences in the shallow marine facies three major sequence boundaries occur respectively in the middle and upper parts of the doushantuo formation and in the middle part of the dengying formation subdivision and correlation of the ediacaran successions of the yangtze platform based on sequence stratigraphy is congruent with the carbon isotope chemostratigraphy of 12 reference sections 1075 samples the sequence boundary sb2 in the middle part of the doushantuo formation is suggested here as the lower xiadongian upper yangtzean series boundary of the ediacaran which coincides with several globally recognizable events namely 1 the end of the neoproterozoic glaciations 2 the first appearance of animals 3 the sudden increase in the diversity of acanthomorphic acritarchs and 4 a negative 13 c excursion the ediacaran system of south china may be subdivided into five stages furthermore the criteria for defining these stages may be applicable throughout the world also the composite carbon isotope profile of the ediacaran of south china can be used as a global reference for chronostratigraphic subdivision and correlation in addition to the globally recognizable negative 13 c excursion in the cap carbonate at the base of the ediacaran the negative 13 c excursion in the uppermost doushantuo wonoka shuram interval represents another globally correlatable major excursion the positive 13 c excursion immediately following the uppermost doushantuo excursion and ending at 548 ma is also useful for global correlation current ediacaran chronostratigraphy and global correlations indicate that the upper doushantuo wonoka shuram negative 13 c excursion ranges from ca 560 ma to 551 ma and therefore coincides with the evolutionary renovation of life feedback between evolutionary innovation and geochemical cycling was the key mechanism for this unique and most strongly negative 13 c excursion in earth history our chronostratigraphic correlations also imply that the earliest known metazoan biotas namely the weng an and characteristic ediacaran biotas do not constitute two temporally separate evolutionary lineages as proposed previously but represent two parallel evolutionary pathways preceding the cambrian explosion of animal life

paleomagnetism and rock magnetic cyclostratigraphy of the ediacaran doushantuo formation south china constraints on the remagnetization mechanism and the encoding process of milankovitch cycles abstract south china provides exceptional and unique sedimentary archives of earth s fundamental changes in ediacaran time however the lack of robust geochronological constraints renders a poorly defined chronostratigraphic framework for ediacaran aged strata in south china thus making it difficult to understand earth s critical changes during this time interval magnetostratigraphy and rock magnetic cyclostratigraphy turn out to be a few reliable methods in chronostratigraphic studies especially in the precambrian here we present a detailed paleomagnetic and rock magnetic study of the ediacaran doushantuo formation in the huanglianba section guizhou province south china the section consists of 75 m thick carbonate succession and has a record of one of the largest carbon isotope excursions in the earth history known as the shuram excursion stepwise thermal demagnetization of doushantuo carbonates reveals single component magnetizations that yield a paleomagnetic pole consistent with the late triassic segment of the apparent polar wander path of south china the secondary origin of doushantuo carbonates magnetization is supported by their magnetic mineralogy based on various rock magnetic experiments and scanning electron microscopic analyses we interpret that the secondary magnetization resides mainly in authigenic pyrrhotite that likely precipitated from the reducing fluids during the late stage of indosinian orogeny in the triassic interestingly the companion high resolution cyclostratigraphic study of a 4 m thick succession at the upper layers of the doushantuo formation in the huanglianba section indicates that the milankovitch cycles were encoded in the variation of magnetic susceptibility immune from the influence of remagnetization variation of magnetic susceptibility is attributed to changes in the abundance of paramagnetic minerals which by implication means that the amount of terrestrial materials transported from the continent was regulated by milankovitch cycles during the deposition of doushantuo carbonates therefore our results suggest that even though carbonates are prone to remagnetization astronomical modulation of deposition could be encoded in rock magnetics of the remagnetized carbonates as a result rock magnetic cyclostratigraphy has potential in remagnetized carbonates for providing a floating astronomical timescale that can be applied to constrain sediment accumulation rates estimate the duration of geological events and construct high resolution chronostratigraphies

threshold of erosion of submarine bedrock landscapes by tidal currents since sea level stabilized 7000 yr bp shelf seas experiencing semi diurnal tides will have been affected by streaming four times per day if tidal erosion of bedrock were even only marginally efficient the 10 million streamings since then should have left geomorphological imprints we examine high resolution multibeam sonar data from three areas with extreme tidal currents the minas passage bay of fundy experiencing 8 knot surface tidal currents was surveyed in 2007 with a multibeam sonar in an area near to transverse dunes which are evidence for bedload transport the data show local overhanging surfaces near to the sediment rock contact potentially created by abrasion by saltating particles however they are uncommon in the straits of messina where surface currents reach 10 knots surveying revealed ridges lying oblique to the flow that are not obviously broken into separate outcrops by erosion in the bristol channel uk sonar data collected where currents reach 3 4 knots at 1 5 m above the bed reveal outcrops of limestone with superimposed sand dunes but only minor rounding of blocks holocene tidal currents have apparently been generally ineffective at eroding bedrock we examine this issue further by compiling extreme tidal streams around the uk and from them estimate shear stresses representing a macro tidal environment where peak surface currents reach 9 7 knots those data are compared with shear stresses in mountainous rivers where long term rates of erosion are comparable with tectonic uplift rates and are thus geomorphologically significant whereas river stresses reach 102 103 pa the largest tidal stresses are generally 101 and only rarely approach 102 pa too small for quarrying to operate generally however the vertical faces in the minas passage may represent the onset of abrasion given this limited evidence for abrasion we explore conditions in the geological past for tides that may have locally eroded bedrock

high frequency paleovariability in climate and co2 levels from vostok ice core records the high resolution of the vostok records provides a unique look at the causes of paleoclimatic variability during the last complete glacial cycle the records present strong evidence for the interaction between orbital forcing and internal physico chemical mechanisms of variability this interaction appears to account for the great wealth of spectral features found in the records

marine volcaniclastics of the hidden lake formation coniacian of james ross island antarctica an enigmatic element in the history of a back arc basin

late pliocene early pleistocene athalassa formation north central cyprus carbonate sand bodies in a shallow seaway between two emerging landmasses the late pliocene early pleistocene athalassa formation accumulated within the neogene mesaoria basin of northern cyprus bordered by two subdued but rising landmasses the kyrenia range to the north and the troodos ophiolitic massif to the south in the eastern part of the basin the formation is dominated by cross stratified bioclastic rich sandstones interpreted as shallow marine carbonate sand bodies the sediments are described in terms of six calcarenite facies and subfacies and one sandstone fades palaeocurrent analysis indicates that the carbonate sand bodies formed near the southern margin of the kyrenia landmass and then migrated southwards across a shallow marine platform the driving force is believed to have been storms generated by strong winds such winds during the late pliocene early quaternary were probably stronger than today in this area other factors influencing deposition of the formation include minor tectonic instability and probable eustatic sea level changes study of the athalassa formation thus provides insights into late pliocene pleistocene palaeoenvironments in the easternmost mediterranean

integrated chemostratigraphy of the doushantuo formation at the northern xiaofenghe section yangtze gorges south china and its implication for ediacaran stratigraphic correlation and ocean redox models abstract the ediacaran doushantuo formation in the yangtze gorges of south china plays an important role in our understanding of biological evolution global correlation and ocean redox conditions because of the availability of high resolution paleontological and geochemical data and numerous radiometric dates however integrated study has been focused on the jiulongwan section that was largely deposited below wave base in a restricted shelf lagoon jiang et al 2011 zhu et al 2011 studies of shallower water successions are lacking and this presents a challenge to test ediacaran stratigraphic correlation and ocean redox models to fill this knowledge gap we conducted a high resolution integrated study of the doushantuo formation at the northern xiaofenghe nxf section approximately 35 km to the northeast and paleogeographically updip of the jiulongwan section with the exception of the basal 20 m nxf sediments were deposited above normal wave base integrated biostratigraphic and chemostratigraphic data indicate that the 140 m thick nxf section correlates with the lower doushantuo formation member i and much of member ii i e the lower ca 70 m of the formation at jiulongwan geochemical data from nxf and other doushantuo sections indicate that euxinic conditions may have been limited to a shelf lagoon represented by the jiulongwan section that was restricted between the proximal inner shelf and a distal shelf margin shoal complex at least during early doushantuo time following the deposition of the doushantuo cap dolostone further integrated studies are necessary to test whether euxinic conditions existed in open marine shelves in south china and elsewhere during the ediacaran period

high resolution rock magnetic cyclostratigraphy in an eocene flysch spanish pyrenees 1 a rock magnetic cyclostratigraphy based on anhysteretic remanent magnetization arm intensity variations was developed for the eocene arguis formation in the spanish pyrenees the arguis formation was sampled for arm cyclostratigraphy rock magnetic and paleomagnetic analyses rock magnetic measurements indicate that the dominant magnetic mineral controlling the arm cyclostratigraphy is depositional magnetite using thermal demagnetization a detailed magnetostratigraphy was developed for the arguis to provide an absolute time framework for the arm cyclostratigraphy the magnetostratigraphy is carried by a combination of depositional magnetite and secondary iron sulfides spectral analysis of the magnetostratigraphically scaled arm time series reveals the presence of significant milankovitch frequencies including eccentricity obliquity and precession the arm time series was tuned to the orbital eccentricity model for the eocene coherency analysis indicates that the eccentricity tuned arm is in phase with october november insolation for this site s paleolatitude varying amounts of terrigenous input delivered by a fluvial source at orbital time scales during the rainy season and diluted by a relatively constant input of marine carbonate is the most likely explanation for the cyclicity of the arm record the absolute age resolution of the arm chronostratigraphy is 1 or less based on an age offset with the reference chronology that was used for the eocene the offset in age between the two chronologies may be due in part to the uncertainty in the chron ages for this part of the eocene the relative age resolution within the arm chronostratigraphy is much better

interplay of tidal and fluvial processes in an early pleistocene delta fed strait margin calabria southern italy abstract the architecture and morphodynamics of modern and ancient tidal straits and in particular the deposits of strait margin zones have been significantly understudied compared to other marginal marine settings even though many reservoirs in the north sea and the norwegian continental shelf are developed in narrow grabens or seaways this paper presents a detailed sedimentological and stratigraphic analysis of an early pleistocene marginal marine succession deposited along the northern margin of the siderno paleostrait southern italy this area represents an excellent case study of sedimentation along a tidal strait margin interpreted to record the interaction of fluvial and tidal processes here syn depositional tectonics produced a complex coastal morphology significantly influencing sedimentation and hydrodynamic processes along the strait margin the emplacement of an isolated tectonic high piano fossati created a ca 3 5 km wide local passageway this morpho structural element induced interplays between fluvio deltaic processes fed from the northern strait margin and tidal current reworking active within the marine strait the field based facies analysis reported here documents an initial stage of non tidal shallow marine sedimentation across the strait a subsequent regression caused river generated hyperpycnal flows and the transfer of large volumes of pebbly and shelly sandstones into deeper water tidal currents became amplified in the strait and in the delta front area they were able to rework river derived sediments generating large dune fields following the local tidal transport pathway strong tidal currents skewed the delta front causing it to be asymmetrical and elongated sand bodies in a direction parallel to the marine strait axis differently from the classical tide influenced deltas in which onshore offshore tidal flow predominates coast parallel deflection and strong asymmetry of delta front deposits is a typical feature of deltas entering tide dominated seaways and straits where strong tidal currents are capable of dispersing large volumes of sand for significant distances along the coast and along the strait axis this process became progressively enhanced during the following transgression when tide modulated currents reworked biocalcarenitic sands over the previous delta deposits generating southeasterly migrating dunes at the end of the transgression strandplain deposits formed in this area this last stage of sedimentation was followed by a dramatic regional scale structural uplift which ended any marine circulation within the strait this work provides new insights on sedimentation in a tide dominated strait and helps to predict sandbody distribution along the strait margin and axis these findings can be applied to any other setting characterized by a narrow possibly structurally confined basin dominated by tidal currents

holocene sedimentation in the shallow nearshore zone off nauset inlet cape cod massachusetts abstract present conditions and sedimentary evolution of the shallow offshore region near nauset inlet on cape cod massachusetts were clarified using high resolution seismic reflection profiles sidescan sonar records surface grab samples and current meter measurements the study area contains three provinces 1 a nearshore province shallower than 18 m with a relatively steep slope 0 6 and a cover of medium sand 2 a northern offshore province covered with coarse sand gravel and boulders interpreted to be glacial drift and 3 a southern offshore province with a gentle seaward dipping slope 0 3 and a surface sediment of coarse sand the glacial drift exposed in the northern offshore province can be traced southward under the coarse sand province the overlying fill is comprised of either outwash sediment derived from the pleistocene south channel ice lobe to the east or holocene aged marine sediments eroded from seacliffs to the north latest holocene sediment appears to be limited to the zone shoreward of 18 m where the medium sand occurs near bottom mean flows measured over two winter months in 10 m water depth average 6 cm sec 1 to the south mean flows exceeded 20 cm sec 1 approx 23 of the time ninety percent of the flows exceeding 20 cm sec 1 were directed to the south reflecting the dominant atmospheric forcing during these winter months waves had an average variance of 650 cm 2 with variance exceeding 5000 cm 2 3 of the time indicating moderate wave activity present processes are actively reshaping the nearshore province which is characterized by many east to northeast trending shore oblique channels that do not extend seaward of the 18 m contour coarse sand in the floors of these channels suggests they may be erosional features and the presence of megaripples oriented perpendicular to the channel axes indicates active transport in these channels megaripple orientation and the current and wave regime of the study area support a rip current origin for these channels

the record of tidal cycles in mixed silici bioclastic deposits examples from small plio pleistocene peripheral basins of the microtidal central mediterranean sea the pliocene pleistocene peripheral marine basins of the mediterranean sea in southern italy from basilicata and western calabria to northern and eastern sicily represent tectonically formed coastal embayments and narrow straits here units of cross stratified mixed silici bioclastic sand 25 to 80 m thick record strong tidal currents the central mediterranean sea has had a microtidal range of ca 35 cm and the local amplification of the tidal wave is attributed to tides enhanced in some of the bays and to the out of phase reversal of the tidal prism in narrow straits linking the tyrrhenian and ionian basins the siliciclastic sediment was generated by local bedrock erosion whereas the bioclastic sediment was derived from the contemporaneous foramol type cool water carbonate factories the cross strata sets represent small to medium sized 10 to 60 cm thick two dimensional dunes with mainly unidirectional foreset dip directions these tidalites differ from the classical tidal rhythmites deposited in mud bearing siliciclastic environments firstly the foreset strata lack mud drapes and instead show segregation of siliciclastic and bioclastic sand into alternating strata secondly the thickness variation of the successive silici bioclastic strata couplets measured over accretion intervals of 2 to 3 m and analysed statistically reveal only the shortest term diurnal and semi diurnal tidal cycles thirdly the record of diurnal and semi diurnal tidal cycles is included within the pattern of neap spring cycles differences between these sediments and classical tidal rhythmites are attributed to the specific palaeogeographic setting of a microtidal sea with the tidal currents locally enhanced in peripheral basins it is suggested that this particular facies of mud free silici bioclastic arenite rhythmites in the stratigraphic record might indicate a specific type of depositional sub tidal environment of straits and embayments and the shortest term tidal cycles

the role of sub milankovitch climatic forcing in the initiation of the northern hemisphere glaciation mechanisms responsible for the initiation of major glaciation in the northern hemisphere at about 2 75 million years ago are poorly understood a laminated terrestrial sequence from pula maar hungary containing about 320 000 years in annual layers between 3 05 and 2 60 million years ago provides a detailed record of rates of climatic change across this dramatic transition an analysis of the record implies that climatic variations at sub milankovitch frequencies less than or equal to 15 000 years were an important driving force during this transitional interval and that as the threshold was approached these increased in frequency and amplitude possibly providing the final trigger for the amplification of northern hemisphere ice sheets

transverse and linear dunes in an upper pleistocene marine sequence corinth basin greece a range of large scale dunes of oolitic calcarenite composition are exposed in the corinth basin of central greece these transverse dunes and a very large linear dune 15 m high lie within an upper pleistocene transgressive marine sequence tidal flow accelerated by constriction through a narrow fault bounded seaway is interpreted to have generated the current velocities necessary to produce the dunes marine facies in the upper pleistocene sequence include beach to offshore conglomerates and sandstones with wave modified sedimentary structures and herringbone cross stratification an offshore facies association comprises variably bioturbated siltstones and sandstones with a varied marine fauna that includes thermophile species such as scleractinian corals and strombus bubonius oolitic sandstone facies also occur oolitic sands were apparently produced in shoal environments subject to tidal and wave action and transported by dominant southerly currents over the southern part of the basin oolites accumulated in a linear dune 2 7 km long and 15 20 m high and in three dimensional transverse dunes up to 10 m high having a variety of compound and simple internal geometries the isolated wsw ene trending linear form exhibits angle of repose sedimentary dips up to 35 of avalanche sets on its se flank and sets typically with dips of 15 20 to the nw internal high angle discontinuities are developed in the se dipping lee face it is proposed that a dominant north to south flow crossed over the crest obliquely resulting in both net erosional and depositional processes on the lee flank a subordinate tidal current may have locally and or periodically crossed the dune crest in a westwards direction a string of transverse dunes which were located adjacent to a fault marine terrace scarp is interpreted to have originally coalesced to form the linear dune the distribution of transverse and linear dunes together with the palaeogeographical reconstruction suggest that a marine connection periodically existed across the corinth isthmus during the late pleistocene due to a combination of active faulting and glacio eustatic highstands of sea level

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

sedimentary facies during early stages of flooding in an extensional basin the breche rouge de carboneras late miocene almeria se spain the intramontane basins of the betic cordil leras se spain formed subsequent to the main phase of orogenic deformation during the middle miocene in a close genetic relation to the trans alboran shear zone left lateral movements along a local branch carboneras fault zone cf strike ne sw of this zone played a major role in controlling the formation and dynamics of the nijar carboneras basin to the south of the fault a major phase of strike slip faulting is recorded during the late tortonian the expression of this event is the brche rouge de carboneras brc which seals a deep denudational surface on top of dislocated fault blocks formed by volcanics of the cabo de gata complex and early tortonian shallow marine calcarenite the sedi mentary facies of this widely distributed unit in the carboneras subbasin mirror the submarine topography and the distribution of the fault zones along strike slip fault zones autoclastic breccias and neptunian dikes preferentially oriented nw se and ne sw occur which are interpreted to represent the near surface expression of the faults red limestone forms the groundmass of the autoclastic breccia and infills of neptunian dikes which exhibit multiple phases of opening of fissures gravita tional sedimentary infill lithification and renewed cre ation of cracks steep relief probably along fault scarps was mantled by epiclastic volcanic conglomerate with a red carbonate matrix well lithified coarse skeletal lime stone rich in planktonic foraminifera formed pavements along sediment starved rocky surfaces in deep water laterally within topographic depressions the pavement limestone grades into thick accumulations of skeletal rudstone composed of fragmented azooxanthellate corals and stylasterid hydrozoans which were concentrated by powerful bottom currents and gravitiy flows within the shallow water zone of dip slope ramps cross bedded calcarenite and calcirudite formed based on textures fabrics and biota rocks of the brc were grouped into nine genetic lithofacies which document cryptic deep aphotic and shallow photic environments typical of a sediment starved extensional basin

bioclastic sediment lobes on a supply dominated upper cretaceous carbonate platform margin montagna della maiella italy a thick bioclastic sediment wedge was deposited on the slope of the maiella carbonate platform margin in the late campanian to late maastrichtian the wedge consists of lobate depositional units laterally and vertically convex structures the complex internal geometries of the lobes combine characteristics of unidirectional sandwaves and the alternating point sources of deltas excellent outcrop permits a detailed documentation and discussion of the depositional processes the sediment wedge constitutes a supersequence which prograded along the platform margin as a result of high sediment supply and forced regression within the supersequence a hierarchy of higher order stratigraphic units sequence sets and sequences are developed the individual bioclastic sediment lobes are interpreted as systems tracts and parasequences of the sequences within the sequence sets

sand waves echinocardium traces and their bathyal depositional setting monte torre palaeostrait plio pleistocene southern italy stacked cross sets up to 2 5 m thick produced by sand wave migration and meniscate trace fossils produced by echinocardium cordatum both considered in the literature as typical of shallow water marine depositional settings commonly occur in the bathyal plio pleistocene deposits of monte torre calabria southern italy the plio pleistocene sediments form two coarsening upward depositional sequences separated by an unconformity and by a palaeobathymetric gap of at least 300 m the lower sequence passes upwards from hemipelagic marls and thin bedded turbidites to thick bedded sandy turbidites then to sand wave deposits alternated with sandy turbidites and finally to base of slope megabreccias facies characteristics and relationships and the occurrence of deep sea faunal associations indicate deposition in the bathyal zone the facies of the upper sequence reflect a fan delta environment no deeper than a few tens of metres the depositional setting of the lower sequence where the sand wave deposits and meniscate trace fossils occur appears to have been a tectonically controlled seaway connecting the tyrrhenian and ionian seas this seaway became progressively narrower with time evolving into a strait the overall coarsening upward trend reflects the upward transition from a low to a high energy environment possibly caused by the tectonic narrowing of the seaway deposition and erosion from high concentration turbidity currents and from tidal bottom currents were important processes periods of tectonic activity producing first the uplift of the seaway margins and culminating with the uplift of the strait sequence itself are marked by scattered rockfall deposits the strait setting causing the development of powerful oxygenated bottom currents produced optimal conditions in the bathyal zone for the colonization of sandy bottoms by a single infaunal r selected species echinocardium sp

anatomy of a late pleistocene clinoformal sedimentary body le castella calabria southern italy a case of prograding spit system abstract the le castella marine terrace is the smallest and youngest terrace of the crotone area southern italy and formed after a rapid marine ingression due to a glacio eustatic rise outpacing the regional uplift of the area the most prominent feature of the terrace deposits is a seaward accreting clinoform about 10 m thick inferred to be formed during forced regressive conditions this prograding body is mostly composed of bioclastic material and shows an internal complexity consisting of alternating oblique and sigmoid elementary units inferred to be produced mainly by changes of accommodation development foreset avalancing was due to sediment accumulation by gravity flow processes while topsets were characterized by the migration of medium to large scale dunes showing a unimodal palaeocurrent pattern oblique with respect to the dip direction of the large scale clinoform foresets the le castella clinoform starts to develop from a topographic step on the basement due to tectonics which also controlled the palaeoshoreline trend the recognized stratigraphic and facies architectures the palaeocurrent pattern and the inferred palaeogeographic setting during deposition all suggest that the le castella clinoform is an example of spit system attached to the mainland and accreted due to longshore transport the present example contributes to establish criteria allowing the recognition of ancient spit systems which still are poorly known and rarely documented in the pre quaternary geological record