mesozoic collision extrusion tectonics in eastern asia abstract the eastern part of the asian continent was intensively deformed in early cretaceous time deformation has been interpreted to be related to subduction tectonics along the eastern continental margin we propose an alternative tectonic framework of collision extrusion tectonics resulting from collision of the indochina block with the eurasian continent this event controlled the jurassic to cretaceous tectonic history in eastern asia and the evolution of the subduction zone along the eastern margin of the continent

sand ripples under sea waves part 3 brick pattern ripple formation an oscillatory flow over a cohesionless bottom can produce regular three dimensional bedforms known as brick pattern ripples characterized by crests perpendicular to the direction of fluid oscillations joined by equally spaced bridges shifted by half a wavelength between adjacent sequences a photo of brick pattern ripples is shown in sleath 1984 p 141 in the present paper brick pattern ripple formation is explained on the basis of a weakly nonlinear stability analysis of a flat cohesionless bottom subject to an oscillatory flow in which three dimensional perturbations are considered

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

observations of wave transformation over a fringing coral reef and the importance of low frequency waves and offshore water levels to runup overwash and coastal flooding many low lying tropical islands are susceptible to sea level rise and often subjected to overwash and flooding during large wave events to quantify wave dynamics and wave driven water levels on fringing coral reefs a 5 month deployment of wave gauges and a current meter was conducted across two shore normal transects on roi namur island in the republic of the marshall islands these observations captured two large wave events that had waves with maximum heights greater than 6 m with peak periods of 16 s over the fore reef the larger event coincided with a peak spring tide leading to energetic highly skewed infragravity 0 04 0 004 hz and very low frequency 0 004 0 001 hz waves at the shoreline which reached heights of 1 0 and 0 7 m respectively water surface elevations combined with wave runup reached 3 7 m above the reef bed at the innermost reef flat adjacent to the toe of the beach resulting in flooding of inland areas this overwash occurred during a 3 h time window that coincided with high tide and maximum low frequency reef flat wave heights the relatively low relief characteristics of this narrow reef flat may further drive shoreline amplification of low frequency waves due to resonance modes these results 1 demonstrate how the coupling of high offshore water levels with low frequency reef flat wave energetics can lead to large impacts along fringing reef lined shorelines such as island overwash and 2 lend support to the hypothesis that predicted higher sea levels will lead to more frequent occurrences of these extreme events negatively impacting coastal resources and infrastructure

sea ripple formation the heterogeneous sediment case abstract ripple formation beneath sea waves is analyzed both by experimental and analytical means when the bottom is made up of a mixture of sands an oscillatory flow is obtained in a closed duct by the oscillations of two rigidly connected pistons located at the ends of the duct the amplitude and period of the oscillations can be continuously varied a fixed tray located at the bottom of the duct and filled with different types of sediments allows ripple formation to be observed the presence of graded sediments is found to have a stabilizing effect and causes longer ripples to appear moreover a selective sediment transport is observed and quantified which tends to pile up the coarse grains at ripple crests leaving the fine ones in the troughs as in the companion paper the theory is based on a linear stability analysis of a flat sandy bottom subject to an oscillatory flow because of the presence of a mixture a modified version of exner equation is used and an hiding factor should be inserted in the sediment transport rate formula the flow regime in the bottom boundary layer is assumed to be turbulent the conditions for ripple appearance are determined along with their wavelengths as they form good agreement is found between experimental data and theoretical findings

the relative contribution of accretion shear and extension to cenozoic tectonic rotation in the pacific northwest large cenozoic clockwise rotations defined by paleomagnetic data are an established fact in the pacific northwest and many tectonic models have been proposed to explain them including 1 rotation of accreted oceanic microplates during docking 2 dextral shear between north america and northward moving oceanic plates to the west and 3 microplate rotation in front of an expanding basin and range province stratigraphic onlap relations and local structure indicate that microplate rotation during docking was not a major contributor to the observed rotations coast range structures basin and range extension and paleomagnetic data from middle miocene 15 ma coast range rocks indicate that dextral shear is responsible for at least 40 of the post 15 ma rotation of the coast range and that basin and range extension is responsible for the remainder reconstructions based on extrapolation of this ratio back to 37 and 50 ma are consistent with reconstructions based on paleomagnetic and stratigraphic relations in older rocks and suggest that dextral shear has been a significant contributor to rotation during most of tertiary time changes in the dextral shear rotation rate over the past 50 m y correlate directly with changes in the velocity of the farallon plate parallel to the coast and provide a strong argument for oblique subduction as the driving mechanism continental reconstructions incorporating shear may provide constraints on the rate of extension in the northernmost basin and range region and suggest 17 extension since 15 ma 39 since 37 ma and 72 since 50 ma near latitude 42 n

note on sediment sorting in a sandy bed under standing water waves we present new quantitative data on the sorting of sediments on a sandy seabed under standing waves starting from a flat bed composed of a homogeneous mixture of a coarse and a fine sand with mean diameters 0 11 and 0 21 mm we observed simultaneous ripple and sand bar formation and sand sorting on the seabed over days of wave action sand bars formed with crests beneath the surface wave nodes and flat plateaus flanked by mounds beneath the antinodes bar crests were composed of sand coarser on average than 0 21 mm while the flat plateaus were covered by sand finer on average than 0 11 mm comparison with two experiments involving sand beds of more homogeneous size distributions shows that the mounds are characteristic of the motion of fine suspensions

japan sea opening history and mechanism a synthesis the respective tectonic effects of back arc spreading and continental collision in asia are considered either as two independent processes or as closely interrelated extrusion tectonics assumes that the opening of the south china sea and the left lateral motion along the red river fault are geometrically linked in a pull apart manner this model is not accepted by several workers because the structural link between the two processes is not clearly demonstrated in the case of the japan sea we can show without ambiguity that back arc opening was controlled by large intracontinental strike slip faults which can be easily understood as effects of the india asia collision far from the indenter the japan sea opened in the early miocene in a broad pull apart zone between two major dextral strike slip shear zones the first one extends from north sakhalin to central japan along 2000 km it has accommodated about 400 km of finite displacement deformation along it varies from dextral transpression in the north to dextral transtension in the south the second is between korea and sw japan and has accommodated a smaller displacement of about 200 km the extensional domain in between lies in the back arc region of japan distributed stretching of the arc crust resulted in the formation of most of the japan sea while localized oceanic spreading at the southern termination of the eastern transpressional shear zone shaped the japan basin the first oceanic crust was formed in a small triangle based on the eastern shear zone and spreading propagated westward inside the pull apart region timing of oceanic crust formation of formation of the dextral shear zones and of block rotation in between as well as the internal structure of the basins and the geometry of deformation along the master shear zones are used to reconstruct the opening history this evolution is discussed by comparison to other manifestations of the arc and back arc activity such as the history of sedimentation and volcanism the paper then suggests that the collision of india can have tectonic consequences as far north as japan and sakhalin and describes the geometrical relation of back arc opening there and diffuse extrusion

correlation of ash flow tuffs discrimination and correlation of ash flow sheets is important in structurally complex long lived volcanic fields where such sheets provide the best keys to the regional stratigraphic framework three dimensional complexities resulting from pulsatory eruptions sectorial emplacement mechanical sorting during outflow thermal and compositional zoning of magmas the physical zoning of cooling units and structural and erosional disruption can make such correlation and discrimination difficult when lithologic magnetic petrographic chemical and isotopic criteria for correlating ash flow sheets are critically evaluated many problems and pitfalls can be identified distinctive phenocrysts pumice clasts and lithic fragments are among the more reliable criteria as are high precision k ar ages and thermal remanent magnetization trm directions in unaltered welded tuff chemical correlation methods should rely principally upon welded or nonwelded pumice blocks not upon the ash flow matrix which is subject to fractionation mixing and contamination during emplacement compositional zoning of most large sheets requires that many samples be analyzed before phenocryst glass or whole rock chemical trends can be used confidently as correlation criteria

feedbacks between flow sediment motion and microbial growth on sand bars initiate and shape elongated stromatolite mounds abstract elongated stromatolites are often used as indicators of current direction and shoreline orientation especially in paleoenvironmental reconstructions however mechanisms that create shore parallel m scale elongated stromatolite mounds in carbonate sand are not well understood we propose that this geometry is initiated by microbial growth on the parts of sand bars that experience low wave induced bed shear stresses we test this idea by growing microbial mats on carbonate sand bars in a laboratory wave tank cyanobacterial mats grow on the bar runnels where sediment motion is negligible but are absent from the bar ridges where the waves generate migrating ripples when microbially promoted lithification reinforces and preserves this initial pattern elongated stromatolites should initiate in the runnels of sand bars with long wavelengths 5 100 m and small width to wavelength ratios 0 3 these dimensions are consistent with modern shore parallel stromatolites in hamelin pool western australia and with patterns of microbial colonization in other sandy sediments this model of elongated stromatolite mounds can inform paleoenvironmental reconstructions by clarifying and quantifying feedbacks among waves sediment transport and microbial growth

sand ripples under sea waves part 2 finite amplitude development in the present paper the authors formulate a theory to predict the time development of sand ripples characterised by small but finite amplitude under the action of surface gravity waves the theory is based on a weakly nonlinear stability analysis of a flat sandy bottom subject to viscous oscillatory flow the parameters of the problem namely the reynolds number of the flow and the reynolds and froude numbers of sediments are assumed to fall within a neighbourhood of the critical conditions determined in blondeaux 1990 the analysis can predict the actual ripple height wavelength and profile when flow separation is absent i e for the case of rolling grain ripples assuming sleath s 1984 criterion for separation the values of the relevant parameters at which transition from rolling grain ripples to vortex ripples occurs are predicted a comparison between theoretical findings and experimental data supports the validity of the present theory

sandbar formation under surface waves theory and experiments 1 we report a combined theoretical and experimental study of sandbar formation under simple harmonic surface waves for coarse grains and weak waves an established empirical rule of bed load transport is used with an asymptotic theory for the fluid flow the surface waves are governed by potential theory and a depth linear eddy viscosity is employed in the turbulent boundary layer at the seabed the derived bed stress is used to predict the sand bed evolution laboratory experiments and corresponding numerical simulations for both high and low beach reflection are discussed for weak reflection the shear stress associated with the return current is found to be important partial simulation of a field record in cape cod bay is also described

evaluating episodic hydrothermal activity in south china during the early cambrian implications for biotic evolution abstract the early cambrian 541 514 ma was a crucial interval for the evolution of life on earth popularly known as the cambrian explosion here we report the timing of changes in hydrothermal and depositional inputs as well as paleo redox state which may have influenced biogeochemical changes according to high resolution petrology fossil distributions isotopic records and inorganic geochemistry the lower cambrian of the south china can be subdivided into four intervals the lowermost cambrian zhujiaqing formation cam i the cambrian stage 2 shiyantou formation cam ii the lower part of the cambrian stage 3 yu anshan formation cam iii and the mid upper cambrian stage 3 and the middle upper part of the yu anshan formation continuing into the canglangpu formation cam iv hydrothermal events are detected during the early cam i cam ii and cam iii intervals during the early cam i and cam ii intervals these events coincided with extensive bottom water euxinia which in turn may have restricted the spread or proliferation of ediacaran fauna and small shelly fauna through the whole cam iii interval further hydrothermal events occurred concurrently with euxinic and ferruginous conditions probably within a single spatially stratified water column again plausibly restricting the spread of aerobic organisms in conjunction with the cessation of hydrothermal events and the gradual lowering of sea level during the late cam iii oxic water environments gradually spread into relatively deep water regions concurrent with the emergence of the chengjiang and qingjiang faunas these data suggest that periodic hydrothermal events may have had a significant impact on the spread radiation and extinction of macroscopic fauna during the early cambrian in south china

a late cretaceous paleomagnetic pole from koto rhyolite southwest japan implications for eastern margin deformation of asia 1 a paleomagnetic pole was obtained from late cretaceous rhyolitic ash flow tuffs and associated ring dikes which are collectively called the koto rhyolite in the eastern part of southwest japan characteristic remanent magnetizations were isolated from 33 sites through thermal demagnetization normal and reversed polarity magnetizations were found and are mutually antipodal although the magnetization directions become more dispersed after tilt correction the clearly defined polarity sequence and the positive contact test between ash flow tuffs and ring dikes ensure that the characteristic magnetizations of ash flow tuffs predate the intrusion of associated ring dikes since no regional tilting is expected we regard the in situ magnetization directions to represent the late cretaceous 70 ma paleomagnetic field d 84 6 i 57 5 95 5 5 in eastern southwest japan the paleomagnetic pole is not significantly different from the coeval poles of western southwest japan this result gives a further support to a microplate model for the miocene clockwise rotation of southwest japan by canceling out the effect of the miocene rotation we were able to obtain a paleomagnetic pole of 70 ma 219 7 e 63 0 n 95 12 2 for southwest japan when the japan arc was incorporated in the eastern margin of asia paleomagnetic poles of late cretaceous age from korea south china coast and restored southwest japan are statistically indistinguishable from each other but significantly differ from that of the continental interior of east asia the observed rotation of about 20 probably results from shear deformation exerted by northeast trending strike slip faults along the eastern continental margin of asia

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

cretaceous and tertiary paleomagnetic results from southeast china and their tectonic implications abstract we report cretaceous and tertiary paleomagnetic data from fujian guangxi and guangdong provinces in south china in guangxi province we sampled early cretaceous redbeds of the xinlong formation at eight localities separated by up to 100 km the high temperature component obtained by thermal demagnetization is of dual polarity and passes the fold test and implies 18 8 counterclockwise rotation and insignificant poleward displacement with respect to cratonic localities in sichuan province a tertiary basin lying in a southeast trending fault zone is also rotated counterclockwise by 40 8 both results can be explained very well by a simple block rotation model for the cenozoic tectonic evolution of western guangxi province that is driven by left lateral shear on southeast trending faults the timing and sense of shear are the same as for india asia collision models involving the extrusion of indochina along the red river fault zone which lies several hundred kilometers to the southwest but the magnitude of fault displacement in guangxi is much less in the coastal provinces of fujian and guangdong we find late cretaceous directions that are rotated clockwise with respect to sichuan province combined with similar clockwise rotations found by two other studies of coeval rocks from the same region the mean rotation for the coastal provinces is 12 8 this could indicate a coherent block rotation of the region driven by extrusion tectonics however the limited number of sampling localities also allows the possibility that the directions reflect local rotations due to dextral shearing driven by circum pacific tectonics

sand ripples under sea waves part 1 ripple formation in the present paper we formulate a predictive theory of the formation of sand ripples under sea waves the theory is based on a linear stability analysis of a flat sandy bottom subject to a viscous oscillatory flow the conditions for decay or amplification of a bottom perturbation are determined along with the wavelength of the most unstable component as a function of the reynolds number of the flow and of the froude and reynolds numbers of the sediments a comparison between theoretical findings and experimental data supports the validity of the present theory an analytical solution for viscous oscillatory flow over a small amplitude wavy bottom is determined for arbitrary values of the ratio r between the amplitude of fluid displacement and the wavelength of bottom waviness previous works by lyne 1971 and sleath 1976 who considered small or large values of r are thus extended

paleomagnetic study of middle cretaceous rocks from yunlong western yunnan china evidence of southward displacement of indochina middle cretaceous red sandstones and siltstones were collected at 20 sites for paleomagnetic study from the nanxin formation around yunlong 25 8 n 99 4 e western part of yunnan province china after stepwise thermal demagnetization high temperature component magnetization with unblocking temperature of about 675 c is isolated a positive fold test at the 99 confidence limit shows that the high temperature component magnetization is primary for the middle cretaceous nanxin formation a tilt corrected formation mean direction is d 40 2 i 49 9 with 95 3 9 corresponding to a paleopole at 54 6 n 171 8 e with a95 4 4 comparison with previously reported cretaceous paleomagnetic directions indicates that the yunlong area has been subjected to southward displacement by 11 9 7 5 corresponding to 1300 800 km with respect to the stable yangtze craton since cretaceous time as well as clockwise rotation through 36 3 13 6 this study elucidates that indochina was squeezed out of the asian continent due to collision of india accompanied with clockwise rotation

confined ductile deformation in the japan arc inferred from paleomagnetic studies abstract miocene rocks collected from the kanazawa and daishoji areas in the western vicinity of the itoigawa shizuoka tectonic line istl were investigated using paleomagnetic and biostratigraphic methods in order to clarify the deformation mode of a continuous granitic sliver in the southern part of the japan arc which was bounded on east side by the istl seven sites in the kanazawa area and nine sites in the daishoji area were found to preserve stable characteristic remanent magnetization chrm through progressive demagnetization by thermal and alternating field methods temporal and spatial changes in chrm directions suggest that the areas were subjected to intra arc tectonic deformation linked with the middle miocene collision of the izu bonin arc which succeeded to coherent clockwise rotation of the southern part of the japan arc associated with the back arc opening around 15 ma the data in this study together with data previously obtained indicate that the angle of relative counterclockwise rotation increases gradually toward the east which was caused by the middle miocene arc arc collision this result and the absence of identifiable faults which could compensate differential rotations imply that the arc was ductilely deforming during the collision event it is also suggested that significant rotation occurred in the eastern confined portion of the uniform sliver of continental crust the confined ductile deformation of the crust observed in the japan arc can be achieved by the irregular compressive force on the fore arc side generated by landmasses on the subducting philippine sea plate and the plausible resisting force induced on the back arc side

multiple longshore sand bars in the upper chesapeake bay abstract in the upper chesapeake bay maryland u s a field surveys were conducted at 18 multiple longshore sand bar sites the multiple bar systems were found in water depths less than approximately 2 m mean sea level and exhibited mild bottom slopes of 0 0052 or less the number of bars composing each system ranged from four to 17 and the spacing between the crests typically increased in the offshore direction ranging from 12 to 70 m bar height also typically increased with distance offshore and ranged from 0 03 to 0 61 m a grain size analysis of crest and trough sediment did not reveal any significant differences and the sediment was categorized as fine sand a review of the literature data indicated that the chesapeake bay multiple bars possessed similar characteristics to those found in gelding bay baltic sea similarities in fetch wave height and tidal range between the two bays may account for this finding the surf scaling parameter indicated that the multiple bar systems were extremely dissipative with regard to wave energy and wave height appeared to be an important factor in controlling bar spacing and bar height a multiple wave break point hypothesis was discussed as a possible mechanism for the formation of chesapeake bay multiple longshore bars and limited observational evidence appeared to support such a mechanism

amount of clockwise rotation of southwest japan fan shape opening of the southwestern part of the japan sea abstract paleomagnetic measurements have been carried out on welded tuffs ranging in age between 58 ma and 112 ma from yamaguchi and go river areas in the central part of southwest japan the new data together with those of younger igneous rocks published previously define the change of paleomagnetic field direction during the late mesozoic cenozoic period for southwest japan the paleomagnetic direction from this area has pointed 56 3 clockwise from the expected field direction estimated from apwp apparent polar wandering path of the whole of eurasia during the period between 100 and 20 ma in comparison with the expected one from the eastern margin of eurasia korea china siberia the cretaceous field direction of southwest japan shows the clockwise deflection by 44 49 these results establish that while the eastern margin of eurasia including southwest japan was rotated more or less with respect to the main part of eurasia during last 100 ma southwest japan was rotated clockwise through more than 40 with respect to the eastern margin of eurasia since 20 ma the large amount of rotation for southwest japan implies that it is rotated by an opening of the southwestern part of the japan sea which widens northeastward fan shape opening the tectonic feature of southwest japan and the japan sea is analogous to that of corso sardinia and the ligurian sea in the mediterranean indicating that the fan shape opening is a specific feature of the rifting of the continental sliver at the continental rim

cenozoic northward translation of the kitakami massif in northeast japan paleomagnetic evidence abstract paleogene and early cretaceous welded tuffs have been sampled from eleven sites at the omoe peninsula 39 6 n 142 0 e in the kitakami massif of northeast japan for paleomagnetic study characteristic paleomagnetic directions with a high unblocking temperature component above 560 c are isolated westerly declinations with shallow inclination are identified after tilt correction in the 62 71 ma heizaki volcanics d 283 5 i 9 4 95 8 0 and in the 114 119 ma harachiyama formation d 274 2 i 20 4 the shallow inclination which was previously reported from early cretaceous plutonic rocks without tilt correction in the kitakami massif has been discovered in the tilt corrected paleomagnetic directions the presence of both normal and reversed polarities suggests reliability of this shallow and westerly paleomagnetic direction the shallow inclination indicates that the kitakami massif was located at low latitude 5 4 n at 71 62 ma taking into account a reference paleomagnetic pole of the paleocene expected from sikhote alin the kitakami massif was translated northward over 25 in latitude since 65 ma the kitakami massif can be subjected to latitudinal northward motion more than 24 during the last 70 ma when it was transported by push of the moving pacific plate and reached the asian continental margin near sikhote alin later than 30 ma we conclude that the kitakami massif was incorporated into northeast japan at some time between 30 and 22 ma after the cenozoic northward translation

ripple and sandbar dynamics under mid reflecting conditions with a porous vertical breakwater abstract this research is an experimental study of ripple and sandbar dynamics under regular and random waves in partially reflective conditions as part of this study a series of small scale flume experiments were performed that reproduced the growth and migration of the bedforms starting from a flat bed or rippled bed with sediment transport in the bedload regime the results showed that the evolution and dynamics of sandbar geometry were slower processes than the evolution of ripples moreover they were governed by the wave field reflective conditions and sediment characteristics sandbar generation was controlled by the intensity of reflection whereas the location of the crests or deposition and erosion areas was constrained by the phase shift of the reflected waves significant differences were also found between sandbars under regular and random waves sandbars under regular waves showed flat or practically flat troughs in contrast sandbars under random waves were almost uniformly covered by ripples the experimental results showed that the concurrence of ripples and sandbars under partially reflected waves has a spatially modulating effect on ripple characteristics i e growth shape and migration celerity which could not be consistently interpreted by using the classical formulas valid for ripples under progressive waves and or without large scale bedforms this variability was more pronounced for regular waves than for random wave trains larger ripples develop in the nodes of the free surface envelope more or less corresponding to the sandbars crests whereas smaller ripples occurred in the antinodes or sandbars troughs the statistics of ripples geometry and celerity were computed with a sample stratification based on their position in reference to the sandbars in addition they were compared in two energetically equivalent tests with regular and random waves respectively although ripples under random waves had a larger wavelength and height than ripples under regular waves the celerity of migration was comparable our results showed that the sandbars modified the equilibrium geometry of ripples furthermore because of roughness streaming was induced by the highest and longest ripples in the sandbar crests the spatial modulation of the ripple celerity was found to be related to the local lagrangian mass transport velocity which was produced by the quasi standing wave inside the bottom boundary layer at the grain diameter scale

sediment transport and beach morphodynamics induced by free long waves bound long waves and wave groups new laboratory data are presented on the influence of free long waves bound long waves and wave groups on sediment transport in the surf and swash zones as a result of the very significant difficulties in isolating and identifying the morphodynamic influences of long waves and wave groups in field conditions a laboratory study was designed specifically to enable measurements of sediment transport that resolve these influences the evolution of model sand beaches each with the same initial plane slope was measured for a range of wave conditions firstly using monochromatic short waves subsequently the monochromatic conditions were perturbed with free long waves and then substituted with bichromatic wave groups with the same mean energy flux the beach profile changes and net cross shore transport rates were extracted and compared for the different wave conditions with and without long waves and wave groups the experiments include a range of wave conditions e g high energy moderate energy low energy waves which induce both spilling and plunging breakers and different turbulent intensities and the beaches evolve to form classical accretive erosive and intermediate beach states the data clearly demonstrate that free long waves influence surf zone morphodynamics and promote increased onshore sediment transport during accretive conditions and decreased offshore transport under erosive conditions in contrast wave groups which can generate both forced and free long waves generally reduce onshore transport during accretive conditions and increase offshore transport under erosive conditions the influence of the free long waves and wave groups is consistent with the concept of the relative fall velocity h wst as a dominant parameter controlling net beach erosion or accretion free long waves tend to reduce h wst promoting accretion while wave groups tend to increase the effective h wst promoting erosion

differential rotation of the eastern part of southwest japan inferred from paleomagnetism of cretaceous and neogene rocks paleomagnetic directions have been determined on late cretaceous and miocene rocks in the nohi area in the eastern part of southwest japan in an effort to clarify within block deformation of the rotated part of southwest japan twenty two sites in the area are found to have a reliable primary magnetic component through progressive demagnetization tests using thermal and alternating field methods tiltcorrected paleomagnetic data in the nohi area are divided into three stages based on geologic age late cretaceous early miocene 23 15 ma and middle miocene 12 10 ma the formation mean direction of 10 sites obtained from late cretaceous nohi rhyolite is d 17 0 i 49 8 and 95 6 1 neogene rock units underlain by nohi rhyolite show two distinct formation mean directions d 13 0 i 52 7 and 95 7 2 for eight sites of early miocene and d 2 5 i 55 6 and 95 6 6 for four sites of middle miocene differential rotation is proposed between the eastern part of southwest japan including the nohi area and the central part of southwest japan which is known to have rotated clockwise through about 50 around 15 ma the spatial distribution of contemporaneous paleomagnetic data in southwest japan suggests that two differentially rotated parts are connected in the western neighborhood of the nohi area it is concluded that the nohi area had rapidly rotated counterclockwise through 48 relative to the central part of southwest japan between 15 and 12 ma together with previous paleomagnetic data from early miocene rocks in the kanto area which is situated to the east of the nohi area the present results suggest that differential rotation of the eastern part of southwest japan is attributed to the formation of northward cuspate shapes of pre neogene terranes which constitute the framework of the japan arc one probable explanation of the formation of cusps is a crustal indentation caused by the collision of landmasses on the philippine sea plate against the japan arc in the middle miocene

fault mechanics and the kinematics of block rotations in many strike slip tectonic settings large rotations up to 100 of crustal blocks have been inferred from paleomagnetic data these blocks are bounded by sets of parallel faults which accommodate the relative motion between the blocks as regional deformation progresses simple geometrical considerations require that the faults must also rotate in this paper we show that on the basis of mechanical considerations the amount of fault rotation permissible under a stationary stress field is limited to 20 to 45 consequently block rotations that are larger than 40 or 45 require more than one set of accompanying faults to accommodate the block rotation examples of such multiple sets with 40 to 45 between them as predicted by the model were recognized in sistan iran in yerington the lake mead area nevada and in southern california

determination of domain structure in igneous rocks by alternating field and other methods abstract af alternating field demagnetization arm anhysteretic remanent magnetization and strong field hysteresis properties of a large collection of mostly continental igneous rocks are reported here the collection included rocks whose magnetic carriers were believed from previous work to be of one of three types md multidomain sd psd single domain pseudo single domain or a bimodal mixture of md grains e g discrete opaques and sd psd material e g silicate inclusions two series of subaerial basalts with a full range of deuteric oxidation classes included examples of all three classes of behaviour sd psd rocks have relatively hard inflected af decay curves decay rate initially increasing then decreasing md rocks have soft exponential like decay curves and bimodal rocks have a combination of these characteristics relative hardnesses of normalized decay curves of remanences acquired in weak intermediate and strong fields the lowrie fuller test are also distinctively different for the three classes and the results support the theory developed in an accompanying paper 1 that lowrie fuller characteristics are an expression of the shapes of decay curves the lowrie fuller test although its result can be expressed as a numerical parameter is not capable of fine scale classification of domain structure or grain size the shape of the arm induction curve does have a quasi continuous variation with grain size however the parameter ar j rs initial anhysteretic susceptibility normalized to saturation remanence which is easily measured with standard paleomagnetic instrumentation is potentially useful for magnetic granulometry although ar itself was not diagnostic of grain size