melt mantle interaction and melt evolution in the sartohay high al chromite deposits of the dalabute ophiolite nw china the sartohay block of the dalabute ophiolite consists chiefly of mantle harzburgite and lherzolite with minor dunite these rocks host voluminous chromite deposits with lenticular or vein like shapes the podiform chromitites are associated with and cross cut by numerous troctolite dykes chromite in the chromitites has al2o3 23 31 wt tio2 0 29 0 44 wt and cr2o3 contents 45 wt with cr s 100cr cr al 60 typical of high al chromite deposits the host peridotites in sartohay have been texturally and geochemically modified by magmas from which the high al chromitites and mafic dykes formed dunites commonly envelop the podiform chromite bodies and show transitional contacts with the peridotites some of the peridotites and chromitites contain plagioclase that crystallized from impregnated melts the dunite locally grades into troctolite with increasing plagioclase contents as a result of melt impregnation peridotites and dunites show variable ca and al contents and lree enrichment the parental magma of the chromitites was likely tholeiitic in composition derived from partial melting of the asthenospheric mantle in a rising diapir the interaction between this magma and pre existing lithospheric mantle composed of depleted lherzolite would have formed a more silicic tholeiitic magma from which high al chromitites crystallized during this interaction harzburgite and dunite were depleted in modal pyroxene and enriched in some incompatible elements such as al ca and lree due to melt impregnation

on the dimensions of passive ripple marks in the nearshore zone abstract it has been proven on the basis of field observations that the length and height of passive ripple marks in the nearshore zone depend primarily on the sediment grain size d as it turns out the relationships d and d may be approximated with a high degree of accuracy by the equation 17 3 d 1 22 83 5 d 1 08 in which and are expressed in centimeters and d in millimeters it follows that passive ripple dimensions together with grain size distribution of bedload can present only a minimum shear stress at a moment preceding storm damping they will never indicate the storm strength in its maximal development and it is therefore impossible to completely reconstruct the ancient conditions of wave generation by passive ripple mark parameters

holocene sea level history on the rio grande do norte state coast brazil abstract the rio grande do norte state coast northeastern brazil lies in an intraplate region which displays elevated holocene shorelines abandoned tidal flats and other intertidal deposits a field and chronological investigation which used 48 radiocarbon dates on unaltered mollusk shells peats coral reefs and vermetids in living position and death assemblages encrusted on beachrock tidal flat and peat deposits was carried out along two littoral zones one trending east west and the other north south the sea level envelope curve for the region indicates at least one sea level oscillation after the maximum holocene highstand which occurred at 5000 cal yr bp this curve shows notable deviations from the mean sea level curve for the central brazilian coast in the early and mid holocene however in general this envelope curve fits a glacio isostatic prediction for the area a significant deviation from this prediction related to a small sea level oscillation occurred from 2100 to 1100 cal yr bp the comparison between the glacio isostatic prediction and the sea level observation enables us to conclude that local events may have disturbed the sea level record minor holocene sea level oscillations which were mainly associated with climate changes or tectonics and superimposed on a major smooth pattern were observed in south africa and australia but in northeastern brazil neotectonic controlled crustal movements or variation in marine and wind currents could provide the answer the data indicate that local events may have an important role in the history of coastal progradation and retreat

palaeoshorelines of glacial lake kuray chuja south central siberia form sediments and process glacial lake kuray chuja which occupied the kuray and chuja basins during the quaternary period marine isotope stages 2 and 3 left distinct shoreline features around the basin margins at the greatest extent the lake had a surface area of 2951 km2 with wind fetches up to 70 km wind waves constructed erosional erosional accumulative and accumulative strandlines the latter including spits tombolos barrier beaches and offshore bars strandlines range in altitude between c 1600 and 2100 m the range in altitudes demonstrating lake level variations through time the shoreline forms and stratigraphy are detailed particular attention is given to the presence of pocket beaches on rock coasts the alluvial strandlines of which have distinctive alongshore gradients although reasonably ascribed to regional differential tectonic uplift the possibility that the local alongshore gradients are augmented as a process response to alongshore drift of sediment in a sediment starved system of closed coastal cells is explored using a simple numerical model

shoreline deposits and diagenesis resulting from two late pleistocene highstands near 5 and 6 metres durban south africa in exposures of pleistocene rocks on the east coast of south africa eight sedimentary facies were distinguished on the basis of petrology grain size internal structures and field relationships these are interpreted as deposits of surf zone breaker zone swash zone backbeach boulder beach and dune environments three phases of deposition and diagenesis are recognized as a result of the stabilising effect of pre existing coastal facies the deposits from successive sea level stands are stacked vertically in a narrow coast normal strip early cementation prevented erosion of the deposits during subsequent transgressions deposition of subsequent facies took place on an existing coastal dune facies 1 a terrace was cut into this dune at a sea level 4 5 to 5 m above present at this sea level clastic shoreline sediments were deposited which make up the main sedimentary sequence exposed facies 2 7 the steep swash zone coarse grain size and comparison with modern conditions in the study area indicate clastic deposition on a high energy wave dominated microtidal coastline vertical stacking of progressively shallower water facies indicates progradation associated with slightly regressive conditions prior to stranding of the succession above sea level during a subsequent transgression to 5 5 or 6 m above present sea level a second terrace was cut across the existing facies which by then were partly lithified a boulder beach facies 8 deposited on this terrace is indicative of high wave energy and a rocky coastline formed by existing cemented coastal facies comparison with dated deposits from other parts of the south african coast suggest a late pleistocene age for facies 2 8 deposition was terminated by subsequent regression and continuing low sea levels during the remainder of the pleistocene cementation of the facies took place almost entirely by carbonate precipitation the presence of isopachous fibrous cements suggests early cementation of facies 1 2 3 and 4 under marine conditions initially as aragonite which has since inverted to calcite facies 5 6 and 7 are cemented only by equant calcite spar evidence of cementation in the meteoric phreatic and vadose zones lowering of the water table during regression caused the remaining pore space in facies 1 2 3 and 4 to be filled with equant calcite spar decementation in a 130 cm wide zone is attributed to water table shifts associated with the later transgression which deposited facies 8 the vertical stacking of the two depositional sequences may be attributed to rapid cementation of facies 2 3 4 5 6 and 7 under humid subtropical conditions this lithified sequence then acted as a focus for deposition of coarse grained shoreline facies facies 8 during the subsequent transgression

early holocene regressive spit platform and nearshore sedimentation on a glaciofluvial complex during the yoldia sea and the ancylus lake phases of the baltic basin sw finland abstract the depositional history of the virttaankangas plain a fan like enlargement of the large sakylanharju glaciofluvial ridge in sw finland is examined the sakylanharju ridge has been interpreted as having formed as an interlobate esker and the morphology of the virttaankangas plain as representing predominantly subaqueous glaciofluvial to glaciolacustrine deposition this investigation uses new sedimentologic outcrop data with extensive subsurface drilling gpr surveys seismic soundings and gravimetric measurement data provided by groundwater investigations to describe the stratigraphy morphology and depositional history of the plain in contrast to earlier interpretations the results emphasise the role of littoral processes in the origin of the virttaankangas plain the plain is interpreted as having originated during the development of a progradational sequence of spit platform and superimposed nearshore sediments deposited during the glacio isostatic forced regression of the yoldia sea and ancylus lake phases of the baltic basin 9900 9000 14 c bp documented depositional history supports an interval of retarded regression at the beginning of the ancylus lake phase i 9500 9200 14 c bp in the sakylanharju area

progradational gravel beach sequences in a moderate to high energy microtidal marine environment the anatomy of progradational gravel beaches was analysed in two different tectonic settings the strongly subsiding messinian foreland basin of the eastern southern alps and the rising pleistocene marine terraces of the outer margin of the apenninic chain progradation took place near the mouths of fan delta or braid delta distributaries debouching in microtidal landlocked basins palaeo adriatic and palaeo ionian seas a wind wave climate comparable to that of the present day was characterized by periodic intense storm activity most of the beachface progradation is thought to have taken place during the post storm recovery and fair weather stages whereas the impact of storms is mostly recorded by the cutting of erosional surfaces on the beachface and by emplacement of poorly sorted and coarse grained gravels on the shoreface by storm intensified seaward trending flows and behind the highest berms by washover processes analysis of the sequences led to the identification of a number of typical divisions which are differently developed in the two settings compared here the characteristics of the apenninic sequences suggest a strongly variable wind wave climate with periodic changes from a relatively dissipative barred morphology during storms accompanied by strong longshore currents and rip development to a more reflective state typical of recovery and fair weather stages the southern alpine sequences on the other hand are characterized by poor evidence of barred morphology and of longshore currents and widespread effects of shear and gravity sorting in the lower beachface gravels these features indicate a comparatively more reflective average state due to location of beaches along the deeply embayed head of the palaeo adriatic and the very narrow directional width of the incoming wave spectrum which was almost shore normal most of the time in addition to well developed shape zonation of gravels the common presence of wave generated gravel megaripples in the southern alpine sequences indicates the greater influence of long period waves due to the greater available fetch distances in both settings the cyclicity is thought to be genetically related to minor changes of sea level

depositional facies of high energy beach to offshore sequence comparison with low energy sequence a study of the nearshore zone and continental shelf of a high energy coast was made in the ventura port hueneme area of california during the summer of 1974 to investigate depositional facies characteristics and compare them with similar facies from a low energy coastal setting analysis of box cores can cores and vibracores permits recognition of three principal zones 1 nearshore facies backshore to 9 m water depth made up primarily of parallel ripple and cross bedded clean sand bioturbation is only locally significant 2 transition facies 9 to 18 m water depth a zone of fine sand and silty sand characterized by an increase in biogenic over physical sedimentary structures that are commonly preserved as laminated to burrowed beds wave ripple bedding and parallel lamination are important structures in this facies 3 offshore facies 18 m water depth sandy silt is the primary texture and bioturbation is the dominant sedimentary structure remnant parallel lamination is the only physical sedimentary structure present comparison of the results of this study with a previous description of a low energy beach to offshore sequence at sapelo island georgia indicates that the two areas do not differ greatly in their facies or overall vertical sequence of sedimentary structures the principal difference is in the thickness of the three facies the california facies are significantly thicker than their georgia counterparts this difference is in direct response to the role of higher wave energy on the california coast

progradational sequences in miocene shoreline deposits southeastern caliente range california abstract an exceptionally well exposed marine nonmarine transition in middle miocene strata exists in the southeastern caliente range california about 50 individual progradational sequences form a succession that ranges in thickness from approximately 1000 m where predominantly nonmarine to more than 2500 m where predominantly marine paleogeographic evidence in basalt flows near the top of the succession and in overlying fluvial deposits indicates that these middle miocene strata were deposited across a north northwest trending shoreline a complete progradational sequence typically is several meters to a few tens of meters thick and includes strata that represent three intertonguing stratigraphic units individual sequences generally rest on a thin gravel deposit interpreted as a transgressive lag on an erosional surface the gravel is overlain by structureless siltstone or fine grained sandstone deposited at water depths where the rate of faunal mixing exceeded that of production of structures by physical processes these rocks grade upward into bedded fine sandstone deposited closer to shore where physical processes exceeded bioturbation crossbedded lenses of coarse sand or fine gravel in the upper part of this facies suggest the presence of fairly long period surface waves the bedded fine sandstone is sharply ove lain by a cross bedded coarse sandstone facies that is interpreted as a combined offshore bar rip channel surf zone assemblage cross strata dip dominantly offshore suggesting substantial deposition from rip currents a secondary shoreparallel mode of cross strata direction suggests longshore currents produced by surface waves from the northwest the crossbedded coarse grained sandstone grades upward into planar bedded medium grained sandstone that is interpreted as a beach foreshore this facies grades upward through structureless medium grained sandstone into nonmarine or lagoonal red and green mudstone of the caliente formation the middle miocene succession was deposited in a subsiding basin that was otherwise remarkably stable tectonically the position of the strand line differed no more than a few kilometers through a period of 1 to 3 m y the average duration of the transgressive regressive cycles a few tens of thousands of years together with their distribution in groups of three or four in the lower two thirds of the succession is consistent with the pattern of long term climatic cycles produced by periodicity of the earth s solar orbit and may be related to eustatic sea level changes attendant to the development of the antarctic ice cap changes in the pattern of progradation in the upper part of the succession and nearby basaltic eruptions may have been precursors to the onset of movement along th san andreas fault in this area 12 14 m y ago

chromian spinels in highly altered ultramafic rocks from the sartohay ophiolitic melange xinjiang nw china abstract the sartohay ophiolitic melange is located in western junggar xinjiang province nw china which is a major component of the core part of the central asian orogenic belt caob chromian spinels in serpentinite talc schist carbonate talc schist and listwaenite in sartohay ophiolitic melange retain primary compositions with cr of 0 39 0 65 mg 0 48 0 67 and fe3

characteristics and petrogenesis of the pale microgranular masses in ophiolite type chromitites in northern xinjiang abstract massive pale microgranular masses pmms with mafic to ultramafic compositions have been discovered in representative chromite deposits i e the sartohay jingyu tangbale saleinuohai hongguleleng and qingshui deposits and related ophiolite belts based on a detailed study of the occurrence petrology alteration minerals and whole rock geochemistry these pmms can be subdivided into six categories olivine rich vitrobasaltic rocks gabbro diabasic rocks ultramafic rocks tuffaceous pyroclastic rocks skarns rodingites without protolith structure and metasomatites the wall rocks of the pmms are mainly harzburgites subordinate chromitites and lherzolites according to comprehensive analyses of the occurrence wall rock types metasomatic relationships and fabrics the pmms are considered to be xenoliths in ultramafic magma the geochemical characteristics of the associated alteration minerals indicate that altered augite endiopsides and regenerated diopsides grossularite andradites and chrysotiles are dominant in the pmms and the chlorites in the pmms can be divided into four categories brunsvigite pycnochlorites diabantites sheridanite chlorophaeite pycnochlorites and clinochlore penninites the pmms have been mostly or completely subjected to rodingitization and exhibit ca rich and si undersaturated features in terms of major element compositions these characteristics indicate that the pmms were formed by metasomatism during the capture process by peridotites with an import of mafic components dominantly magnesium and an export of felsic components accompanied by serpentinization and chloritization the trace element characteristics of the pmms are obviously influenced by the wall rock type pmms in contact with peridotites generally have higher rare earth element ree and trace element contents than the primitive mantle are characterized by slightly left sloping chondrite normalized ree patterns with weakly positive to negative eu anomalies and exhibit various degrees of sr and k depletions pmms in contact with chromitites have lower ree and trace element contents than the primitive mantle distinctly left sloping chondrite normalized ree patterns with obviously positive eu anomalies and sr and k enrichments the eu sr and k anomalies show an obvious complementary relationship between the peridotites and the captured pmms and metasomatites which is most likely indicative of ca metasomatism by the ultramafic magma the breakdown of clinopyroxene in peridotites liberated ca which accumulated and infused into the metasomatites consequently the results of this study suggest that no less than two different genetic mechanisms might account for the generation of pmms the dominant characteristics of the fabric resulted from the processeses of xenolith formation and metasomatism by ultramafic magma in the early stage whereas the characteristics of the mineral assemblages and geochemical components resulted from rodingitization in the later stage

coesite and clinopyroxene exsolution lamellae in chromites in situ ultrahigh pressure evidence from podiform chromitites in the luobusa ophiolite southern tibet abstract we report in situ petrological evidence of deep mantle origin from podiform chromitites in the luobusa ophiolite southern tibet analytical transmission electron microscopy measurements reveal that chromites in podiform chromitites from the luobusa ophiolite have numerous exsolution lamellae of diopsidic clinopyroxene and coesite which indicate an ultrahigh pressure origin of over 3 gpa 100 km deep the presence of these lamellae coupled with abundant micro inclusions of clinopyroxene requires high solubility of sio2 and cao in the host chromite and suggests a precursor of chromite a cafe2o4 structured high pressure polymorph stable at pressures over 12 5 gpa 380 km deep these nano scale observations and geological occurrence indicate that the mantle peridotite under the tibetan mid ocean ridge was transported from the deep mantle at least 100 km probably more than 380 km deep by the mantle convection it implies that the root of mantle upwelling has a much deeper origin than previously believed

segmentation of the 2010 maule chile earthquake rupture from a joint analysis of uplifted marine terraces and seismic cycle deformation patterns abstract the segmentation of major fault systems in subduction zones controls earthquake magnitude and location but the causes for the existence of segment boundaries and the relationships between long term deformation and the extent of earthquake rupture are poorly understood we compare permanent and seismic cycle deformation patterns along the rupture zone of the 2010 maule earthquake m8 8 which ruptured 500 km of the chile subduction margin we analyzed the morphology of mis 5 marine terraces using lidar topography and established their chronology and coeval origin with twelve luminescence ages stratigraphy and geomorphic correlation obtaining a virtually continuous distribution of uplift rates along the entire rupture zone the mean uplift rate for these terraces is 0 5 m ka this value is exceeded in three areas which have experienced rapid emergence of up to 1 6 m ka they are located at the northern central and southern sectors of the rupture zone referred to as topocalma carranza and arauco respectively the three sectors correlate with boundaries of eight great earthquakes dating back to 1730 the topocalma and arauco sectors located at the boundaries of the 2010 rupture consist of broad zones of crustal warping with wavelengths of 60 and 90 km respectively these two regions coincide with the axes of oroclinal bending of the entire andean margin and correlate with changes in curvature of the plate interface rapid uplift at carranza in turn is of shorter wavelength and associated with footwall flexure of three crustal scale normal faults the uplift rate at carranza is inversely correlated with plate coupling as well as with coseismic slip suggesting permanent deformation may accumulate interseismically we propose that the zones of upwarping at arauco and topocalma reflect changes in frictional properties of the megathrust resulting in barriers to the propagation of great earthquakes slip during the 1960 m9 5 and 2010 events overlapped with the 90 km long zone of rapid uplift at arauco similarly slip in 2010 and 1906 extended across the 60 km long section of the megathrust at topocalma but this area was completely breached by the 1730 m 9 event which propagated southward until carranza both arauco and topocalma show evidence of sustained rapid uplift since at least the middle pleistocene these two sectors might thus constitute discrete seismotectonic boundaries restraining most but not all great earthquake ruptures based on our observations such barriers might be breached during multi segment super cycle events

unraveling sea level variations and tectonic uplift in wave built marine terraces santa maria island chile abstract the architecture of coastal sequences in tectonically active regions results mostly from a combination of sea level and land level changes the objective of this study is to unravel these signals by combining sequence stratigraphy and sedimentology of near shore sedimentary sequences in wave built terraces we focus on santa maria island at the south central chile margin which hosts excellent exposures of coastal sediments from marine isotope stage 3 a novel method based on statistical analysis of grain size distributions coupled with facies descriptions provided a detailed account of transgressive regressive cycles radiocarbon ages from paleosols constrain the chronology between 53 and 31 cal ka bp because the influence of glaciations can be neglected we calculated relative sea level curves by tying the onset of deposition on a bedrock abrasion platform to a global sea level curve the observed depositional cycles match those predicted for uplift rates between 1 2 and 1 8 m ka the studied sedimentary units represent depositional cycles that resulted in reoccupation events of an existing marine terrace our study demonstrates wave built marine terrace deposits along clastic shorelines in temperate regions can be used to distinguish between tectonic uplift and climate induced sea level changes

implications of geochemical and gravity data for the nature of strata beneath the blue ridge piedmont thrust sheet usa abstract the nature of the rock beneath the blue ridge piedmont brp decollement is inferred from a combined geochemical and geophysical study of the grandfather mountain window gmw gravity modeling and geochemistry show the gmw is probably underlain by a duplex of rift related rocks and crystalline basement rather than a duplex composed of carbonate rocks geochemical results suggest that some of the rocks beneath the present day gmw were near peak metamorphic temperatures at 300 ma this age for peak temperatures plus structural relations in the gmw are broadly consistent with the rocks and age of peak temperatures in the pine mountain terrane where the brp decollement is exposed comparison of the gravity profiles for the gmw with other brp structural culminations suggest that they too are underlain by similar rocks this model of a duplex of rift related rocks and crystalline basement implies 40 km less shortening for the southern appalachians than the carbonate duplesx model

a new phase diagram for combined flow bedforms abstract combined flows which involve a combination of unidirectional and wave induced oscillatory flow are omnipresent in coastal and lacustrine environments despite the extensive progress made in understanding the bedforms generated by such flows in past studies there still remains a wide range of unexplored flow conditions where the bedform geometry and hence consequent sedimentary structures have not been explored especially for strong unidirectional flows greater than 0 30 m s 1 and intermediate oscillation periods between 2 and 8 seconds to address this gap in our knowledge the stability of bedforms in a 0 25 mm diameter sand bed was studied under pure unidirectional pure oscillatory and combined flow conditions with oscillation periods of 4 5 and 6 s the maximum orbital velocity uo was varied from 0 00 to 1 00 m s 1 while the unidirectional component uu was varied from 0 to 0 50 m s 1 the experimental data collected under unidirectional flows stronger than 0 30 m s 1 allows expansion of current understanding of the bed configurations for current dominated combined flows where the phase boundary between combined flow bedforms and current ripples was uncertain under these flow conditions ten distinctive bedform states can be recognized no motion nm 2d symmetric ripples 2d sr 3d symmetric ripples 3d sr 3d symmetric dunes 3d sr 3d asymmetric ripples 3d ar 3d quasi asymmetric ripples 3d qar 3d asymmetric dunes 3d ad 3d current ripples 3d cr 3d current dunes 3d cd and upper stage plane bed uspb each of these bedform stages is described quantified and characterized in dimensional phase diagrams a complete re evaluation of the nomenclature for combined flow bedforms is proposed which includes their planform and cross sectional geometry in order to better represent the bed morphologies this new nomenclature also unifies past research on bedforms in both unidirectional and oscillatory flows and thus presents a new synopsis of bedforms developed under such flows one of the main changes proposed that allows integration with the nomenclature used in unidirectional flows is the reclassification of large ripples as dunes furthermore the introduction of the planform and cross sectional geometries as properties by which to classify bedforms leads to the definition of a stable phase space for two dimensional symmetrical ripples and three dimensional quasi asymmetrical ripples these new data and analysis allow proposition of a new unified phase diagram for combined flows

gravelly shoreface deposits a comparison of modern and ancient facies sequences the morphology and dynamics of modern gravel shorefaces are poorly documented this hinders the interpretation of possible ancient counterparts a comparative study of a modern chesil beach england and an ancient baytree member of the cardium formation alberta gravel shoreface shows that the two systems are very similar close to and above sea level with a high about 1 m gravel plunge step lying below plane bedded sands and gravels of the beachface the shoreface at chesil beach is dominated by asymmetrical gravel wave ripples these are oriented offshore near the toe of the shoreface and onshore in shallower depths this may reflect offshore movement during storms and landward reworking during fair weather the baytree member is over 12 m thick and comprises over 80 conglomerate conglomerate is decimetre bedded massive or cross bedded with sets over 60 cm thick produced by gravel bedforms migrating alongshore it is interbedded with discontinuous cm to dm bedded sandstones which may be cross bedded pebble fabric and cross bed orientation both indicate strong alongshore sediment transport near the base of the section pebble orientations suggest that gravel wave ripples developed below the zone of strong longshore flows differences between these two examples may be attributed to different directions of wave approach

reconstruction of paleo wave conditions during the late pleistocene from marine terrace deposits monterey bay california the santa cruz coastal terrace fringes much of the northern monterey bay region california it consists mainly of a regressive sequence of high energy barred nearshore marine sediments deposited during the last sangamonian highstand of sea level this sequence can be sub divided into several depth dependent facies on the basis of paleo current data and vertical sequence of sedimentary structures these include a lower shoreface facies deposited in 10 16 m water depth an upper shoreface facies including both a storm dominated assemblage and a surf zone assemblage deposited in 0 10 m water depth and a foreshore facies deposited in the swash zone up to 3 5 m above high tide the magnitudes of the storm events responsible for depositing these sediments were estimated by calculating paleo wave heights using a variety of criteria e g critical threshold equations breaker depths berm heights in addition the climate and paleogeography during the deposition of these sediments were essentially the same as today allowing the use of present day wave statistics to estimate the frequency of these storm events the largest storms formed offshore flowing currents e g rip wind forced and possibly storm surge ebb currents that resulted in the deposition of approximately 30 of the sediments seaward of the surf zone however the magnitude and frequency of these events are unknown the remaining 70 of the sediment beyond the surf zone was deposited in response to smaller storm waves which were on the average at least 1 6 m high such waves presently occur no more than 15 of the time sediments deposited during fairweather conditions i e the remaining 85 of the time have a low preservation potential and are generally not preserved in this facies in contrast surf zone sediments were deposited by a variety of processes associated with waves whose maximum offshore heights were probably 2 2 m such waves presently occur up to 92 of the time sediments within the swash zone were deposited by waves up to 3 m high the largest of which presently occur approximately 2 of the time most of the sediments were deposited by storms of intermediate magnitude and frequency different facies however appear to preferentially record events of different recurrence intervals in particular surf zone sediments were deposited under relatively small storm and post storm conditions whereas sediments deposited farther offshore record increasingly larger less frequent storm events relatively rare events e g the 100 or 1000 yr events do not appear to have significantly affected sedimentation in these nearshore environments

podiform chromitites of the tari misaka ultramafic complex southwestern japan as mantle melt interaction products petrological and geochemical data for chromian spinel from the tari misaka ultramafic complex southwest japan are discussed in this complex the spinels form a chromitite pod coated by a dunite envelope and are collectively enclosed by clinopyroxene bearing harzburgite chromitite and its dunite envelope are distinctly different from the surrounding harzburgite in terms of the chromian spinel chemistry the ti content is five to ten times higher in spinels of the enveloped chromitite than in those of the harzburgite although the cr ratio cr cr al the atomic ratio for both is almost constant or varies only slightly 0 4 0 5 this eliminates a comagmatic origin for the harzburgite dunite chromitite association spinel chemistry for both major and trace elements is almost the same in the chromitite and its dunite envelope except for the mg ratio and the co and mn contents which have a changed subsolidus as a function of the spinel mode thus the dunite and chromitite could be comagmatic but fractional crystallization of the dunite after or before chromitite deposition is not possible the chemistry of the chromian spinel and the mode of occurrence of the dunite chromitite association are consistent with an origin by interaction of an exotic melt with wall rock harzburgite the dunite may be of replacive origin the exotic melt would react with the harzburgite at the new contact to form dunite and a secondary si rich melt the melt thus formed could mix with a successive inflow of a more primitive melt the mixed melt would be expected to have chromite chromian spinel as the only liquidus phase precipitating chromitite next to the replacive dunite the dunite envelope podiform chromitite is most commonly formed in the mantle beneath island arcs the spread in cr ratios of spinel in podiform chromitites is almost comparable with that of spinel in primitive arc related magmas the presence of chromitite in the upper mantle beneath the japan arcs is consistent with this interpretation

density and seismic velocities of chromitite body in oceanic mantle peridotite density and seismic velocities of the chromitite bodies from the oman ophiolite were calculated and compared with those of oceanic peridotites the oman chromitite is composed of olivine and chromian spinel and the olivine spinel volume ratio varies from 20 to 90 vol chromian spinel in the chromitite is enriched in magnesiochromite component and fo content of olivine ranges from 94 to 96 compressibility of a natural chromian spinel mg 0 77 fe 2 0 23 cr 0 46 al 0 50 fe 3 0 04 o 4 was measured with in situ synchrotron x ray diffraction experiments using a diamond anvil cell up to 10 gpa at 300 k the third order birch murnaghan equation of state yields the isothermal bulk modulus of k t 192 7 gpa its pressure derivative of k t 4 1 and the zero pressure volume of v 0 560 6 2 a 3 based on calculations using present and previous studies the adiabatic bulk modulus of magnesiochromite component was estimated to be 189 gpa using petrological and the mineral physics data density and seismic velocities v v p v s were calculated the seismic velocities are higher than those of peridotites in the oceanic upper mantle and decrease with decrease of the spinel olivine ratio the contrast between chromitite and oceanic peridotite are 5 0 8 1 for v 2 7 4 9 for v s and 4 1 6 7 for v p in the moho transition zone chromitite and 2 6 6 5 for v 1 4 3 3 for v s and 2 2 5 2 for v p in the discordant mantle chromitite this contrast is large enough to be detected by seismological observations and becomes a key to knowing the distributions of chromitite in the oceanic upper mantle

cyclic deposits and hummocky cross stratification of probable storm origin in upper cretaceous rocks of the cape sebastian area southwestern oregon abstract cyclic deposits containing hummocky cross stratification occur in the upper part of the cape sebastian sandstone of bourgeois 1980 a shallow marine transgressive sandstone of late cetaceous age on the southern oregon coast the cycles average 1 6 m in thickness and consist where complete of a lower hummocky cross stratified sandstone a middle planar and ripple bedded sandstone with a shale bed in its middle part and an upper bioturbated sandstone noteworthy features of the hummocky cross stratification include the presence of depositional domes in addition to scoured depressions the absence of significant bedform migration and the presence of a small proportion of dip angles greater than the angle of repose 34 in addition to the large proportion of low 15 deg dip angles the lower stratified fining upward part of the cycle up to the top of the shale bed is interpreted as having accumulated under conditions of initially great but gradually decreasing current velocity and deposition rate the currents probably had a strong oscillatory component and the depositional event is inferred to have been a storm the part of the planar and ripple bedded sandstone above the shale bed was probably deposited during relatively fair weather after the storm but before re establishment of a normal benthic fauna the bioturbated sandstone is interpreted to have been deposited during fair weather or during minor storms separated by long intervals of fair weather

quaternary sedimentology of the rose creek fan delta walker lake nevada usa and implications to fan delta facies models the 3 2 km long rose creek fan delta of west central nevada is prograding from an active rift margin into the 32 m deep walker lake a case study of the forms processes and facies of this fan delta reveals that the proximal and medial zones mainly are of sub aerial origin and the distal zone is of lacustrine origin pebbly to bouldery rock avalanche mounds 100 m thick facies a and muddy to bouldery debris flow levees 0 5 to 2 0 m thick facies b dominate the proximal zone whereas mostly matrix supported cobbly pebbly debris flow lobes 0 1 to 1 0 m thick facies c typify the medial zone surficial pebble lags and gully fills facies d are widespread in both zones but in exposures comprise only partings or lenticles between debris flow units the distal fan delta mainly consists of lakeshore to lake bottom tracts formed by extensive wave reworking of debris flow facies nearshore deposits include erosional cobbly boulder lag beaches facies e pebbly constructional beaches attached at headcuts or on barrier spits facies f pebbly upper shoreface facies g and sandy lower shoreface facies h tracts positioned lakeward of the beach and pebbly landward dipping foresets facies i and backshore pond sand and mud facies j present landward of the spits erosional lag beaches fringe the windward north side of the fan delta front attached constructional beaches characterize the central zone and southward elongating barrier spits typify the leeward south side extending from the zone of greatest projection of the fan delta into the lake shoreline facies asymmetry results from largely unidirectional longshore drift caused by high fetch to the north and minimal fetch to the south combined with the arcuate shape of the fan delta front the spits overlie a platform deposited below common wave base consisting of south east trending cones of pebbly gilbert foresets facies k and sandy toesets facies l typically slumped silt and mud facies m fringe both this platform and lower shoreface sand in deeper water this case demonstrates facies types and patterns that are inconsistent with the widely promoted fan delta facies model having a front consisting of an apron of radially directed gilbert foresets deposited where sub aerial flows enter the lake the rose creek fan delta front instead features a sharp contact between sub aerial and lakeshore facies formed where waves erode sort and redistribute heterogeneous debris flow sediment into the various shallow to deep lake facies gilbert foresets are present only in the lee of the fan delta where sediment moving by longshore drift reaches the brink of the spit front this facies scenario results from the infrequency of fan building events versus nearly constant wind induced waves a scenario that in contrast to the popular gilbert model probably is the norm for fan deltas the level of walker lake and thus the position of wave reworking on the rose creek fan delta fluctuated over a range of 157 m during the last 18 kyr producing complex interfingering between sub aerial and lakeshore facies across a 1700 m wide radial belt typifying a wave modified freestand lacustrine fan delta

composition and textures of chromite and platinum group minerals in chromitites of the western ophiolitic belt from pampean ranges of cordoba argentina abstract chromitite bodies hosted in the neoproterozoic western ophiolitic belt of pampean ranges of cordoba argentina were studied at los congos and los guanacos ultramafic bodies with regard to the composition and textures of the chromite and platinum group minerals primary chromite composition is only preserved in some massive chromitites from the los guanacos ultramafic body and is similar to al rich ophiolitic chromitites suggesting that they crystallized from melts with back arc basin basalts babb affinity in the suprasubduction mantle subsequently these chromitites underwent a prograde metamorphism chromites from chromitites and associated metamorphosed ultramafic rocks show complex replacement and exsolution textures mineral chemistry and texture indicate that the chromite composition records two main metamorphic trends a first trend defined by chromite from massive chromitite in which there is an enrichment in fe3 and fe2 cr remain relatively constant and slightly depleted in al mg a second trend is defined by chromite from disseminated chromitite and metamorphosed dunite and harzburgite in which a fe rich phase is replacing the al rich chromite this alteration trend is characterized by enrichment in the total iron content fe3 fe2 and a strong depletion in al and mg the chemical composition of all analyzed spinels from los guanacos and los congos as plotted on the ternary fe3 cr al diagram correlates well with the cr spinels from the upper amphibolite to granulite facies metamorphism platinum group minerals pgm identified include native osmium laurite erlichmanite irarsite platinum and a number of inadequately identified phases such as an oxide or hydroxide of ru pt and ir ru pt telluride ir ru as se and ir ru ti compounds native osmium was the only pgm which remained unaltered other pgm underwent mineralogical reworking during metamorphism although it is difficult to establish the extent of platinum group element mobilization based on mineralogical observation our results suggest that the ru os ir pgm in the los guanacos and los congos chromitites were modified in situ producing re distribution of these pge on a small scale the presence of rare pt and pge as se minerals was possibly related to remobilization of pt as and se by fluids during the alteration processes

experimental constraints on the formation of the tibetan podiform chromitites abstract the discovery of diamonds and highly reduced minerals in podiform chromitites which have generally been interpreted as magmatic rocks formed from partial melts of upper mantle peridotites under low pressure conditions has raised many questions about the origin of these enigmatic bodies in order to provide experimental constraints on the formation and emplacement of podiform chromititesin ophiolites we carried out a number of multi anvil experiments in the magnesiochromite sio 2 system at temperatures of 1000 1600 c and pressures of 5 15 gpa the experimental results demonstrate that magnesiochromite is stable up to 14 gpa and decomposed into eskolaite cr 2 o 3 together with a quenchable modified ludwigite structured phase fe mg 2 al cr 2 o 5 at higher pressures thus placing an approximate maximum depth for chromite crystallization and or metamorphism this depth corresponds to the top of the mantle transition zone mtz at 410 km the ludwigite structured post chromite phase has significant implications for understanding phase transformations and cr incorporation partitioning of minerals in the mtz on the basis of our results we propose a multi stage model for the formation of podiform chromitites that incorporates the geochemical textural and mineralogical features of these bodies

grain scale plastic deformation of chromite from podiform chromitite of the naga manipur ophiolite belt india implication to mantle dynamics abstract the mantle peridotites of the naga manipur ophiolite belt india host concordant podiform chromitite bodies that preserve various magmatic and deformation structures magmatic structures preserve evidence of a gradual transition from nodular to massive varieties nodular types are least affected by deformation deformation structures restricted mainly in massive types include intracrystalline features of brittle as well as crystal plastic processes within chromite brittle deformation is preserved as grain fracturing and intense microbrecciation along narrow zones forming protocataclasite crystal plastic deformation has generated chromite subgrains and new grains in response to recovery and recrystallization processes subgrains are polygonal in shape and the boundaries between them are commonly straight forming a mosaic with most meeting at triple junctions subgrains are commonly internally zoned and the mosaics formed by them correlate well with the compositional maps subgrains show high al at their cores and high fe at their boundaries in response to differential diffusive chemical re equilibration we discuss how this compositional resetting related to deformation is significant in various geologic studies related to tectonic setting and thermobarometric evolution of an area deformation mechanisms are likely to have started with crystal plastic processes and later switched over to the brittle regime the preservation of all grain scale deformation structures in the chromitite bodies of the naga manipur ophiolite belt is suggestive of mantle dynamics vertical accretion and horizontal movement in particular

compositions of chromite associated minerals and parental magmas of podiform chromite deposits the role of slab contamination of asthenospheric melts in suprasubduction zone environments abstract podiform chromitites in the mantle sections of ophiolites belong to either high cr metallurgical or high al refractory varieties their highly variable compositions are reflected by different cr s 100cr cr al and cr2o3 and al2o3 contents of the chromite falling in the boninitic and morb fields respectively parental magmas of high cr chromitites have higher sc mn co and ni and lower ti v zn and ga concentrations than morb melts their trace element patterns are similar to those of boninites except for ni and zn in contrast high al chromitites have parental magmas characterized by generally flat morb normalized patterns showing slight enrichments in v mn and co and depletion in ni and zn regardless of their compositions both types of chromitites have chondrite normalized platinum group element pge patterns showing enrichment in ipge and depletion in ppge a variety of platinum group minerals are typically present in both types occurring either as euhedral inclusions or along fractures in chromite grains these minerals have a wide span of re os isotopic compositions reflecting a variety of origins there is a diversity of unusual minerals and mineral inclusions associated with podiform chromitites the presence of these minerals suggest that grains of amphibolite plagioclase amphibole and zircon and eclogite coesite kyanite and garnet were present in the magmas from which chromite crystallized multiphase mineral inclusions demonstrate that podiform chromitites form from hydrous mafic magmas in suprasubduction zone environments ssz we propose a new model in which chromitite formation was involved in intra oceanic subduction zones initiated in closing oceanic basins continued subduction carries oceanic and possibly continental crustal materials to deep levels where they are metamorphosed under greenschist amphibolite and eclogite facies conditions the tearing and breakoff of the subducted slab possibly along the transitional contact between amphibolites and eclogites create a slab window through which the underlying asthenosphere rises and melts to generate cr rich mafic magmas these upward migrating magmas pass through the subduction zone and assimilate the subducted slab as a result of slab contamination these magmas become more siliceous more oxidized and more hydrous rapidly triggering chromite crystallization minute grains of chromite are suspended in the upward moving magmas as they migrate through the overlying metasomatized mantle wedge such chromite bearing magmas eventually deposit chromite in magma conduits in the uppermost mantle close to the moho where the upward flow changes from vertical to subhorizontal and velocity is greatly reduced highly reduced and ultrahigh pressure minerals including diamonds are reported in literature both in podiform chromitites and host peridotites of ophiolites some of these minerals in association with host peridotites may have been brought by the uprising asthenosphere at mid oceanic ridges due to the mantle convection it is also possible that some diamonds may have formed in the subducted slab below about 150 km some minerals of subducted slabs are preserved because they are encapsulated in chromite grains where they are protected from the ssz melts some of these ssz mantle wedges are emplaced on land to become podiform chromitite bearing ophiolites

storm generated sedimentary structures in subtidal marine facies with examples from the middle and upper ordovician of southwestern virginia abstract the role of storms is of major importance in forming stratification in open shelf facies though storm processes on modern shelves are not fully understood enough is known to see how sediments are influenced storms transport sand away from coastal areas and suspend and transport sand and mud on the open shelf when wave base is lowered storms generate winnowed lag deposits of shells or gravel but coarser sediment and shells of megafauna are little transported except in very near shore environments the martinsburg formation middle and upper ordovician of southwestern virginia was deposited on a storm influenced open marine platform in contrast to the classic turbidite flysch basin of the martinsburg in the great valley of virginia to the northeast deposition of most martinsburg sediments was due to storms sediments deposited during single storm events occur in characteristic fining upward sequences 1 to 80 cm thick in both carbonate and terrigenous clastic dominated areas of the platform individual storm deposits consist of a sharp erosional base overlain by a couplet of whole fossil packstone and laminated calcarenite siltite or quartzose siltstone to very fine sandstone which is gradational to shale packstones are typically intraclastic have shells aligned parallel o bedding and convex up often with adhering or contained mud and have abundant infiltration textures such as cement filled shelter voids packstones grade abruptly to a laminated bed with horizontal plane lamination large and small scale in phase undulatory lamination and wave ripple cross lamination commonly occurring in ordered vertical sequences laminated beds contain escape burrows are weekly graded and have irregularly mounded upper bed surfaces laminated beds grade upward to shale containing horizontal branching burrows and marine fossils the faunal content of the fining upward sequences matches that of the interbedded shale storm generated beds vary greatly in thickness laterally and frequently pinch out completely fining upward sequences formed by scouring winnowing and suspension of the sand and mud during the height of the storm to form the erosional base and autochthonous lag of whole fossils storms preferentially preserve whole fossils rather than fragmenting them infiltration of finer sediment into the lag deposit and deposition of the laminated bed occurred as the storm waned laminated beds are molded into a distinctive suite of sedimentary structures by wave generated currents the shale represents deposition of finest storm suspended material and continued hemipelagic sedimentation similar sequences are widely distributed in the geologic record variability of storm generated sequences can be related to changing water depth thus storm deposits may be useful in basin analysis to estimate relative water depths and trace transgressive and regressive events

wave formed structures and paleoenvironmental reconstruction clifton h e and dingier j r 1984 wave formed structures and paleoenvironmental reconstruction in b greenwood and r a davis jr editors hydrodynamics and sedimentation in wave dominated coastal environments mar geol 60 165 198 wave formed sedimentary structures can be powerful interpretive tools because they reflect not only the velocity and direction of the oscillatory currents but also the length of the horizontal component of orbital motion and the presence of velocity asymmetry within the flow several of these aspects can be related through standard wave theories to combinations of wave dimensions and water depth that have definable natural limits for a particular grain size threshold of particle movement and that of conversion from a rippled to fiat bed indicate flow velocity limits the ratio of ripple spacing to grain size provides an estimate of the length of the near bottom orbital motion the degree of velocity asymmetry is related to the asymmetry of the bedforms though it presently cannot be estimated with confidence a plot of water depth versus wave height h h diagram provides a convenient approach for showing the combination of wave parameters and water depths capable of generating any particular structure in sand of a given grain size natural limits on wave height and inferences or assumptions regarding either water depth or wave period based on geologic evidence allow refinement of the paleoenvironmental reconstruction the assumptions and the degree of approximation involved in the different techniques impose significant constraints inferences based on wave formed structures are most reliable when they are drawn in the context of other evidence such as the association of sedimentary features or progradational sequences

unexpectedly high pge chromitite from the deeper mantle section of the northern oman ophiolite and its tectonic implications unusually high platinum group element pge enrichments are reported for the first time in a podiform chromitite of the northern oman ophiolite the chromitite contains 1 5 ppm of total pge being highly enriched in the ipge subgroup ir os and ru and strongly depleted in the ppge subgroup rh pt and pd its platinum group minerals pgms are classified into three types arranged in order of abundance 1 sulphides os rich laurite laurite erlishmanite solid solution and an unnamed ir sulphide 2 alloys os ir alloy and ir rh alloy and 3 sulpharsenides irarsite and hollingworthite the high pge concentrations are observed only in a discordant chromitite deep in the mantle section which has high cr 0 7 spinel with an olivine matrix all the other types of chromitite in the moho transition zone mtz and concordant pods in the deeper mantle section are poor in pges and tend to have spinels with lower cr up to 0 6 this diversity of chromitite types suggests two stages of magmatic activity were responsible for the chromitite genesis in response to a switch of tectonic setting the first is residual from lower degree partial melting of peridotite which produced low cr pge poor chromitites at the moho transition zone and to a lesser extent within the mantle possibly beneath a fast spreading mid ocean ridge the second chromitite forming event involves higher degree partial melting which produced high cr pge rich discordant chromitite in the upper mantle possibly in a supra subduction zone setting

nearshore wave induced cyclical flexing of sea cliffs 1 evolution of a tectonically active coast is driven by geomorphically destructive energy supplied by ocean waves wave energy is episodic and concentrated sea cliffs are battered by the geomorphic wrecking ball every 4 25 s we measure the response of sea cliffs to wave assault by sensing the ground motion using near coastal seismometers sea cliffs respond to waves in two distinct styles high frequency motion 20 hz reflects the natural frequency of the sea cliff as it rings in response to direct wave impact low frequency motion in the 0 1 0 05 hz 10 20 s band consistently agrees with the dominant nearshore wave period integrating microseismic velocities suggests 50 m and 10 m displacements in horizontal and vertical directions respectively displacement ellipsoids exhibit simultaneous downward and seaward sea cliff motion with each wave video footage corroborates the downward sea cliff flex in response to the imposed water load on the wave cut platform gradients in displacement amplitudes documented using multiple seismometers suggest longitudinal and shear strain of the flexing sea cliff on the order of 0 5 4 strains during each wave loading cycle as this sea cliff flexure occurs approximately 3 million times annually it has the potential to fatigue the rock through cyclical loading local sea cliff retreat rates of 10 cm yr imply that a given parcel of rock is flexed through roughly 109 cycles of increasing amplitude before exposure to direct wave attack at the cliff face

beach and nearshore facies southeast australia abstract the morphology texture and facies sequence on seven sand beaches located in low moderate and high wave energy microtidal environments in southern australia were investigated using box coring and scuba observations systematic variation in facies occur both within and between the beaches low energy reflective beaches are limited in lateral and vertical extent and in facies to beach laminations separated by coarse step deposits from finer nearshore cross lamination facies moderate energy intermediate beaches characterised by rip circulation possess increasingly wider surfzones with ridge and runnel and bar trough facies separating the beach and step facies from the more extensive nearshore sequence high energy dissipative beaches may have 500 m wide surfzones containing multiple bar trough topography fine beach laminations with backwash structures grade into 4 5 m thick bar trough sequences then the extensive nearshore facies as wave energy increases from low h b h b 2 5 m the vertical extent of the beach to nearshore sequence increases from

sedimentology of rocky shorelines 1 a review of the problem with analytical methods and insights gained from the hulopoe gravel and the modern rocky shoreline of lanai hawaii abstract hypotheses advanced concerning the origin of the pleistocene hulopoe gravel on lanai include mega tsunami abandoned beach multiple event rocky shoreline and for parts of the deposit native hawaiian constructions and degraded lava flow fronts uplift of lanai shorelines has been suggested for deposits occurring up to at least 190 m these conflicting hypotheses highlight problems with the interpretation of coarse gravel deposits containing marine biotic remains the geological records of the processes implied by these hypotheses should look very different discrimination among these or any other hypotheses for the origins of the hulopoe gravel will require careful study of vertical and lateral variations in litho and biofacies facies architecture contact relationships and stratal geometries of this deposit observations of modern rocky shorelines particularly on lanai adjacent to hulopoe gravel outcrops have shown that distinctive coarse gravel facies are present several of which occur in specific geomorphic settings tectonic isostatic and eustatic changes which cause rapid shoreline translations on steep slopes favour preservation of former rocky shorelines and associated sedimentary deposits both above and below sea level the sedimentary record of those shorelines is likely to be complex the modern rocky shoreline sedimentary environment is a hostile one largely neglected by sedimentologists a range of high energy processes characterize these shorelines long period swell tsunami and storm waves can erode hard bedrock and generate coarse gravel they also erode older deposits depositing fresh ones containing mixtures of materials of different ages additional gravelly material may be contributed by rivers draining steep hinterlands to fully evaluate rocky shoreline deposition in the broadest sense for both the hulopoe gravel and other deposits sedimentary facies models are needed for rocky shorelines occurring in a range of settings recognition and description of rocky shoreline deposits are crucial for correctly interpreting the geological history of oceanic and volcanic arc islands for distinguishing between ancient tsunami and storm deposits and for interpreting coarse grained deposits preserved on high energy coasts of continents problems include not only the absence of appropriate sedimentary facies models linking rocky shoreline deposits and environments but also until recently lack of a systematic descriptive scheme applicable to coarse gravel deposits generally two complementary methods serve to integrate the wide range of bed and clast attributes and parameters which characterize complex coarse gravel deposits the composition and fabric caf method has a materials focus providing detailed description of attributes of the constituent clasts petrology the proportions of gravel sand and mud and the ways in which these materials are organized the sedimentary facies model building fmb method emphasizes the organization of a deposit on a bed by bed basis to identify facies and infer depositional processes the systematic use of a comprehensive gravel fabric and petrography log gfpl in conjunction with detailed vertical profiles provides visual representations of a range of deposit characteristics criteria useful for distinguishing sedimentary facies in the hulopoe gravel are grain size modes amount of matrix bed geometry sedimentary structures bed fabric and clast roundness

modern shallow water graded sand layers from storm surges bering shelf a mimic of bouma sequences and turbidite systems abstract a sequence of graded sand layers interbedded with mud extends offshore over 100 km from the yukon delta shoreline across the flat shallow 100 kin such shallow water graded layers off lobate deltas may be distinguished from similar deep water turbidites by 1 the predominance of trough cross lamination perhaps resulting from wave oscillation effects in the proximal part of the system and 2 gradation to common shallow marine fossils bioturbation and storm lag layers n distal areas

recognition and hydrologic significance of passive margin updip sequences an example from eocene coastal plain deposits u s a abstract sequence stratigraphic interpretations are extended to a passive margin updip setting using sedimentological observations from cores and well to well correlations in eocene coastal plain strata of south carolina in the succession studied formation contacts tend to follow sequence boundaries even as lithologies vary within individual sequences sequence boundaries at the base of the congaree formation and near the top of the tinker formation formed during relative sea level fall associated with second order global cycles these boundaries can be recognized clearly in both downdip and updip areas of the passive margin three other sequence boundaries which occur at the base and top of the warley hill formation and within the tinker formation are interpreted as formed during relative sea level fall associated with third order global cycles hydrostratigraphic units in the strata studied conform to depositional patterns that were controlled by changes in sea level and sediment influx sand of the gordon aquifer comprises a thick aggradational succession deposited predominantly in the nearshore shelf environment as accommodation increased during relative rise in sea level because of high rates of sedimentation in the proximal setting aggradational stacking of nearshore sands may be common to other updip marine strata in accommodation dominated regimes the overlying gordon confining unit consists of marine shelf clay and carbonate sediment deposited in response to maximum transgression during subsequent relative sea level fall accumulation of shoreface deposits produced a progradational succession that is represented by the lower part of the upper three runs aquifer unlike formation contacts boundaries between the clastic aquifers and confining units do not follow the third order sequence boundaries because of lithologic variations within the sequences an increasing degree of breaching through the gordon confining unit which results in downward contaminant migration into the gordon aquifer occurs in the updip direction because of nearly continuous sand deposition near the base of the interval studied contaminants migrate locally through the crouch branch confining unit because of erosional breaches formed by scour during sea level lowstand in this example and in other strata deposited in an updip passive margin setting the extent to which confining units are breached at sequence boundaries decreases in the downdip direction resulting in better protection of the adjacent aquifer

hydrodynamic evolution from quartz microtextures of a beach ridge in qinghai lake china abstract beach ridges are landforms that exist on beach shorelines and can supply abundant information regarding palaeoenvironments to better understand the hydrodynamic processes of beach ridges a quartz microtexture analysis was carried out in this study the microtextural features of a total of 1063 quartz grains from seven beach ridge samples and eight reference samples from rivers a dune and a nearby beach were observed and analysed by scanning electron microscopy the qualitative and quantitative results suggest that the quartz microtextures of the beach ridge samples present more fresh surfaces and percussion marks than the river samples but less angularity the upper sequence samples from the beach ridge present higher values of fresh surfaces and percussion marks and lower dissolution than the lower sequence samples a cluster analysis shows that the hydrodynamic conditions of qinghai lake underwent pronounced changes from weak to strong and then to weak at the present time furthermore quantitative analyses indicate that the beach ridge and river sedimentary environments can be distinguished through the microtextural features of the 250 125 m size fraction however more grain size fractions should be observed and analysed to interpret the hydrodynamic conditions the quartz microtextural analysis of beach ridges may be an effective method reflecting the palaeohydrodynamic conditions

stratigraphy and structure of the indus suture in the lower swat pakistan nw himalaya abstract we present a geological map detailed structural description and new subdivisions of the indus suture zone lithologies in northeast pakistan lower swat region the indus suture zone is a dominantly fore arc related assemblage obducted onto the indian plate initial southward thrusting was followed by the reactivation of the indus suture as a ductile brittle normal fault significant strike slip faulting may have taken place at this stage later brittle reverse faults demonstrate that shortening outlasted normal faulting the comparison of the structural evolution of the indus suture zone and the indian plate shows that both terrains were sharing the deformational history possibly since the earliest stage of collision the lower swat area records a full orogenic cycle from early rifting through continent arc collision to orogenic collapse we present a geodynamic model that integrates all these elements

a system for measuring bottom profile waves and currents in the high energy nearshore environment abstract a new data acquisition system capable of measuring waves currents and the nearshore profile in breaking waves as high as 5 m has been developed and successfully field tested components of the mechanical system are a sled carrying a vertical mast a double drum winch placed landward of the beach and a line that runs from one drum of the winch around three blocks which are the corners of a right triangle to the other drum of the winch the sled is attached to the shore normal side of the triangular line arrangement and is pulled offshore by one drum of the winch and onshore by the other the profile is measured as the sled is towed along the shore normal transect using an infrared rangefinder mounted landward of the winch and optical prisms mounted on top of the sled s mast a pressure sensor and two axis electromagnetic current meter are mounted on the frame of the sled these data are encoded on the sled and telemetered to a receiving recording station onshore preliminary results suggest that near bottom offshore flowing currents during periods of high energy swell are important in forcing changes to the configuration of the nearshore profile

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

geomorphology and tectonics of uplifted coasts new chronostratigraphical constraints for the quaternary evolution of tyrrhenian north calabria southern italy abstract the tyrrhenian coastal sector of north calabria stretching between torre s nicola and the lao river belongs to the inner extensional sector of the neogene apennines thrust belt it is characterised by a stair of quaternary marine and fluvial terraces representing the geomorphic response to the interaction between the quaternary sea level fluctuations and the regional trend of tectonic uplift experienced by the margins of the tyrrhenian back arc basin since the last century several authors studied the north calabria coasts where the flight of terraces preserves significant marine and continental successions and proposed several paleo geomorphological and tectonic reconstructions in this paper we present a new stratigraphic and morphostructural setting of the north calabria coasts based on both chronostratigraphical constraints obtained from marine deposits and detailed geomorphological analysis a ten order stair of marine terraces stepping between 240 and 0 m a s l was recognized and time constrained by the age of the fornaci s nicola marine succession which was ascribed by integrated paleoecological biostratigraphical and paleomagentic analyses to the early middle pleistocene mis 19 15 in particular the 240 200 and 160 m a s l high strandlines were ascribed to the early pleistocene and the ones between 100 and 15 m a s l to the middle pleistocene the total amount of the vertical motion experienced by the studied area was estimated and evaluation of the average rates of uplift for the middle and late pleistocene times were also given considering the elevation a s l of the oldest terraces a tectonic uplift of at least 240 m was calculated for the north calabria coasts since the early pleistocene times 100 m of which gained from the beginning of the middle pleistocene on the other hand the 8 m high late pleistocene strandlines display a negligible vertical displacement affecting the area during the last 130 ka the entire staircase of terraces preserves a record of slowing down in the rate of uplift which attained an average value of 0 15 mm year during the middle pleistocene

the role of summer monsoon typhoons in the formation of nearshore coarse grained ripples depression and sand ridge systems along the shimizu coast suruga bay facing the pacific ocean japan abstract coarse grained ripples cgrs develop within the seafloor depression sand ridge systems along the shimizu coast in the northwestern part of suruga bay facing the pacific ocean central japan in this paper we analyze data from high resolution bathymetry seafloor observation by an underwater video camera and high resolution seismic surveys and seafloor trenching of shallow strata obtained between 2005 and 2007 to describe their geomorphological and sedimentological characteristics in detail and to examine the formative processes and maintenance of the systems in water depths of 5 30 m cgrs occur in seafloor depressions that are approximately 40 70 cm deeper than the surrounding sandy seafloor in many cases the ripples develop in depressions between shore normal sand ridges composed mainly of fine sand

estimating palaeowind strength from beach deposits abstract the geological record of past wind conditions is well expressed in the coarse gravel cobble and boulder beach deposits of quaternary palaeolakes in the great basin of the western usa and elsewhere this paper describes a technique using the particle size distribution of beach deposits to reconstruct palaeowind conditions when the lakes were present the beach particle technique bpt is first developed using coarse beach deposits from the 1986 87 highstand of the great salt lake in utah combined with instrumental wind records from the same time period next the bpt is used to test the hypothesis that wind conditions were more severe than at present during the last highstand of lake lahontan 13 ka which only lasted a decade or two at most the largest 50 beach clasts were measured at nine beach sites located along the north west and south sides of antelope island in the great salt lake all of which formed in 1986 87 at these sites the largest clast sizes range from 10 to 28 cm b axis and fetch lengths range from 25 to 55 km nearshore wave height was calculated by assuming that the critical threshold velocity required to move the largest clasts represents a minimum estimate of the breaking wave velocity which is controlled by wave height shoaling transformations are undertaken to estimate deep water wave heights and ultimately wind velocity wind estimates for the nine sites using the bpt range from 6 5 to 17 4 m s 1 which is in reasonable agreement with the instrumental record from salt lake city airport the same technique was applied to eight late pleistocene beaches surrounding the carson sink sub basin of lake lahontan nevada using the bpt estimated winds for the eight sites range from 9 7 to 27 1 m s 1 the strongest winds were calculated for a cobble boulder beach with a fetch of 25 km instrumental wind records for the 1992 99 period indicate that wind events of 9 12 m s 1 are common and that the strongest significant wind event 9 m s 1 for 3 h reached an average velocity of 15 5 m s 1 based on this preliminary comparison it appears that the late pleistocene western great basin was a windier place than at present at least for a brief time

metallogeny of the chrome ores of the xerolivado skoumtsa mine vourinos ophiolite greece implications on the genesis of ipge bearing high cr chromitites within a heterogeneously depleted mantle section abstract chrome ore deposits comprise less than 1 of the volume of a pervasively serpentinized dunite body 3 5 km 3 that constitutes the xerolivado skoumtsa mine of the vourinos ophiolite in northwestern greece ores have been examined to aid determination of their geological mode of occurrence their mineralogy and mineral chemistry cr spinel and olivine and platinum group element pge geochemistry the ore bodies are highly deformed and of the schlieren type where cr spinel rich and serpentine after olivine rich layers 1 20 cm thick alternate the cr spinel displays a limited range in cr 100 cr cr al atomic ratio 77 85 and tio 2 content 0 05 0 22 wt the mg 100 mg mg fe 2 of cr spinel shows a wider variation 52 74 indicating that subsolidus mg sp fe 2 ol re equilibration occurred remnant fresh olivine in the serpentine rich layers is typical forsterite fo 100 mg mg fe 2 93 95 the cr rich chromitite ores have total pge and au abundances that range between 74 3 and 205 ppb they show a general enrichment in ir and ru over ppge rh pt and pd resulting mostly in a negatively sloping c1 chondrite normalized pge profile with a quite strong ru peak field observations indicate that the schlieren banding of the deformed ore bodies is a tectonometamorphic feature acquired within ductile deformation of the ophiolitic slab geochemical calculations demonstrate that the parental melts of the xerolivado skoumtsa high cr chromitites were boninitic their high ru content and variation in cr sp values indicate a polygenetic origin from geochemically similar but spatially distinct melt inputs these melts originated within a hydrated mantle wedge beneath a forearc basin within an evolving lithospheric slab we emphasize that the pge budget of the xerolivado skoumtsa chromitites was not inherited from interactions of the migrating melts with their parental harzburgites but it is an intrinsic feature of the deep seated and heterogeneously depleted mantle source of these magmas

sedimentology of gravelly lake lahontan highstand shoreline deposits churchill butte nevada usa abstract gravelly shoreline deposits of the latest pleistocene highstand of lake lahontan occur in pristine depositional morphology and are exposed in gravel pits along churchill butte in west central nevada four environments differentiated at this site are alluvial fan colluvium lakeshore barrier spit lake lower shoreface spit platform and lake bottom lakeshore deposits abut along erosional wave headcuts either unsorted muddy to bouldery colluvium fringing churchill butte bedrock or matrix supported cobbly and pebbly debris flow deposits of the silver springs fan the lakeshore barrier spit is dominated by granule pebble gravel concentrated by wave erosion of the colluvial and alluvial fan facies the lakeward side of the barrier consists of beachface deposits of well sorted granules or pebbles in broad planar beds 1 10 cm thick and sloping 10 15 they interfinger downslope with thicker 10 25 cm and less steep 5 10 lakeward dipping beds of fine to medium pebble gravel of the lake upper shoreface interstratified with the latter are 10 40 cm thick sets of high angle cross beds that dip southward alongshore higher angle 15 20 landward dipping foresets of similar texture but poorer sorting comprise the proximal backshore on the landward side of the barrier they were deposited during storm surges that overtopped the barrier berm gastropod rich sand and mud also deposited by storm induced washover are found landward of the gravel foresets in a 15 m wide backshore pond algal stromatolites ostracodes and diatoms accumulated in this pond between storm events the lake lower shoreface extending from water depths of 2 to 8 m consists of a southward prograding spit platform built by longshore drift the key component of this platform is large scale sandy pebble gravel in 16 southward dipping gilbert foresets that grade at a water depth of about 6 7 m to 4 dipping sandy toesets a shift from bioturbated lower shoreface sand and silt to flat and laminated lake bottom silt and mud occurs between water depths of 10 40 m and over a shore normal distance of 250 m this lake bottom mud facies unlike the others is areally expansive

evidence for the emplacement of ca 3 0 ga mantle derived mafic ultramafic bodies in the ukrainian shield abstract the archean bedrock of the ukrainian shield is divided into western and central blocks by a n w trending tectonic zone known as the golovanevsk suture zone within this zone there are numerous mafic ultramafic bodies including the chromitite bearing lipovenki and kapitanov massifs the chromitites of these massifs possess mineralogical and textural features and platinum group element systematics similar to those typically observed in ophiolitic podiform chromitites although there is no field evidence for an ophiolitic structure the geochemical evidence strongly suggests an origin in the oceanic lithosphere the re os ratios of the chromites and whole rock chromitites are extremely low and consequently their 187 os 188 os ratios have increased little since crystallization osmium isotope model ages indicate formation at approximately 3 0 ga suggesting that the massifs represent portions of the archean oceanic lithosphere

origin of podiform chromite deposits by magma mingling abstract i have oversaturated the immiscible system sio2 al2o3 feo k2o with fecr2o4 to study the fractionation of chromite between conjugate siliceous and fayalitic melts although both melts are oversaturated with chromite chromite only nucleates in the fayalite rich melt where the crystal melt interfacial energy sl is lowest in less than three days at 1150 c all excess chromium in the bulk composition is concentrated as cumulus chromite in the fayalitic melt pools producing nodular cumulate textures as observed in podiform chromite ore when these results are applied to the lithospheric mantle podiform chromite deposits may form when droplets of olivine normative high pressure low viscosity melt mingle with siliceous low pressure more viscous melt in shallow magma conduits it is inferred from the experimental analogue that chromite only nucleates in the melt where sl is lowest which in the mantle would be the high pressure melt the low pressure melt only serves as the diffusive chromium reservoir the richest chromite ores form when the volume ratio of the melt nucleating chromite is small relative to the ambient melt

storm related sedimentation influenced by coastal configuration in the stratigraphic record of a tectonically active shelf upper pleistocene le castella terrace italy abstract analysis of patterns of coastal circulation and sediment dispersal is an essential step for the study of controlling factors influencing the long term dynamics of coastal systems modern settings offer the possibility to monitor relevant parameters over relatively short time spans however geological examples complement this perspective by providing a time averaged record where longer trends and stratigraphically significant processes can be evaluated this study investigates the shallow marine deposits of le castella terrace upper pleistocene southern italy to document how patterns of circulation influenced by coastline configuration can affect the preserved millennial scale depositional record of a progradational shoreline system the regressive portion of the le castella terrace deposits developed during a relative sea level highstand and falling stage consists of a progradational wedge mainly composed of redistributed skeletal particles of a coeval shallow water carbonate factory preservation of the morphology of the paleocoastline and abundant current related sedimentary structures allow reconstruction of the predominant sediment dispersal dynamics responsible for the formation of this sedimentary wedge facies and paleocurrent analysis indicate offshore and alongshore sediment transport modes consistent with coastal circulation driven by storms normally incident to the shoreline and a sharp change in coastline orientation this coastal inflection influenced circulation patterns causing flow separation and eddy formation in the lee of the curved coastline syndepositional tectonic deformation also affected the architecture of the preserved deposits controlling the nucleation and development of a clinostratified body and determining localized lateral stratigraphic variability this study illustrates how transient but recurrent circulation patterns associated with changes in coastal orientation and related to high energy storm events can leave a predominant signature in the stratigraphic record of microtidal shallow marine successions

seismic stratigraphy and late quaternary shelf history south central monterey bay california abstract the south central monterey bay shelf is a high energy wave dominated tectonically active coastal region on the central california continental margin a prominent feature of this shelf is a sediment lobe off the mouth of the salinas river that has surface expression high resolution seismic reflection profiles reveal that an angular unconformity quaternary underlies the entire shelf and separates undeformed strata above it from deformed strata below it the salinas river lobe is a convex bulge on the shelf covering an area of approximately 72 km 2 in water depths from 10 to 90 m it reaches a maximum thickness of 35 m about 2 5 km seaward of the river mouth and thins in all directions away from this point adjacent shelf areas are characterized by only a thin 2 to 5 m thick and uniform veneer of sediment acoustic stratigraphy of the lobe is complex and is characterized by at least three unconformity bounded depositional sequences acoustically these sequences are relatively well bedded acoustic foresets occur within the intermediate sequence and dip seaward at 0 7 to 2 0 comparison with sedimentary sequences in uplifted onshore pleistocene marine terrace deposits of the monterey bay area which were presumably formed in a similar setting under similar processes suggests that a general interpretation can be formulated for seismic stratigraphic patterns depositional sequences are interpreted to represent shallowing upwards progradational sequences of marine to nonmarine coastal deposits formed during interglacial highstands and or during early stages of falling sea level acoustic foresets within the intermediate sequence are evidence of seaward progradation acoustic unconformities that separate depositional sequences are interpreted as having formed largely by shoreface planation and may be the only record of the intervening transgressions the internal stratigraphy of the salinas river lobe thus suggests that at least several late quaternary regressions and transgressions may be recorded under the present shelf this record may represent the last major eustatic cycle of sea level an interval not observed in uplifted onshore pleistocene marine terraces

distribution of platinum group elements and os isotopes in chromite ores from mayari baracoa ophiolitic belt eastern cuba the mayari baracoa ophiolitic belt in eastern cuba hosts abundant chromite deposits of historical economic importance among these deposits the chemistry of chromite ore is very variable ranging from high al cr 0 43 0 55 to high cr cr 0 60 0 83 compositions platinum group element pge contents are also variable from 33 ppb to 1 88 ppm and corre late positively with the cr of the ore bulk pge abundances correlate negatively with the pd ir ratio showing that chromite concentrates mainly os ir and ru which gives rise to the characteristic negatively sloped chrondrite normalized pge patterns in many chromitites this is consistent with the mineralogy of pges which is dominated by members of the laurite erlichmanite solid solution series rus2 oss2 with minor amounts of irarsite irass os ir alloys ru os ir fe ni alloys ni rh as and sulfides of ir os rh cu ni and or pd measured 187 os 188 os ratios from 0 1304 to 0 1230 are among the lower values reported for podiform chromitites the 187 os 188 os ratios de crease with increasing whole rock pge contents and cr of chromite furthermore cos values of all but one of the chromitite samples are negative indicating a subchondiritc mantle source cos decrease with increasing bulk os content and decreasing 187 re 188 os ratios these mineralogical and geochemical features are interpreted in terms of chromite crystallization from melts varying in composition from back arc basalts al rich chromite to boninites cr rich chromite in a su prasubduction zone setting chromite crystallization occurs as a consequence of magma mixing and assimi lation of preexisting gabbro sills at the mantle crust transition zone cr pge abundances and bulk os isotopic composition of chromitites are determined by the combined effects of mantle source heterogeneity the degree of partial melting the extent of melt rock inter actions and the local sulfur fugacity small scale l mt o cm chemical and isotopic heterogeneities in the plati num group minerals are controlled by the mechanism s of chromite crystallization in a heterogeneous environ ment created by the turbulent regime generated by suc cessive inputs of different batches of melt

relative sea level fall since the last interglacial stage are coasts uplifting worldwide the growing interest in quantification of vertical ground motion stems from the need to understand in detail how the earth s crust behaves for both scientific and social reasons however only recently has the refinement of dating techniques made possible the use of paleoshorelines as reliable tools for tectonic studies although there are many local studies of quaternary vertical motions of coastlines we know of no comprehensive worldwide synthesis here we provide a compilation of 890 records of paleoshoreline sequences with particular emphasis on the last interglacial stage marine isotopic stage mis 5e 122 ka the quality of dating mis 5e makes it a reliable marker to evaluate vertical ground motion rates during the late quaternary on a global scale the results show that most coastal segments have risen relative to sea level with a mean uplift rate higher than 0 2 mm yr i e more than four times faster than the estimated eustatic drop in sea level the results also reveal that the uplift rate is faster on average for active margins than for passive margins neither dynamic topography nor glacio hydro isostasy may explain sustained uplift of all continental margins as revealed by the wide distribution of uplifted sequences of paleoshorelines instead we suggest that only plate tectonic processes reconcile all observations of quaternary coastal uplift we propose that long term continental accretion has led to compression of continental plates and uplift of their margins therefore this study concludes that plate tectonics processes impact all margins and emphasizes the fact that the notion of a stable platform is unrealistic these results therefore seriously challenge the evaluation of past sea levels from the fossil shoreline record

fluid present deformation aids chemical modification of chromite insights from chromites from golyamo kamenyane se bulgaria abstract chemical signatures of chromitites are commonly used to track the evolution of the earth s mantle however chemical modification during deformation may have important implications for the interpretation of chromites signatures here we describe the details of how deformation promotes chemical modification in chromite physicochemical characteristics of the chromites were quantified by measuring crystallographic orientation relationships using electron back scattered diffraction ebsd and electron microprobe analysis emp chromites show porphyroclastic textures with coarse grained porphyroclasts ca 0 2 5 mm and fine grained neoblasts 3 and cr and lower mg values than the cores of large grains we interpret f1 and f2 to represent chromite recrystallized by heterogeneous nucleation and subgrain rotation recrystallization respectively crystallographic preferred orientation cpo and misorientation data on the well developed low angle subgrain boundaries in coarse grains and f2 grains indicate that deformation in chromite was accommodated mainly by dislocation creep with the dominant activation of the 111 slip system the retrograde p t exhumation path predicted by thermodynamic and chemical modeling suggests that these fine grained chromites were produced when the initial chromitites reacted with oxidizing fluids during retrograde metamorphism 1 0 gpa and 500 700 c our results show that deformation in the dislocation creep regime in a chemically open system has induced chemical modification and homogenization within chromite aggregates as well as strain localization this close physicochemical link offers new avenues of interpreting the chemical signatures of chromites utilizing their microstructurally controlled variation or lack thereof

high cr and high al chromitites from the sagua de tanamo district mayari cristal ophiolitic massif eastern cuba constraints on their origin from mineralogy and geochemistry of chromian spinel and platinum group elements article i nfo several chromitite bodies of variable sizes are hosted in dunite harzburgite of the small b3 km mining district of sagua de tanamo in the mayari cristal ophiolitic massif eastern of cuba the chromian spinel in these bodies displays a large range in cr cr cr al atomic ratio from 0 74 to 0 45 in high cr chromitites cr and ti contents increase from harzburgite to dunite to chromitite a roughly opposite trend of variation in cr is observed in high al chromitites although in this case ti distributes randomly the differences in the type of chromian spinel i e high cr or high al in the chromitite coincide with a different behavior of the platinum group elements pge whereas high cr chromitites are rich in pge and contain abundant grains of platinum group minerals pgm high al chromitites are systematically poor in pge and in pgm the calculated melts in equilibrium with chromian spinel of high cr chromitite are island arc thoeliites iat with boninitic affinity whereas those in equilibrium with chromian spinel of high al chromitites are back arc basin basalts babb the formation of high cr chromitites is interpreted as a result of the extensive reaction of harzburgite with migrating island arc tholeiite melts of boninitic affinity melt rock reaction produces boninitic melts with variable composition and porous dunitic channels in which the mixing mingling of melts promotes crystallization of mononomineralic high cr chromian spinel in contrast high al chromitites formed by the mixing mingling of babb melts within conduits not in equilibrium with dunite percolation of primitive babb melts through pre existing dunite dissolved olivine producing melt conduits in which babb melts mixed and formed high al chromian spinel the higher pge and pgm in high cr chromitites is not only a function of the degree of partial melting but is linked to interaction between the migrating melt and mantle harzburgite during the formation of the chromitite the coexistence of both types of chromitites in one small mining district reflects the temporal and or spatial variations of separate melt intrusions emplaced in different subarc mantle domains during the opening of a back arc basin in a supra subduction zone environment

sedimentary facies and stratigraphy of a last interglacial coastal barrier in south brazil shoreline sedimentation during the last interglacial highstand on the rio grande do sul coastal plain southern brazil is represented by a sandy barrier that extends almost uninterrupted for hundreds of kilometers along the coast facies analyses of high quality exposures in several sandpits situated in the northern part of the coastal plain provided an opportunity to examine the stratigraphic nature of these deposits based on distinct assemblages of physical and biogenic sedimentary structures the vertical sequence of facies reveals a regressive prograded barrier with vegetated coastal dune sands overlying beach and shallow marine sediments progradation was probably promoted by abundant supplies of nearshore sand during the highstand and early fall of sea level forced regression associated with the last interglacial period around 125 ka as indicated by elevations of ophiomorpha burrows the maximum level reached by the sea was around 7 m above the present sea level paleocurrent data suggest that in the studied area shoreline orientation hydrodynamics and sediment transport during the last interglacial highstand were similar to present day conditions

metallogenic epochs in the inner zone of southwest japan abstract the principal metallogenic epochs in the inner zone of southwestern japan are classified by considering mainly radiometric and microfossil age data as follows 1 early cambrian epoch characterized by podiform type chromite deposits hosted in ophiolite complexes these are the earliest formed mineral deposits in the japanese islands and probably formed in the shallow mantle of island arc settings 2 carboniferous to permian epoch characterized by besshi type base metal sulfide deposits mainly associated with submarine lavas and tuffs of basaltic composition including their metamorphosed equivalents and by bedded cupriferous pyrite deposits associated with submarine acidic tuffs both types of deposits would have been formed in a back arc basin environment geochemically influenced by an island arc 3 middle triassic to jurassic epoch characterized by most of the bedded manganese deposits associated with bedded cherts including their metamorphosed equivalents which would have formed by hot spring activity in an ocean basin environment with a limited current circulation the manganese deposits and their host rocks are the result of seafloor accretion 4 late cretaceous to paleogene epoch characterized by extensive continental arc magmatism volcanic and plutonic resulting in formation of various mineral deposit types related mainly to ilmenite series late cretaceous or magnetite series paleogene granitic rocks related to the former are polymetallic skarns and veins containing cu sn and w also related to this metallogenic activity are stratabound hydrothermal clay deposits of kaolin pyrophyllite and sericite associated with pre ilmenite series granitoids subaerial felsic pyroclastic rocks molybdenite bearing veins and replacement type sericite deposits are characteristics of the magnetite series terranes with local skarns and vein occurrences as with ilmenite series granitoids occurring in southwestern japan eastward younging is also recognized in these mineral deposits regardless of ore type 5 neogene epoch characterized by intense submarine volcanism of acidic composition and associated kuroko deposits in the green tuff region a major tectonic division and a major metallogenic province of the neogene tertiary of japan these mineral deposits would be related to japan sea opening in the non green tuff region important mineralization events are represented by sedimentary uranium deposits and veins characterized by au sb or hg occurrences 6 plio pleistocene epoch characterized by epithermal au ag and au ag cu veins associated with subaerial andesitic to dacitic volcanic rocks of plio pleistocene age volcanism of this and following epochs is characteristic of an island arc setting and 7 quaternary epoch characterized by volcanic sulfur deposits and minor iron sand deposits