a self consistent model of melting magma migration and buoyancy driven circulation beneath mid ocean ridges numerical modeling and analysis are used to investigate the processes leading to the eruption of mantle derived magma at mid ocean ridges our model includes the following effects melting due to decompression magma migration by percolation and circulation of the mantle driven by both the oceanic plates and the distribution of buoyancy beneath the ridge the distribution of buoyancy is due to both the low density of the liquid and the difference in the density of the residual solids relative to unmelted mantle material the calculation of densities is based on a simple petrological model in which garnet spinel lherzolite melts to form a basaltic liquid and a harzburgite residue we find that the system spontaneously evolves to a state in which a rapid upwelling beneath the ridge axis faster than the plate velocity is confined laterally by stably stratified residual material beneath the newly formed plates this effect is exaggerated if a modest decrease in the shear viscosity of the solid upon melting is included our results provide a simple explanation for the narrowness of the zone of crustal formation at mid ocean ridges the model also predicts a transition from steady state to episodic crustal formation as the spreading velocity is reduced perhaps giving rise to along axis variations in the character of seafloor spreading the narrow rapid upwelling gives rise to substantial porosities at depths that are a large fraction of the depth to the solidus this may allow the liquid at depth to segregate into macroscopic channels which would account for the consensus from experimental petrology that the liquids parental to morb are derived from well below the base of the crust

middle to late miocene foredeep basin successions in an arc arc collision zone northern tanzawa mountains central honshu japan abstract middle to late miocene coarse siliciclastic and volcaniclastic deposits are distributed along a narrow longitudinal reverse fault and fold belt between the kanto and tanzawa mountains central honshu japan the coarse clastic piles represent foredeep basin successions characterized by a progressive shallowing sequence from basin plain through submarine volcano submarine fan slope to fan delta systems the siliciclastic deposits are clastic wedges that prograded directly into and down the axis of the foredeep basin during the uplift and progressive unroofing of the orogenic northern highlands of the kanto mountains this was accompanied by syndepositional deformation of the basin fills which is mainly represented by the northward tilting and gave rise to active longitudinal drainage on the southern flank of the kanto mountains interbedded volcaniclastic deposits on the other hand were mainly derived from small submarine volcanoes emplaced on the landward basin slope and may represent near trench magmatism evolution of the foredeep basin successions can be explained by collision of the tanzawa block a paleo volcanic island with central honshu honshu arc since the late miocene following northward subduction of the izu bonin volcanic arc ridge which was emplaced by westward subduction of the pacific plate beneath the philippine sea plate

franciscan complex olistostrome at crescent city northern california an olistostrome and bounding turbidites are exposed within the late mesozoic franciscan complex along the crescent city california coastline facies grade in character from mutti ricci lucchi 1978 mixed facies b c and d to f the olistostrome to mixed a b and e progressing upwards within the franciscan stratigraphic section the facies f unit outcrop is up to 600 m thick and extends 12 km along strike it consists of oblate to tabular blocks up to 200 m in maximum dimension of greenstone tonalite radiolarian chert limestone phyllite and greywacke dispersed in a scaly argillite matrix the olistostromal origin of the unit is indicated by depositional contacts with bounding turbidites by the presence of abundant recycled sedimentary clasts within the unit and by the presence of sedimentary breccias and associated dismembered slump folded turbidites both within the olistostrome and among subjacent turbidites sandstones are chiefly feldspathic litharenites that were very likely derived from the partially dissected late mesozoic sierran klamath magmatic are franciscan rocks record an early pervasive layer parallel flattening strain in such features as extensional faults necking and pinch and swell structures several scales of extensional faulting account for the juxtaposition of turbidites of different facies and or with varying degrees of stratal disruption the formation of sandstone lozenges and the formation of scaly foliation in the olistostrome matrix the latter resulted from the juxtaposition of lenticles with varying concentrations of silt and clay these were ultimately derived from the finer divisions of turbidite beds that were incorporated into the olistostrome the presence of gradational contacts between some sandstone olistoliths and the olistostrome matrix and of sandstone dykes that intrude fractures and associated drag folded turbidite beds indicate that franciscan sediments were not lithified during their early deformation these sediments were deposited in either a trench or trench slope basin and were first deformed either by gravity collapse of the trench slope cover or less likely by vertical loading beneath the toe of the accretionary wedge they later were folded during internal shortening of the growing franciscan accretionary prism

deep water facies and depositional setting of the lower conception group hadrynian southern avalon peninsula newfoundland the lower part of the hadrynian conception group is exposed in coastal outcrops near holyrood pond st mary s bay deep water sediments of the mall bay formation 800 m are overlain by glaciogenic debris flows of the gaskiers formation 250 300 m and then by renewed turbidite deposition in the lower part of the drook formation 1000 m examined formation thickness 1500 m the main facies in the mall bay and drook formations are thinly to very thickly bedded sand stone mudstone couplets turbidites amalgamated in the thicker and coarser beds and graded stratified siltstones mudstones these are interpreted as deposits on an extensive basin floor and on the lower and middle parts of small scale submarine fans that prograded from fringing volcanic islands paleocurrent data indicate a complex paleogeography dominated by active volcanic islands probably like some modern volcanic arcs the gaskiers formation was generated by glaciation of these islands the malll bay formation contains lenticular and w

debris flow olistostromes and slumping on a distal passive continental margin the palombini limestone shale sequence of the northern apennines an olistostrome accumulation up to 530 m thick occurs in the casanova area of the northern apennines it lies within or above the calciturbiditic palombini limestone shale sequence and is part of the allochthonous vara complex sediments originally deposited on oceanic crust the olistostromes are poorly sorted monomict matrix supported submarine debris flow deposits with rigid plugs they have a compactional foliation and a compaction modified planar clast fabric created during flow although diachronous in the main part of the area the olistostromes have a vertical gradational contact with the overlying slumped palombini in which recumbent asymmetric fold hinges and trains and slump boudins are present many criteria indicate soft sediment deformation fold asymmetry indicates a uniformly sw dipping palaeoslope the textural gradation from slumps to olistostrome beds plus slump folds and boudins as olistostrome clasts show that the olistostromes are dismembered slumps in vertical sections variations in limestone petrography volume percentage and size of clasts confirm that the olistostromes were derived from the palombini as a series of bed by bed slumps keeping pace with sedimentation of the palombini from olistostrome clast sizes and bed thicknesses a depositional slope of 4 is estimated the olistostromes are not precursor sediments shed from advancing nappes as in the bracco ridge model of some authors rather they were formed at the foot of a distal block faulted passive continental margin long before nappe emplacement

deep water facies processes and models a review and classification scheme for modern and ancient sediments abstract a review of previous work on modern and ancient deep water facies processes and models is presented with a new classification scheme involving 40 distinct facies related to 15 conceptually distinct facies groups these facies are fixed points in a spectrum of facies generated in a process continuum from resedimentation processes through semi permanent bottom currents to pelagic settling in essence the scheme is descriptive of the sedimentary attributes of sediments although it is designed to aid interpretation of possible sediment transport deposition processes the classification scheme is three tier with facies classes groups and constituent facies and is hierarchical to allow flexibility in its use there are seven facies classes with classes a e defined largely on the basis of grain size differences class f on the basis of internal organization and class g on composition the facies classes are class a gravels muddy gravels gravelly muds and pebbly sands with 5 gravel grade class b sands with 80 sand grade and 80 mud 40 silt and 0 20 sand class e muds and clays with 95 mud grade for the purpose of large scale mapping or reconnaissance fieldwork either the level of facies classes or groups may be appropriate whereas for more detailed sedimentology the more detailed facies level will be necessary

the effects of pressure and porosity on the micromechanics of the brittle ductile transition in quartzite room temperature experiments on a quartzite with 7 porosity show that with increasing pressure there is a transition from brittle faulting to ductile cataclastic flow at about 600 mpa in contrast experiments on nonporous quartzite show only faulting up to 1000 mpa the transition to cataclastic flow in the porous quartzite is due to the changing influence of the pores microstructural observations and elastic theory suggest that the transition occurs at the pressure where the differential stress producing a compressive stress concentration sufficient to initiate pore collapse becomes less than that producing a tensile stress concentration sufficient to nucleate axial microcracks at the tops and bottoms of pores cataclastic flow of the porous quartzite is only transient deformation remains distributed and accompanied by work hardening only as long as pore collapse continues to 16 strain at higher strains microcracking produces a net dilatancy which causes strain weakening that leads to faulting at 26 strain at a confining pressure of 750 mpa the faults are stable whereas at 1000 mpa they are unstable the results indicate that porous rocks may undergo limited ductile deformation at shallow levels in the crust but higher strains will cause deformation to localize

submarine fan sedimentation at a convergent margin the cretaceous mangapokia formation new zealand abstract the middle cretaceous mangapokia formation pahaoa group near te awaiti southeast north island new zealand consists of indurated poorly fossiliferous alternating sandstone and argillite minor conglomerate grit pebbly sandstone and pebbly mudstone terrigenous sedimentary assemblage and minor basalt coloured argillite chert and micritic limestone ocean floor assemblage seven lithofacies are distinguished in the sedimentary assemblage on the basis of lithology bed thickness and geometry sand mud ratio grain size and internal sedimentary features facies 1 10 15 of total exposure which includes all sediments coarser than sand grade comprises seven subfacies as follows lenticular and erosive beds of coarse grained subfacies 1ai medium grained subfacies 1aii and fine grained subfacies 1aiii predominantly clast supported conglomerate grit subfacies 1aiv and pebbly sandstone subfacies 1av displaying numerous types of graded bedding and sedimentary structures were all deposited predominantly from high concentration turbidity currents or bed load inertia flows minor chaotic sand or mud matrix supported conglomerate lenses subfacies 1bi and beds which show clear evidence of post depositional remobilisation subfacies 1bii represent debris flow deposits thick lenses of sandstone and minor argillite interbeds facies 2 were deposited from large volume inertia flows possibly grainflows facies 3 the most common lithofacies consists of laterally more extensive medium thickness graded beds of alternating sandstone and argillite with rare bouma sequences these deposits are proximal turbidites which accumulated in environments more distal than facies 1 and 2 thin bedded facies 4 and very thin bedded facies 5 alternating sandstone and argillite and argillite dominated sequences with minor interbedded sandstone facies 6 were deposited in interchannel depressions on channel levees or in areas distant from high concentration flows rare discontinuous graded bedded sandstones containing common flame structures facies 7 interbedded with conglomerate facies represent within channel turbidites a lower inner submarine fan channel overbank assemblage facies association a an inner middle submarine fan channel lobe assemblage facies association b and a mid fan assemblage facies association c are distinguished two large scale progradational suites of facies reflecting large scale migration of the inner fan channel complex are superimposed upon numerous small scale depositional cycles resulting from lateral migration of numerous braided channels within the inner and mid fan environments the volumetrically minor ocean floor assemblage is restricted to zones of melange chemically the basalts are tholeiitic with trace element concentrations similar to modern ocean floor basalts radiolarian bearing cherts and coloured argillites are highly oxidised and chemically similar to some modern oceanic pelagic sediments the juxtaposition of relatively coherent strongly folded and tectonically imbricated trench fill submarine fan sediments and minor ocean floor material is consistent with contemporaneous sedimentation and accretion at the base of the i inner trench slope in a convergent plate setting the mangapokia formation is interpreted to represent the youngest part of the torlesse terrane and hence in southern north island torlesse deposition and concurrent subduction tectonism were probably continuous at least until the middle cretaceous

the hunghae formation se korea miocene debris aprons in a back arc intraslope basin during early to middle miocene times a sudden opening of the ulleung tsushima back arc basin in the east sea sea of japan led to the development of intraslope basins along the rifted southwestern margin southeast korea abrupt subsidence resulted in the deposition of the 200 m thick hunghae formation middle miocene a sand mudstone sequence that can be divided into five facies facies i sand and mudstone couplet and ii coarse sand are turbiditic in origin as evidenced by massive graded crudely layered and parallel laminated sand beds facies iii homogeneous mudstone is characterized by various lignite and plant fragments clastic and biogenic grains that are randomly oriented suggestive of hemipelagic deposition facies iv chaotic deposit is characterized by the disruption of beds the presence of isolated siltstone blocks or balls and large clasts in the muddy matrix indicative of retrogressive rockfall and slide slump facies v conglomerate is of debris flow origin as evidenced by clast and matrix supported features floating large clasts and absence of traction structures individual facies are organized into two types of facies association 1 homogeneous mudstone facies iii associated randomly with the rest facies i ii iv and v indicative of hemipelagic and episodic sediment gravity flow processes respectively 2 conglomerate facies v coarse sand facies ii and sand mudstone couplet facies i representing the flow transformation from debris flow to high and low concentration turbidity currents these facies associations are similar in many respects to modern and ancient debris or slope aprons found elsewhere numerous isolated slide slump blocks wedged conglomerates with armoured mudstone balls discontinuous lignite containing sand mudstone beds chaotic structure and growth faults suggest that the deposition occurred on a steep slope intraslope basin off coalescing fan deltas mainly by unchannellized sediment gravity flows ancient deposits with irregular facies sequences can be viewed as debris apron systems which provide alternatives to submarine fan models in many clastic basins with a line rather than point source

the palaeogene yamak sand rich submarine fan complex haymana basin turkey abstract the haymana basin is a constituent trough of the central anatolian basin which was the site of rapid subsidence and accompanying flysch sedimentation during the late cretaceous and early tertiary following closure of the vardar ocean and collapse of the carbonate platform forming its southern border the eocene yamak formation maximum thickness 1210 m abruptly succeeds fine grained sediments of the bahcecik formation interpreted as a basin plain facies lutite interbeds from the yamak yield a bathyal marine microfauna and the formation is characterised by a high proportion of thick medium to coarse sandstones and pebble to cobble rudites of turbidite and mass flow origin arranged in thick packets of moderate lateral extent many of these sand bodies are channelised with thinning and fining upward sequences in which thick amalgamated sandstones and rudites are prominent most of the subordinate thickening and coarsening upward sequences are erosively succeeded by channelised bodies these features indicate that the coarse yamak sediments were deposited in a sand rich submarine fan complex in which the channelised mid fan was the dominant depositional regime the lateral and vertical relationships of yamak facies associations indicate that the individual fans were relatively small elongate and strongly channelised they show little evidence of lateral migration or coalescence but apparently result from superposition of successive low sinuosity channels with only occasional development of channel mouth lobes in the sense of mutti and ricci lucchi 1972 1975 facies distributions and palaeocurrent evidence show that sediment was generally conveyed to south and southeast through the yamak fan system however following a prolonged phase of quiescence on the fan and formation of an extensive blanket of purple muds the uppermost yamak is marked by northwards progradation of a new channelised fan system

glacially influenced deep marine sedimentation of the late precambrian gaskiers formation newfoundland canada the late proterozoic conception group exposed on the avalon peninsula in newfoundland canada is a 4 km thick turbidite succession containing a conformable 300 m thick sequence of diamictites the gaskiers formation near the base massive and crudely stratified diamictites form beds up to 25 m thick which have a tabular geometry with slightly erosive basal contacts and are interbedded with mudstones and fine grained thin bedded turbidites these diamictites are interpreted as submarine debris flow deposits disrupted diamictites form strongly deformed units that contain large complexly folded rafts of mudstone and turbidite facies these diamictite units are interpreted as submarine slumps diamictites contain glacially striated and faceted clasts clasts and matrix are predominantly of volcanic provenance one outcrop shows interbedded volcanic agglomerate and diamictite and volcanic bombs can also be identified the interbedding of diamictites with turbidites and the stratigraphic context provided by the thick sequences of turbidites below mall bay formation and above drook formation indicate a deep marine slope setting of diamictite deposition diamictite facies record remobilization and downslope transfer of large volumes of unstable volcanic and glacial debris initially deposited in a shallower water marginal marine zone the regional tectonic framework suggests the conception group accumulated in a deep southward opening ensialic rift basin with active but waning volcanic centres to the north the gaskiers formation may be representative of other late precambrian glacially influenced diamictite sequences that were deposited around the north atlantic region and in europe these deep marine diamictite sequences characterized by debris flows turbidites and slump deposits can be contrasted with more extensive shallow marine shelf diamictite sequences found in association with dolomites and tidally influenced shallow water facies in other basinal settings

eocene turbidite population statistics from shelf edge to basin floor spitsbergen svalbard abstract there is a need for better tools in the interpretation of depositional sub environments of deep marine facies using seismic scale outcrops of eocene shelf margin clinoforms in spitsbergen we have statistically characterized the turbidite beds in terms of grain size bed thickness and dominant sedimentary structure at four different lowstand sites in individual mappable clinoforms these sub environments include 1 upper slope canyon and gully fill 2 upper to middle slope late prograding wedge 3 lower slope channel levee complex and 4 basin floor fan the falling stage basin floor fan and slope canyon gully deposits are generally coarser grained than the rising stage sub environments they also have far fewer siltstone and mudstone beds and have significantly more beds of upper medium to very coarse grain size compared to the rising stage channel levee and prograding wedge deposits thin beds are particularly voluminous in the late prograding wedge and channel levee systems whereas only the basin floor fans and canyon fill have large numbers of beds thicker than 10 cm turbidity currents deposit sediment at distinctly different sites between shelf edge and basin floor at different times during the development of the base level cycle differences between these sub environments are both qualitative and quantitative and are demonstrable using statistical analysis the results of this statistical analysis from well exposed easily identifiable architectural elements can be used to reconstruct the shelf margins of analogous basins where only sparse outcrop or well data are available

grain scale permeabilities of synthetic quartzite with volumetrically minor phlogopite corundum or aluminosilicate abstract in order to examine grain scale permeabilities in materials that are microstructurally similar to those of the lower crust and upper mantle we produced porous synthetic quartzites with small fractions of an additional minor mineral powdered quartz was mixed with minor amounts of either corundum or phlogopite and run in ag capsules at 800 850 c and 1 4 gpa for 5 to 10 days the resulting quartzites generally exhibited microstructural equilibrium and contained phlogopite corundum or aluminosilicate the minor mineral in all runs typically resided along quartz grain boundaries at low volume fractions x but increasingly occurred as porous clusters within corner pores at higher x in all polished sections the smallest quartz bound pores appeared free of the minor mineral pore geometry of all materials differed from that observed in pure synthetic quartzite pores exhibited an increased number of facets a small decrease in the dihedral angle and partial filling of larger pores by the minor phase measurements of permeability k were both higher and lower than those of monomineralic quartzite with similar with k decreasing as a function of x this decrease is likely the result of pore throat reduction either through fluid redistribution or obstruction of fluid pathways

sedimentology and evolution of the martinsburg formation upper ordovician fine grained turbidite depositional system central appalachians the upper ordovician martinsburg formation of eastern pennsylvania consists of mudstone siltstone and sandstone turbidites that accumulated in a tectonically active foreland basin the mudstone rich bushkill member the stratigraphically lowest unit of the martinsburg in this area grades upward into approximately equal proportions of mudstone siltstone and sandstone of the ramseyburg member many of the turbidites of these units are arranged in small scale 1 9 m fining upward sequences that are interpreted as reflecting the influence of external or allocyclic controls such as variations in the local rate of sea level rise and or variations in the intensity of tectonic activity in shelf nearshore or hinterland areas rather than more commonly cited autocyclic mechanisms the thick approximately 2000 m bushkill ramseyburg coarsening upward sequence records progradation of a muddy turbidite depositional system along the axis of the foreland basin although this sequence accumulated during a caradocian eustatic rise in sea level sedimentation rates landward of the shoreline were apparently great enough to allow for long term seaward progradation of the shelf source the paucity of depositional lobe like facies coarsening upward sequences in the bushkill member allows for tentative comparison of the progradational bushkill ramseyburg system with the active fan lobe of the mississippi fan progradation of the bushkill ramseyburg system ceased abruptly when mudstone turbidites and laminated black shale of the upper unit of the martinsburg the pen argyl member accumulated the great thickness of some mudstone turbidite beds of the pen argyl member is interpreted to record topographic confinement of the central appalachian foreland basin which may have helped to preclude continued progradation of the bushkill ramseyburg turbidite system

late devonian to early carboniferous turbidite facies and basinal development of the eastern klamath mountains california abstract the late devonian to early carboniferous bragdon formation eastern klamath mountains california is a thick turbidite sequence deposited as a submarine fan complex within an arc related basin laminated mudstone and less abundant classical turbidites comprise most of the lower part of the bragdon and represent a lower fan environment amalgamated beds of normally graded to massive sandstone and pebbly sandstone occur throughout the bragdon but are most abundant in its upper half where they are associated with very thick channel fill beds of pebbly sandstone and conglomerate the upper half of the bragdon formation represents a mid fan to upper fan environment and it also includes closely interbedded classical turbidites interpreted as interchannel or levee deposits an upper slope facies of bioturbated mudstone with an early carboniferous fauna occurs at the top of the formation clastic material in the bragdon formation indicates little contemporaneous vulcanism and was probably derived from lower paleozoic metasediments which were uplifted to the north deposition of the bragdon was initiated by rifting and subsidence of an underlying middle devonian arc complex infilling of the resulting basin during the late devonian and early carboniferous is indicated by overlap of turbidite facies across middle devonian arc deposits and by an upward stratigraphic trend in the bragdon from lower fan to upper fan and slope environments

lithogic partitioning of fluids and melts under conditions of mechanical equilibrium the grain scale distribution of fluid or melt in a lithologically complex system is governed by the relative energies of the mineral fluid interfaces and the grain boundaries accordingly spatial changes in mineralogy imply accompanying changes in the connectivity and even the amount of fluid or melt present at equilibrium the hypothesized phenomenon of local variation in fluid or melt abundance with spatial changes in mineralogy is referred to here as lithologic partitioning of fluid or melt the phenomenon is potentially important because it could lead to the existence of highly permeable or impermeable zones in lithologically complex regions of the crust and upper mantle to verify and evaluate the concept of lithologic partitioning of aqueous fluid experiments were conducted in simple analog systems by annealing juxtaposed cylinders of two different rock types at 700 925 degrees c and 1 0 1 5 gpa these polycrystalline fluid partition couples included the following rock pairs calcite fluorite quartz fluorite and quartz clinopyroxene with overall aqueous fluid volume fractions phi ranging from approximately 0 015 to 0 10 in calcite fluorite couples fluid is partitioned by a factor of approximately 1 5 5 into the fluorite the actual value depends upon the chemical purity of the fluorite in fluorite quartz couples the fluid is partitioned into the quartz by a factor of 2 5 and in quartz clinopyroxene couples it is enriched in the clinopyroxene by a factor of approximately 3 similar experiments were done in a partially molten mantle system by juxtaposing peridotite and orthopyroxenite cylinders in the presence of approximately 6 basaltic melt in this case however no preference of the melt for one host rock relative to the other could be verified in general lithologic partitioning is a factor to be reckoned with as we seek understanding of fluid related petrologic and geochemical phenomena the effect is clearly capable of rapid and significant re distribution and localization of fluids in mineralogically variable systems

depositional models for fine grained sediment in the western hellenic trench eastern mediterranean sediment in tectonically active topographically restricted settings of the western hellenic arc eastern mediterranean consists primarily of clayey silt and silty clay failure of metastable sediment temporarily stored on relatively steep slopes is triggered by earthquake tremors and eustatic oscillations redeposition of these materials by gravitative transport has resulted in markedly different lithofacies from site to site most piston cores include three late quaternary stratigraphic units that can be correlated with sections in other parts of the eastern mediterranean numerous radiocarbon age determinations enhance the correlation seven fine grained sediment types are identified in cores from eight distinct depositional environments some muds are closely related to specific environments slump and debris flow deposits on slope and high relief environments or to time well laminated mud during the latest pleistocene mid holocene or to both uniform and faintly laminated muds restricted to trench basins turbiditic and hemipelagic muds are common throughout the study area mud distribution patterns correlate closely with calculated sedimentation rates we propose two depositional models for these sediments the first emphasizes downslope transformations resulting in progressively reduced flow concentration during transport from slump and debris flow turbidity current low density turbidity current or turbid layer mechanisms the distal end member deposits settling from low concentration flows are thick rapidly emplaced fine grained uniform muds closely associated with faintly laminated muds these were ponded in flat trench basin plains planktonic and terrigenous fractions in the turbiditic finely laminated and uniform muds record mixing of materials of gravitative and suspension origin during redeposition this sequence prevails under conditions of minimal stratification of water masses as characterized by the present mediterranean in the second model developed for conditions of well developed water mass stratification well laminated rather than uniform mud prevails as the end product of low concentration flows these very finely laminated and graded muds record particle by particle settling from detached turbid layers concentrated along density interfaces they include material from turbid layers complemented by the normal rain of pelagic material stratification barriers resulted in region wide distribution of such deposits in both slope and trench environments

braided and meandering submarine fan channel deposits tesnus formation marathon basin west texas abstract exposures of predominantly mid fan channel deposits from the tesnus formation upper mississippian lower pennsylvanian of west texas provide an opportunity to examine possible meandering and braided deposits in a single submarine fan system within the tesnus six fan related sedimentary facies are recognized i amalgamated sandstone without vertical thickness trends ii amalgamated sandstone with thinning upward trends iii massive matrix rich sandstone iv interbedded sandstone and shale v chaotic sandstone and shale and vi black mudrock and chert the arrangement of sedimentary facies the nature of facies contacts and sandstone geometries differ significantly for braided versus meandering channel deposits sheet like braided channel deposits commonly exhibit a more random facies ordering and abrupt facies transitions whereas pod shaped meandering channel deposits commonly possess a more orderly arrangement of facies from base to top facies i vi in sequential order with gradual facies transitions the aforementioned differences in channel deposit characteristics are believed due primarily to variations in the migrational history of the braided abandonment and rapid shifting versus meandering gradual erosion and migration channel networks

sedimentology and possible paleoceanographic significance of mudstone turbidites and associated deposits of the pen argyl member martinsburg formation upper ordovician eastern pennsylvania abstract the pen argyl member the stratigraphically highest unit of the upper ordovician martinsburg formation of eastern pennsylvania consists of the three mudstone facies laminated mudstone uniform mudstone and black shale these deposits conformably overlie a coarsening upward sequence of fine grained and classic sandstone turbidites of the underlying bushkill and ramseyburg members respectively petrographic and x radiographic analysis suggests that laminated and uniform mudstone facies beds accumulated from muddy turbidity currents interbedded black shale facies beds however are interpreted to reflect slow gravitational settling of sediment in a density stratified anoxic basin the marked transition from sandstone and siltstone turbidite deposits of the ramseyburg member to mudstone turbidite and black shale deposits of the pen argyl member may reflect the combined effects of a caradocian rise in sea level increased organic carbon production lack of sand size sediment and a tropical to subtropical location of the basin density stratification such a model however does not explain adequately the very thick laminated and uniform mudstone facies beds common only to the pen argyl member an alternative hypothesis involves amplification of global eustatic and climatic related oceanographic effects by local or basinal influences the very thick beds of the laminated and uniform mudstone facies by comparison with lithologically similar deposits of the eastern mediterranean are interpreted to have been ponded in a topographically restricted basin accordingly deposition of the pen argyl member may record a significant change in basin morphology from a wide extensive basin to a topographically restricted or enclosed anoxic basin

anatomy of a siliciclastic turbidite basin the gorgoglione flysch upper miocene southern italy physical stratigraphy sedimentology and sequence stratigraphic framework abstract the gorgoglione flysch is a tortonian siliciclastic turbidite formation well exposed in the lucania apennines southern italy with an average thickness of 1500 m it is one of the few examples of collisional basin succession for which field sedimentological investigations and visual correlations have permitted the reconstruction of the physical stratigraphy of proximal to distal turbidite deposits a northern and a southern turbidite complex have been identified they are divided by a structural high and both consist of three turbidite systems the middle and upper systems are composed of growth stages that show proximal to distal downcurrent facies variations the stacking pattern of each turbidite stage of growth consists of 5 10 cycles with thicknesses between 10 and 100 m mesocycles each of which is composed of cycles with a thickness of less than 10 m microcycles stratigraphical and sedimentological data are fitted to a sequence stratigraphy scheme represented by two nonconformity bounded depositional sequences internally composed of type i ii and iii stages of growth with aggradational to retrogradational and progradational stacking patterns the sequence stratigraphy scheme can be used as a model for turbidite collisional basins and is predictive of the stratigraphical features geometry and stacking patterns of depositional units formed when physiographic sedimentary basin evolution occurs under a regime of tectonic control this process consists of three phases i formation of the basin on top of a argille varicolori formation thrust system ii in sequence substratum thrust propagation towards the foreland basin confinement and elongation aggradational type i and retrogradational type ii stages of growth with two main sediment entry points iii deformational regime change with deactivation of in sequence thrusting decrease of deformation rate and decrease of lateral and vertical mobility the basin assumes a foreland ramp type configuration with development of a thick type iii pelitic stage of growth related to a predominant eustatic control

till stratigraphy and sedimentology at the margins of terrestrially terminating ice streams case study of the western canadian prairies and high plains complex glacigenic sediment sequences arranged in large arcuate assemblages and demarcating the lobate termini of fast ice flow corridors in western canada represent the terrestrial equivalents of the trough mouth fans of the marine palaeo ice stream record intensive sedimentological and stratigraphic investigations at a regional scale are employed in the interpretation of thick units or sequences of diamicton and two depositional scenarios are proposed first glacier marginal till thickening and the stacking of till wedges takes place in areas where an ice stream margin was stationary for short periods of time stacks of subglacial traction tills potentially record annual sub marginal incremental thickening at ice stream margins especially in areas where densely spaced recessional push moraines appear to record seasonal climatic forcing second proglacial lake and valley infilling with glacilacustrine rhythmites and mass flow diamictons is associated with the advection of sub marginal till into preglacial bedrock depressions and records ice stream marginal oscillations and debris influx into discontinuous proglacial lakes which act as subaqueous sediment sinks for materials that would otherwise have been used to construct sub marginal till wedges and moraines glacial overriding modifies the deposits produced in both scenarios through deformation and the dislocation and entrainment of bedrock and sediment rafts at the margins of bedrock valley walls resulting in the widespread development of glacitectonites and megablocks the occurrence of the thickest deposits as preglacial valley fills may be significant in groundwater siphoning away from subglacial deforming layers and the promotion of sticky spots

depositional mechanisms of deep sea coarse clastic sediments cap enrage formation quebec cambro ordovician cap enrage deep sea sediments consist of six main facies 1 coarse conglomerates 2 graded stratified cross bedded fine conglomerates 3 dispersed pebbly sandstones 4 liquefied pebbly sandstones 5 ungraded cross bedded fine conglomerate and pebbly sandstones 6 massive sandstones facies 1 and coarser parts of facies 2 beds have unimodal grain orientations in bedding with unimodal a axis imbrications finer facies 2 beds have unimodal or bimodal grain orientations in bedding with bimodal up and downstream a axis imbrications facies 3 4 and 6 beds have unimodal bimodal or random grain orientations in bedding the a axis imbrications vary as follows mainly bimodal for facies 3 bimodal or unimodal for facies 4 and dominantly unimodal for facies 6 facies 5 beds result from fractional reworking of previous deposits by strong bottom currents velocities 70 125 cm s dilute spillover flows all other facies were deposited mostly from concentrated clast dispersions

late pleistocene debris flow deposits in large glacial lakes in british columbia and alaska the movement of late wisconsin 30 000 b p ice sheet lobes counter to the direction of regional drainage ponded large lakes up to 5000 km2 in both the upper fraser river valley in british columbia and the cooper river valley in alaska along the fraser river near quesnel glaciolacustrine sediment gravity flow complexes contain thick up to 10 m and laterally extensive up to 3 km diamict units containing large rafts of poorly lithified tertiary rocks diamicts offlap and thin away from tertiary bedrock highs and were emplaced by subaqueous debris flows these flows probably evolved from slumps and slides associated with the downslope failure of unstable tertiary bedrock slopes triggered by rising lake levels a process akin to first filling slope failures around the margins of man made lakes in alaska along the copper river valley massive and stratified diamicts were also deposited by debris flows and are interbedded with thin bedded turbidites poorly sorted gravels and normally graded diamicts debris flow deposits show basal grooves internal compressional structures and rafted clasts that protrude from bed tops flows originated by slumping of rapidly deposited and underconsolidated glacial sediments around the basin margins an important factor in flow generation has been the combination of steep substrate slopes and frequent earthquake shock observations in both british columbia and alaska stress the significance of sediment gravity flow processes acting to deposit glacial sedimentary successions in large ice contact lake basins

a precambrian upper basin slope and prodelta in northeast finnmark north northway a possible ancient upper continental slope abstract the 60 m to 540 m thick lower naeringselva member of the basnaering formation crops out on varanger peninsula north norway and is part of the 9 km thick late precambrian barents sea group it is underlain by at least 3 2 km of submarine fan deposits and is the oldest part of a 2 5 km to 3 5 km thick fluvio deltaic succession basnaering formation the upper part of the member is delta front deposits the lower naeringselva member mainly comprises fine grained thin bedded deposits divided into four facies 1 facies i parallel laminated mudstone 2 facies ii current rippled siltstone interpreted with facies i as low density low velocity turbidity current deposits 3 facies iii structureless mudstone interpreted as possible hemipelagic deposits and 4 facies iv wave rippled fine very fine grained sandstone interpreted as due to wave action soft sediment deformation is abundant as various styles of slide slump and in situ disturbed layers up to tens of meters thick erosional depositional discordances are evident between packets of beds the stratigraphic position and sedimentology of the lower naeringselva member suggest that it is part of an ancient upper basin slope and prodelta with submarine fan deposits on the lower basin slope paleocurrent data with a limited number of slide fold readings imply that deposits from downs lope flowing sediment laden currents prograded the slope towards the east north east apart from sporadic storm events the slope was below wave base modern analogues for the lower naeringselva member appear to be the upper part of continental slopes separating submarine fan from delta deposits as in the mississippi delta slope fan system

sediment slides and turbidity currents on the laurentian fan sidescan sonar investigations near the epicenter of the 1929 grand banks earthquake the epicenter area of the 1929 grand banks earthquake on the continental slope south of newfoundland has been investigated using sea marc i a deeply towed midrange sidescan sonar with a 4 5 khz subbottom profiler shallow slides pass downslope into debris flows on the muddy continental slope east of the epicenter at the head of the eastern valley of the laurentian fan west of the epicenter arcuate slide scars cut undisturbed upper slope sediment and lead downslope to a lineated erosional seabed at a water depth of about 1600 m this erosional seabed passes into extensive fields of 100 m wavelength gravel waves situated on the broad irregular valley floor the gravel waves become better developed downslope and extend at least to water depths of 3000 m all these morphological features appear fresh on the sidescan sonograms suggesting that they date from the 1929 earthquake event and the distribution of slides corresponds to the area of instantaneous cable breaks in 1929 the upper limit of erosion on valley walls suggests that the 1929 turbidity current was less than 300 m thick timing of cable breaks downfan suggests that flow velocities were sufficient to rework gravel deposits into large bedforms during waning flow stages over elevated areas of the valley floor similar cross bedded coarse sands and gravels are common in ancient channel deposits

sedimentation of deep water slope base and inner fan deposits the drosgol formation ashgill west central wales abstract the sedimentology of the drosgol formation is summarised in terms of nine sedimentary facies with particular attention given to the pebbly mudstones and major arenites sedimentary facies geometry and palaeocurrents suggest the interpretation of the major arenites as inner fan channel deposits locally preserving their levees the lower less organised part of the formation suggests a slope base environment with small scale channelling slumping and development of mass flow deposits a new definition of the upper boundary of the formation is proposed and map references are given to key localities

the jersey shale formation a late precambrian deep water siliciclastic system jersey channel islands abstract the late precambrian jersey shale formation with an estimated thickness of 2500 m is described in terms of six facies i laminated mudstone ii ripple laminated very fine grained sandstone iii graded medium to fine grained sandstone iv cross stratified medium grained sandstone v clast supported pebble cobble conglomerate and vi chaotic beds five facies associations are recognised association i canyon or inner fan channel fill association ii middle fan channel fill association iii lower middle fan outer fan deposits and association iv divided into lobe lobe fringe and fan fringe deposits in an outer fan the jersey shale formation and the overlying approximately 2300 m thick andesitic rhyolitic volcanic group are believed to have accumulated in an active convergent plate margin setting

coarse grained submarine fan and slope apron deposits in a cretaceous back arc basin antarctica the cretaceous of west james ross island antarctica represents the proximal fill of a late mesozoic back arc basin that was probably initiated by oblique extension during the early development of the weddell sea the succession records sedimentation in two contrasting depositional systems a laterally persistent slope apron flanking the faulted basin margin interrupted both spatially and temporally by coarse grained submarine fans slope apron deposits are dominated by thinly interbedded turbiditic sandstones and mudstones mudstone association interspersed with non channelized chaotic boulder beds intraformational slump sheets and isolated exotic blocks representing a spectrum of mass flow processes from debris flow to submarine gliding localized sand rich sequences sandstone breccia association represent sandy debris lobes at the mouths of active slope chutes the submarine fan sediments conglomerate association are typified by coarse conglomerates and pebbly sandstones interpreted as the deposits of high density turbidity currents and non cohesive debris flows three assemblages are recognized and are suggested to represent components of the inner channelled zone of coarse grained submarine fans from major fan channels through ephemeral marginal channels or terraces to levee or interchannel environments the occurrence of both slope apron and submarine fan depositional systems during the early and mid cretaceous is attributed to localized input of coarse arc derived sediment along a tectonically active basin margin periods of extensive fan development were probably linked to regional tectonic uplift and rejuvenation of the arc source region cyclicity within individual fan sequences is attributed to migration or switching of fan channels or canyons slope apron sedimentation was controlled largely by intrabasinal tectonics local unconformities and packets of amalgamated slide sheets and debris flow deposits probably reflect episodic movement on basin margin faults differential subsidence across the basin margin anchored the basin slope for at least 20 myr and precluded basinward progradation of shallow marine environments

earthquakes as a triggering mechanism for debris flows and turbidites on the calabrian ridge abstract debris flows and turbidites have been described in piston cores bottom photographs and side looking sonar records from basin floors amid the rugged irregular topography of the calabrian ridge a sediment transport process is inferred which began with a rotational slump on the steep basin wall subsequently transformed into a debris flow and turbid cloud such events occurred approximately every 1500 years because the debris flow turbidite deposits are correlative between basins some relatively widespread mechanism such as an earthquake is required to initiate the slope failure the estimated intensity of ground shaking as a result of historical earthquakes on the nearby calabrian and hellenic arcs has been used to develop a relationship between frequency of occurrence and intensity of ground shaking extrapolation of this relation to infrequent large magnitude events shows that the 1500 yr event is small enough to be geologically plausible but large enough to cause slope failure on basin walls it is possible that the historical record fortuitously contains one of these large magnitude long repeat time events which may have caused the most recent of the observed debris flows in 1903

on the rheologically critical melt fraction abstract with increasing melt fraction the strength of partially molten granite decreases from a value characteristic of solid competent rock to a value nearly equal to that of the melt previously published mechanical and microstructural data indicate that deformation in partially molten rocks often involves brittle processes thus the pressure in the melt is expected to be important in determining strength when the volume changes during deformation strength and fluid flow will be coupled by such parameters as permeability k storage capacity per unit volume or storativity s melt compressibility f grain size d fluid viscosity and strain rate experiments on brittle rock at low temperatures show that the strain rate at which the internal fluid pressure can be maintained constant is approximately proportional to k s an evaluation of published experimental data suggests that this relation also holds for partially molten granites indicating that the strength of these rocks depends on their transport properties since the permeability is related to below a critical melt fraction rcmf the melt pressure will change if deformation is not iso volumetric by assuming a power law relationship between k and we estimate that rcmf f d m 1 n 1 where m and n relate permeability to grain size and respectively

paleoenvironmental dynamics of low order paleovalleys in the late quaternary palmas cacador summit surface southern brazil abstract the quaternary dynamics of landscapes in the subtropical continental region of brazil is not still well understood pedostratigraphic records of low order paleovalleys paleovalley heads and 1st and 2nd order paleovalleys of the palmas cacador summit surface serve as important resources for the identification of landscape component responses relief soil sediment and vegetation of plateau areas of southern brazil in the light of environmental changes driven by climatic variations of the late quaternary we integrated litho pedo allo and chronostratigraphic descriptions with carbon stable isotope analysis phytoliths indices and 14c and osl dating we found that at 44 86 ky bp there was a change in the hydrodynamics of 2nd order perennial channels humid climate controlled possibly by tectonics at 28 35 to 23 69 to 28 ky bp regressive pedogenesis in dry climate began with a predominance of erosion by overland flows at 2 60 to 23 69 ky bp full regressive pedogenesis occurred under a continuous climate regime of drier characteristics punctuated by millenary climatic fluctuations to a wetter regime of between 4 60 and 19 77 ky bp echoing the results postulated by the knox s model during this period the most pronounced modifications to the landscape were made with a change in vegetation from campo cerrado to campo limpo with changes in erosion patterns caused first by overland flows and then earthflows debris flows and with the gradual silting filling and burying of gullies valley heads and 1st and 2nd order valley bases since 2 60 ky bp the area returned to a predominance of progressive pedogenesis in wet and cold climates finally we found that at the local scale low order basins

grain boundary microstructures in micaceous quartzite significance for fluid movement and deformation processes in low metamorphic grade shear zones observation by scanning electron microscopy of a sericitic quartzite from a low grade 1 cm wide shear band developed from an originally pure quartzite revealed a nonconnected intergranular porosity the isolated pores occur principally on quartz quartz grain boundaries pores surrounding isolated mica flakes show very irregular geometries reflecting a highly unstable disequilibrium crystal fluid interface but regular frequently crystallographic pore shapes predominate in other grain boundaries statistical analysis reveals that the pores are principally concentrated on grain boundaries oriented perpendicular to the two foliations developed within the shear band i e grain boundaries at 45 and 90 to the shear band boundaries indicating that the fluid phase occupied extensional sites relative to both the overall and local scale of one microlithon strain ellipsoids there is a strong spatial relationship between interfacial porosity and the presence of mica with the most porous grains occurrin

grain growth in synthetic marbles with added mica and water evolution of grain size in synthetic marbles was traced from compaction of unconsolidated powder through primary recrystallization and normal grain growth to a size stabilized by second phases to form the marbles reagent grade caco3 was mixed with 0 1 and 5 volume mica and heat treated under pressure with added water densification with negligible recrystallization occurred within one hour at 500 c and 500 mpa confining pressure primary recrystallization occurred at 500 550 c causing increases of grain size of factors of 2 5 resulting samples had uniform grain size gently curved grain boundaries and near equilibrium triple junctions they were used subsequently for normal grain growth studies normal grain growth occurred above 550 c at 800 c grain size d increased from 7 m d0 to 65 m in 24 hours growth rates fit the equation d n d 0 n kt where k is a constant and n 2 6 minor amounts of pores or mica particles inhibit normal grain growth and lead to a stabilized grain size dmax which depends on the size of the second phases and the inverse of their volume fraction raised to a power between 0 3 and 1 once dmax is reached normal growth continues only if second phases are mobile or coarsen or if new driving forces are introduced that cause unpinning of boundaries normal grain growth in solnhofen limestone was significantly slower than in pure synthetic marble suggesting that migration is also inhibited by second phases in the limestone

quaternary mud turbidites from the south shetland trench west antarctica recognition and implications for turbidite facies modelling a piston core from the basinal part depth of 5188 m of the south shetland trench west antarctica yielded a terrigenous mud section 11 m long which can be subdivided with great precision into turbidite and hemipelagite layers mud turbidites mean bed thickness 44 cm alternate regularly with and are best distinguishable from their hemipelagite host mean bed thickness 17 cm by the following features i sharp basal contacts ii terrigenous sand free textures except basal well sorted silt laminae and the absence of outsized ice rafted components iii a laminated little to non bioturbated internal structure iv distinct textural and compositional grading and v marked steps on water content and sediment density logs mud turbidites recovered from the south shetland trench differ from an earlier model mud turbidite sequence by their i excessive about six times larger bed thickness ii complex internal organization manifested in multiple repetitions up to four of the same structural interval s in sequential or nonsequential order iii distinctive very fine grained cap of highly porous clay rich in fragments of siliceous biogenics iv widespread zones of penesyndepositional deformation and v evidence of flow reversals these features are interpreted to record deposition from large muddy turbidity currents subjected to flow transformations including soliton and or seiche related reversals induced by ponding and interactions of the flow with the topographical confinements of the trench it is concluded that contained muddy turbidites cannot be adequately modelled using published sequences differentiation of single model and contained mud turbidites offers obvious advantages in basin analysis and in understanding the plethora of turbidity current related depositional mechanisms of deep sea mud

late quaternary calcareous clayey silty muds in the obock trough gulf of aden hemipelagites or fine grained turbidites

sedimentation in the conway trough a deep near shore marine basin at the junction of the alpine transform and hikurangi subduction plate boundary new zealand the conway trough is a 40 km 10 km 1000 m deep rectangular tectonically controlled sedimentary basin situated on an active plate boundary the basin lies at the junction of the alpine transform and hikurangi subduction sectors of the indo australian pacific plate boundary it is incised into cainozoic sedimentary rocks and contains a thick fill of late neogene sediment study of the continental shelf near the conway trough indicates 1 that transport mechanisms operate in a net north easterly direction and 2 that the neritic sediment drift system is confined to within a few kilometres of the shoreface with the result that 3 large areas of the shelf south of the trough comprise bare bedrock or relict late pleistocene sediment despite reaching to within 3 km of shore the conway trough receives little modern bedload sediment as indicated by a paucity of sand fill however the trough has intercepted some holocene bedload since the main channel contains redeposited graded gravel and sand with a c 14 age of 4670 yr satellite imagery and piston cores reveal that abundant mud is provided to the trough much of it from river sources up to 200 km to the south some of this sediment is inferred to move by turbid layer transport through conway trough and out via kaikoura canyon into nearby hikurangi trough nonetheless sedimentation rates in the conway trough may be as high as 1 7 m 1000 yr 1 the conway trough forms a modern example of a transform basin varying neogene examples of which are found widely in north eastern south island sedimentation models are constructed to compare transform and transduction basins particularly with respect to the effects of pleistocene sea level changes

deposition of the cambrian continental rise the st roch formation near st jean port joli quebec detailed mapping between plage victor and st jean port joli has enabled us to add a 550 m section to the top of the existing 450 m section of hubert making the longest continuous section anywhere

style scale and significance of sand bodies in the northern and central belts southwest southern uplands sedimentological and biostratigraphical data from the rhinns of galloway and adjacent areas in sw scotland confirm that deep water depositional systems consistently operated along and were sourced from the northwestern margin of an asymmetrical basin during the late ordovician and early silurian while pelagic facies accumulated simultaneously to the se providing a scenario analogous to many modern trench systems most of the observed sedimentological anomalies with regard to this general model can be explained within the context of the varied styles of trench filling depositional systems briefly reviewed here and the major stratigraphic and sedimentologic features can be best explained in terms of a geotectonically evolving fore arc region two main phases of development are recognized a llandeilo late ashgill during this time interval the fore arc trench region was tectonically juxtaposed against an active continental margin arc small to medium scale se prograding sand rich fans were formed within a relatively narrow trench leading to axial diversion of the fans initially to ne but later mainly to sw simultaneously a coarse volcanilithic sediment apron flanking the arc migrated gradually northeastwards probably in response to relative fault displacement of the arc and trench b llandovery during this time interval the fore arc trench region was dominated by a variety of mainly fan type depositional systems which were exclusively sourced at least until the uppermost llandovery from the northwestern margin the juxtaposition of coeval depositional systems differing significantly in sedimentological style and composition strongly suggests that the llandovery sedimentation in this region occurred in several structurally separated sub basins within the main trench system

sediment gravity flow deposits of an ordovician deep sea fan system western precordillera argentina abstract ordovician siliciclastic sequences of portezuelo del tontal formation ptf in the western precordillera argentina are interpreted to be deep sea deposits which formed on a passive continental margin several facies and layer divisions have been identified and interpreted as high and low density turbidites debrites and contourites hemipelagites outer and inner upper middle submarine fan subenvironments have been recognized outer fan associations consist of lobe and lobe fringe sequences inner fan associations are defined by coarse grained and channelized deposits the vertical arrangement of facies associations is interpreted in terms of progradational and retrogradational processes some sharp progradational and retrogradational transitions were controlled by allocyclic factors such as sea level changes and tectonics of the source areas the submarine fan model for the ptf is an intermediate type between the pelite rich and the sand rich fans it was formed in a narrow and elongate deep sea basin controlled by the contemporaneous evolution of an oceanic rift in the direction of progradation

transition from basin plain to shelf deposits in the carboniferous flysch of southern morocco abstract in the jebilet palaeozoic inlier 20 km north of marrakech there are extensive exposures of carboniferous flysch deposits although there are some structural complications due to over riding nappes with associated chaotic breccias one clearly unbroken succession from basin plain turbidites to shallow marine deposits can be examined the succession is more than 2 km thick and is dated as upper viscan in the uppermost part the lowermost unit of b and c based turbidites shows no sequential organisation and is interpreted as a typical basin plain association above this are similar turbidites arranged in thickening upward sequences that may represent outer fan or base of slope deposits succeeding these are thin bedded turbidites with interbedded units formed by mass movement that represent a slope deposit the overlying lenticular bedded facies resembles previously described overflow deposits of submarine fan channels but is here interpreted as comprising storm generated deposits on the outer shelf upper slope these deposits are genetically linked with the overlying parallel laminated sandstones with irregular rippled tops for which a storm surge origin is suggested the upper part of the succession shows cross bedded oolitic bioclastic sandy limestones with bipolar current structures sandwiched between low energy siltstones containing thin graded silt sand beds these are collectively interpreted as shelf deposits that formed under different depths due to transgressive regressive events the sequence differs from many described in the literature in that there is an absence of most submarine fan facies locally a nne ssw basin strike is proposed with a basin margin to the ese but there is at present little control on regional palaeogeography

deposition of ungraded muds from high density non turbulent turbidity currents turbidity current deposits of mud have recently been found up to 10m in thickness resulting from single depositional events1 2 turbidites 1 5 m thick from the madeira abyssal plain3 4 display long segments with little vertical change of grain size5 6 this suggests that the currents froze in some way making them unable to sort sediment here we suggest that a decline in flow speed of these currents led to a concentration gradient in silt close to the bed that was sufficiently steep to stratify the flow a concentration gradient of 18 kg m 3 over 1 5 m height gives a layer richardson number above the critical value of 0 25 for damping of turbulence we propose that with turbulence severely damped a dense suspension of fine material consolidates like a static suspension while continuing to flow downslope the current changes from a fully turbulent flow to a decelerating flow with suppressed turbulence and increasing density in the latter state interparticle forces prevent differential settling of the coarser grains

reflected sediment gravity flows and their deposits in flysch of middle dalmatia yugoslavia the eocene flysch of middle dalmatia comprises several beds that are interpreted to have been deposited from reflected sediment gravity flows their compositions are similar and two bed types are differentiated complex beds that are debrite plus turbidite couplets and turbidites the sequence alternations in the turbidite part of the bed opposing ripples within the same bed and opposite flow directions indicated by flutes and ripples are indicative of flow reflections the influence of seiches is suggested by the occurrence of symmetrical oscillation ripples the palaeotransport directions of reflected flows show wide dispersal a geometry of small fault controlled sub basins with centripetal palaeotransport patterns is proposed

submarine volcaniclastic rocks in this chapter we are concerned with underwater volcaniclastic eruptions and products as well as pyroclastic flows and debris generated on land and transported by mass flowage into the sea submarine fallout deposits derived from land based eruptions are treated in chapter 7 clastic materials redistributed as mass flows or turbidity currents originating from the rapid build up of tephra and epiclastic volcanic debris along coastal parts of volcanoes are also discussed in various places throughout the text e g chap 13

turbidites and iron formations beardmore geraldton ontario application of a combined ramp fan model to archaean clastic and chemical sedimentation sandy turbidites grain flows conglomeratic mass flows and oxide facies iron formation are present in the late archaean beardmore geraldton terrain a metasedimentary belt which extends for at least 80 km in an e w direction the marine portion of this basin contains four lithofacies associations la 1 thinbedded iron formation clastic sediment association this association represents a continuum of deposit types containing iron formation subtypes are defined on the basis of bedding attributes and the proportion of iron formation to sand silt 2 thin bedded turbidite dominated association these sediments consist mostly of silt sand beds which either show no vertical trends or thin and fine upwards over a few metres 3 medium bedded turbidite dominated association most of these sediments are medium to coarsegrained vertically unstructured sand sequences with occasional structured intervals 4 thick bedded association this is dominated by poorly graded sands up to 7 8 m in thickness sand beds are characterised by a thin basal zone of coarse sand and pebbles a large central interval containing a mixture of medium and coarse sand and a thin upper zone of fine sand silt the overall depositional system was initiated by transport of sediment by braided streams to the strand area where it accumulated in distributary mouth bars we infer a nearshore break in slope locally with large channels la 4 extending from close to the strand line across deltaic surfaces to the deeper portions of submarine fans structured portions of la 3 however many deltaic surfaces probably were not tapped by major channels but merged downslope into a submarine ramp sediment was transported across the ramp by slump events and sheet like grain flows unstructured portions of la 3 iron formation and la 2 sediments probably accumulated both in upper mid ramp areas with low sediment delivery rates and distal to fan ramp successions as major streams on the braid plain changed position associated submarine channels and slump fed ramp deposits also would have shifted laterally this produced overlap of different facies associations in both the fan and ramp environments which may explain why observed vertical trends in bedding are limited to several metres we suggest that on narrow active archaean cratonic margins additional non regular processes such as variations in sediment supply related to periods of heightened pyroclastic activity and seismic activity associated with the arc also contributed to the lack of vertically structured sequences turbidite sequences in such environments in general may contain important contributions from both submarine ramp and submarine fan sedimentation

inclusion host relations involving accessory minerals in high grade metamorphic and anatectic rocks in general accessory minerals are expected to participate in partial fusion of their host rocks to a degree determined simply by their solubilities in the melt the possibility must be recognized however that a given accessory grain may be physically isolated from the melt by inclusion within a residual major mineral because of the importance of accessory minerals to crustal rock trace element and isotope geochemistry and because of their common existence as inclusions in major phases we undertook an evaluation of the factors that affect inclusion formation during ultrametamorphism three approaches are taken 1 a review of interfacial energy considerations is used to show that the free energy of the system is lowered by location of accessory minerals at major phase grain perimeters and that the magnitude of this effect is proportional to the square of the accessory grain radius 2 annealing and partial melting experiments 1000 c 10 and 15 kbar on rock analogs are described and the results are shown to confirm the predicted tendency of accessory minerals to occupy grain boundaries and 3 the results of a study of accessory phase rutile and zircon distribution in a migmatite from the tibetan slab are reported again in confirmation of the prediction that accessories tend to be situated at majorphase grain perimeters the latter two aspects of the study reveal that although included accessory grains are common their generally small size results in only a minor contribution to the bulk rock budget of accessory mineral components most of the mass of these components is contained within populations of generally larger accessory grains located at major phase grain boundaries accordingly the assumption that accessory minerals are involved in crustal melting is generally valid

deformation of an early preboreal deposit at nykvarn se sweden as a result of the bulldozing effect of a grounding iceberg abstract an early preboreal glaciomarine deposit near nykvarn se sweden consists from bottom to top of a submarine outwash fan a full glacio marine deposit and a near coast marine unit of poorly sorted ice rafted debris the top part of the succession shows soft sediment deformations that have the same characteristics as material moved forward by a bulldozer these deformation structures are interpreted as being due to grounding of an eastward moving iceberg this caused detachment of the lower part of the succession in the way that sand is pushed forward by a bulldozer the iceberg most likely calved off the retreating ice front which extended into sea due to a sudden subglacial discharge of meltwater jokulhlaup which event seems related to the breakthrough of an ice dam that could no longer withstand the pressure of a growing water volume produced by increased ice melting

reverse flow in turbidity currents the role of internal solitons pickering hiscott 1985 have demonstrated amply the presence of reverse flow units within the thick bedded calcareous wacke tcw beds of the turbiditic cloridorme formation middle ordovician gaspe peninsula quebec canada these reverse flow units are underlain and overlain by units which reveal flow in the primary obverse direction in this paper a model is proposed for this reverse flow based on the probable nature of the primary turbidity flow it appears that the initial flow was highly elongated thickness h length l with h 500 m velocity u 2 m s 1 and sediment concentration c 1 25 o the rate of momentum loss of the flow is estimated by means of a useful parameter which we call the drag distance symbol dd defined by where h and l are the thickness and length of the flow respectively ccd is a combined drag coefficient representing friction on the bottom and at the upper interface and fcd is a form drag coefficient related to the shape and size of the head dd is the distance travelled by a current of constant h and l flowing over a horizontal bottom and obeying a quadratic friction law for an e fold reduction in velocity simple considerations confirmed by our own experiments described in this paper show that such an elongated turbidity current cannot be reflected as a whole from an adverse slope when the nose of the current reaches the slope it forms a hump which surges backwards and sooner or later breaks up into a series of internal solitons the latter probably numbering 4 7 will cause reverse flow at a given point as they pass by provided that the residual velocity in the tail is not too great flow in the original obverse direction will be re established after the passage of the solitons quiescent periods in front of between and behind the solitons when soliton associated currents cancelled out the residual obverse flow would allow the deposition of thin mud drapes additional flow reversals observed in a few of the tcw beds cannot be explained readily by the re passage of solitons since wave breaking at the ends of the basin would cause massive energy loss internal seiches are the preferred explanation for these later reversals

grain growth kinetics of quartz and calcite aggregates grain growth rates for novaculite flint and jasper have been determined between 1000 and 800 c and 15 to 2 kb water pressure a pre treatment established an equilibrium microstructure and a nearly uniform mean grain diameter bar d 0 at 1000 c and 15 kb the grain growth data are linear on a log bar d bar d 0 vs log time plot and there is no significant difference between the three samples although the jasper contained 5 10 vol iron oxide at lower pressures and temperatures the growth curves are approximately parallel to the 1000 c and 15 kb data but growth is slower and that for jasper is slower than for the other two the growth rate is strongly dependent on the solubility of quartz in the intergranular fluid and the activation energy is about 11 kcal mole the data are used to estimate the growth rate of quartz at metamorphic conditions and to help evaluate the conditions where growth of dynamically recrystallized grains may be significant the growth rate of calcite grains s

the upper jurassic boulder beds and related deposits a fault controlled submarine slope ne scotland during the late jurassic kimmeridgian rifting in the north sea large scale normal faults developed to form relatively deep marine basins the north western margin of one of these basins defined by the helmsdale fault is described to show the nature of sedimentation associated with a submarine fault scarp subsidence to the se of the helmsdale fault led to a fault scarp down which various sediment mass flows moved including debris flow rockfall high and low concentration turbidity currents and possible storm surge wash over deposits redeposition by soft sediment sliding was important as a slope accretion process deep channels were incised into the slope and infilled by coarse grained elastics contemporaneous small scale submarine fans located farther off in the present north sea may have developed as a result of slope bypassing sediment flows down such channels the succession is characterized by extreme sediment heterogeneity compared to many deep water environments and it may be part of an ancient fan delta the main influences upon slope accretion were the synsedimentary movements on the helmsdale fault and the nature of the available sediment input such that the succession represents structurally controlled and sedimentologically modified slope development

sedimentation in the chile trench depositional morphologies lithofacies and stratigraphy the depositional bodies of the chile trench trench fans the axial channel sheeted basins ponded basins and axial sediment lobes control the spatial distribution of modem lithofacies in the basin sheeted basins south of 41 s are presumably fed by closely spaced submarine gullies that approximate a line of source of sediment supply along the base of the slope trench fans 41 s 33 s are built at the mouths of major submarine canyon systems which act as point sources of sediment supply the axial channel follows the northward gravitational gradient draining the distributary networks of trench fans into the longitudinal transport system down gradient northern fan lobes are severely dissected by erosional processes evidently periods of proximal deposition alternate with periods of massive sediment remobilization and progradation of the axial dispersal system into more distal environments channelized basins in the canyon mouth areas yield to sheeted basins depositional surface maintains an axial gradient or ponded basins depositional surface is strictly flat in inter canyon areas tectonic disruption of the oceanic basement can locally augment the axial gradient and stimulate flow channelization or reverse the gradient and induce sediment ponding a large margin parallel sediment lobe is built at the base of a high axial escarpment near 33 s where the axial channel crosses a transverse discontinuity at the convergent plate boundary five lithofacies are defined by q mode factor analysis of sediment textures and hydro dynamic structures in 27 cores from the chile trench the channel facies thick amalgamated sand massive to laminated or cross bedded is deposited by high energy processes within the coarse grained bedload of turbidity currents it forms in distributary and axial channels the levee facies rhythmically bedded internally structureless graded sand and graded silt is deposited from concentrated sediment suspensions that quickly lose momentum during channel spillover it forms on channel flanks although constructional levees are not always present the basin 1 facies more complete bouma sequences both upper and lower flow regime structures forms in ponded basins where flows are confined by a high relief seaward trench wall the basin 2 facies graded and laminated silt lower flow regime structures forms in low energy environments such as interchannel areas distal basins trench walls and elevated topographic features the contourite facies silt and sand laminations winnowed from hemipelagic muds and distal turbidites is best developed in sediment starved basins where geostrophic currents are constricted and accelerated between the steep inner and outer trench walls the trench wedge records a coarsening upward sequence as the oceanic plate migrates toward and into the trench during plate convergence and becomes more proximal to sediment sources along the base of the continental margin near canyon mouths prograding trench fans drive the axial channel seaward into the trench wedge and the coarsening upward sequence is truncated by a time transgressive erosional unconformity abandoned axial channel deposits are carried landward beneath prograding fans to record a fining upward sequence above the basal unconformity channel migration and lobe aggradation may produce fining and coarsening upward sequences on depositional fan lobes but sequences on the erosional lobes are fragmented by numerous truncation surfaces

submarine fan deposited sandstone and rudite in a mid cenozoic interarc basin in maewo vanuatu new hebrides the volcaniclastic lower sarava formation of north eastern maewo was deposited in a late oligocene early miocene deep sea fan environment eight lithofacies can be recognized from a westward trending deep sea fan which prograded at a depth of 4 25 km within an extinct interarc basin these lithofacies include massive spilite rich rudite graded coarse rudite arenite graded fine rudite arenite intraformational rudite brown and grey siltstone minor calcarenite and a lithofacies composed of turbidites with bouma sequences the sediment was essentially derived from the vitiaz palaeoarc to the east non calcareous red and green siltstone and minor airfall tuff was deposited distal to the arenite and rudite in areas or during periods of slower sedimentation slightly more than half of the lower part of the sarava formation is represented by massive rudite graded coarse rudite arenite and graded fine rudite arenite these deposits and some of the calcarenites and massive arenites were deposited from decelerating high density turbidity currents some of the thicker rudite arenites may have been induced by tsunamis classical turbidites deposited perhaps from low density turbidity currents are rare the petrography of igneous clasts indicates that late oligocene early miocene volcanism on the vitiaz palaeoarc was largely basaltic andesitic but there were some dacitic eruptions

depositional environments along a carbonate ramp to slope transition in the silurian of washington land north greenland during the earliest silurian subsidence and tilting of a relatively flat carbonate platform produced a homoclinal carbonate ramp transitional to the slope of a deep water basin further subsidence associated with a flexure differentiated the slope from the carbonate ramp subsequently a linear reef tract developed along part of the flexure producing a steep reef scarp slope at the outer homoclinal carbonate ramp margin and accentuating the initial basin slope isolated reefs also developed on the slope the reef tract which influenced slope depositional environments considerably marked the transition from the shallow homoclinal carbonate ramp facies to the deeper slope environments background slope sedimentation was primarily terrigenous mudstone deposited out of suspension and by very dilute muddy turbidity flows superimposed were calcarenites and conglomerates derived from the carbonate ramp margin and reefs deposited by low to high density turbidity flows debris flows and possibly grain a

microstructure evolution of aqueous fluid bearing wehrlites implications for the fluid distribution in polymineralic rocks 1 the microstructure of aqueous fluid bearing wehrlites was experimentally studied in order to investigate the fluid distribution in polymineralic rocks wehrlites of various forsterite diopside ratios were synthesized with 1 0 1 5 wt water at 1200 c and 1 2 gpa for 1 5 668 hours conspicuous grain growth drag and coagulation of pore fluids were observed in the time series experiments the pore fluids were classified into two types those surrounded only by a single phase g type and those surrounded by both forsterite and diopside i type in the short time runs the relative volume fraction of i type pores in all the pores fi agrees well with the value calculated from an ideal pore distribution model in which all the grains are randomly distributed the fi of wehrlites with various forsterite diopside ratios increased with average grain size and reached a steady state value at 80 90 in about 160 163 hours the increase of fi is explained by interphase boundary trapping g type pore fluids move faster than i type and the number of g type becoming i type by being trapped into the interphase boundary per unit time is larger than that of i type pores transforming to g type the experimental results suggest that large fractions of pore fluids might be distributed at the grain junctions surrounded by more than two mineral phases in natural rocks as a result of grain growth the connectivity of the fluid network in polymineralic rocks may be strongly influenced by modal composition of the rocks as well as by the dihedral angles among the fluid and two mineral phases

subaqueous sediment gravity flow deposits practical criteria for their field description and classification a new method for the description and classification of subaqueous sediment gravity flow deposits is proposed the classification scheme employs a convenient letter code and divides deposits individual beds into descriptive categories of two hierarchical levels facies and subfacies facies as the higher rank categories are distinguished chiefly on the basis of sediment type i e bed grain size texture a total of 13 facies have been distinguished g gravel gs gravel sand couplet gys gravelly sand s sand sm sand mud couplet ms mud sand couplet tm silt mud couplet mt mud silt couplet m mud mys muddy sand sym sandy mud myg muddy gravel gym gravelly mud subfacies as the lower rank categories are distinguished within the individual facies on the basis of the bed s internal structures the number of subfacies is unlimited and their labelling code includes particular facies symbols see above preceded by lower case letters denoting specific sedimentary structures and their vertical arrangement subfacies thus refer to the bed s intervals or divisions which are labelled as follows m massive unstratified and ungraded g graded unstratified and graded s plane stratified x cross stratified 1 parallel and or cross laminated q liquefied for example subfacies gsg graded to plane stratified gravel are gravel beds that have a lower graded interval and an upper plane stratified interval subfacies xg cross stratified gravel are gravel beds that are cross stratified throughout subfacies sls plane stratified to laminated sand are sand beds that have a lower plane stratified interval and an upper laminated parallel and or cross laminated interval

the character of seismo turbidites in the s 1 sapropel zakinthos and strofadhes basins greece the early holocene s 1 sapropelic sequence in the northwest hellenic trench has been studied in six piston cores from the zakinthos and strofadhes basins the s 1 sequence 0 7 3 5 m thick consists principally of silt to mud turbidites with rare thick disorganized sandy turbidites these lithofacies are described and compared with fine grained turbidites from the literature petrographical data including the abundance of organic carbon and planktonic microfossils indicate that the principal source of sediment to the turbidites was from the continental slope on the basis of composition and texture five turbidite units can be correlated between the two basins these basins are fed by separate but adjacent drainage systems the apparently synchronous occurrence of turbidites in the two drainage systems suggests that the turbidity currents were seismically triggered some of the turbidites show poorly organized beds which may reflect the slump origin and the short 30 km distances of travel turbidites were deposited more frequently in the s 1 sapropelic interval than in the over and underlying sediments application of slope stability analysis shows that on the 8 slopes above the basins a 10 cm thick sapropel would have a factor of safety of about 2 and would fail with earthquake accelerations in excess of 0 08 g the frequency of earthquakes likely to produce such accelerations is similar to the observed frequency of turbidites the low strength of the sapropelic sediment makes it particularly susceptible to such failure similar thin skinned slumping may be an important process for the initiation of turbidity currents in other environments where there are steep slopes or high sedimentation rates

contained reflected turbidity currents from the middle ordovician cloridorme formation quebec canada an alternative to the antidune hypothesis the parautochthonous cloridorme formation is a syn orogenic flysch succession that was deposited in an elongate foredeep basin as mainly lower middle fan outer fan and basin floor deposits the basin floor deposits about 1 5 km thick are confined to members 1 2 and 1 and are characterized by graded thick 1 10 m mud rich calcareous greywacke beds previously interpreted as deposits of concentrated muddy unidirectional turbidity currents that locally generated backset antidune lamination in internally stratified flows the dominant flow directions were from east to west but west to east transport also occurred as seen in the orientation of ripples climbing ripples flutes consistently overturned flames and grain imbrication we believe that the flows that deposited these thick calcareous greywacke beds reversed by roughly 180 one or more times during deposition of the lower sandy part of the beds flow reversals are consistent with the sharp grain size breaks and mud partings within sandy divisions measurement of grain fabric relative to stratification in the most celebrated antidune bedforms indicates flow from west to east thus the bedforms were produced by west to east migration of megaripples not by the upcurrent migration of antidunes the thick muddy beds were deposited by large volume muddy flows that were deflected and reflected from the side slopes and internal topographic highs of a confined basin floor much like the contessa and similar beds of the italian apennines large quantities of suspended mud were ponded above the irregular basin floor and settled to produce the thick silty mudstone caps seen on each bed because of their mode of emplacement we propose that these beds be called contained turbidites