sedimentology and hydrocarbon potential of yager structural complex possible paleogene source rocks in eel river basin northern california the yager structural complex of coastal northern california is composed of paleogene mudrocks turbidites and related deep marine deposits the strata are folded but lack the severe and pervasive stratal disruption that characterizes surrounding accreted terranes such as the franciscan coastal belt lithofacies associations and depositional cycles define three environmental settings slope feeder channel and restricted basin the rocks probably represent a sequence of trench slope and slope basin deposits that accumulated above a broadly coeval basement of accreted coastal belt rocks yager strata are possible source beds for hydrocarbons within the late cenozoic eel river basin type iii kerogen is dominant and organic carbon content and hydrocarbon yield are relatively low nevertheless the thermal maturity of yager shales is well within the window of peak hydrocarbon generation this level of maturation is attributed to a combination of middle tertiary thrust faulting and subsequent depositional burial beneath the neogene wildcat group

sedimentology and reservoir potential of matilija sandstone an eocene sand rich deep sea fan and shallow marine complex california the matilija sandstone of the santa ynez mountains of southern california records a major regressive event in the eocene santa ynez basin in which turbidites were deposited and subsequently covered by shallow marine deposits despite thick favorable source beds and generally good initial reservoir characteristics the matilija sandstone is not a productive unit in the basin low reservoir permeability generally less than 1 md and porosity 1 to 10 are interpreted to be the result of early compaction cementation and diagenesis the lower part of the matilija sandstone is a 1 300 ft 400 m thick sand rich deep sea fan complex which overlies basin plain turbidite deposits of the juncal formation the matilija sandstone consists of anastomosing outer fan lobes lobe fringe and interlobe deposits overlain by channelized middle and inner fan deposits the upper matilija sandstone consists of shallow marine cross bedded sandstone red beds and carbonate evaporite lignite sequences which overlie the turbidites deposition of the matilija sandstone was terminated by a rapid basin deepening event which culminated in deposition of basin plain slope and turbidite deposits of the cozy dell formation the lower matilija sandstone deep sea fan deposits have a high sandstone to shale ratio 4 1 to 10 1 and consist of submature arkoses folk 1980 the depositional lobes consist of facies b c and d turbidites and a channelized sequence of facies a and b turbidites the average sandstone is medium grained moderately sorted subangular to subrounded and massive containing 40 quartz 35 feldspar about equal amounts of plagioclase and potassium feldspars 10 lithic fragments mostly volcanic and metamorphic types and minor amounts of detrital clay illite mica chert and heavy minerals early compaction carbonate cementation and authigenic pore lining and pore filling chlorite albite potassium feldspar quartz and localized laumontite have reduced the initial porosit and permeability the only remaining porosity is secondary resulting from the dissolution of detrital feldspars and minor fracture porosity

a rate and state dependent ductile flow law of polycrystalline halite under large shear strain and implications for transition to brittle deformation we have conducted double shear biaxial deformation experiments in layers of nacl within its fully plastic fp regime up to large shear strains 50 with velocity steps from this we have empirically formulated a rate and state dependent flow law which explains the transient mechanical behavior the steady state flow stress in the fp regime can be explained by a power law with a stress exponent 8 5 and an activation enthalpy of 1 3 ev with the instantaneous response having a higher stress exponent 13 8 although there is data scatter the transition to brittle regime is associated with weakening from the ductile flow law in fp regime the mechanical response is characterized by a monotonic decay to a new steady state while in the transitional regime by a peak decay behavior the transient flow law obtained here is of considerable importance in the study of the brittle ductile transition in rocks

lithofacies analysis of the dezadeash formation jura cretaceous yukon canada the depositional architecture of a mud sand rich turbidite system abstract the dezadeash formation is a northwest trending belt of predominantly jura cretaceous deep marine siliciclastic rocks in southwestern yukon canada it is truncated to the southwest by the denali fault system a major transcurrent fault along which 370 km of dextral slip occurred in post early cretaceous time and it is flanked to the northeast by the kluane schist a mainly mica quartz schist assemblage of unknown age and origin this study provides a robust quantitative description of lithofacies comprising a point source mud sand rich turbidite system approximately 16 335 m of measured strata from 75 sections throughout the dezadeash formation indicate that up to 29 lithofacies types are present and these are dominated by thin to thick bedded sandstone mudstone couplets and medium to thick bedded sandstone the various lithofacies are grouped into conglomerate sandstone sandstone mudstone and siltstone mudstone lithofacies associations which are interpreted as slide channel lobe transition lobe and overbank architectural elements respectively stacked channel lobe transition and lobe elements predominate but the depositional architecture displays no apparent overall vertical trend the dezadeash formation represents mainly the lower middle and lower subdivisions of a point source mud sand rich turbidite system that records a single stage of fan growth as it prograded transversely from a volcano plutonic arc into the basin

geomorphological variability among microtidal estuaries from the wave dominated south african coast abstract over 300 independent river outlets exist around the microtidal wave dominated south african coast most of these are located in drowned river valley settings and have acquired their present morphology during the holocene marine transgression a variety of geomorphological forms are identified in these estuaries that result from variation in antecedent topography fluvial sediment supply and marine sediment supply five distinctive estuary types are identified on the basis of contemporary morphodynamics these are categorised into three types of normally open estuary that maintain a semi permanent connection with the open sea and two types of normally closed estuary which are separated from the sea for long periods by a continuous supratidal barrier the contemporary morphodynamics and sedimentary environments of each estuary type are discussed open estuaries include barrier inlet systems maintained by fluvial discharge termed river dominated estuaries and tidal discharge termed tide dominated estuaries a third category of open estuary lacks a supratidal barrier due to inadequate marine sediment availability closed estuaries receive marine influence via barrier overwash and occasional breaching but are typically enclosed behind a continuous supratidal barrier two categories of closed estuary are identified perched and non perched perched estuaries develop behind high berms and maintain a water level above high tide level in the open sea they are often dominated by fresh to brackish water and breach and drain periodically non perched estuaries are developed behind low elevation barriers fronted by wide dissipative beach profiles high overwash frequency introduces marine water into such systems breaching of such estuaries does not produce dramatic draining as the water level may only drop according to the stage of the open sea tidal cycle the variety of estuary types suggests several potential pathways may exist in estuarine development and that the progressive infilling model is an over simplification

cyclic stacking pattern architecture and facies of the turbidite lobes in the macigno sandstones formation chattian aquitanian northern apennines italy abstract this study presents a detailed facies analysis of an 800 m thick stratigraphic succession in the basinal turbidites of the macigno sandstones formation msf recording the first foredeep in the northern apennines italy this stratigraphic succession shows an evident stacking pattern that besides the basal part 200 m thick dominated by fine grained and thin beds is characterized by seven magnificently exposed sandstone lobes from 90 to 19 m thick separated by well developed fine grained interlobe deposits thanks to the detailed facies analysis not only a well defined architectural hierarchy has been identified but a facies scheme has also been proposed whereby cyclic recurring of three facies associations has in turn been identified each facies association records a well determined evolutionary stage of lobe development where an early depositional stage of the lobe building phase is followed by a flow impact and bypass stage recording flow decelerations and hydraulic jumps induced by the morphology created by the underlying depositional lobe the latter phase promotes a switching and channel feeder avulsion that heralds the third phase of abandonment with the deposition of fine grained interlobes the facies stacking pattern and the evolutionary model of the msf also supported by other similar field and experimental works are intended as a contribution to the understanding of intrinsic autogenic mechanisms at the basis of sand rich depositional lobe development

input storage and distribution of large woody debris along a mountain river continuum the drome river france abstract large woody debris lwd input storage and distribution were studied along the drome river a french alpine river with an active shifting channel and a well developed riparian forest lwd input from the floodplain is low 669 6 mg year 1 between 1948 and 1971 and 569 3 mg year 1 between 1971 and 1991 based on estimates of average lwd mass per study plot a range of 766 2122 mg year 1 of lwd were stored within the active channel e g unvegetated bars and low flow channel 60 km course covering 492 ha lwd accumulations are mainly observed on gravel bars at a limited number of preferential sites they are relatively rare and are randomly distributed in the low flow channel consequently lwd location is mainly associated with the decrease of flow level in shallow sectors in the low flow channel lwd stop en route is primarily caused by in channel structures such as boulders or vegetated islets general geomorphological factors e g pattern slope etc provide less explanation of lwd distribution moreover the residence time of lwd accumulations on the drome river is short lwd storage 1 3 3 7 times the annual lwd input from the floodplain and their morphogenic role is negligible few of the accumulations are buried or characterized by vegetation shoots and associated pools

a microphysical model for fault gouge friction applied to subduction megathrusts a microphysical model is developed for the steady state frictional behavior of illite quartz fault gouge and applied to subduction megathrust p t conditions the model assumes a foliated phyllosilicate supported microstructure which shears by rate independent frictional slip on the aligned phyllosilicates plus thermally activated deformation of the intervening quartz clasts at low slip rates or high temperatures the deformation of the clasts is easy accommodating slip on the foliation without dilatation with increasing velocity or decreasing temperature the shear of the clasts becomes more difficult increasing bulk shear strength until slip is activated on inclined portions of the phyllosilicate foliation where it anastomoses around the clasts slip at these sites leads to dilation involving clast matrix debonding balanced at steady state by compaction through thermally activated clast deformation model predictions taking pressure solution as the thermally activated mechanism show three regimes of velocity dependent frictional behavior at temperatures in the range of 200 500 c with velocity weakening occurring at 300 400 c in broad agreement with previous experiments on illite quartz gouge effects of slip rate normal stress and quartz fraction predicted by the model also resemble those seen experimentally extrapolation of the model to earthquake nucleation slip rates successfully predicts the onset of velocity weakening behavior at the updip seismogenic limit on subduction megathrusts the model further implies that the onset of seismogenesis is controlled by the thermally activated initiation of fault rock compaction through pressure solution of quartz which counteracts dilatation due to slip on the fault rock foliation

slope and deep sea fan facies and paleogeography of upper cretaceous chatsworth formation simi hills california the upper cretaceous chatsworth formation is a sand rich deep sea fan deposit consisting of thick channelized sequences and interchannel deposits typical of middle fan facies it has poorly developed outer fan lobes and slope facies petrographic and x ray diffraction xrd data indicate the arkosic deposits of the chatsworth formation were derived from an uplifted granitic terrane paleocurrent studies indicate northward sediment transport and an east trending slope regional comparisons of the simi hills with the santa monica and santa ana mountains suggest these terranes were once contiguous and covered part of a deep sea fan system that comprised much of the southern california area subsequently these terranes have been offset along the malibu cucamonga and elsinore faults and rotated in response to the opening of the los angeles basin and to other adjustments in the tectonic framework of the area the chatsworth formation is thought to be part of a forearc basin deposit similar to the great valley sequence and not part of the salinian borderland block the original geographic position of the forearc basin was to the south of the sierra nevada mountains and the great valley sequence

the role of orogen transversal tectonic structures on the syn and post depositional evolution of a foredeep succession the case of the cervarola sandstones formation miocene northern apennines italy abstract in collisional belts foredeep turbidites are tracers of the evolution of the orogenic wedge syn depositional tectonics affects the sedimentary facies distribution of the turbidite deposits while post depositional tectonics generates the major structures that deform the foredeep basins the aquitanian to burdigalian cervarola turbiditic succession is one of the main oligo miocene foredeep units that characterize the northwestern portion of the northern apennines the reconstructed syn and post depositional evolution of the cervarola succession reveals that orogen transversal tectonic structures strongly and persistently controlled this turbiditic succession from the time turbidites were infilling the foredeep basin aquitanian burdigalian to the time this foredeep deposits became a major and complex thrust sheet of the northern apennines orogenic wedge post burdigalian present the syn depositional history of the cervarola turbiditic succession has been defined through a detailed facies analysis that has allowed the basin morphology to be accurately constrained then the post depositional history has been addressed to define the multi scale deformations preserved in the cervarola succession through the following approaches 1 analysis of published geological maps 2 detailed field mapping 3 construction of geological cross sections across the major folds 4 analysis of meso scale structures and 5 analysis of a seismic reflection profile the study has outlined that the foredeep basin morphology was tectonically controlled and segmented by compressive structures transversal to the nw se basin elongation the same structures were also present during the post depositional compressive phases that built up the orogenic wedge and they have been even reactivated in the latest extensional events that have dismembered the mountain range these orogeny transversal and long lasting 23myrs lineaments cross cut the entire tectonic stacking of the northern apennines affecting tectonic units which suffered different amount of translation during the mountain building making the reconstruction of the geological evolution possible only with an integrated approach as performed in this work

quantifying the hierarchical organization of compensation in submarine fans using surface statistics abstract stratigraphy is often interpreted within hierarchical or scale dependent frameworks that subdivide deposits based on distinct jumps in characteristics such as duration of deposition or scale while the interpretation is logically valid few studies quantitatively demonstrate that the jumps exist rather recent work has quantitatively shown some characteristics of stratigraphy to be fractal or scale invariant compensational stacking the tendency for sediment transport systems to preferentially fill topographic lows is a concept widely used in stratigraphic interpretation here we use the compensation index a metric that quantifies the strength of compensational stacking in sedimentary deposits to describe the architecture of stratigraphy exposed in outcrops of submarine fan strata in the carboniferous ross sandstone representing contrasting architectural styles 1 predominantly lobe elements and 2 predominantly channel elements in both datasets the stratigraphic architecture is classified into hierarchical classes of beds stories and elements results are the following first at both sites we document statistically significant increases in the strength of compensation across larger hierarchical levels supporting the use of hierarchical interpretations of stratigraphy it is therefore plausible for some characteristics of sedimentary systems to be hierarchical and others to be fractal second we document that lobe elements stack more compensationally than channel elements we interpret this pattern to document that compensation increases along a longitudinal transect through this distributive submarine fan

high frequency cyclicity milankovitch and millennial scale in slope apron carbonates zechstein upper permian north east england the upper permian zechstein slope carbonates in the roker formation zechstein 2nd cycle carbonate in north east england consist of turbidites interbedded with laminated lime mudstone studies of turbidite bed thickness and relative proportion of turbidites percentage turbidites in 20 cm of section reveal well developed cyclicities consisting of thinning upward and thickening upward packages of turbidite beds these packages are on four scales from less than a metre up to 50 m in thickness assuming that the laminae of the hemipelagic background sediment are annual allows the durations of the cycles to be estimated in addition counting the number and thickness of turbidite beds in 20 cm of laminated lime mudstone which is approximately equivalent to 1000 years each lamina is 200 m gives the frequencies of the turbidite beds the average thicknesses and the overall sedimentation rates through the succession for 1000 year time slots figures obtained are comparable with modern rates of deposition on carbonate slopes the cyclicity present in the roker formation can be shown to include milankovitch band ca 100 kyr short eccentricity ca 20 kyr precession and ca 10 kyr semi precession cycles and sub milankovitch millennial scale cycles 0 7 to 4 3 kyr eccentricity and precession scale cycles are related to highstand shedding and relative sea level change caused by milankovitch band orbital forcing controlling carbonate productivity the millennial scale cycles which are quasi periodic probably are produced by environmental changes controlled by solar forcing i e variations in solar irradiance or volcanic activity most probable here are fluctuations in carbonate productivity related to aridity humidity and or temperature changes precession and millennial scale cycles are defined most strongly in early transgressive and highstand parts of the larger scale short eccentricity cycles the duration of the roker formation as a whole can be estimated from the thickness of the laminated lithotype as ca 0 3 myr

velocity dependence of strength and healing behaviour in simulated phyllosilicate bearing fault gouge abstract despite the fact that phyllosilicates are widespread in fault zones little is known about the strength of phyllosilicate bearing fault rocks under brittle ductile transitional conditions in this study we explored the steady state strength and healing behaviour of a simulated phyllosilicate bearing fault rock i e muscovite plus halite and brine at room temperature normal stresses of 1 9 mpa atmospheric fluid pressure and sliding velocities of 0 001 13 m s using a rotary shear apparatus while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behaviour the strength of mixtures containing 10 50 muscovite is both normal stress and sliding velocity dependent at low velocities 1 m s velocity weakening frictional behaviour occurs along with the development of a structureless intermixed cataclastic microstructure the steady state porosity of samples deformed in this regime increases with increasing sliding velocity we propose that this behaviour involves competition between dilatation due to granular flow and compaction due to pressure solution towards higher sliding velocities dilatation increasingly dominates over pressure solution compaction so that porosity increases and frictional strength decreases during periods of zero slip pressure solution compaction occurs causing a significant strength increase on reshearing our results imply that cataclastic overprinting of mylonitic rocks in natural fault zones does not require any changes in temperature or effective pressure conditions but can simply result from oscillating fault motion rates our healing data suggest that foliated aseismically creeping fault segments will remain weak and aseismic whereas segments that have slipped seismically will rapidly re strengthen and remain in the unstable velocity weakening regime

sand rich turbidite system of the late oligocene northern apennines foredeep physical stratigraphy and architecture of the macigno costiero coastal tuscany italy

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

petrology and geochemistry of siliciclastic rocks of mixed feldspathic and ophiolitic provenance in the northern apennines italy provenance in clastic sedimentary rocks in the northern apennines is determined by integrated petrographic and geochemical criteria thus mafic poor arkoses in the gottero formation senonian paleocene deposited prior to the alpine orogeny were derived from granitic provenance in the sardinian corsican massif in the gottero formation chemical criteria distinguish between very low input of detrital mafic material and co c and ni added entirely by adsorption on clay minerals post alpine orogeny feldspathic sandstones in the macigno formation mid oligocene lower miocene and cervarola formation lower miocene reflect a more diverse provenance of granitic metamorphic ophiolitic and sedimentary rocks in the apennines and alps the macigno and cervarola rocks are distinguished by serpentine gabbro and diabase fragments and higher chlorite contents than in the gottero rocks chemically the macigno and cervarola rocks contain distinctive signatures expressed in higher mgo co cr and ni contents of the mafic ultramafic detritus a wider range and more scattered cr and ni variation and higher niggli ti for a given niggli al alk content the mgo co cr and ni abundances indicate up to 10 ultramafic ophiolitic detritus in the macigno and cervarola sandstones and up to 17 ophiolitic detritus in associated shales estimated by comparison of mixtures of feldspathic sands with ligurian peridotites up to 10 basaltic ophiolitic detritus in these sediments is suggested by cao and fe2o3 total abundances petrographic data indicate that a major part of the detritus in the macigno and cervarola formations is from alpine granitic basement of calc alkaline granite to tonalite plutons and gneisses but apart from higher ba in macigno and cervarola sandstones than in the gottero sandstones this is difficult to identify chemically the trace elements cr ni ba rb ce la y co cu ga pb and zn generally have positive correlations with niggli al alk a chemical surrogate measure of sheet mineral clays micas and chlorites content whereas sr which is associated with carbonate and feldspar shows negative correlation with al alk an olistostrome unit contains the most weathered detritus but otherwise shows similar chemical variation to the other formations methods to 1 identify separately mafic and ultramafic inputs 2 recognize in shales co cr and ni derived from ophiolitic sources and non ophiolitic sources 3 estimate the minimum mafic ultramafic proportion in a sediment may have general application elsewhere in sedimentary and metasedimentary rocks

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

prediction of effects of woody debris removal on flow resistance a simple technique for predicting the darcy weisbach friction factor for river channels with varying amounts of large woody debris was developed first debris density is determined based on measurement or visual estimation of cross sectional areas of debris formations in the plane perpendicular to flow the darcy weisbach friction factor is then computed using debris density channel geometry mean flow velocity and the debris drag coefficient the debris drag coefficient may be computed fom a power function with experimentally determined coefficients for verification of the proposed procedure debris density and friction factors were measured in river reaches in western tennessee and southeastern new south wales australia friction factors computed using the procedure were within 30 of measured values for straight sand bed reaches and within 38 of measured values for sinuous gravel bed reaches the computational procedure explained 84 of the variance in observed values

sedimentation in deep sea lobe elements implications for the origin of thickening upward sequences the frequency and origin of thickening upward packages in the sediments of deep sea environments has been a topic of much recent debate excellent bed scale exposures in the carboniferous ross formation western ireland allow single surfaces to be traced laterally and the detailed architecture of whole packages to be evaluated using multiple vertical logs the deposits comprise architectural elements including bed sets lobe elements and composite lobes with the lobe elements being arranged in thickening upward depositional packages results show that these packages are the result of the progradation of each lobe element whereby each package records a vertical trend from distal to proximal deposits accompanied by an increasing frequency of megaflutes and ultimately the development of broad erosional surfaces we propose a six stage model for lobe element evolution that documents successive phases of deposition sediment bypass erosion and lobe abandonment this new model provides a mechanism for lobe element switching and explains the development of thickening upward successions this allows the re examination of existing process models for these sedimentary packages in deep sea sediments

anatomy of collapsed and re established delta front in lower cretaceous of eastern spitsbergen gravitational sliding and sedimentation processes spectacular coastal cliff exposures in an early cretaceous deltaic succession near kvalvagen in eastern spitsbergen norwegian arctic show a variety of styles of gravity driven deformation and resedimentation associated with delta front progradation and instability the large scale collapse involved a distributary channel sand unit some 20 m thick and the underlying delta slope prodelta shaly heterolithics the deformation was essentially brittle whereby large blocks of the delta front succession slid and rotated its gross style involved two large cuspate tear away scars at least 1 1 5 km wide and 50 60 m deep separated by narrow remnant buttresses of in situ strata the basement in the region was tectonically active and the delta front failure was most likely sei mically triggered initial infill of the collapse scars involved slumps and debris flows derived from scar walls and locally from the sliding blocks themselves these deposits partly smoothed the local topography created by the slide blocks this early infill was followed by deposition of thin mainly muddy turbidites probably shed from the scar walls by small localized failure renewal of fluvial supply of sand led to the main infill of the scar depressions this stage involved effluent generated turbidites heterolithic and increasingly sandier turbidites and liquefied sandflows derived from unstable oversteepened distributary mouthbars the mouth bar systems eventually achieved stability and prograded across the infilled scars they were affected by periodic storm wave attack and sudden increa es of water depth the scar infill at that stage was subject to minor growth faulting possibly related to new seismic tremors

a statistical test for significance of thinning and thickening upwards cycles in turbidites abstract in turbidite successions asymmetric cycles identified in vertical sections are often used as indicators of sedimentary processes in submarine fan models thickening and coarsening upwards cycles are thought to characterize depositional lobes whereas thinning and fining upwards cycles are believed to be produced by filling and abandonment of channels a non parametric statistical test based on the signs of differences between consecutive bed thickness values may be used to determine whether the cycles in a particular measured section are statistically significant the test can be modified to deal with bed thickness values that have been smoothed by moving averages and with multiple partial sections in an incompletely exposed unit

the puncoviscana trough a large basin of late precambrian to early cambrian age on the pacific edge of the brazilian shield during the late precambrian to early cambrian a large basin with a homogeneous psammitic pelitic sediment fill existed in the area of the nw argentine andes it is now exposed in different tectonic levels this basin of meridional elongation was situated on a stable continental margin at the western edge of the brazilian shield it was underlain by segmented older continental crust according to the modal and chemical composition of the greywackes and subgreywackes a predominant metasedimentary source may be supposed four clastic facies types indicate a transport by gravity currents within a submarine fan system while massive red pelites represent cut off periods and rare carbonates deposition on rises the gravity currents derived from easterly directions the sedimentation age is proved by a rich ichnofauna and some medusoid impressions

interseismic re strengthening and stabilization of carbonate faults by non dieterich healing under hydrothermal conditions abstract friction experiments consisting of a velocity stepping stage a slide hold slide shs stage and a second velocity stepping stage have been performed to study the frictional healing behavior of carbonate fault gouge and the effects of healing on the velocity dependence of friction at 20 140 c and at 50 mpa effective normal stress dry experiments show classical dieterich healing characterized by a transient peak in friction after each hold period with no effects of shs testing on steady state friction or velocity dependence by contrast the wet tests show 1 an increase in apparent steady state friction upon re sliding after a hold period and 2 a pronounced increase in the velocity dependence parameter a b after the shs stage while the first of these non dieterich type healing effects has been observed in previous hydrothermal experiments on simulated quartz gouges it has not been reported previously for carbonate gouges the observed effect of shs testing on a b has never been reported our findings suggest that under in situ hydrothermal conditions interseismic fluid assisted deformation processes such as pressure solution can significantly promote fault re strengthening in carbonates and can cause slip stabilization if the results are applicable to active faults in carbonate terrains they have important implications for understanding how the extent of the seismogenic zone and how earthquake magnitude and aftershock distributions may evolve with repeated cycles of natural seismicity and interseismic healing

quartzose turbidites of the accretionary complex of barbados ii variations in bedding styles facies and sequences abstract barbados provides the only subaerial exposures of the barbados ridge an accretionary complex lying outboard of the lesser antilles volcanic arc within nine measured sections of quartzose turbidites five major types of sequences are recognized 1 1 progradational sequences basin plain outer fan of uniformly fine grained flat based base absent turbidites that thicken upward and gradually become coarser grained and base present at the top of the sequence 2 2 a single rejuvenation rapid progradational sequence was identified as an abrupt progradational sequence above abandoned lobe deposits and is not characterized by stacked well developed upward thickening successions as many progradational sequences are 3 3 channelized successions of coarse grained base present turbidites arranged in packets 5 20 or 50 140 m thick which are midfan and inner fan deposits respectively the distinction between predominance of base present and base absent turbidites seems to correspond with the interpreted change from midfan channelized to outer fan sheet flow deposition 4 4 one example of a major retrogradational sequence of midfan deposits above inner fan sandstones has been found on barbados minor sequences of facies retrogradation are relatively common in the outer fan environment where upward thinning sandstone beds overlie upward thickening units to define symmetric sequences 5 5 abandonment successions are major as indicated by massive accumulations of mudstone minor as indicated by abrupt reversals of upward thickening trends in outer fan lobe deposits and cryptic where indicated by thick 4 m bioturbated zones of massive sandstone

crustal scale seismic profiles across the manila subduction zone the transition from intraoceanic subduction to incipient collision 1 we use offshore multichannel seismic mcs reflection and wide angle seismic data sets to model the velocity structure of the incipient arc continent collision along two trench perpendicular transects in the bashi strait between taiwan and luzon this area represents a transition from a tectonic regime dominated by subduction of oceanic crust of the south china sea west of the philippines to one dominated by subduction and eventual collision of rifted chinese continental crust with the luzon volcanic arc culminating in the taiwan orogeny the new seismic velocity models show evidence for extended to hyperextended continental crust 10 15 km thick subducting along the manila trench at 20 5 n along transect t1 as well as evidence indicating that this thinned continental crust is being structurally underplated to the accretionary prism at 21 5 n along transect t2 but not along t1 to the south coincident mcs reflection imaging shows highly stretched and faulted crust west of the trench along both transects and what appears to be a midcrustal detachment along transect t2 a potential zone of weakness that may be exploited by accretionary processes during subduction an additional seismic reflection transect south of t1 shows subduction of normal ocean crust at the manila trench

statistical appraisal of bed thickness patterns in turbidite successions andaman flysch group andaman islands india abstract the bed thickness distribution of two turbidite successions in the oligocene andaman flysch group india which differ in terms of their paleogeography and sediment supply has been assessed statistically the purpose was to evaluate depositional cyclicity using the non parametric waldron test and also to assess possible environmental control on the bed thickness magnitude distribution both sections reveal a positively skewed distribution in bed thickness patterns the z value obtained through waldron s test failed to reject the null hypothesis of randomness and thus discards a cyclic pattern juxtaposition of sediments of different proximalities in an elongated forearc fan complex is the possible cause for this absence of cyclicity the studied sections however differ in their bed thickness magnitude distribution slope turbidite successions with sediment supply solely from the outer arc reveals a scaling behavior while the outer fan succession with mixing of sediments from different sources show a negative exponential distribution this highlights the possible control of the depositional system and sediment supply on the bed thickness magnitude distribution of turbidite successions irrespective of the triggering mechanism unequivocal application of the power law distribution in turbidite successions demands reconsideration

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

late quaternary depositional systems and sea level change santa monica and san pedro basins california continental borderland a suite of seismic reflection data that provides different degrees of resolution and penetration was used to map the depositional systems that have developed in santa monica and san pedro basins during the late quaternary submarine fan growth particularly at the mouths of hueneme and redondo canyons has been the dominant mode of basin filling mass movement processes ranging from creep to large scale catastrophic slumping have been important locally in general large scale fan growth fits normark s model in which the suprafan is the primary locus of coarse sediment deposition smaller scale morphologic and depositional patterns on the hueneme and redondo fans e g distributary channels and coarse sediment concentrations basinward of the inner suprafan suggest that a significant amount of coarse sediment presently bypasses the suprafans however long distance coarse sediment transport was particularly pronounced during late wisconsinan lowstand of sea level and resulted in progradation of lower mid fan and lower fan deposits as sea level rose rapidly between 18 000 y b p and 10 000 y b p shelves trapped much of the sediment supply consequently rates of basin sedimentation decreased markedly and the area of fan developmen was restricted as the rate of shelf sedimentation decreased concomitantly with a decrease in the rate of sea level rise 10 000 y b p sediment transport to the basins was renewed and modern depositional patterns were established fan development also has been influenced by large scale mass movement extensive mid fan overbank flow and the consequent development of sediment waves deflection of turbidity currents by bathymetric obstacles and local tectonism correlations between sand layer characteristics and high resolution echo types for fan and basin plain deposits show trends similar to some of those observed in deep sea depositional environments however because santa monica and san pedro basins are small enclosed tectonically active basins that receive sediment from relatively large drainage areas proximal to distal changes in sand layer thickness abundance and frequency are less pronounced than those observed in deep sea environments

large wood in the snowy river estuary australia abstract in this paper we report on 8 years of data collection and interpretation of large wood in the snowy river estuary in southeastern australia providing quantitative data on the amount sources transport decay and geomorphic actions no prior census data for an estuary is known to the authors despite their environmental and economic importance and the significant differences between a fluvial channel and an estuarine channel southeastern australian estuaries contain a significant quantity of large wood that is derived from many sources including river flood flows local bank erosion and anthropogenic sources wind and tide are shown to be as important as river flow in transporting and stranding large wood tidal action facilitates trapping of large wood on intertidal bars and shoals but channels are wider and generally deeper so log jams are less likely than in rivers estuarine large wood contributes to localised scour and accretion and hence to the modification of estuarine habitat but in the study area it did not have large scale impacts on the hydraulic gradients nor the geomorphology

patterns and processes of wood debris accumulation in the queets river basin washington field surveys in the 724 km 2 queets river basin on the west slope of the olympic mountains in nw washington reveal basin wide patterns of distinctive wood debris wd accumulations that arise from different mechanisms of wd recruitment hydraulic geometry and physical characteristics of wd individual pieces of wd in an accumulation or jam can be separated into key racked and loose members ten types of wd accumulations are identified based on the mode of recruitment and the orientation of key racked and loose debris relative to the channel axis although some types of wd accumulation have few geomorphic effects others form stable in stream structures that influence alluvial morphology at both subreach and reach length scales ranging from less than 1 to greater than 10 channel widths in the queets river stable accumulations of wd directly influence channel anabranching planform geometry flood plain topography and establishment of long term riparian refugia for old growth forest development the classification of wood debris accumulations in the queets river basin is based on physical observations that offer a template potentially applicable to other forested mountain regions d 2002 elsevier science b v all rights reserved

shelf and deep sea sedimentation in eocene forearc basin western oregon fan or non fan the lower eocene tyee and flournoy formations in the southern and central coast range of oregon contain unusual associations of shelf and deep sea facies deposited in an elongate portion of a forearc basin the sandstone rich nature and abrupt transition of sedimentary facies suggest that a variation of existing deep sea fan models is present the 6 500 ft 2 000 m thick sequence calls for shelf sandstone virtually cascading into deep water along a line shelf edge rather than from a point source submarine canyon to feed a sand rich system facies are described in terms of a sand rich fan system from south to north these facies include deltaic shelf inner fan mid fan outer fan and basin plain the deltaic facies contains coarse grained cross bedded distributary channel sandstone and interbedded coal some prograding deltaic sand extended to the edge of the narrow eocene shelf and cascaded into the basin many complex nested channels up to 1 200 ft 350 m wide and 130 ft 40 m deep were incised into fine grained shelf and slope sediments at slope depths line source these channel and shelf slope deposits comprise an inner fan facies a single large canyon or feeder channel point source typical of some fan systems was not recognized mid fan facies consist of broad coalescing channels filled with thick am lgamated sandstone beds sandstone shale ratios in the mid fan facies are from 85 to 15 up to 95 to 5 outer fan facies have sandstone shale ratios of 60 to 40 and contain well developed graded turbidite beds about 5 ft 1 5 m or less in thickness interbedded with shale basin plain facies consist of fine grained strata sandstone shale ratios of 30 to 70 deposited at the north end of the basin these thin bedded deposits also contain graded fine grained turbidite sandstones paleogeographic reconstructions based on paleocurrent data facies distribution and sandstone composition indicate sediment derivation from the pre cenozoic klamath mountains terrane and a volcanic arc system to the south and southeast the average sandstone composition is 19 quartz 27 feldspar 19 volcanic rock fragments 7 other rock fragments and 28 accessories and cement paleocurrent data from cross bedding and groove and flute marks indicate transport directions from south to north instead of a radially dispersed fan pattern the stratigraphic succession of the tyee flournoy system indicates a general shoaling trend and a progradation of deltaic facies across a narrow shelf and out over the basin fill during the early eocene the predominance of sandstone and confinemen within a narrow basin account for a turbidite facies differing from more familiar mixed sandstone and shale submarine fan facies models

turbidites in foreland and on thrust basins of the northern apennines abstract turbiditic sediments are associated with all stages of development of the apennines orogen not only the classical flysch of oligo miocene age macigno cervarola marnoso arenacea but also the coeval smaller bodies based on thrust sheets loiano of ranzano sequence and the younger molasse of the plio pleistocene foredeep except for more recent ones quaternary turbidite units are affected to some degree by thrusting and later block faulting the equivalent marginal deposits were also deformed uplifted and eroded to a great extent however identification and correlation of sequences and paleoenvironments across the orogenic belt can be helped by a deposits with rather strong eustatic imprint high stands and b preservation of marginal sediments by early remobilization cannibalism into deeper depocentres the following categories of basins can be recognized main foreland basin or foredeep in front of thrust sheets based on undeformed or previously rifted continental crust thrust top basins meso autochthonous auct in absence of a well defined major foredeep satellite basins thrust based but inwardly associated with a foredeep and of much smaller size linear dimensions in the order of kilometers and ten of kilometers volume of fill in the order of tens to hundreds cubic kilometers the foredeep persisted for the whole orogenic cycle but changed its character and was more or less segmented two main stages can be recognized conventionally labelled as the flysch stage up to the late miocene appenines mostly submerged and the molasse stage late miocene to recent present relief already in existence satellite basins floating on the ligurian sheet epi ligurian persisted up to the mid pliocene but received turbidites only in the oligocene and miocene others were created later on thrusts of different style involving the foreland sedimentary cover piggyback basins of ori and friend 1984 turbidite lithosomes of the flysch group are the largest ones volumes up to 30 000 km 3 with maximum size and lateral continuity of individual beds megaturbidites they are not seen as overlapping units filling coexisting and adjacent basins but as distinct superposed isochronous units within which only time transgressive sedimentation could occur macigno thus stands for all oligocene turbidites of the northern apennines foredeep cervarola for early miocene ones and marnoso arenacea for mid late miocene ones it is assumed that these units reflect sedimentary cycles of some order correlatable with global charts and splittable into depositional sequences sensu vail and collaborators

the shochary ridge sequence southeastern pennsylvania a possible ordovician piggyback basin fill abstract the central appalachian orogen of eastern pennsylvania is underlain in part by three fault bounded deep water clastic sequences the windsor township formation of the hamburg klippe greenwich slice the martinsburg formation and the shochary ridge sequence deep water sandstones of the windsor township formation were deposited in a trench on oceanic lithosphere in early middle ordovician time clastic detritus of the late middle early late ordovician martinsburg formation accumulated as part of a longitudinal deep sea clastic system in the central appalachian foreland basin deposits of the coeval shochary ridge sequence comprise a 1500 m thick coarsening upward sequence of hemipelagic mudstone and siltstone turbidites although devoid of the type of bedding cyclicity implicit to published submarine fan models the shochary ridge sequence may have accumulated as part of a morphologically poorly developed deep sea fan in which submarine channels and depositional lobes never formed or were poorly developed at best the coarsening upward nature of the shochary ridge sequence probably reflects progradation of its depositional system in response to either an inferred late middle early late ordovician glacially induced reduction in sea level and or an increase in tectonic activity in the hinterland sedimentologic and paleocurrent data suggest that deposits of the shochary ridge sequence did not accumulate as part of the martinsburg depositional system palinspastic restoration places the shochary ridge depocenter to the southeast of the martinsburg basin i e on the orogen side of the foreland basin accordingly the shochary ridge sequence is interpreted to reflect gradual filling of a basin that existed within the active thrust terrane to the southeast of the martinsburg depocenter this basin a piggyback or slope basin formed on martinsburg strata that had been tectonically incorporated into the northwest migrating thrust terrane as the frontal thrust advanced into the foreland basin

storm deposited sandstones tempestites and related ichnofossils of the late ordovician georgian bay formation southern ontario canada the late ordovician geogian bay formation of southern ontario canada comprises up to 250 m of grey to blue grey shales interbedded with highly fossiliferous calcareous sandstones these strata were deposited in equatorial paleolatitudes after 448 ma in a shallow foreland basin created by overthrusting along the eastern margin of north america the taconic orogeny the georgian bay formation comprises the middle part of an upward shallowing progradational sequence from deep water transgressive shales of the underlying whitby formation to muddy tidal flat sequences of the overlying queenston formation exposures in brickyard and river cuts near toronto and northwards along a narrow outcrop belt along the foot of the niagara escarpment show laterally extensive 100 m sharp based sheets of sandstone up to 1 m thick with gutter casts and washed out hypichnial trace fossils dominantly planolites and paleophycus on their lower bedding surfaces detailed examination of sandstone beds in outcrop and i

permeability evolution during non linear viscous creep of calcite rocks permeability storage capacity and volumetric strain were measured in situ during deformation of hot pressed calcite aggregates containing 10 20 and 30 wt quartz both isostatic and conventional triaxial loading conditions were used the tests were performed at confining pressure of 300 mpa pore pressures between 50 to 290 mpa temperatures from 673 to 873 k and strain rates of 3 10 5 s 1 argon gas was used as the pore fluid the initial porosities of the starting samples varied from 5 to 9 with higher porosity correlated to higher quartz content microstructural observations after the experiment indicate two kinds of pores are present 1 angular crack like pores along boundaries between quartz grains or between quartz and calcite grains and 2 equant and tubular voids within the calcite matrix under isostatic loading conditions the compaction rate covaries with porosity and increases with increasing effective pressure most of the permeability reduction induced during compaction is irreversible and probably owes to plastic processes as has been found in previous studies on hot pressed calcite aggregates permeability k is nonlinearly related to porosity o over small changes in porosity the two parameters are approximately related as k mathbf alpha mathbf phi n the exponent n strongly increases as porosity decreases to a finite value from about 4 to 6 depending on quartz content suggesting a porosity percolation threshold when subjected to triaxial deformation the calcite quartz aggregates exhibit shearenhanced compaction but permeability does not decrease as rapidly as it does under isostatic conditions during triaxial compaction the exponent n only varies between 2 and 3 non isostatic deformation seems to reduce the percolation threshold and in fact enhances the permeability relative to that at the same porosity during isostatic compaction our data provide constraints on the governing parameters of the compaction theory which describes fluid flow through a viscous matrix and may have important implications for expulsion of sedimentary fluids for fluid flow during deformation and metamorphism and melt extraction from partially molten rocks

nanocrystalline slip zones in calcite fault gouge show intense crystallographic preferred orientation crystal plasticity at sub seismic slip rates at 18 150 c a central aim in fault mechanics is to understand the microphysical mechanisms controlling aseismic seismic transitions in fault gouges and to identify microstructural indicators for such transitions we present new data on the slip stability of calcite fault gouges and on microstructural development down to the nanometer scale our experiments consisted of direct shear tests performed dry at slip rates of 0 1 10 m s at a constant normal stress of 50 mpa at 18 150 c the results show a transition from stable to potentially unstable slip above 80 c all samples recovered showed an optical microstructure characterized by narrow 30 40 m wide riedel and boundary shear bands marked by extreme grain comminution and a crystallographic preferred orientation cpo boundary shear bands sectioned using fib sem focused ion beam scanning electron microscopy revealed angular grain fragments decreasing from 10 to 20 m at the outer margins to 0 3 m in the shear band core where dense aggregates of nanograins also occurred transmission electron microscopy applied to foils extracted from boundary shears using fib sem combined with the optical cpo showed that these aggregates consist of calcite nanocrystals 5 20 nm in size with the 104 201 dislocation glide system oriented parallel to the shear plane and direction our results suggest that the mechanisms controlling slip include cataclasis and localized crystal plasticity because crystal plasticity is strongly thermally activated we infer that the transition to velocity weakening slip is likely due to enhanced crystal plasticity at 80 c this implies that tectonically active limestone terrains will tend to be particularly prone to shallow focus seismicity

types of submarine fan lobes models and implications different lobe models imply significantly different reservoir geometries thus one must apply the proper lobe model to ancient fan sequences braided suprafan lobes are characterized by stacked channel sand bodies with good lateral and vertical communication and they constitute excellent reservoir facies depositional lobes composed of sheet like sand bodies with good lateral and moderate vertical communication exhibit properties of good reservoir facies fanlobes which refer to meandering channels and associated levee facies of large mud rich submarine fans such as the mississippi fan are characterized by offset stacked sand bodies with poor lateral and vertical communication these lenticular sands have the potential to be moderately good reservoir facies ponded obes which represent mud rich slump facies of slope environments comprise poor reservoir facies because of low sand content and poor sand body connectivity furthermore the presence of contorted mud layers in ponded lobes is expected to hinder fluid flow external mounded reflections in seismic profiles often are interpreted as lobes however there are no definite seismic criteria to delineate mud rich lobes from sand rich lobes

shallow water turbidites an example from the mallacoota beds australia abstract a late ordovician turbidite sequence the mallacoota beds exhibits vertical lithofacies associations that suggest deposition in a fan like environment however there are also features indicating occasional episodic reworking by water currents reworking features include both wave current and unidirectional ripple pavements sharp topped turbidites a difference in current direction between superimposed current rippling and underlying bouma c division ripples lensiodal quartzites and occasional hcs beds comparisons between the mallacoota beds and the depositional products of a variety of open ocean currents would indicate that storm related currents were the most likely reworking mechanism this would indicate that the sequence was deposited within storm wave base depositional depths for part of the sequence are estimated at 90 200 m based on a wave generated ripple model therefore these turbidites may have been produced by storm surge with channeling within the turbidites due to the localisation of rip currents during hurricane conditions a generalised model for the characteristic features of turbidites deposited between fair weather wave base and storm wave base is presented it is suggested that such turbidites will contain only occasional examples of reworking and that the frequency of such reworking events per stratigraphic interval might be used as a relative measure of water depth throughout a sequence moreover those turbidite sequences that have sharp contacts between the sandstones and the overlying mudstones may have been modified by storms and therefore deposited in shallower water than previously thought

mechanical behavior and microstructure of simulated calcite fault gouge sheared at 20 600 c implications for natural faults in limestones we report ring shear experiments on simulated calcite fault gouges performed at fixed temperatures t within the range from 20 to 600 c the experiments were performed wet using pore fluid pressures pf of 10 pf 60 mpa one series of experiments employed a constant effective normal stress neff of 50 mpa while in a second series neff was sequentially stepped from 30 to 100 mpa in all experiments sliding velocity v was stepped in the range from 0 03 to 100 m s the results showed stable velocity strengthening behavior at 20 c but velocity weakening at 100 to 550 c for all v steps to 3 m s which was frequently accompanied by stick slip at 600 c velocity strengthening occurred microstructural observations suggest increasing importance of ductile deformation with increasing temperature as reflected by a localized shear band structure at 20 c giving way to a pervasive shear plane parallel grain shape fabric at 600 c using existing flow equations for dense calcite polycrystals we show that dislocation and or diffusion creep of 10 30 m sized bulk gouge grains likely played a role in experiments performed at t 400 c we suggest that the observed velocity weakening behavior can be explained by a slip mechanism involving dilatant granular flow in competition with creep controlled compaction our results have important implications for the breadth of the seismogenic zone in limestone terrains and for the interpretation of natural fault rock microstructures specifically while samples sheared at 400 550 c exhibited essentially brittle frictional mechanical behavior stick slip the corresponding microstructures resembled that of a mylonite

mass transfer from the alps to the apennines volumetric constraints in the provenance study of the macigno modino source basin system chattian aquitanian northwestern italy a quantitative provenance approach is applied to the late oligocene early miocene macigno modino turbidite complex which accumulated in the foreland basin developed in front of the growing northern apennines but was supplied from the rapidly rising western alps at the northwestern end of the basin as well as the traditional recognition of source rock lithologies and their gross paleogeographic location the provenance approach adopted here evaluates the relative contributions to the clastic complex from different types of source rock and estimates the volume of material transferred from the alps to the apennines within the macigno modino source basin system and the overall volume of rock assumed to have undergone erosion in order to supply it these elements are used to constrain the possible source of the clastics and to infer the main paleogeological features of the source area it is concluded that an estimated volume of ca 17 20 103 km3 of basement mainly metamorphic rocks together with ca 103 km3 of intermediate composition volcanic rocks was transferred as detritus from the western alps area to the northern apennines foreland basin creating the 250 300 km long 50 km wide and up to 2 7 km thick macigno modino clastic complex lithology and paleogeography combined with volume estimates and current knowledge of the regional geology of the western alps consistently suggest that the bulk of the sediments funnelled into the macigno modino complex were derived from the uplifted ivrea crustal block which formed a crystalline massif some 5000 km2 in extent that rose ca 3 km during the oligocene forming one of the main elements of western alpine geology during that time

statistical analysis of turbidite bed thickness patterns from the alpine fold and thrust belt of western and southeastern greece abstract a statistical evaluation of turbidite bed thickness was performed for 11 turbidite successions which constitute part of foreland basins formed along the alpine fold and thrust belt of western and southeastern greece the purpose was to compare the results from this study with previously published investigations and discuss if and how statistical approaches could contribute to the environmental analysis of turbidite deposits in tectonically complex areas bed thickness datasets exhibit a clear non normal signal in their distribution behavior statistical analysis was focused on i fitting of widely used non normal theoretical distribution models using robust non parametric goodness of fit statistical tests and ii detecting the possible presence of asymmetric bed thickness cycles and or non random bed thickness clustering results indicate that the studied bed thickness datasets are well characterized by a bimodal lognormal distribution model probably reflecting deposition from both high and low density turbidity currents several datasets exhibit distributions characterized by power law tails exponential distribution types were not observed all datasets exhibit non random thinning upward bed thickness trends probably due to tectonically induced gravity flows proposed methods for identifying depositional sub environments using turbidite bed thickness statistics were found to have limited applicability observations of the present study may prove useful for the environmental analysis of turbidite deposits in fold and thrust belt areas characterized by limited outcrop exposures

paleocene carbonate turbidites of the şarkisla region turkey their significance in an orogenic basin abstract a paleocene carbonate sequence occurs in the southwestern part of the sivas refahiye basin arkisla province sivas turkey and is located in the northeast of central anatolia conclusions concerning the late mesozoic to early cenozoic sedimentary evolution have been derived mainly from the carbonate turbidites the vertical and lateral relationships of these rocks suggest deposition in a submarine fan complex three major megacycles characterized by a thickening and coarsening upward trend are seen in the upper cretaceous lower paleocene succession they are considered to represent basin facies in the lower levels passing upward into sediment attributed to distal fan facies on the basis of bed thickness distributions and bioclastic hemipelagic ratios agglomerates occur as laterally discontinuous mass flow deposits which formed on the slopes of local volcanoes located in the deeper part of the basin thin lava sheets are the products of stratovolcanoes which result from regional tectonic subsidence olistoliths occurring at several stratigraphic levels probably are the result of seismic events related to contemporaneous volcano tectonic activity two major turbiditic megacycles occur also in the middle and upper parts of the succession middle and upper paleocene the lower megacycle of this sequence conforms to the distal division of a suprafan lobe while the upper part is marked by a conspicuous thickening and coarsening upward character indicating a suprafan lobe environment this evidence is consistent with an overall progradation of the fan complex during the paleocene paleocurrent features and slump structures indicate that the marginal slopes of the basin extended in a northeast southwest direction and were inclined to the north sedimentologic stratigraphic tectonic and volcanic data from this sequence suggest that during the paleocene this area formed as an arc related basin

sedimentology of a late cenozoic collisional sequence the misis complex adana southern turkey abstract this study is concerned with miocene sequences formed within part of the cukurova basin of southern turkey a major downwarp created during the early stages of collision between the afro arabian plate and the tauride anatolian microplate assemblage we report here the results of a combined stratigraphical sedimentological structure and geochemical study of the misis complex a structurally elevated segment of cukurova basin fill this analysis has demonstrated the structurally imbricated nature of the misis sequences and the tectonic juxtaposition of originally well separated coeval facies the initial discernible phase of basin filling pre burdigalian was marked by deep marine conditions and marginal tectonic instability probably related to a late phase of tauride nappe advance the subsequent phase of crustal extension burdigalian early tortonian produced expansion of the cukurova basin limits and an upwards shoaling succession in which sediment transport towards the southwest gradually became dominant as a result of earlier suturing and uplift in northeasterly sectors of the collision zone the miocene arenites of the misis complex are petrographically diverse with common siliciclastic and carbonate detrital admixtures and mineralogically immature and their position in petrotectonic fields indicates a compound provenance from both recycled orogen and magmatic arc sources a noteworthy petrographic feature is the compositional similarity of arenites from both shallow and deep marine facies the general succession of neogene facies observed in the cukurova basin and misis complex is consistent with their evolution within a perisutural foreland basin but this interpretation is complicated by petrographic and geochemical features attributed to remnants of an older magmatic arc later stages of basin filling are also marked by the local occurrence of anomalous palaeoenvironmental associations including olistostromic units attributed to contemporaneous intra basinal tectonism

deep sea fan deposits in the macigno formation middle upper oligocene of the gordana valley northern apennines italy abstract facies characteristics are described for a 2300 m thick turbidite succession of the macigno formation middle upper oligocene which crops out as a continuously exposed section in the gordana valley northern apennines in the study area the macigno formation consists of two sandy members separated by a shaly member the sandy members contain lithic associations characteristic of submarine fan deposits and form distinct fan complexes the middle shaly member represents a period of basin starvation three main facies associations are recognized in the macigno fan deposits fan fringe outer fan lobe and braided midfan facies associations the fan fringe deposits consist of monotonous or small scale cyclically arranged thin bedded turbidites the outer fan lobe deposits are composed of medium to very thick bedded classical turbidites internally organized in thickening upward cycles with minor intercalations of thin bedded sandstone beds two distinct types of outer fan lobe deposits distal and proximal are recognized on the basis of rock type internal organization and vertical facies relationships the midfan deposits consist of amalgamated massive sandstone and pebbly sandstone which display repeated thinning upward cycles the three main facies associations are superposed t define major thickening and coarsening upward cycles reflecting distinct episodes of fan progradation the relationships between the facies associations of the macigno deposits and the existing models of submarine fan sedimentation are discussed after the deposition of the fan complexes fan sedimentation in this part of the basin was replaced by movements of allochthonous units heralded by large olistostromes

crystallographic preferred orientations may develop in nanocrystalline materials on fault planes due to surface energy interactions a layer of substantially noncrystalline material composed of partially annealed nanopowder with local melt was experimentally generated by comminution during 1 5 mm total slip at 2 5 10 6 m s 1 pconf 0 5 gpa and 450 c or 600 c on saw cut surfaces in novaculite the partially annealed nanopowder comprises angular grains mostly 5 200 nm diameter in a variably dense packing arrangement a sharp transition from wall rock to partially annealed nanopowder illustrates that the nanopowder effectively localizes shear consistent with generation of nanoparticles during initial fragmentation not by progressive grain size reduction dislocation densities in nanopowder grains or immediate wall rock are not significantly high but there are planar plastic defects spaced at 5 200 nm parallel to the host quartz grain s basal plane we propose these plastic defects developed into through going fractures to generate nanocrystals the partially annealed nanopowder has a crystallographic preferred orientation cpo that we hypothesize developed due to surface energy interactions to maximize coincident site lattices csl during annealing this mechanism may also have generated cpos recently described in micro nanocrystalline calcite fault gouges

the long term control of vegetation and woody debris on channel and flood plain evolution insights from a paired catchment study in southeastern australia abstract numerous case studies have demonstrated that alluvial and semi alluvial rivers in se australia have undergone dramatic metamorphosis in historical times however very few studies place these changes within a long term evolutionary context as a consequence the magnitude of and ultimate controls on the changes to river form and processes are not fully appreciated in this study a paired catchment analysis is undertaken between two moderate sized sand bed rivers in east gippsland australia from the thurra river direct insight is gained into the predisturbance control exerted by riparian vegetation and wood in a lowland alluvial river this river is effectively in the same condition today as it was at the time of the arrival of europeans in australia in contrast the adjacent cann river which has been settled by europeans for 150 years but was previously very similar to the thurra river exhibits stark differences today channel morphodynamics observed within the thurra river when coupled with historical and geomorphic evidence for the former condition of the cann river provide a detailed reference by which the recent changes to the cann river are measured chronostratigraphic evidence from both flood plains places recent channel behavior within an evolutionary context extending well into the pleistocene since european settlement the study reach of the cann river has experienced a 360 increase in channel depth a 240 increase in channel slope a 700 increase in channel capacity and up to a 150 fold increase in the rate of lateral channel migration the contemporary condition of the cann river channel differs profoundly to that which has prevailed over at least the previous 27 ka the first order control on the historical channel metamorphosis is the removal of riparian vegetation and woody debris wd numerous thresholds have been crossed as a result of historical channel changes particularly the relationship between average length of woody debris pieces and channel width consequently channel recovery will not simply be achieved by reintroducing the pre existing riparian vegetation and woody debris load devising sound management strategies and realistic management targets for the cann river or any similarly altered river requires an understanding of the long term channel and flood plain evolutionary history as well as the underlying controls on historical changes

frictional heterogeneities on carbonate bearing normal faults insights from the monte maggio fault italy observations of heterogeneous and complex fault slip are often attributed to the complexity of fault structure and or spatial heterogeneity of fault frictional behavior such complex slip patterns have been observed for earthquakes on normal faults throughout central italy where many of the mw 6 to 7 earthquakes in the apennines nucleate at depths where the lithology is dominated by carbonate rocks to explore the relationship between fault structure and heterogeneous frictional properties we studied the exhumed monte maggio fault located in the northern apennines we collected intact specimens of the fault zone including the principal slip surface and hanging wall cataclasite and performed experiments at a normal stress of 10 mpa under saturated conditions experiments designed to reactivate slip between the cemented principal slip surface and cataclasite show a 3 mpa stress drop as the fault surface fails then velocity neutral frictional behavior and significant frictional healing overall our results suggest that 1 earthquakes may readily nucleate in areas of the fault where the slip surface separates massive limestone and are likely to propagate in areas where fault gouge is in contact with the slip surface 2 postseismic slip is more likely to occur in areas of the fault where gouge is present and 3 high rates of frictional healing and low creep relaxation observed between solid fault surfaces could lead to significant aftershocks in areas of low stress drop

selective alteration of arkose framework in oligo miocene turbidites of the northern apennines foreland impact on sedimentary provenance analysis

amalgamation surfaces bed thicknesses and dish structures in sand rich submarine fans numeric differences in channelized and unchannelized deposits and their diagnostic value abstract hydraulic differences between channelized and unchannelized flows in sand rich submarine fans result in different distributions of amalgamation surfaces bed thicknesses and dish structures in successions of these two different environments distribution trends of these fabrics were quantified for the sand rich fans of the reiselsberger sandstein cenomanian turonian these trends can be used as criteria to distinguish channelized from unchannelized paleoenvironments of sand rich submarine fans amalgamation surfaces in the studied fans channelized regions are considerably more abundant than in the unchannelized fan areas in unchannelized deposits tabular amalgamation surfaces outnumber nontabular ones whereas the opposite occurs in channelized successions these results indicate a higher degree of erosive power of gravity driven sediment flows in channels as a result of a greater flow thickness higher flow velocity and turbulence the average turbidite layer thickness in channelized successions is markedly greater than in unchannelized deposits layer as defined herein this is mainly attributed to the combined effects of differences in sediment fall out rate and the inefficiency of sand rich suspensions to transport sand in the proximal and channelized fan areas more sediment is deposited from a flow in the form of a layer than in distal unchannelized fan regions despite a higher degree of erosion in channels the greater average bed thickness in channel fills is a function of layer thickness and more frequent amalgamations bed as defined herein dish structures seem to be considerably more common in midfan than in outer fan successions this may indicate a higher sedimentation rate from individual suspension currents in midfan areas

sedimentary and volcanic evolution of a neoproterozoic continental margin bleida anti atlas morocco abstract a tentative geodynamic evolution of the neoproterozoic continental margin of the northern border of the west african craton is reconstructed using both sedimentological observations and geochemical arguments from volcanic rocks the rifting stage was marked first by intermittent subsidence of a very shallow shelf environment leading to deeper water sedimentation conditions with local surges of deltaic channels this rifting stage was also characterized by the eruption of a 500 m thick pile of submarine basic lava flows with geochemical characteristics similar to those generally observed in basaltic lavas erupted during continental rifting this first rifting stage 790 ma clauer 1976 was succeeded by a drastic change both in sedimentation and volcanism the younger sediments are deep water distal turbidites with associated pyritic black shales they include a few highly differentiated tholeiitic flows and sedimentary exhalative copper deposits linked to felsic volcanism these changes are attributed to the development of deep water oceanic basins along the northern border of the west african craton the closure of this pan african oceanic domain occurred by transpression tectonics along this major lithospheric transform zone which is roughly e w trending

variation in bed thickness in a turbidite succession dezadeash formation jurassic cretaceous yukon canada evidence of thinning upward and thickening upward cycles abstract analysis of the vertical variation in thickness of turbidites in an 883 in thick stratigraphic section of the dezadeash formation jurassic cretaceous yukon canada indicates that the turbidites are comprised of alternating sequences of thick beds and thin beds visual inspection reveals that 40 thick bedded cycles or megasequences are present fourier analysis indicates 38 cycles five different methods i e freehand signs of differences test correlation analysis least squares and moving averages used to determine the trend in bed thickness of the megasequences demonstrate that asymmetric cycles are present and most of these methods show that thickening upward trends are more common than thinning upward trends the best objective method for determining the asymmetry of megasequences appears to be correlation analysis viz pearson s spearman s and kendall s correlation coefficients and possibly the least squares method this particular section of the dezadeash formation is characterized by asymmetric cycles that are both common and statistically convincing and thickening upward sequences are more plentiful than thinning upward sequences

confronting hysteresis wood based river rehabilitation in highly altered riverine landscapes of south eastern australia abstract this study evaluates an experiment in river rehabilitation which uses large wood to stimulate and emulate natural system processes in an effort to reverse channel degradation excess sediment transport and habitat simplification that has resulted from two centuries of human induced disturbances particularly desnagging the experiment involved the reintroduction of 436 logs 350 t within 20 engineered log jams eljs over an 1100 m reach commencing in 1999 the experiment was set up as a standard baci design with a control reach 3 km upstream in the 5 years since implementing the rehabilitation strategy the study reach has experienced five floods greater than the mean annual and a further five events capable of mobilising the gravel bed five surveys of channel terrain have been completed since treatment implementation and the changes to net sediment storage and morphologic diversity assessed in comparison to the control reach seven surveys of the fish population in the reach have also been undertaken during the project to measure the ecological response to the introduced wood the experiment has demonstrated the effectiveness of elj technology in achieving engineering and geomorphic goals to date the treatment has halted further degradation of the river and increased sediment storage with the test reach now storing on average 40 m3 1000 m2 more sediment than in the control these values it would appear represent a new reach scale dynamic equilibrium storage level over decadal timescales additional sediment storage amounts to 3 5 m3 m3 of wood added at the reach scale this additional storage represents a reduction of just 2 or less of the post european expansion in channel capacity suggesting far greater efforts are required than those employed here to reverse the cumulative effects of 180 years of channel erosion and simplification pool and bar area in the test reach increased by around 5 and 3 5 respectively while the corresponding values in the control were around 1 5 and 1 respectively two indices of morphologic diversity were measured for each bed survey the standard deviation of 3d residuals of change compared with the baseline survey sdi 3d and the standard deviation of thalweg residuals from the line of best fit sditr the sdi 3d index shows both reaches increased in complexity through the study with the treatment increasing more than the control 0 37 and 0 29 respectively the sditr index does not detect clear changes because of the low signal to noise ratio however it does suggest the test reach was more complex than the control at the outset the observed increase in fish abundance after the first 12 months of monitoring reported previously is now far less distinct 4 years on a pattern seemingly reflecting the relatively minor increases in critical pool habitat and habitat diversity over the same period although no significant differences were detectable in fish species richness or total abundance from the reach aggregate data after 4 years analysis of individual structures show them to be high quality habitat for native fish compared to the rest of the reach and the upstream control these results highlight the challenges river managers face in achieving measurable improvements in the health of aquatic ecosystems in highly altered rivers managers must confront hysteresis in a biophysical and institutional sense when attempting to reverse the degradation of rivers the scale of treatment implemented in this experiment was at the upper end of the spectrum of rehabilitation efforts currently being undertaken in australia suggesting that far greater resources and longer timescales are required to achieve the levels of improvement in the diversity of stream habitat expected by the community the study also highlights problems with the strategy of attempting to meet multiple objectives within a reach scale rehabilitation project while this treatment successfully met some geomorphic study objectives maximising the benefits for fish habitat would require a strategy focused primarily on the creation of complex woody habitat within deeper pools particularly pools immediately below riffles

tidal triggering of low frequency earthquakes near parkfield california implications for fault mechanics within the brittle ductile transition 1 studies of nonvolcanic tremor nvt have established the significant impact of small stress perturbations on nvt generation here we analyze the influence of the solid earth and ocean tides on a catalog of 550 000 low frequency earthquakes lfes distributed along a 150 km section of the san andreas fault centered at parkfield lfe families are identified in the nvt data on the basis of waveform similarity and are thought to represent small effectively co located earthquakes occurring on brittle asperities on an otherwise aseismic fault at depths of 16 to 30 km we calculate the sensitivity of each of these 88 lfe families to the tidally induced right lateral shear stress rlss fault normal stress fns and their time derivatives and use the hypocentral locations of each family to map the spatial variability of this sensitivity lfe occurrence is most strongly modulated by fluctuations in shear stress with the majority of families demonstrating a correlation with rlss at the 99 confidence level or above producing the observed lfe rate modulation in response to shear stress perturbations requires low effective stress in the lfe source region there are substantial lateral and vertical variations in tidal shear stress sensitivity which we interpret to reflect spatial variation in source region properties such as friction and pore fluid pressure additionally we find that highly episodic shallow lfe families are generally less correlated with tidal stresses than their deeper continuously active counterparts the majority of families have weaker or insignificant correlation with positive tensile fns two groups of families demonstrate a stronger correlation with fault normal tension to the north and with compression to the south of parkfield the families that correlate with fault normal clamping coincide with a releasing right bend in the surface fault trace and the lfe locations suggesting that the san andreas remains localized and contiguous down to near the base of the crust the deep families that have high sensitivity to both shear and tensile normal stress perturbations may be indicative of an increase in effective fault contact area with depth synthesizing our observations with those of other lfe hosting localities will help to develop a comprehensive understanding of transient fault slip below the seismogenic zone by providing constraints on parameters in physical models of slow slip and lfes

wood storage in three mountain streams of the southern andes and its hydro morphological effects this study analyses large wood lw storage and the associated effects on channel morphology and flow hydraulics in three third order mountain basins drainage area 9 12 km2 covered in old growth nothofagus forests ranging from the temperate warm chilean andean cordillera to the sub antarctic tierra del fuego argentina amount characteristics and dimensions of large wood 10 cm diameter 1 m long were recorded as well as their effects on stream morphology hydraulics and sediment storage results show that major differences in lw abundance exist even between adjacent basins as a result of different disturbance histories and basin dissection massive lw volumes i e 1000 m3 ha 1 can be reached in basins disturbed by fires followed by mass movements and debris flows potential energy dissipation resulting from wood dams is about a quarter of the total elevation drop in two streams with a gross sediment volume stored behind wood dams of around 1000 m3 km 1 which appears to be of the same order as the annual sediment yield finally the presence of wood dams may increase flow resistance by up to one order of magnitude copyright 2007 john wiley sons ltd