flow characteristics of metresa an oligocene seismoturbidite in the dukla unit polish carpathians metresa is a thick distinctive turburdite within the menilite shales in the carpathians of south east poland it was deposited by a se flowing turbidity current derived from the silesian cordillera and can be traced for 55 km downcurrent it has a width of at least 15 km the current contained roughly 3 km3 of sediment and conforms to the definition of a seismoturbidite grain size analyses of samples from the nine localities where metresa is exposed indicate average velocities decreasing from 2 m s 1 to less than 1 m s 1 over the 55 km massive divisions are poorly developed instead the turbidite although graded tends to be laminated throughout flat lamination predominates with intercalated cross lamination and erosion structures at various levels small scale cross lamination presumably associated with ripples occurs at some upper levels an exceptional feature is a large scale wave like structure somewhat resembling hummocky cross stratification the structures are not consistent with the inferred velocities it is suggested that the stability fields relating structures to stream power herein called the allen fields are displaced in respect to deposition from waning turbidity currents

core evidence of paleoseismic events in paleogene deposits of the shulu sag in the bohai bay basin east china and their petroleum geologic significance abstract the shulu sag located in the southwestern corner of the jizhong depression bohai bay basin of east china is a ne sw trending elongate cenozoic half graben basin the lowermost part of the third member of the shahejie formation in this basin is characterized by continental rudstone and calcilutite to calcisiltite facies based on core observation and regional geologic analysis seismites are recognized in these lacustrine deposits which include soft sediment deformation structures sedimentary dikes hydraulic shattering diapir structures convolute lamination load flame structures ball and pillow structures loop bedding and subsidence structures synsedimentary faults and seismoturbidites in addition mixed source rudstones consisting of the paleozoic carbonate clasts and in situ calcilutite clasts in the lowermost submember of shahejie 3 appear in the seismites suggesting an earthquake origin a complete representative vertical sequence in the lowermost part of the third member found in well st1h located in the central part of the shulu sag shows from the base to the top underlying undeformed layers synsedimentary faults liquefied carbonate rocks allogenetic seismoturbidites and overlying undeformed layers seismites are widely distributed around this well and there are multiple sets of stacked seismites separated by undeformed sediment the nearby nw trending taijiazhuang fault whose fault growth index is from 1 1 to 1 8 and the nne trending xinhe fault with a fault growth index of 1 3 1 9 may be the source of the instability to create the seismites these deformed sedimentary layers are favorable for the accumulation of oil and gas for example sedimentary dikes can cut through many layers and serve as conduits for fluid migration sedimentary faults and fractures induced by earthquakes can act as oil and gas migration channels or store petroleum products as well seismoturbidites and mixed source rudstones are excellent reservoirs due to their abundant primary or dissolved pores

sedimentary structures tentatively attributed to seismic events abstract fingerprints of earthquakes in the sedimentary record are as yet difficult to identify this is particularly true for failure phenomena dewatering slumping fault graded and turbidite structures that could have been triggered also by other kinds of energy input other promising candidates are strange biostratinomic features convex down stacking of shells current orientation in wave ripple accumulations as well as certain preservational features found in geosynclinal pelagic limestones but in every case verification of the seismic origin is still needed

a new conceptual model for the deposition process of homogenite application to a cretaceous megaturbidite of the western pyrenees basque region sw france abstract the north pyrenean megaturbidite is a 19 63 m exceptional thick bed deposited during the late turonian and extending over more than 90 km in the basque region country sw france its thickness varies from more than 63 m to about 19 m from east mauleon area to west basque coast it represents a total compacted volume of about 90 km3 of carbonates on the field rare sedimentary structures are visible in the turbidite bed they consist of laminar planar lamination and rare cross laminations in the eastern region and antidune like structures in the western region five sites have been sampled with a vertical step of 50 cm to 1 m thin sections have been quantitatively analyzed for counting the terrigeneous fraction the quartz grain size and the mineral orientation the deposits fine westward which suggests a source located in the east of the mauleon basin this is consistent with the quartz grain orientation in the lower part of the megaturbidite the deposits fine upward from medium sand to clayey silt this is consistent with the classical definition of homogenites and suggests that these kinds of deposits are turbidites these observations also suggest that the term megaturbidite is appropriated for these deposits the sedimentary analysis indicates that the deposit results from a single event the volume of sediment involved in the process as well as the quartz grain orientation indicating flow motion in the opposite direction of the initial flow and the antidune like structure suggest the formation of reflected flows and the formation of standing waves over the complete water column in the basque flysch sub basins corresponding to a seiche effect the origin of the megaturbidite is probably an earthquake generated collapse on the carbonate platform this example allows providing a new conceptual model for the process of homogenite deposition this model explains the deposition of thick fine grained crudely graded megaturbidites

reading of the trigger records of sedimentary events a problem for future studies abstract sedimentary records of various three to four dimensional patterns of nature have recently attracted the special attention of many geologists the dramatic development of rhythmic sequence stratigraphy is a conspicuous recent instance the significance of event sedimentation in geohistory however has not been examined sufficiently the problem to how to read the records of triggers or thresholds of sedimentary events has been ignored the difficulty of solving this problem concerns the difference in patterns between natural sedimentary processes and their resulting sediments terminological confusion of event deposits is another cause which hinders our taking note of this problem a few examples of endeavours to discriminate the threshold of sedimentary events are shown by the analysis of two kinds of turbidites of the mid guatemala trench the investigation of slump derived turbidites of the suruga trough and the study of the seismoturbidites in lake biwa well focused investigations of features of trigger known sediments is the best strategy to find the criteria for discriminating the triggers or thresholds based on sedimentary records of various sedimentary events from this point of view more detailed studies of the santorini eruption induced homogenites the k t boundary impact induced tsunamiites together with the lake biwa seismic turbidites are very important further efforts should be made to find and investigate as many trigger identifiable sediments as possible

cretaceous palaeogene flysch zone of the east alps and carpathians identification and plate tectonic significance of dormant and active deep sea trenches in the alpine carpathian arc

multidirectional synchronously triggered seismo turbidites and debrites revealed by x ray computed tomography ct on 21 april 2007 a mw 6 2 earthquake struck aysen fjord chilean patagonia and caused onshore and offshore mass movements which triggered tsunamis and density flows in the fjord to better understand the facies successions in and the intercalation of the density flow deposits a study was made of the 2007 deposits in 22 short sediment cores taken in the inner aysen fjord by combining grain size analysis with x ray computed tomography scanning it was possible to demonstrate that the encountered facies correspond to classical divisions of debrites and turbidites the single event deposits consist of a succession of several sub deposits deposited under different flow directions and can be interpreted as stacked turbidites orientations of i folds ii imbricated mud clasts iii backsets and foresets of climbing ripples and iv asymmetrical convolute lamination were used to determine relative flow directions at the location of the cores by assigning the basal flow of the stacked debrites and turbidites to the closest principal mass flow the absolute flow directions of the sub deposits were determined which in combination with multibeam basin floor morphology allowed reconstruction of the 2007 density flow successions in aysen fjord furthermore alternating flow directions provide evidence for a seiche induced by the density flows it was concluded that x ray computed tomography scans provide crucial information for reconstructing palaeoflows and can be a useful tool in marine and lacustrine sedimentology and palaeoseismology the multidirectionality of sub deposits in turbidites is next to differences in mineralogy a new criterion to identify stacked turbidites these multidirectional stacked turbidites are an indication of simultaneous triggering of density flows and can therefore in most cases be attributed to earthquakes ruling out other triggers such as floods storms or other sediment failures this article is protected by copyright all rights reserved

active synsedimentary tectonism on a mixed carbonate siliciclastic continental margin third order sequence stratigraphy of a ramp to basin transition lower sekwi formation selwyn basin northwest territories canada the lower part of the early cambrian sekwi formation in the selwyn basin of the northwest territories canada is composed of two regional unconformity bounded sequences s0 and s1 which record the first widespread carbonate deposition during the initial palaeozoic transgression onto the western margin of laurentia these early cambrian sequences are unique to the western north american cordillera representing the only record of primarily deep water deposition on a tectonically active mixed carbonate siliciclastic ramp during this period more specifically the geometry of the sekwi ramp changed during deposition of s0 and s1 from a shallowly dipping homoclinal ramp during the s0 transgressive systems tract to a steeply dipping tectonically modified ramp during the early highstand systems tract of s0 the steeply dipping ramp profile of s0 was preserved into the early transgressive systems tract of s1 the sekwi ramp returned to a gently sloping ramp during the late highstand systems tract of s1 and remained so throughout the remainder of sekwi deposition the evolving shape of the sekwi ramp is attributed to syndepositional down to the basin faulting during deposition of both s0 and s1 and is recorded by i the westward thickening irregular geometries of s0 and s1 ii geographical restriction of deep water facies including sediment gravity flow deposits iii the presence of large allochthonous blocks and iv the clast composition of sediment gravity flow deposits sediment gravity flow deposits play an unusually important role in the sequence stratigraphic interpretation of the lower sekwi formation as they delineate depositional packages including the maximum flooding zone the transitions between portions of systems tracts and the inferred locations of syntectonic extensional faults syntectonic faults increased accommodation basinward of an extensive ooid shoal complex that developed along the sekwi ramp crest greatly influencing sequence geometry and initiating the downslope motion of sediment gravity flows the syndepositional faulting probably was a continuation of extension that began during the latest neoproterozoic rifting of western laurentia the composition of sediment gravity flow deposits track changing accommodation space on the lower sekwi ramp and can be used to differentiate systems tracts that probably were related more to tectonism than eustasy

slumping and sliding in miocene and recent developing arc basins onshore and offshore sumba indonesia abstract neogene slidemasses in eastern sumba are discussed and compared to neogene and quaternary analogues in seismic profiles from the offshore lombok and savu basins the onshore examples were deposited in deep marine base of slope environments within the reach of large amounts of clastics derived from a volcanic arc i e in a setting comparable to that of the recent slides onshore three types of slides are distinguished ranging from mud clast rich debris flows type 1 their possible seismic origin is discussed elongate lenticular slumps type 2 to over 100 m thick slide masses of intimately mixed and folded strata together with rafts of less deformed sediments type 3 the offshore analogues may be twice as thick both in the field and in the seismic profiles such slides are found at various superimposed levels five superimposed units can be distinguished in a seismic profile in the savu basin near the westernmost extension of the offshore sumba ridge a giant blocky slide occurs all slide masses are located on slopes with increasing gradients due to differential vertical movements tectonically induced oversteepening is therefore considered a main cause of failure in outcrops the upper surfaces of the slides are almost flat this contrasts with a hummocky topography seen in some of the offshore examples

an ams radiocarbon method to determine the emplacement time of recent deep sea turbidites abstract this paper reports the evaluation of a novel method based on accelerator mass spectrometer ams radiocarbon dating of planktonic foraminifera to evaluate the times of emplacement of recent deep sea turbidites it assumes that the standing stock of relatively large 150 m planktonic foraminifera in the bioturbated surface mixed layer of box cores represents an integration of the flux from the water column since the turbidite was emplaced and exploits the potential of the ams method to analyse the resultant small samples which can be readily separated the method is evaluated by application to three atlantic turbidites which form the present day sediment surfaces on the horseshoe madeira and tagus abyssal plains the time of emplacement of madeira abyssal plain turbidite is estimated at 1120 730 and 870 years before present each 120 140 years in three different cores the resultant weighted mean emplacement time 930 76 years before present is somewhat older than previous estimates by geochemical methods the times of emplacement for the horseshoe 240 and 140 years before present each 120 years and tagus 300 120 years before present abyssal plains are both consistent with initiation by the lisbon earthquake of 1755

depositional processes of uniform mud deposits unifites hedberg basin northwest gulf of mexico new perspectives structureless mud deposits unifites are a common depositional phenomenon in the intraslope basins of the continental slope of the northwest gulf of mexico high resolution acoustic data and long sediment cores from hedberg basin middle slope were used to provide a better insight into the origin of these enigmatic depositional units the unifite occurring in hedberg basin is structureless under visual observations but x ray radiographs reveal that it consists of three divisions 1 u1 division representing waning sequences of fine grained mud turbidites 2 u2 division characterized by faint normally graded mud layers with occasionally wispy silty interlaminae and 3 u3 division characterized by a uniform appearance with no obvious sedimentological structures other than a faint banding of slightly siltier and slightly more clayey layers high resolution geophysical data reveal that there is no connection between intrabasinal sediment failures and the occurrence of unifites we suggest that unifites have resulted from the deposition of a long lasting 1 53 months pulsating showing internal surges fine grained turbidity current dated at 28 629 ka that originated from the flow transformation of a series of massive sediment failures on the shelf edge and or upper continental slope the fine grained nature of the turbidity current is probably caused by the depositional segregation of the flow by depositing its coarsest material in intraslope basins in more proximal locations we propose that the uniform texture of the unifite is attributed to the development of a stratification interface lower stratified layer generated by the continuous introduction of a turbulent sediment cloud in the intraslope basins the lowest two unifite divisions are considered to develop prior to and during the development of the stratified layer

holocene sediments from the southern chile trench a record of active margin magmatism tectonics and palaeoseismicity abstract sedimentology petrography and the provenance of holocene sediments from the southern chile trench 36 47 s were investigated in an integrated approach combining description of a collection of gravity cores measurements of physical properties quantitative x ray petrography and modal analysis the sediments studied were trench hemipelagic sediments fan deposits and more distal hemipelagic sediments from the nazca plate the trench is mostly fed by multiple point sources via submarine canyons sandy turbidites show a southward increase in sediment maturity whereas volcanic lithic fragments and plagioclase represent the dominant fraction in the north quartz content strongly increases in the southern part of the study area in line with source lithologies further north active volcanoes in the main cordillera represent almost the entire provenance signal as a result of a strong contribution of highly erodible volcanic rocks recurrence rates of sandy and silty turbidites in the trench fan sediments indicate a link to the palaeoseismic record on land our study documents the potential usefulness of proximal turbidites to reconstruct palaeoseismicity even at a scale of single segments of the plate boundary

measurements of the aeolian sand transport saturation length the wavelength at which a dune pattern emerges from a flat sand bed is controlled by the sediment transport saturation length which is the length needed for the sand flux to adapt to a change in wind strength the influence of the wind shear velocity on this saturation length and on the subsequent dune initial wavelength has remained controversial in this paper we present direct measurements of the saturation length performed in a wind tunnel experiment complementary to this initial dune wavelengths are measured under different wind conditions in particular after storms using the linear stability analysis of dune formation it is then possible to deduce the saturation length from field data both direct and indirect measurements agree that the saturation length is almost independent of the wind strength this result supports the idea that grain inertia is the dominant dynamical mechanism limiting sediment transport saturation on dunes

transparent layers in seismic reflection records from the central ionian sea mediterranean evidence for repeated catastrophic turbidite sedimentation during the quaternary abstract echosounding and scs records from the ionian and sirte abyssal plains show below the holocene augias megaturbidite two additional thick transparent layers which by analogy are interpreted as turbidites estimated thicknesses are 10 and 35 m upper and lower as a minimum no consideration of presumable variations of acoustic velocities the resulting sediment volumes are about 26 and about 200 km 3 respectively both layers occupy the entire abyssal plain basins similar to the holocene augias megaturbidite a provenance of mobilized sediments from the gulf of sirte into the basins is assumed the ages of the two turbidites have been estimated at 235 000 and 650 000 years respectively it is speculated that mobilization was triggered by tsunamis related to volcanic events or earthquakes in the southern aegean region

the hilt bed an upper cretaceous compound basin plain seismoturbidite in the hornbrook forearc basin of southern oregon and northern california usa abstract the hilt bed is a thick laterally continuous marker bed of fine to medium grained sandstone that crops out for a nw se along strike distance of about 50 km on the southwestern flank of the cretaceous hornbrook forearc basin of northern california and southern oregon the hilt bed forms part of the blue gulch mudstone member of the hornbrook formation and is everywhere underlain and overlain by basin plain mudstone that contains thin interbeds of turbidite sandstone and siltstone the bed is as thick as 4 71 m in the central part of the outcrop belt and thins progressively to the nw and se it was derived from erosion of igneous and metamorphic basement rocks of the klamath mountains which flank the basin to the sw paleocurrents measured from flute casts at the base of the bed indicate sediment transport to the ne the hilt bed can be divided into a compound succession of nine bouma divisions all of which are generally present in outcrop the succession consists in ascending stratigraphic order of bouma abababcde divisions the basal a division is typically the thickest and coarsest layer with overlying divisions generally thinner and more variable in thickness the bed appears to have been deposited as a compound turbidite by at least three separate turbidity currents that appear to have been generated either by the same triggering event or by a rapid succession of related events only the uppermost part of the bed thus contains a complete bouma sequence the unidirectional paleocurrent indicators lateral continuity and extent of the three flows that make up the bed incompleteness of the two lower bouma sequences and absence of interbedded shale or bioturbated levels suggest that the three turbidity currents reached the basin floor at almost the same time to yield the bed the compound nature of the hilt bed suggests that a major seismic event triggered the three large flows which probably originated in either a single submarine canyon or three adjacent canyons

ten turbidite myths abstract during the past 50 years the turbidite paradigm has promoted many myths related to deep water turbidite deposition john e sanders 1926 1999 a pioneering process sedimentologist first uncovered many of these turbidite myths this paper provides a reality check by undoing 10 of these turbidite myths myth no 1 turbidity currents are non turbulent flows with multiple sediment support mechanisms reality turbidity currents are turbulent flows in which turbulence is the principal sediment support mechanism myth no 2 turbidites are deposits of debris flows grain flows fluidized flows and turbidity currents reality turbidites are the exclusive deposits of turbidity currents myth no 3 turbidity currents are high velocity flows and therefore they elude documentation reality turbidity currents operate under a wide range of velocity conditions myth no 4 high density turbidity currents are true turbidity currents reality ph h kuenen 1950 introduced the concept of turbidity currents of high density based on experimental debris flows not turbidity currents high density turbidity currents are sandy debris flows myth no 5 slurry flows are high density turbidity currents reality slurry flows are debris flows myth no 6 flute structures are indicative of turbidite deposition reality flute structures are indicative only of flow erosion not deposition myth no 7 normal grading is a product of multiple depositional events reality normal grading is the product of a single depositional event myth no 8 cross bedding is a product of turbidity currents reality cross bedding is a product of traction deposition from bottom currents myth no 9 turbidite facies models are useful tools for interpreting deposits of turbidity currents reality a reexamination of the annot sandstone in se france which served as the basis for developing the first turbidite facies model suggests a complex depositional origin by plastic flows and bottom currents myth no 10 turbidite facies can be interpreted using seismic facies and geometries reality individual turbidity current depositional events commonly centimeters to decimeters in thickness cannot be resolved in seismic data all turbidite myths promote falsehood and should be abandoned

late cretaceous carbonate turbidites of the northern apennines shaking adria at the onset of alpine collision abstract thick and regionally widespread deepwater carbonate turbidite successions the upper cretaceous helminthoid flysch were deposited during the initial stages of alpine collision despite the dominant intrabasinal origin bulk composition and heavy minerals of minor terrigenous mode indicate provenance from different crustal levels of the european and adria plates these data allow us to place the helminthoid flysch units within a late cretaceous paleogeographic reconstruction of the northern apennine tethys the depositional characters of these turbidites indicate the coexistence of an active tectonic setting a paleogeographic location prone to carbonate ooze production and storage and limited terrigenous sources outside the basin

origin of a thick redeposited carbonate bed in eocene turbidites of the hecho group south central pyrenees spain large scale carbonate beds interbedded in basin plain turbidites of the eocene hecho group northern spain are interpreted as giant turbidity current deposits because of their internal organization and lateral extent one such bed the roncal unit has been traced down the axis of the basin for 75 km and commonly reaches thicknesses in excess of 100 m internally the roncal unit displays an overall upward decrease in grain size from a basal megabreccia with large slabs of carbonate platform debris to a calcareous mudstone the roncal unit was probably deposited from a highly mobile and competent sediment gravity flow generated by an earthquake shock which led to the catastrophic collapse and subsequent transport of the upper part of a carbonate platform flanking the basin

tsunami induced sediment transport in the abyssal mediterranean sea an unusual stratigraphic unit nicknamed homogenite fills topographic lows in the complex ridge and trough bathymetry at two survey sites on the western mediterranean ridge and the calabrian ridge on near bottom 4 khz seismic reflection profiles this unit us an acoustically transparent near surface flat lying layer whereas in cores it is a homogeneous gray marl as much as 7 m thick grain size decreases upcore within the unit implying that it was deposited in a single event controlled by gravitational settling the stratigraphic position of the homogenite relative to a firmly dated sapropel bed suggests emplacement between 4400 and 3100 yr b p the source of the homogenite is inferred to be the nearby basin walls farther east two other sites with similar rugged topography lack homogenite entirely a triggering mechanism is required which is capable of initiating massive sediment transport simultaneously in many separate basins at the western two survey sites but which is not effective at the eastern sites a large archeologically recorded earthquake of the correct age is considered and rejected because its epicenter is closer to the nonhomogenite bearing sites than to the sites where this sediment type was observed and because several other earthquakes of comparable magnitude have since been recorded in the area whereas the homogenite is unique the 3 500 yr b p collapse of the caldera of the volcano of santorini caused a huge tsunami which is recorded archeologically and geologically around the eastern mediterranean because of refraction of the tsunami by the bathymetry and because the caldera collapsed in its southwest corner a disproportionate amount of tsunami energy was directed toward the western area where homogenite is observed in contrast the homogenite free sites were relatively sheltered an order of magnitude calculation shows that the near bottom oscillating currents accompanying the santorini tsunami were at or above the threshold erosion velocity at the homogenite bearing sites in addition the near bottom pressure pulse under the tsunami at the homogenite bearing sites was sufficient to cause liquefaction of sediments neither mechanism was adequate to cause sediment transport or slope failure at the homogenite free sites

large scale slumping deduced from structural and sedimentary features in the lower palaeozoic anglo brabant fold belt belgium distinguishing slump folds from tectonic folds in poorly exposed areas can be difficult especially when the scale of the slump folds exceeds outcrop scale in the southeastern part of the single phase deformed lower palaeozoic anglo brabant fold belt a comparison of cleavage fold relationships and stratigraphic polarity shows that a 200 m thick interval of middle caradoc fine grained turbidites in the core of a large synform was overturned prior to tectonic deformation this overturning is attributed to large scale slumping which was most likely a result of middle caradoc seismic activity the exposed portion of the large slump sheet contains only a few small slump folds and intraformational breccias making up less than 5 of the exposed thickness if the beds were not overturned large scale slumping would never be suspected and the small slump folds would probably be interpreted as localized features in an overall stable sedimentary pile this may explain why so few ancient large scale slides and slumps have been reported the small amount of internal deformation makes them very difficult to recognize especially when dealing with poorly exposed areas as such large ancient slides and slumps may be more common than suggested by the geological literature

deep sea tsunami deposits triggered by the explosion of santorini 3500 y bp eastern mediterranean abstract the collapse of the santorini caldera after the catastrophic eruption of the bronze age 3500 y bp caused a tsunami wave that had catastrophic effects in the ionian basin including its deepest parts pelagic turbidites of local origin were deposited on the bottom of small perched basins of the southern calabrian western and central mediterranean ridges type a homogenite whereas a megaturbidite of distal origin presumably triggered by the tsunami wave hitting the shoreline of the sirte gulf was deposited on the ionian and sirte abyssal plains extending eastwards as far as the western herodotous trough depositing a thick acoustically transparent layer type b homogenite three core transects crossing the deformation front of the mediterranean ridge are presented and discussed a fourth transect of giant piston cores was collected on the abyssal plains located to the south of the mediterranean ridge all those to the west of the collision zone contain the holocene homogenite with a thickness in excess of 20 m whereas the cores taken from the herodotous abyssal plain east of the collision zone are devoid of the homogenite sedimentological analyses were performed on the only giant core that penetrated the sandy base of the homogenite and the underlying pelagic sediments of late pleistocene last glacial age the african provenance of this typical type b homogenite is corroborated by shallow water fauna derived from the north african shelf no sedimentological characteristics peculiar to tsunamiites are observed in the deep sea homogenite of the eastern mediterranean

sedimentary features of seismoturbidites triggered by the 1983 and older historical earthquakes in the eastern margin of the japan sea abstract both mass failure deposits and turbidites are widely distributed in the epicentral area of the 1983 earthquake mw 7 9 in the eastern margin of the japan sea this basin is semi enclosed with no active conduits for the entrance of coarse detrital sediments seismic reflection surveys and sediment cores reveal that mass failure deposits which are distributed on the continental slopes merge into turbidites in the basin plain hence the mass wasting process is a major transportation process in this region one gravity core gh93 816 was recovered from the southeastern margin of the japan basin close to the epicentral area of the 1983 japan sea earthquake sedimentological results show that five turbidite beds are intercalated in the top 68 cm of the column occurrence of the b tm tephra at the depth of 68 71 cm indicates that these turbidite beds were developed during the last 1000 years the high 137cs concentration in the top 20 cm of the core implies that the uppermost turbidite bed was deposited after 1954 based on these age limits for the top and the bottom of the studied interval we estimate the recurrence intervals of turbidites as 160 330 years we suggest that these turbidites were generated by submarine slides which were triggered by the 1983 and older historical earthquakes in this region these seismoturbidites are characterized by amalgamated beds irregular structure sequences grain size breaks fluctuations abrupt changes in composition within bed and variable composition among beds from these features we infer that deposition resulted from a series of turbidity currents associated with multiple or line sources for example multiple shallow slides that were regionally initiated by the same earthquake the sedimentary features described herein may be useful as criteria for identifying modern seismoturbidites in other settings as well as seismoturbidites in the geologic record however further study is needed for the distinction of this type of turbidites from other types e g tempestites reflected turbidites

neoproterozoic cambrian synsedimentary magmatism in the central iberian zone spain geology petrology and geodynamic significance petrographic geochemical and field studies in low grade metamorphic areas ciudad rodrigo hurdes sierra de gata domain crhsg central western spain show that neoproterozoic lowermost cambrian series in the central iberian zone ciz record two kinds of provenance sources including 1 detrital material derived from recycled orogens and 2 a cadomian coeval juvenile contribution that governs their isotopic signature evidence of magmatism contemporaneous with neoproterozoic cambrian sedimentation is provided by the presence of coherent massive volcanic rocks metabasalts metaandesites and metarhyolites volcaniclastic shales sandstones conglomerates and breccias the appearance of volcanogenic lithic fragments and crystals mixed in different proportions with siliciclastic constituents and also present within calcareous components in the sedimentary succession reinforces this evidence although most of the selected volcanic and volcaniclastic samples appear to show tholeiitic affinity some of them display calc alkaline affinity different trace element ratios such as sm nd nb yb and ta yb suggest a magmatic evolution in the same tectonic setting the geochemical results reported here support the existence of an active geodynamic setting as a direct contributor to the synsedimentary and magmatic content of the neoproterozoic lowermost cambrian successions in the ciz in particular the relatively high end t values and the high range of f sm nd ratios are consistent with an active margin during the neoproterozoic early cambrian the existence of tectonic activity is also confirmed by the presence of synsedimentary deformation and volcanic rocks all of these traits favour a geodynamic model in which the iberian cadomian segment represented in the ciz would have been part of an active northern margin of gondwana with an associated magmatic arc and related basins during neoproterozoic lower cambrian times a proposed link between the ossa morena and the central iberian zones might account for late cadomian pull apart basins developed on both sides of the magmatic arc sharing the same scenario and involving similar magmatic activity during the neoproterozoic cambrian transition

sedimentary characteristics and depositional models of two types of homogenites in an eocene continental lake basin shulu sag eastern china abstract homogenites are homogeneous and structureless fine grained rocks they have been studied extensively in marine settings and are typically interpreted as being related to catastrophic events such as earthquakes however studies on lacustrine homogenite like rocks are limited new core data from the shulu sag in china reveal that thick massive calcilutites exist in the lower shahejie 3 formation which formed during the middle eocene rifting stage based on petrographic geochemical and mineralogical data these massive calcilutites are interpreted as homogenites and grouped into two types type a homogenite is composed of intrabasinal materials characterized by high calcite total organic carbon toc content and 13c value type a homogenite has two facies successions the first of which is characterized by homogeneous appearance capped by an erosional interface and the second is characterized by repeated massive laminated calcilutite successions type b homogenite contains abundant allochthonous materials displaying relatively high dolomite content and low calcite toc and 13c content type b homogenite represents the topmost finer portion of a graded megabed which includes from base to top grain supported carbonate conglomerates slumped deformed portions and debrites the whole unit can be considered as a megaturbidite earthquakes are the most reasonable triggers of homogenite formation in the shulu sag type a homogenites are thought to be derived by fluidification resuspension and decantation of lacustrine fines due to shock waves generated by an earthquake type b homogenites might be deposits of distal turbidity currents and turbid clouds transformed from other gravity flows the results of this study provide a better understanding of the formation of homogenites caused by earthquakes in a confined lacustrine basin

palaeogeography of the upper cretaceous eocene carbonate turbidites of the northern apennines from provenance studies the upper cretaceous helminthoid flysch hf of the northern apennines consists of thick and regionally widespread deep water carbonate turbidite successions deposited during the initial stages of alpine collision the hf spans the time from turonian to early eocene and is mainly composed of intrabasinal carbonate ooze mixed with clay siliciclastic terrigenous beds are also present but they are a volumetrically minor component of the successions petrographic and sedimentological signatures indicate that the hf was deposited in distinct basins located below the carbonate compensation depth bulk composition and heavy minerals of terrigenous beds indicate provenance from different crustal levels of the european and adria plates the petrographic and palaeobathymetric characteristics of these turbidites indicate the coexistence of an active margin tectonic setting a palaeogeographical position suitable for carbonate ooze production and storage and limited supply of terrigenous detritus into the basin palaeotectonic reconstructions and stratigraphic data suggest that adria represented a vast repository of penecontemporaneous carbonate mud the presumably intense seismic activity related to the pre collisional alpine orogeny promoted large scale failures of shelf and or slope biogenic muddy sediments resulting in the deposition of a large volume of carbonate turbidites only occasionally turbidity currents probably linked to exceptional fluvial floods generated pure terrigenous beds with different petrographic signatures for each hf succession the oceanic crust of the tethyan domain and its overlying sediments have been extensively involved in the long lasting subduction processes that ultimately led to the eocene continental collision in the alps coward dietrich 1989 large volumes of carbonate turbidites known in the apennines as helminthoid flysch hf were deposited within deep sea trenches and on the remnant ocean basin floor abbate sagri 1970 argnani et al 2004 during the period preceding collision between africa and europe dewey et al 1973 1989 sedimentary successions comparable with the hf crop out in a fairly continuous belt along the alpine system from the northern apennines to the eastern alps fig 1a rowan 1990 and span the time from turonian to early

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

density surges two dimensional experiments some new aspects of the development of density surges in channels are developed from recent experimental results a density surge is characterized by the flow of a finite amount of dense fluid this dense fluid may be a saline water solution a saline water solution with tracers sand in suspension or a pure suspension sand in suspension in fresh water the experimental results show in particular that 1 the velocity of the surge is effectively proportional to the square root of the initial volume 2 the velocity of the surge increases with the increase of the initial density of the heavy fluid proportionally to the square root of the ratio of density difference to the ambient fluid density 3 the speed of the surge increases again with an increase of the slope for pure suspensions the experiments show that velocities slow down much more quickly than for saline solutions with the same initial density due to loss of negative buoyancy the effects of the initial density and of the size of the grains on the distribution of sediments are described

ostracoda crustacea as indicators of subaqueous mass movements an example from the large brackish lake tangra yumco on the southern tibetan plateau china abstract a conceptual model of subaquaeous mass movements and ostracod distribution in lacustrine sediment event layers was tested integrated methods geophysical sedimentological and microfossil analyses were performed on a short sediment core retrieved from 220 m water depth in the large brackish lake tangra yumco on the southern tibetan plateau central asia the event layers of the core and their underlying and overlying sediments were investigated four major event layers composed of sandy silt with graded bedding are interpreted as turbidites the fifth layer consisting of fine sand and silt and without graded bedding is characterized as a debrite the ostracods small bivalved aquatic crustaceans identified are leucocytherella sinensis huang 1982 leucocythere dorsotuberosa huang 1982 limnocythere inopinata baird 1843 and fabaeformiscandona gyirongensis huang 1982 ostracod evidence is a good proxy for the evaluation of massive sediment event layers formed by subaqueous mass movements four assumptions of a conceptual model were confirmed i fine grained sediments of event layers turbidite deposits contain very low numbers of ostracods compared to the underlying and overlying sediments ii ostracods are sorted according to size and display high abundance and high proportion of adult valves of leucocytherella sinensis at the base of event layers iii a relatively low number of carapaces is present within the event layers and iv the recolonization of newly event generated habitats by pioneer assemblages transforming into pre event association gradually

hydrogeology and design of groundwater heat pump systems groundwater can serve as an environmentally friendly and renewable energy source when utilized in a groundwater heat pump system installation of such systems has been increasing worldwide in recent years performance of a groundwater heat pump system depends on local hydrogeological and thermo geological conditions it is important that aquifer properties be determined to be representative of the site when designing a system in order to maximize efficiency reduce installation costs and minimize any environmental impacts factors that need to be considered are the groundwater temperature profile to the depth at which the temperature becomes relatively stable hydraulic and thermal conductivities diffusivity of the soil and rock layers groundwater levels and groundwater quality selection of groundwater and heat pump coupling techniques relies on to a large extent an accurate conceptual site scale model of groundwater conditions and understanding of environmental and legal constraints

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

low sea level stand emplacement of megaturbidites in the western and eastern mediterranean sea piston cores from the balearic and herodotus abyssal plains in the mediterranean sea show that the late pleistocene to holocene sedimentary sequence is dominated by turbidite muds on each plain one turbidite bed is conspicuous by its thickness and this bed can be correlated basinwide on the basis of geochemical compositional analysis and its apparent correspondence with a distinct acoustically transparent layer on high resolution seismic records these megabeds on the two plains represent megaturbidites of very large volume 300 600 km3 each and are shown by ams radiocarbon dating to have been emplaced during the last low stand of sea level at the height of the last glacial maximum the megabed on the balearic abyssal plain is derived from the southern european margin and is the main sedimentation event over the last 120 ka it emplaced as much material as was deposited by smaller flows during the previous 25 ka sedimentation rate curves for the balearic abyssal plain show that falling sea level correlates with increased terrigenous deposition and that gross sedimentation rates in the basin increased as sea level fell from 120 18 ka due to more frequent emplacement of distal turbidites the herodotus abyssal plain megabed is derived from the libyan egyptian continental shelf west of the nile delta and was the dominant sedimentation event in this basin during the past 60 kyr high resolution seismic profiles from the ionian and sirte abyssal plains in the central mediterranean also suggest possible low sea level emplacement of megabeds in these regions available evidence suggests widespread emplacement of megaturbidites throughout the mediterranean at the last glacial maximum although the triggering mechanisms for these events remain speculative catastrophic destabilisation of the margin after a long period of accumulation with an increased rate of sediment supply is suggested

influence of sea level and basin physiography on emplacement of the late pleistocene herodotus basin megaturbidite se mediterranean sea radiocarbon 14c dates from pelagic intervals above a megaturbidite in the herodotus basin give direct evidence of emplacement at the beginning of the last glacial period approximately 27 125 calendar years before present as sea level lowered rapidly and entered a low stand phase the herodotus basin megaturbidite is a basinwide deposit that forms a recognisable acoustically transparent layer on 3 5 khz high resolution seismic profiles and covers an area of approximately 40 000 km2 it thins from about 20 m in thickness proximally to some 10 m distally over a basin length in excess of 400 km the total volume is estimated at around 400 km3 which is significantly more than the volume of sediment that could have been displaced from its most likely source area the funnel shaped marginal embayment of the gulf of salum to the west of the nile cone the additional material may have been derived in part from synchronous failures on other parts of the libyan egyptian shelf and slope but most is believed to have come from large scale erosion at the base of the very large volume turbidity current that was generated from the original slide detailed sedimentary analyses of cores recovered from the megaturbidite show its distinctive characteristics graded sand silt mud and bioturbated mud units poorly developed structures proximally becoming more distinct and ordered distally variation in grain size and structures that suggest either flow separation reflection around topographic highs and or an inherently unstable flow and a mixed source bioclastic terrigenous composition these features together with its size and lateral extent would make any similar megabed an excellent marker horizon in basin analysis a combination of factors was responsible for triggering the initial slide debris flow event that evolved downslope into this mega turbidity current these include lowered sea level that destabilised the outer shelf upper slope sediments tectonic oversteepening of the margin relatively high rates of sedimentation and seismic activity

a depositional model for seismo turbidites in confined basins based on ionian sea deposits abstract this study investigates ionian sea seismo turbidite st deposits that we interpret to be triggered by major historic earthquakes and tsunamis in the calabrian arc st beds can be correlated with the ad 1908 mw 7 24 messina ad 1693 mw 7 41 catania and ad 1169 mw 6 6 eastern sicily earthquakes while two previously unknown turbidites might have been generated by the ad 1818 mw 6 23 catania and ad 1542 mw 6 77 siracusa earthquakes textural micropaleontological geochemical and mineralogical signatures of sts reveal cyclic patterns of sta stb stc and std sedimentary units for each earthquake with an associated tsunami the sta unit contains multiple st stacks with different mineralogy geochemistry foraminiferal assemblages and sedimentary structures that are deposited from synchronous multiple slope failures and turbidity currents the stb homogenite graded mud unit overlying the sta unit is deposited by the waning flows of the multiple turbidity currents that are trapped in the ionian sea confined basin the stc laminated and marine sourced unit results from seiching of the confined water mass that appears to be generated by earthquake ruptures combined with tsunami waves the std unit is a tsunamite cap deposited by the slow settling suspension cloud created by tsunami wave backwash erosion of the shoreline and continental shelf this tsunami process interpretation is based on the textural gradation of the upper unit and a more continental source of the tsunamite cap which includes c n 10 and the presence of inner shelf foraminifera with a lack of abyssal species this interpretation is in agreement with the lack of a tsunamite cap for the turbidite likely linked to the ad 1542 historic earthquake that is not associated with a tsunami the new sedimentologic criteria identifies the final seiche and tsunamite cap deposits of sts and provides a model that can now be tested in other locations to better understand the different depositional processes of seismo turbidites in confined basins

the south pyrenean eocene carbonate megabreccias revisited new interpretation based on evidence from the pamplona basin abstract the south pyrenean foreland basin contains numerous units of eocene carbonate megabreccias intercalated with siliciclastic turbidites and derived by resedimentation of shallow marine carbonate platforms previous studies were limited mainly to the foreland eastern part known as the jaca basin the present study from the pamplona basin a western part of the foreland trough sheds new light on the origin and regional significance of these south pyrenean eocene carbonate megabreccias specms the number of the specm units in the foreland basin is higher than previously recognized and their age is somewhat older than originally assumed the specm units appear to occur as time stratigraphic clusters which can be correlated with the relative sea level lowstands and linked with phases of tectonic activity the megabreccias were derived from a carbonate platform system hosted by the foreland basin s southern passive margin the episodic instability and mass wasting were triggered by phases of structural steepening forebulge uplift accompanied by high magnitude earthquakes with the former causing platform emergence increased load stresses and excess pore water pressure in the carbonate ramp the specm deposits were emplaced by cohesive debris flows evolving into high density turbidite currents an ideal specm unit consists of 1 an immature homogeneous debrite in the proximal part 2 a differentiated bipartite debrite and turbidite in the medial part and 3 an incomplete base missing debrite overlain by turbidite or a turbidite alone in the distal part the debrite component volumetrically predominates in the specm units and the original terms megaturbidite and seismoturbidite thus seem to be inappropriate for these deposits

evolution of a permian carbonate platform to siliciclastic basin indochina plate thailand abstract in thailand during the permian an extensive carbonate platform developed on the margin of the indochina plate and near to a coeval and deeper siliciclastic dominated marine basin this basin separated the indochina plate to the east from the shan thai plate to the west sedimentation in the area of both platform pha nok khao platform and basin nam duk basin was ended by a late permian early triassic orogenic event that caused closure of the palaeo tethys ocean tectonism has controlled the pattern of platform sedimentation and supplies of carbonate and clastic sediments into the basin area the pha nok khao platform developed on an extensive distally steepened ramp like margin along which carbonates and siliciclastics accumulated adjacent to this platform to the west the nam duk basin received coeval hemipelagic siliciclastics and minor amounts of carbonates biostratigraphic evidence based on foraminiferal assemblages suggests an early to middle permian age equivalence between platform and basin lithofacies the platform strata are exposed along the loei fold and thrust belt in northeast thailand and basin strata are exposed within the phetchabun fold and thrust belt in central thailand respectively the two belts extend in a north south direction and their rocks exhibit extensive karstification on the basis of seismic data platform lithologies extend further east in the subsurface beneath the continental sediments of the khorat group into kampuchea and laos facies groups of the platform environments include restricted platform platform interior and outer platform the facies groups of the basin environments include basin margin and basin plain minor layers of volcaniclastics and green coloured tuffites are interbedded with both the platform carbonate layers and basinal pelagic layers suggesting active volcanism during sedimentation the carbonate lithofacies of the shallow platform to the east in the loei fold belt grade westward into turbidites in the phetchabun fold belt and include shales and sandstones with minor carbonates farther to the west they pass into hemipelagic lithofacies of shale and carbonate lithologies and fauna of the limestones suggest tropical to subtropical climate during deposition

gordo megabed a possible seismite in a tortonian submarine fan tabernas basin province almeria southeast spain abstract the mainly tortonian sediments of the tabernas basin contain the elements of a well developed small submarine fan synsedimentary unconformities and randomly intercalated megabeds in both basin plain and fan lobe deposits indicate tectonic activity during fan growth one of the megabeds the gordo megabed overlies dislocated and deformed fan lobe and basin plain deposits the megabed with a thickness of up to 40 m has a sheet like geometry and consists of four superimposed sedimentary units unit i is a matrix supported conglomerate and contains reefal limestone debris metamorphic rocks and mainly at its top large slabs of ripped up fan sediments up to 60 m across the irregular surface of the unit is filled in by unit ii a cobble pebble conglomerate this conglomerate is covered by unit iii a sandstone layer of 6 8 m thickness which grades into unit iv a normal graded to massive mudstone the extra basinal content of the megabed is conservatively estimated at 0 9 km3 its total volume at 6 km3 from sedimentary structures and textures it is inferred that unit i represents a deposit from a debris flow while unit ii consists of a complex mixture of deposits of debris flow and turbulent flow and units iii and iv are deposits from a turbulent flow the megabed is interpreted to originate from a single catastrophic collapse along the basin margin because of its exceptional volume the sheet like geometry and the random position within the fan sequence the megabed is referred to as a seismite the depositional history succeeding a tectonic triggering is envisioned as follows the collapse of the basin border evolved through stages of sliding and slumping into a debris flow body transformation of the debris flow produced turbulent flow it is tentatively assumed that the debris flow outraced its turbidite

seismoturbidites a new group of resedimented deposits abstract turbidite beds of exceptionally large volume and areal extent occur in both modern and ancient deep water basins these beds which may reach individual volumes in excess of 100 km3 are apparently the product of catastrophic gravity flows triggered by earthquakes along the margins of highly mobile basins most commonly elongate flysch troughs turbidite beds produced by these catastrophic events are generally characterized by very distinctive geometry internal structures and composition and are termed herein seismoturbidites characteristically these sediments lack time persistent features of deep sea fans such as channels and lobes seismoturbidites may occur as scattered intercalations diluted within otherwise normal turbidite sequences thus forming generally excellent markers for basin wide correlations or as closely spaced repetitive units comprising the bulk of the sedimentary fill of certain flysch basins in both cases they may offer a tremendously useful tool for a better understanding of the distribution of paleoseismic zones in time and space

widespread erosion and mass failure from the 51 ma montagnais marine bolide impact off southwestern nova scotia canada12 1this article is one of a series of papers published in this cjes special issue on the theme of mesozoic cenozoic geology of the scotian basin 2earth sciences sector contribution 20120241 the 51 ma montagnais impact crater on the outer scotian shelf is well known but the potential effects from the impact event on the slope and rise seaward of the crater have until now remained poorly understood through detailed seismic stratigraphic correlation and ties to available wells we define a threefold seismic stratigraphic subdivision for upper cretaceous to eocene strata on the shelf and slope calibrated to the most recent biostratigraphic results using this framework we identify a number of depositional and erosional products that are temporally consistent with a late ypresian impact event within the limits of seismic and biostratigraphic resolution we link a series of prominent failure scarps on the outer shelf and upper slope to a single widespread mass transport deposit mtd on the lower continental slope rise and abyssal plain failed material amassed in a large debris field referred to here as the montagnais mtd it covers an area of 93 000 km2 and travelled up to 580 km f

supplementary information computational modeling of the wind erosion on a sinusoidal pile using a moving boundary method geomorphology volume 130 issues 3 4 pages 299 311 july 2011 abstract supplementary information note to facilitate the replication of the simulation and results reported in the above mentioned paper

late quaternary turbidite input into the east mediterranean basin new radiocarbon constraints on climate and sea level control the late pleistocene holocene 0 30 ka bp allochthonous sedimentation in the herodotus basin of the eastern mediterranean has been controlled in part by a combination of regional climatic change and eustatic sea level fluctuation a new series of radiocarbon dates made on planktonic foraminifers and pteropod shells taken from the pelagic and hemipelagic intervals between individual turbidite units has given bracketing dates for each major turbidity current event that deposited sand and mud on the herodotus basin plain two partly independent cycles are evident climate induced cycles have lead to an alternation of periods of turbidites sourced from the nile delta fan system with those from the north african shelf and anatolian rise these correlate with pluvial and inter pluvial climatic periods recognized in the nile hinterland sea level cycles have tended to focus turbidite emplacement from whatever source at periods of sea level fall within the latest wisconsin and sea level rise from the wisconsin holocene period in addition to the herodotus basin megaturbidite hbm described previously six other beds with volumes in excess of 25 km3 and wide lateral extent across the basin can be termed megaturbidites there is no simple sea level or climate control on the timing of these events so we must conclude that triggering and emplacement of megaturbidites is independent and variable

sumeini group oman evolution of a mesozoic carbonate slope on a south tethyan continental margin abstract deposition of the mostly mesozoic sumeini group occurred on the slope between the shallow marine arabian carbonate platform and the deep oceanic hawasina basin or south tethys sea these strata record the evolution of the northeast arabian continental margin from permian and triassic rifting to ocean basin closing with the late cretaceous obduction of the semail ophiolite platform margin type and its evolution can be inferred from exposures of these slope sediments at jebel sumeini in the western oman mountains in the lower permian base of the sequence bedded spicular limestones suggest deep marine conditions this is followed by an enigmatic thick sequence of bedded dolomite in the early to middle triassic small carbonate submarine fans formed along a distally steepened slope a subsequent interval of terrigenous clastic sedimentation was followed by development of a steep escarpment margin during ladinian to norian time with coralgal reefs at the shelf break and a debris apron at the base of the scarp the late triassic is marked by another influx of terrigenous sediment which accompanied widespread emergence of the platform in the jurassic a thick apron of thin bedded limestone formed on the slope this apron was cut by channelized gullies that now include blocks of older reefal material and oolitic sands a well documented submergence of the platform during the tithonian and early cretaceous led to the deposition of radiolarian cherts on the slope and basin upper lower cretaceous megabreccias up to 200 m thick suggest an interval of localized slope instability and or tectonism continued deposition of bedded limestone and marl with lesser calcirudite marks the top of stratigraphic sequence at jebel sumeini the early to middle triassic carbonate submarine fan deposits occur as discrete lenticular sequences of bedded calciturbidite modified grain flow and debris flow deposits which were derived from mostly slope sources the ladinian to norian base of slope debris apron deposits were derived from both slope and shallow marine sources including reefs and appear to form a laterally extensive but narrow belt of thick lenticular to sheet like beds of debris which accumulated over a long interval of time coarse limestones in the jurassic gullied slope deposits are distinct in that they occur randomly as individual channelized beds in a sequence dominated by thin bedded lime mudstones thick lower cretaceous megabreccias are distinguished by their great lateral distribution and general lack of matrix

platform margin collapses and sequence stratigraphic organization of carbonate slopes cretaceous eocene gargano promontory southern italy we describe the sequence stratigraphic organization and the associated sedimentological characteristics of cretaceous to eocene slope and base of slope carbonate successions the study area is located in the gargano promontory which belongs to the stable foreland of southern italy the succession consists of three superimposed depositional sequences separated by major unconformities the upper two sequences are clear examples of sequence stratigraphic organization in fact they both start with huge megabreccia wedges lst followed upward by thin pelagic units tst and a thick package of calciturbidites and debrites that alternate with pelagic mudstone hst the cretaceous highstand systems tract is clearly arranged in a number of coarsening upward cycles while the eocene one which also comprises a toplap shallow water unit is not the gargano stratigraphic palimpsest and the entire margin of the apulia platform show remarkable similarities with present day carbonate platform margins and slopes where irregular convex bankward embayments suggest large scale failures it is clear that classic sequence stratigraphic organization can result from simple platform dismantling having no or little time relation with global sea level fluctuations in fact as the margin failure lst interrupts the carbonate production a period of starvation tst along the entire slope and base of slope follows necessarily finally when the margin once again becomes active and productive sediment exportation starts again and the system begins to prograde hst

frasnian upper devonian integrated facies analysis magnetic susceptibility and sea level fluctuations in the nw algerian sahara changes in the palaeoenvironment are investigated in two representative frasnian sections of the nw algerian sahara integrating sedimentology and magnetic susceptibility ms the ben zireg section is characterized by condensed and ferruginous calcareous deposits in the south marhouma section the sedimentation rate is high dominated by muddy nodular limestones with several hypoxic shale intervals in both sections sediments were mostly emplaced on pelagic outer ramps below the limit of storm wave base evolving through time from proximal to distal setting investigations of the temporal evolution of facies and ms data permit a first estimate of the local sea level trends in nw algeria these trends match the overall long term rise of sea level recognized worldwide from frasnian zone 5 upwards noteable positive excursions of the sea level curve related to the semichatovae transgression as well as to the late frasnian transgression prior to the late kellwasser event can be established in this area although the sharp regression of sea level at the upper kellwasser level can be confirmed from our data no particular trend is depicted at the transition of conodont zones frasnian zones 12 13 where the presence of the lower kellwasser level has not yet been clearly recognized

hybrid event bed character and distribution linked to turbidite system sub environments the north apennine gottero sandstone north west italy this study documents the character and occurrence of hybrid event beds deposited across a range of deep water sub environments in the cretaceous palaeocene gottero system north west italy detailed fieldwork 5200 m of sedimentary logs has shown that hybrid event beds are most abundant in the distal confined basin plain domain 31 of total thickness in more proximal sectors hebs occur within outer fan and mid fan lobes up to 15 of total thickness whereas they are not observed in the inner fan channelised area six hybrid event bed types heb 1 to heb 6 were differentiated mainly on basis of the texture of their muddier and chaotic central division h3 the confined basin plain sector is dominated by thick max 9 57 m average 2 15 m and tabular hybrid event beds heb 1 to heb 4 their h3 division can include very large substrate slabs evidence of extensive auto injection and clast break up and abundant mudstone clasts set in a sandy matrix dispersed clay ca 20 these beds are thought to have been generated by highly energetic flows capable of delaminating the sea floor locally and carrying large rip up clasts for relatively short distances before arresting the unconfined lobes of the mid fan sector are dominated by thinner average 0 38 m hybrid event beds heb 5 and heb 6 their h3 divisions are characterised by floating mudstone clasts and clay enriched matrices dispersed clay 25 with hydraulically fractionated components mica organic matter and clay flocs these hybrid event beds are thought to have been deposited by less energetic flows that underwent early turbulence damping following incorporation of mud at proximal locations and by segregation during transport although there is a tendency to look to external factors to account for hybrid event bed development systems like the gottero imply that intrabasinal factors can also be important specifically the type of substrate available muddy or sandy and where and how erosion is achieved across the system producing specific hybrid event bed expressions and facies tracts this article is protected by copyright all rights reserved

genesis of limestone megabreccias and their significance in carbonate sequence stratigraphic models a review a re appraisal of the factors controlling the deposition of carbonate megabreccias and their sequence stratigraphic significance is presented based on an examination of the mechanisms for instigating carbonate seafloor slope instability and a review of the depositional settings of these distinctive rock deposits limestone megabreccias have classically been interpreted as formed by the catastrophic collapse of high angle metastable oversteepened carbonate platform margins however a review of megabreccia occurrence shows that these deposits formed on a broad range of carbonate slope angles and that metastable oversteepened slopes are not necessary for their genesis a re evaluation constructed from first principles of mechanisms promoting submarine gravitational instability indicates that pore water overpressure of confined aquifer horizons beneath the seafloor rather than slope oversteepening is the critical control on megabreccia deposition catastrophic release of overpressure may initiate gravitational instability of previously kinematically stable slopes the relative importance of endogenic processes intrinsically linked to the depositional system and exogenic processes operating independently in generating megabreccias is assessed two particularly important mechanisms in generating megabreccias are endogenic processes causing overpressure at discrete hydrologically confined horizons beneath the seafloor during relative sea level falls and increases in stress as pore fluid drains from the sediment when the platform top becomes subaerially exposed during relative lowstands of sea level the increased likelihood of megabreccia genesis during relative sea level falls is supported by an empirical trend identified from a review of the stratigraphic distribution of documented megabreccias exogenic causes of gravitational instability with inherently random periodicity especially seismicity may account for the small number of documented megabreccias that do not conform to this underlying trend the proposed endogenic pattern favouring megabreccia deposition during relative sea level falls is important in a sequence stratigraphic context megabreccia deposits may build volumetrically significant toe of slope wedges and aprons during relative lowstands of sea level partially compensating for the decrease loss in the supply of fresh granular sediment as the platform top carbonate factory contracts lowstand wedges and aprons in carbonate systems therefore generally differ in composition from equivalent highstand deposits in being composed not of calciturbidite deposits but of megabreccias cannibalized from the upper slope

detecting a sequence boundary across different tectonic domains an example from the middle miocene of the northern apennines italy sequence stratigraphic concepts can provide a powerful tool for understanding the tectono sedimentary evolution of areas extending across different tectonic domains an example is provided by the upper serravallian strata of the northern apennines where a sedimentological and biostratigraphic study allows a sequence boundary to be traced across the foredeep and piggy back basin successions turbidite sedimentation of predominantly alpine and subordinate apenninic provenance occurred in the apenninic foreland basin throughout the middle miocene deep water sedimentation in the foredeep was laterally associated with deposition in shelf to slope environments in the piggy back basins in the piggy back basin succession the upper serravallian sequence boundary is a laterally extensive unconformity within homogeneous marly deposits this unconfonnity is laterally correlative with the base of lenticular turbidite bodies a stratigraphic lacuna affecting zone n14 characterizes the marginal areas where glaucony rich deposits assigned to zone n15 unconformably overlie marls displaying association of zone n13 in the depocentres where no significant stratigraphic gap has been detected the sequence boundary is narrowly constrained to lowermost zone n14 the upper serravallian unconformity of the piggy back basins succession is correlative with time equivalent features in two distinct parts inner basin and outer basin of the foredeep in the inner basin the sequence boundary separates basin margin turbidites from overlying slope hemipelagites in a more external position outer basin the sequence boundary is the base of a characteristic mega turbidite of apenninic provenance turrito layer in other sectors of the outer basin where turbidite sedimentation was entirely of alpine provenance the sequence boundary has no clear physical expression the observed facies distribution in the study area suggests that an important thrusting event affected the northern apennines in the late serravallian resulting in submarine channel incision and nondeposition in the piggy back basins compressional activity in the foredeep was responsible for the closure of the inner basin and subsequent shifting of turbidite sedimentation in the outer basin slope instability led to widespread remobilization of previously deposited turbidites triggering turbidite events of huge volume the different characteristics of the sequence boundary in the various parts of the foredeep constitute an example of differential response of a multisourced supply system to tectonic deformation

the tsunamite problem the genetic term tsunamite is used for a potpourri of deposits formed from a wide range of processes overwash surges backwash flows oscillatory flows combined flows soft sediment deformation slides slumps debris flows and turbidity currents related to tsunamis in lacustrine coastal shallow marine and deep marine environments tsunamites exhibit enormous variability of features e g normally graded sand floating mudstone clasts hummocky cross stratification etc these sedimentary features may also be interpreted as deposits of turbidity currents turbidites debris flows debrites or storms tempestites however sedimentary features play a passive role when these same deposits are reinterpreted as tsunamites on the basis of historical evidence for tsunamis and their triggering mechanisms e g earthquakes volcanic explosions landslides and meteorite impacts this bipartite sedimentological vs historical approach which allows here classification of the same deposit as both turbidite and tsunamite has blurred the distinction between shallow marine and deep marine facies a solution to this problem is to classify deposits solely by a descriptive sedimentological approach the notion that tsunami waves can directly deposit sediment in the deep sea is unrealistic because tsunami waves represent transfer of energy and they are sediment starved during tsunamis and major storms submarine canyons serve as the physical link between shallow water and deep water environments for sediment transport tsunami related deposition involves four progressive steps 1 triggering stage offshore 2 tsunami stage incoming waves 3 transformation stage near the coast and 4 depositional stage outgoing sediment flows in this progression deep water deposition can commence only after the demise of incoming tsunami waves due to their transformation into outgoing sediment flows deposits of these sediment flows already have established names e g debrite and turbidite therefore the term tsunamite for these deposits is obsolete

turbidite deposition in five miocene bathyal formations along an active plate margin north island new zealand with notes on styles of deposition at the margins of east coast bathyal basins abstract five miocene turbidite formations whakataki oldest greenhollows tanawa pakowhai waihoki youngest in northern wairarapa north island new zealand are described the whakataki formation widespread on the east coast of wairarapa formed at the onset of the kaikoura orogeny earliest miocene to recent on a deep sea plain whereas younger formations were deposited in a part of a long lived slope basin the tawhero basin situated between the greenhill anticline in the west and the tinui fault in the east the whakataki and the mud rich tanawa formations were probably largely fan deposited whereas the greenhollows pakowhai and waihoki formations are largely non fan deposited the mid miocene tanawa formation has turbidites which invariably lack sole structures even in areas close to the mouths of small submarine channels canyons i e in proximal locations and contains sandstone mudstone couplets usually with t b or t c basal this is thought to indicate that the formation was largely deposited from low velocity turbidity currents the early miocene greenhollows formation and the latest miocene waihoki formation are composed of couplets containing thick sandstone parts and they represent sheeted high density turbidity currents features recognised within miocene northern wairarapa deep sea turbidite formations are 1 fan and non fan styles of deposition 2 deposition from high or low velocity turbidity currents 3 thick turbidites having a sheet like distribution in three of the formations 4 deposition of turbidites at mid or upper bathyal depths 5 syndepositional deformation and 6 the small size of the basin in which the four youngest formations were deposited little sediment is deposited at the margin of slope basins where there is substantial syndepositional uplift whereas at the margins of turbidite basins formed in foreare areas there is thick massive upper bathyal slope deposited siltstone

pillow beds a new type of seismites an example from an oligocene turbidite fan complex alicante spain a new type of soft sediment deformed beds termed pillow beds originally a packet of calcarenitic turbidites show sand in sand loading with plane lower and upper surfaces the pillow beds have some resemblance to ball and pillow structures and they are considered to have formed as a result of dewatering the pillow beds are oligocene in age and are part of turbidite lobes in a submarine fan system which was fed through a canyon along the southern border of the ancient iberian continent three hypotheses may explain their occurrence overloading sliding or seismic shock a seismic origin is preferrred on the basis of the flat undeformed lower surface of the pillow beds excluding dewatering of and loading into the previously deposited beds furthermore the pillow bed structures are related to grain size and may show repetitions thus excluding sliding the scale and nature of the pillow beds suggest they could be the result of an earthquake with a magnitude of 6 7 on the richter scale

low sea level emplacement of a very large late pleistocene megaturbidite in the western mediterranean sea large volume turbidites termed megaturbidites or megabeds result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea such large sediment failures can generate tsunamis and in terrains underlain by gas hydrates clathrates may be associated with the release of substantial amounts of the greenhouse gas methane it has been proposed that the megaturbidite events may be triggered by seismic activity or may result from gas hydrate release itself caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level previous conclusions on the significance of sea level change however have been conditional because of the lack of absolute times of turbidite emplacement here we use accelerator mass spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large volume 500 km3 bed in the balearic basin of the western mediterranean this turbidite is exceptional in its magnitude and represents the main sedimentation event in the balearic basin over the past 100 kyr our data provide an estimate of 22 000 calendar years before present for emplacement of the megabed a time when sea level stood at its lowest level during the last glacial maximum the coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level although other triggering mechanisms such as seismic shock cannot be ruled out

the interaction between tectonics and mudflow deposits within the main conglomerate formation in the 2 8 2 7 ga witwatersrand basin abstract the black bar is an erosively based unit comprising diamictites overlain by mudstones and interbedded siltstones and sandstones it is situated within the fluvially deposited main conglomerate formation an economically important component of the witwatersrand supergroup the unit is well developed on east rand proprietary mines ltd e r p m situated 25 km east of johannesburg conglomerate reefs angelo leader main reef main reef leader south reef were deposited on erosional surfaces which bound tectono stratigraphic packages the black bar also represents a tectono stratigraphic package in the middle of the main conglomerate formation the main conglomerate formation was deposited during a phase of tectonism which has been associated with nearby marginal faults in previous papers this tectonism manifests itself in the study area as a rising anticline which acted as a syndepositional topographic high over which successive packages were deposited on erosion surfaces regionally the main conglomerate formation forms the base of the central rand group which directly overlies the jeppestown shale subgroup a sequence of fine grained sediments deposited in a large marine or lacustrine water body it therefore marks a rapid transition to subaerial fluvial conditions the black bar extends into the east rand goldfield and is an important stratigraphic marker in the stratigraphy of the main conglomerate formation because of its correlation with the green bar in the carletonville goldfield and the cab in the west rand the black bar facies distribution on e r p m has been used in this paper to explain regional variations between the carletonville and east rand goldfields deposition of the black bar diamictites is attributed to a mudflow mechanism texturally clasts and sand grains are similar to those found in underlying conglomerates and associated sandstones geochemically the black bar has a similar major element composition to the underlying jeppestown shale it is therefore likely that the conglomerates sandstones and shale all acted as source components to the black bar it is thought that tectonic activity and gravitational instability were the important factors in the development of the black bar movements on marginal faults would have increased depositional slopes and triggered slumps and mudflows tectonic uplift on the margin was complemented by basin subsidence this led to a transgression represented by the deposition of turbidites and laminated mudstones and siltstones which form the upper portion of the black bar package this implies that the diamictites like the mudstones were largely deposited subaqueously further uplift reintroduced fluvial conditions with the erosively based main reef leader and south reef packages

the dali ash island of rhodes greece a problem in interpreting submarine volcanigenic sediments in the southern part of rhodes greece rhyolitic subaqueous pyroclastic deposits are interbedded with tertiary deep water marine sediments the lowermost and best exposed of these deposits the dali ash is described here the deposit has been previously described as a deep water welded subaqueous ignimbrite this paper shows that there is no evidence of welding and texture previously reported were misidentified the dali ash consists of a lower massive unit 5 m thick overlain by a sequence of ash turbidites 2 5 m thick the lower unit was deposited by a high concentration turbidity current and the ash turbidites by dilute turbidity currents foraminifera are dispersed throughout the deposit and indicate that all the sedimentary gravity flows were cold water particulate systems a palaeomagnetic study also suggests they were deposited cold