sedimentary features of the seismo turbidites lake biwa japan abstract seismo turbidite layers are deposited at the foot of the steep slope of the half graben in which lake biwa has accumulated sedimentary studies especially of grain size distribution of selected turbidites provide excellent information for clarifying the distinctive features of general seismo turbidites development of the two constituent sublayers lower sandy sublayer and upper silt sublayer lack or limited appearances of traction indicating structures and characteristic grain size distribution in the two constituent sublayers are most remarkable and significant the characteristic grain size distribution features are coarse tail grading in a relatively thick sandy sublayer exceptionally rapid distribution grading through the thin boundary interval between the two sublayers height increase and fluctuation of the silt mode and high clay content brief discussion was made on the causes of these sedimentary features the need and importance of further comparative studies of various turbidites known triggering forces are emphasized

analytical model for resilient modulus and permanent deformation of geosynthetic reinforced unbound granular material abstractto consider the benefit of geosynthetic reinforcement in a mechanistic empirical pavement design method the resilient modulus and permanent deformation behavior of a geosynthetic reinforced unbound granular material ugm must be considered many researchers conducted repeated load triaxial rlt tests to investigate the resilient and permanent deformation behavior of the geosynthetic reinforced ugm however these tests are difficult to perform and the results are often interpreted empirically thus implementation of the research results is limited in this study an analytical model was developed to predict the resilient modulus and permanent deformation of the geosynthetic reinforced ugm in rlt tests the analytical model is compatible with the resilient modulus and permanent deformation models in the current mechanistic empirical pavement design guide both planar and three dimensional geosynthetics can be analyzed using this model rlt test results from two published studies were selected

the provenance of middle jurassic sandstones in the scotian basin petrographic evidence of passive margin tectonics the tectonic and geomorphological evolution of the scotian margin and its hinterland is poorly known between late triassic rifting and the early cretaceous progradation of major deltas this study determined sedimentary provenance of middle jurassic mohican formation sandstones from three wells using heavy minerals and mineral chemistry indicator minerals such as xenotime altered ilmenite and varietal types of garnet and tourmaline are similar to those in hauterivian barremian sandstones in the western scotian basin which are almost exclusively derived from the meguma terrane the wells adjacent to the canso ridge have more zircon and less ilmenite indicating a greater contribution of polycyclic reworking but with an ultimate source in the meguma terrane zircon and ilmenite were likely derived in part from carboniferous sandstones in eastern mainland nova scotia and cape breton island any river drainage from the inboard terranes of the appalachians either was diverted through the fundy basin or entered the easternmost scotian basin where the mohican formation is 5 5 km thick along the linear continuation of the southwest grand banks transform such sediment did not reach the canso ridge suggesting that the cobequid chedabucto fault zone in orpheus graben was not a significant physiographic feature this tectonically controlled paleogeography in the middle jurassic is quite different from that during active rifting in the late triassic early jurassic middle jurassic quiescence was followed in the tithonian early cretaceous by renewed tectonic uplift associated with rifting of grand banks from iberia and labrador from greenland

the role of premagmatic rifting in shaping a volcanic continental margin an example from the eastern north american margin both magmatic and tectonic processes contribute to the formation of volcanic continental margins such margins are thought to undergo extension across a narrow zone of lithospheric thinning 100 k

the cambrian to devonian odyssey of the brabant massif within avalonia a review with new zircon ages geochemistry sm nd isotopes stratigraphy and palaeogeography abstract this study provides an up to date and comprehensive review of the early palaeozoic evolution of the brabant massif belonging to the anglo brabant deformation belt situated at the southeastern side of avalonia microplate it is the only well known part of the northern passive margin of the rheic ocean the cambrian silurian sedimentary pile is 13 km thick with 9 km for the cambrian only the unraveling of this continuous registration reflects the successive rifting and drifting of avalonia from the gondwana mainland followed by soft collisional processes with baltica and finally the formation of laurussia based on recently established detailed stratigraphy sedimentology and basin development on u pb la icp ms analyses of igneous and detrital zircon grains along with geochemical data including sm nd isotopes a new geodynamic and palaeogeographic evolution is proposed brabant megasequence 1 lower cambrian to lowermost ordovician 9 km thick represents an embayment of the peri gondwanan rift from which the rheic ocean has evolved detrital zircon ages demonstrate that the brabant is a typical peri gondwanan terrane with a major pan african neoproterozoic age and a mixed west african and amazonian source palaeoproterozoic archaean and some mesoproterozoic age the transition towards the avalonia drifting is marked by an unconformity and a short volcanic episode the northward drift of avalonia towards baltica is recorded by the megasequence 2 middle to upper ordovician 1 3 km thick the source for mesoproterozoic zircons vanished as the result of the rheic ocean opening and the isolation from amazonian sources the transition to megasequence 3 is marked by a drastic change in palaeobathymetry and an important sub volcanic episode during a tectonic instability period 460 430 ma reflecting the avalonia baltica soft docking as also shown by the reappearance of mesoproterozoic detrital zircons typical of baltica unradiogenic nd isotope signature end 4 5 and tdm model ages 1 3 1 7 ga for brabant magmatic rocks indicate an old recycled component megasequence 3 uppermost ordovician to lowermost devonian 3 5 km thick includes the onset of a silurian foreland basin that reflects the tectonic inversion of the core of the massif brabantian orogeny in response to the baltica avalonia laurentia collision finally the comparison with the strikingly similar cambrian successions of the harlech dome wales avalonia and the meguma terrane nova scotia peri gondwana allows the construction of a new early cambrian palaeogeographic model for the whole avalonia microplate in which the meguma terrane is included

effects of fluid flow cooling and deformation as recorded by 40ar 39ar rb sr and zircon fission track ages in very low to low grade metamorphic rocks in avalonian se cape breton island nova scotia canada 40ar 39ar in situ uv laser ablation of white mica rb sr mineral isochrons and zircon fission track dating were applied to determine ages of very low to low grade metamorphic processes at 3 5 0 4 kbar 280 30 c in the avalonian mira terrane of se cape breton island nova scotia the mira terrane comprises neoproterozoic volcanic arc rocks overlain by cambrian sedimentary rocks crystallization of metamorphic white mica was dated in six metavolcanic samples by 40ar 39ar spot age peaks between 396 3 and 363 14 ma rb sr systematics of minerals and mineral aggregates yielded two isochrons at 389 7 ma and 365 8 ma corroborating equilibrium conditions during very low to low grade metamorphism the dated white mica is oriented parallel to foliations produced by sinistral strike slip faulting and or folding related to the middle late devonian transpressive assembly of avalonian terranes during convergence and emplacement of the neighbouring meguma terrane exhumation occurred earlier in the nw mira terrane than in the se transpression was related to the closure of the rheic ocean between gondwana and laurussia by nw directed convergence the 40ar 39ar spot age spectra also display relict age peaks at 477 465 ma 439 ma and 420 428 ma attributed to deformation and fluid access possibly related to the collision of avalonia with composite laurentia or to earlier ordovician silurian rifting fission track ages of zircon from mira terrane samples range between 242 18 and 225 21 ma and reflect late palaeozoic reburial and reheating close to previous peak metamorphic temperatures under fluid absent conditions during rifting prior to opening of the central atlantic ocean

meguma terrane orocline u pb age and paleomagnetism of the silurian mavillette gabbro nova scotia canada

deep marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons abstract submarine canyons provide a unique setting for tidal processes to operate from shallow marine to deep marine environments in modern canyons current meter measurements at varying water depths 46 4200 m show a close correlation between the timing of up and down canyon currents and the timing of semi diurnal tides these tidal bottom currents in submarine canyons commonly attain maximum velocities of 25 50 cm s based on core and outcrop studies of modern and ancient deep marine deposits it is proposed here that sand mud rhythmites double mud layers climbing ripples mud draped ripples alternation of parallel and cross laminae sigmoidal cross bedding with mud drapes internal erosional surfaces lenticular bedding and flaser bedding can be used to interpret deposits of deep marine tidal currents this approach is an alternative to the conventional approach in which most deep water traction structures e g climbing ripples and cross bedding would be attributed to deposition from turbidity currents underwater photographs show active mass flows i e slides slumps grain flows and debris flows in modern canyons box cores taken from modern submarine canyons e g la jolla california and conventional cores and outcrops of ancient canyon fill facies oua iboe pliocene nigeria and the annot sandstone eocene oligocene se france contain deposits of both tidal processes and mass flows this facies association in the rock record can be used as a criterion for recognizing submarine canyon settings in a channel mouth environment deep marine tidal deposits are likely to develop elongate bars that are aligned parallel to the channel axis within the channel whereas turbidites are more likely to develop depositional lobes that are aligned perpendicular to channel axis turbidite depositional lobes are much larger than the channel width whereas tidal sand bars are much smaller than the channel width therefore the wrong use of a turbidite lobe model with sheet geometry in lieu of a tidal bar model with bar geometry will result in an unrealistic overestimation of sandstone reservoirs in deep water exploration

evaluation of additional confinement for three dimensional geoinclusions under general stress state three dimensional cellular geoinclusions e g geocells scrap tires offer all around confinement to the granular infill materials thus improving their strength and stiffness the accurate evalu

a petrological and geochronological study of a 360 ma metallogenic event in maritime canada with implications for lithophile metal mineralization in the canadian appalachians the occurrence of ca 360 ma greisen related molybdenite mineralization in the clayton hill biotite muscovite leucomonzongranite 1 km2 is unusual for the southwestern meguma terrane of the maritime appalachians where 380 ma granite related sn mineralization dominates the presence of extensive hornfelsing and occurrence of mineralized sn w cu zn skarns in the area suggests a larger intrusion occurs at depth the intrusion and mineralization are constrained to 361 ma based on concordant re os molybdenite and 40ar 39ar muscovite ages which equates to other ca 360 ma granites in the area hence magmatism of this age is more widespread than previously considered the intrusion is highly evolved 74 wt sio2 metaluminous a cnk 1 1 05 a cnk molar ratio al2o3 cao na2o k2o and depleted in cafemic and transition elements rare earth elements ree 106 23 ppm are strongly fractionated with light rare earth elements lree enriched la lun 10 and negative eu anomalies biotite is

derivation of the early carboniferous wedgeport pluton by crystal fractionation of a mafic parental magma a rare case of an a type granite within the meguma terrane nova scotia canada the cambrian ordovician metasedimentary rocks of the meguma terrane canadian appalachians were extensively intruded by silicic plutons during middle devonian to early carboniferous times syn plutonic but volumetrically minor mafic ultramafic intrusions were also emplaced in most localities the silicic plutons and mafic ultramafic intrusions do not appear to be petrogenetically related and are likely derived from different sources the attwoods brook gabbronorite of sw nova scotia yielded an in situ zircon weighted mean 206pb 238u age of 357 9 3 3 ma that is within the uncertainty of the age of the neighbouring wedgeport pluton 357 1 ma the wedgeport pluton is a rare example of a mantle derived peraluminous a type granite within the meguma terrane the similar ages and nd isotopes of the attwoods brook gabbronorite end t 1 1 to 4 0 and wedgeport pluton end t 2 1 to 3 3 suggest the two intrusions are petrogenetically related fractional crystallization modelling demonstrates that a parental magma similar to the attwoods brook gabbronorite can produce residual silicic liquids that resemble the granites of the wedgeport pluton indicating that they could be members of the same intrusive complex the emplacement of the gabbronorite and wedgeport pluton occurred during a period of tensional plate stress that was contemporaneous with rifting of the maritimes basin that produced the fountain lake continental flood basalts and a type granites of the cobequid highlands within the avalon terrane it is possible that the early carboniferous rocks of sw nova scotia are related to the rifted related magmatism within the maritimes basin

the provenance of jurassic and lower cretaceous clastic sediments offshore southwestern nova scotia jurassic and cretaceous sandstones in the shelburne subbasin and fundy basin offshore nova scotia are poorly known but are of current interest for petroleum exploration the goal of this study is to determine the provenance of sandstones and shales which will contribute to a better understanding of regional tectonics and paleogeography in the study area mineral and lithic clast chemistry was determined from samples from conventional cores and cuttings from exploration wells using scanning electron microscopy and an electron microprobe whole rock geochemical composition of shales was used to test the hypotheses regarding provenance of mesozoic clastic sedimentary rocks in the sw scotian basin lower jurassic clastic sedimentary rocks in the fundy basin contain magnetite biotite and chlorite suggesting local supply from the north mountain basalt and meguma terrane whereas pyrope and anthophyllite suggest small supply from distant sources in the sw scotian basin detrital minerals lithic clasts and shale geochemistry from middle jurassic to early cretaceous indicate a predominant meguma terrane source and transport by local rivers rare spinel and garnet grains of meta ultramafic rocks only in the middle jurassic at the mohawk b 93 well suggest minor supply from the rising labrador rift via the same river that transported distant sediments to the fundy basin lower cretaceous sandstones from the mohican i 100 well contain minor garnet spinel and tourmaline from meta ultramafic rocks characteristic of sediment supplied to the central scotian basin at that time the dominant meguma terrane provenance precludes thick deep water sandstones in the eastern part of the shelburne subbasin but the evidence of middle jurassic distant river supply through the fundy basin is encouraging for deep water reservoir quality in the western part

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

seamounts at the continental margin of california a different kind of oceanic intraplate volcanism davidson guide pioneer gumdrop and rodriguez seamounts located at the continental margin offshore california between latitudes 37 5 n and 34 0 n may represent a previously unrecognized type of intraplate oceanic volcanism morphologically unlike typical oceanic island volcanoes or near ridge seamounts they are complex northeast trending ridges that reflect the ridge parallel structure of the underlying oceanic crust 40ar 39ar laser fusion ages of mineral separates indicate at least two episodes of volcanism at ca 16 and ca 12 ma younger by 7 11 m y than the underlying ocean crust volcanic rocks are predominantly differentiated alkalic basalt hawaiite and mugearite the lack of coherent liquid lines of descent is consistent with small batches of magma forming fractionally crystallizing and erupting in isolation from the previous and subsequent batches the presence of mantle xenoliths suggests that magmas originated in the upper mantle xenoliths of alkalic cumulates and xenocrysts of feldspar amphibole and titanomagnetite are consistent with fractionation in the upper mantle as well sr nd and pb isotope ratios of some samples are from depleted mantle sources like those of morb mid oceanic ridge basalt others indicate more variably enriched mantle sources magmas formed by small percentage partial melting of variably enriched morb source type mantle according to the samples high abundances of incompatible elements such as nb ta and th coeval middle miocene basalts in onshore coastal california have a similar isotopic range but their trace elements show a subduction related signature if the coeval volcanic rocks offshore originated in a slab window as proposed for those onshore they were not influenced by a slab component although a slab window origin is plausible for the middle miocene volcanism later episodes of small sporadic eruptions on and offshore probably resulted from decompression melting of mantle rising along existing zones of weakness undergoing extension related to continued movement along transform fault systems

paleoseismicity of the cascadia subduction zone evidence from turbidites off the oregon washington margin cores from cascadia deep sea channel contain sequences of turbidites that can be correlated and dated by the first occurrence of volcanic glass from the mount mazama eruption 6845 50 radiocarbon yrbp turbidity currents from the tributaries appear to have occurred synchronously to form single deposits in the main channel there being only 13 turbidite deposits in the lower main channel since the mazama eruption instead of the twice as many expected if the tributaries had behaved independently in addition to the cascadia channel 13 post mazama turbidites have been deposited in the astoria canyon and at two sites off cape blanco sample locations that span 580 km of the oregon washington margin pelagic intervals deposited between the turbidites suggest that in each place the turbidity currents occurred fairly regularly every 590 170 years on average the best explanation of the spatial and temporal extent of the data is that the turbidity currents were triggered by 13 great earthquakes on the cascadia subduction zone the variability of turbidite timing is similar to that for great earthquake cycles the thickness of the topmost pelagic layer suggests the last event was 300 60 years ago from three places along the margin but this number may be a biased underestimate it is however consistent with the youngest sudden subsidence event on the washington coast the turbidite data demonstrate that the near term hazard of a great earthquake on the cascadia subduction zone is of the order of 2 10 in the next 50 years

detrital muscovite geochronology and the cretaceous tectonics of the inner scotian shelf southeastern canada1 2 geochronology of detrital muscovite from the lower cretaceous of the central scotian basin has shown predominant supply of meguma terrane detritus including muscovite with alleghanian mid carboniferous to permian ages from the inner scotian shelf in this study 87 detrital muscovite grains from five wells in the eastern scotian basin representing depositional ages from tithonian to early albian were dated by single grain 40ar 39ar techniques previous work shows that the provenance of this sediment was different from wells in the central scotian basin compared with the central scotian basin the muscovite age populations from the eastern scotian basin have more 20 versus 7 pre devonian ages derived from inboard terranes of the appalachians in both the central and eastern scotian basin most old grains are found in the tithonian and the aptian albian with fewer in the valanginian and almost none in the kimmeridgian and the hauterivian barremian these data suggest rapid unroofing of the megum

the bouma sequence and the turbidite mind set abstract conventionally the bouma sequence bouma a h 1962 sedimentology of some flysch deposits a graphic approach to facies interpretation elsevier amsterdam 168 pp composed of ta tb tc td and te divisions is interpreted to be the product of a turbidity current however recent core and outcrop studies show that the complete and partial bouma sequences can also be interpreted to be deposits formed by processes other than turbidity currents such as sandy debris flows and bottom current reworking many published examples of turbidites most of them hydrocarbon bearing sands in the north sea the norwegian sea offshore nigeria offshore gabon gulf of mexico and the ouachita mountains are being reinterpreted by the present author as dominantly deposits of sandy debris flows and bottom current reworking with only a minor percentage of true turbidites i e deposits of turbidity currents with fluidal or newtonian rheology in which sediment is suspended by fluid turbulence this reinterpretation is based on detailed description of 21 000 ft 6402 m of conventional cores and 1200 ft 365 m of outcrop sections the predominance of interpreted turbidites in these areas by other workers can be attributed to the following 1 loose applications of turbidity current concepts without regard for fluid rheology flow state and sediment support mechanism that result in a category of turbidity currents that includes debris flows and bottom currents 2 field description of deep water sands using the bouma sequence an interpretive model that invariably leads to a model driven turbidite interpretation 3 the prevailing turbidite mind set that subconsciously forces one to routinely interpret most deep water sands as some kind of turbidites 4 the use of our inability to interpret transport mechanism from the depositional record as an excuse for assuming deep water sands as deposits of turbidity currents 5 the flawed concept of high density turbidity currents that allows room for interpreting debris flow deposits as turbidites 6 the flawed comparison of subaerial river currents fluid gravity flows dominated by bed load transport with subaqueous turbidity currents sediment gravity flows dominated by suspended load transport that results in misinterpreting ungraded or parallel stratified deep sea deposits as turbidites and 7 the attraction to use obsolete submarine fan models with channels and lobes that require a turbidite interpretation although the turbidite paradigm is alive and well for now the turbidites themselves are becoming an endangered facies

fluidization and injection in the deep water sandstones of the eocene alba formation uk north sea the nauchlan member of the late eocene alba formation uk north sea consists of a deep water channel fill that was extensively modified by post depositional sand remobilization and injection sandstone textures facies associations and the geometry of the channel fill were affected a suite of sand rich facies was produced by large scale fluidization and injection within the channel fill and above it these facies termed here unstratified facies are characterized by the absence of stratification surfaces and by discordant relationships with bedding in the adjacent succession they reflect variable degrees of disruption of the primary sedimentary structures caused by escaping pore fluid the velocity of which is estimated at least in the order of 0 1 ms 1 adjacent mudstones were severely disrupted by hydraulic fracturing and fragments of fractured mudstone were incorporated into the fluidized sand average porosity was decreased in the sandstones affected by fluidization two main phases of sand injection are inferred to occur at different burial depths a shallow burial phase below 100 m produced thin dykes with ptygmatic folds the second phase occurred at the boundary between eocene and oligocene 300 m burial depth and resulted in large scale tabular wing like dykes that project from the edges of the channel fill the significant pore fluid overpressure which was required to hydraulically fracture the thick mudstone seal and to fluidize the large volume of sand was likely to be built up by static liquefaction of the source sand and was possibly enhanced by hydrocarbon gas influx

ocean warming and gas hydrate stability on the mid norwegian margin at the storegga slide abstract the sensitivity of oceanic gas hydrates and submarine slope stability to the combined forcing of sea level changes and bottom water perturbation is a critical issue for risk assessment in the storegga slide area on the mid norwegian margin evidence for the existence of gas hydrates both inside and outside the storegga slide complex comes from reflection seismic profiles where a bottom simulating reflection marks today s base of the gas hydrate stability zone paleo bottom water temperatures show a relatively fast increase at approximately 12 5 10 ka calendar years following the younger dryas while stable warm water conditions have prevailed since then despite sea level rise this warm water inflow caused a major reduction in the thickness of the gas hydrate stability zone along the upper slope of the mid norwegian margin modelling results indicate that critical hydrate stability conditions and consequently the maximal potential pore pressure build up occur at the location of the storegga slide headwall although the major phase of hydrate melting predates the storegga slide event dated at 8 2 ka calendar years reduced hydrate stability conditions could have facilitated or contributed to sub marine slope failure additionally the bottom simulating reflections within the slide complex seem to have nearly adjusted to new equilibrium conditions highlighting the dynamics of hydrate stability in continental margin sediments under environmental changes climate change geohazards

turbidites as records of intense palaeoearthquakes in lake biwa japan abstract some 20 turbidites were collected in the uppermost 3 m of surface sediments in lake biwa southwest japan these turbidites correlate in age to historical earthquakes that caused severe loss of lives and property near lake biwa the age of each turbidite was estimated precisely based on sedimentation rate by weight and the age of tephra markers below the turbidites the magnitudes and epicentres of major historical earthquakes during the last 1300 years are available from historical documents empirical equations relating intensity distance to the epicentre and magnitude enable us to calculate the ground shaking at lake biwa from these historical earthquakes earthquakes having intensity stronger than grade iv l on the japan meteorological agency jma earthquake scale that is 44 gal acceleration at lake biwa all coincide with the turbidite ages this intensity is apparently the lower threshold for turbidity current initiation in lake biwa

petrology age and tectonic setting of the seal island pluton offshore southwestern nova scotia the seal island pluton outcrops only on small islands located on the continental shelf 45 km south of nova scotia although geophysical data indicate that the pluton is part of large granitoid units that cover thousands of square kilometres farther offshore based on the island outcrops the seal island pluton consists of biotite monzogranite and muscovite biotite monzogranite of uncertain relative age metasedimentary xenoliths combined with characteristic magnetic patterns indicate that the pluton intruded the cambrian ordovician meguma group compared with the biotite monzogranite the muscovite biotite monzogranite is higher in sio2 more peraluminous and more depleted in heavy rare earth elements and also has lower end 1 39 versus 0 82 possibly the result of more contamination by meguma group sedimentary rocks the biotite monzogranite yielded a late devonian u pb zircon age of 362 8 0 7 ma although the relatively minor petrological differences between the two units do not preclude a co m

mixed siliciclastic carbonate systems and their impact for the development of deep water turbidites in continental margins a case study from the late jurassic to early cretaceous shelburne subbasin in offshore nova scotia progradation of deltaic systems that reach the shelf edge is considered a primary mechanism to deliver sand to continental margins sediment bypass processes can dominate the outer shelf to upper slope transition causing poor preservation of reservoir quality sandstones turbidites can carry the bulk of the coarse fraction downdip where a thicker sand pile can be deposited once the channel to lobe transition is reached predicting this lateral and vertical variability along the slope is challenging this configuration can be further complicated when mixed siliciclastic carbonate systems are present the roseway missisauga case study from nova scotia is used here to explore potential implications associated with the development of deep water turbidites that are time equivalent to outer shelf mixed siliciclastic carbonate units two scenarios are possible 1 the carbonate factory is dominant and the development of carbonate reefs and pinnacles on the outer shelf prevents the passage of siliciclastic systems beyond the shelf break in this case the siliciclastic component is sequestered within the inner outer shelf 2 favorable conditions for carbonate production gradually deteriorate by the activation of fluviodeltaic systems that prograde outboard reaching the slope region in this last scenario low relief and lateral discontinuous carbonate shoals are ubiquitous in the outer shelf representing the last outboard remnants of the carbonate factory shelf edge deltas circumvent or breach these carbonate shoals establishing sedimentary pathways on the shelf break region that connect with deep water turbidites observations suggest that this last scenario is the most likely in this part of the scotian margin during the late jurassic to early cretaceous

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

internal tides in monterey submarine canyon abstract the m2 internal tide in monterey submarine canyon is simulated using a modified version of the princeton ocean model most of the internal tide energy entering the canyon is generated to the south on sur slope and at the head of carmel canyon the internal tide is topographically steered around the large canyon meanders depth integrated baroclinic energy fluxes are up canyon and largest near the canyon axis up to 1 5 kw m 1 at the mouth of the upper canyon and increasing to over 4 kw m 1 around monterey and san gregorio meanders the up canyon energy flux is bottom intensified suggesting that topographic focusing occurs net along canyon energy flux decreases almost monotonically from 9 mw at the canyon mouth to 1 mw at gooseneck meander implying that high levels of internal tide dissipation occur the depth integrated energy flux across the 200 m isobath is order 10 w m 1 along the majority of the canyon rim but increases by over an order of magnitude near the canyon head where internal ti

comment on late holocene rupture of the northern san andreas fault and possible stress linkage to the cascadia subduction zone by chris goldfinger kelly grijalva roland burgmann ann e morey joel e johnson c hans nelson julia gutierrez pastor andrew ericsson eugene karabanov jason d chaytor jason patton and eulalia gracia goldfinger et al 2008 conclude that in the northern san andreas fault and cascadia margins holocene turbidites i e deposits of turbidity currents were triggered by earthquakes however their conclusion falters because of 1 selective data sets that were used for establishing seismicity as the sole triggering mechanism of turbidites 2 flawed sedimentological concepts and criteria that were applied for interpreting turbidites and 3 faulty methodologies that were employed for correlating turbidites over long distances this same turbidite i e sedimentological theme has also been published previously by goldfinger et al 2003a b 2006 2007 as with the recent article in bssa their previous publications on the subject matter were published in journals that are concerned primarily with geophysical topics as a result critical sedimentological conclusions which are an integral part of the articles by goldfinger et al have not been subjected to a rigorous scrutiny therefore i would like to comment on the following three issues along the washington oregon california margin potential triggering mechanisms of sediment failures and related turbidity currents are 1 earthquake adams 1990 2 tectonic oversteepening greene et al 2006 3 tsunami adams 1990 geist 2005 4 cyclone adams 1990 shanmugam 2008a fig 4 5 ebb tidal current puig et al 2003 6 submarine volcanic activity davis et al 2002 7 sediment loading adams 1990 and 8 gas hydrates chapman et al 2004 the link between gas hydrate decomposition and mass movements on the norwegian margin was discussed by mienert et al 2005 in the cascadia margin a total of 40 cyclones along the oregon coast were reported for the 1984 2006 period moritz and moritz 2006 a total of 24 tsunamis were reported along the oregon coast for the 1868 1994 period table 1 cyclones and tsunamis are powerful agents of sediment failures shanmugam 2008a on the outer continental shelf of the gulf of mexico for example the

recognising different sediment provenances within a passive margin setting towards characterising a sediment source to the west of the british late carboniferous sedimentary basins to investigate whether sediments with subtly different provenances could be recognised within a passive margin setting samples were taken from westphalian sedimentary rocks of the pennine basin south wales coalfield culm basin of britain and from northern ireland although previous work has shown that 3 major source areas were responsible for the infill of the pennine basin this study is restricted to sediments believed to have been derived from the west their nominally similar western provenance was confirmed using sm nd isotope techniques and their deposition in a passive margin setting was established using elemental discrimination diagrams while the overall sediment provenance may have been from the west the trace element geochemistry indicates that at least two major sediment pathways can be distinguished plots of eu eu gdn ybn along with ternary plots of cr v ti zr gdn ybn or sc cr suggest different source areas for the culm basin and the south wales coalfield in the culm basin the cr v ratio generally exceeds 1 25 with a small eu anomaly and a low gdn ybn ratio the cr v ratio is less than 1 25 in the south wales with a larger eu ratio and a higher gdn ybn than the culm basin significant separation of the culm basin and the south wales coalfield during the early westphalian by the bristol channel bray fault may have been a factor contributing to the provenance differences late carboniferous dextral displacement along this fault brought these basins into close juxtaposition and it is unlikely that the bristol channel landmass formed a common source area for these two basins

the coastal ocean off oregon and northern california during the 1997 8 el nino abstract the evolution and decay of el nino 1997 8 was observed in coastal waters off oregon in a sequence of cruises along 44 6 n from the coast to more than 150 km offshore hydrographic observations were made during eleven cruises between july 1997 and april 1999 at stations on the newport hydrographic line which had been occupied regularly from 1961 to 1971 the data from the earlier decade provide a basis for defining normal conditions and allow comparisons with the recent el nino in terms of t s spiciness and geostrophic velocity independent of el nino the ocean in july 1997 was already anomalously warm offshore of 50 km and above 100 m by september 1997 there were unambiguous indications of el nino isotherms and isohalines sloped down toward the coast indicating poleward flow over shelf and slope and anomalously spicy water was present at the shelf break in november 1997 and february 1998 shelf break waters were even warmer and there was strong poleward flow inshore of 100 km extending to depths greater than 200 m the april 1998 section closely resembled that of april 1983 another el nino year but by june 1998 the anomalies were mostly gone november 1998 was near normal and the sections from subsequent cruises resemble the mean sections from 1961 1971 four cruises between november 1997 and november 1998 included sampling at several latitudes between 38 and 45 n as expected these sections show significant alongshore gradients but also a surprising degree of homogeneity in the anomalous features associated with el nino in the temperature salinity spiciness and geostrophic velocity fields the anomalous signature of el nino was stronger at its winter peak in 1998 than in 1983 but the signature in the temperature and spiciness fields and in coastal sea level did not persist as long as in 1983 by april 1999 the coastal ocean from 38 n to 45 n was significantly colder than it had been in april 1984

a revised biostratigraphic and well log sequence stratigraphic framework for the scotian margin offshore eastern 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 20120137 in this study we build on a foundation of previous biostratigraphic studies for the scotian basin offshore eastern canada by conducting new quantitative multidisciplinary biostratigraphic studies of the mesozoic sections in eight wells bonnet p 23 chebucto k 90 cohasset l 97 glenelg j 48 glooscap c 63 mohican i 100 south desbarres o 76 and south griffin j 13 these wells were chosen to provide good spatial coverage stratigraphic penetration and correlation with the seismic grid we have also evaluated pre existing biostratigraphic data and undertaken the well log sequence stratigraphic interpretation of upper triassic to cenozoic sediments in 16 additional wells using a consistent multidisciplinary event scheme derived from the new wells key to the dating of some horizons has been integration of the palynology and micropaleontology disciplines mostly used previously on the scotian margin with new nannofossil data simultaneously we have closely integrated the biostratigraphic results with

the german bank pluton offshore sw nova scotia age petrology and regional significance for alleghanian plutonism permian plutonism is widespread in the u s appalachians but not in the canadian sector of the appalachians the german bank pluton sampled in two boreholes offshore southwestern nova scotia gave a u pb age of 300 1 ma determined by isotope dilution thermal ionization mass spectrometry id tims on thermally annealed and chemically etched zircon grains electron microprobe dating of monazite yielded an age of 308 13 ma late paleozoic plutonism in the canadian appalachians was dominated by northwestward subduction of the rheic ocean whereas the rheic ocean in the u s appalachians closed by southeasterly subduction a slab tear therefore developed at the southwestern margin of the rheic ocean slab beneath the canadian appalachians the high sr and ba metaluminous magnetite granite of the german bank pluton resulted from melting of underplated lower crust and or lithospheric mantle by a rising asthenospheric diapir related to this slab tear geochemically the german bank pluton is similar to most 300 265 ma plutons of the southern appalachians except in its strongly negative nd isotopic composition that results from the underthrusting of a ca 2 ga lower crustal block of saharan craton

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

pre mesozoic basement rocks offshore nova scotia canada new constraints on the accretion history of the meguma terrane basement samples from offshore wells and geophysical data show that the meguma terrane forms the basement of mesozoic cenozoic sedimentary basins as far as 200 km offshore nova scotia the data provide constraints on avalon meguma terrane interaction during middle to late paleozoic events in the appalachian orogen the basement consists of metasedimentary rocks intruded by late paleozoic granitoid plutons principally magnetite bearing granodiorites which contrast with more peraluminous ilmenite bearing devonian granodiorite and granite onshore offshore tonalites have a subduction related trace element signature that is similar to the signature in minor devonian gabbro and tonalite intrusions on land nd sr and pb isotopes suggest three sources for meguma terrane plutons 1 2 ga basement possibly saharan shield and sediments derived therefrom this basement may be present beneath the southwestern scotian shelf 2 late proterozoic underthrust avalonian basement and basement autochthonous to the meguma terrane and 3 melts from mantle last remobilized in the late proterozoic pan african orogeny seismic reflection profiles show meguma terrane thrust northward over a wedge of avalon basement extending 30 km south of the surface suture there is no evidence that the devonian tonalites are directly related to subduction the lack of either ophiolites or paleozoic pelagic sediment suggests that convergence of the avalon and meguma terranes was achieved principally by strike slip motion resulting from low angle continent continent convergence with only a minor thrust component the widespread devonian carboniferous igneous activity of the amalgamated meguma and avalon terranes was a consequence of regional extension which resulted in decompression melting of upper mantle and production of mafic magmas variably mixed with crustal material