submarine debris flow impact on pipelines part i experimental investigation estimating the impact forces exerted by a submarine debris flow on a pipeline is a challenge and there is room for considerably more work to advance the state of the art to this end an experimental program was performed to investigate the impact on two pipeline installation scenarios 1 suspended pipeline and 2 laid on seafloor pipeline the results and observations from the experimental investigation are discussed the definition of reynolds number was modified for non newtonian fluids and an ad hoc method was developed to estimate the drag force exerted by an impact perpendicular to the pipe axis the method may be used in prototype situations to estimate the drag force from submarine debris flow impact on pipelines the experimental program was complemented by computational fluid dynamics cfd analyses the details of which are discussed in the accompanying paper

glaucony and sequence stratigraphy a conceptual framework of distribution in siliciclastic sequences abstract detailed analysis of recent literature on glaucony and selected case studies eocene isle of wight miocene northern apennines shows that the presence of glaucony alone is not diagnostic of a specific systems tract of a depositional sequence a reliable sequence stratigraphic interpretation of glaucony bearing units requires additional information on glaucony including 1 spatial distribution 2 maturity distinction between nascent slightly evolved evolved and highly evolved glaucony and 3 genetic attributes differentiation of autochtonous from allochthonous and intrasequential from extrasequential glaucony autochthonous glaucony is common at various stratigraphic levels in the transgressive systems tract tst and the lower highstand systems tract hst showing an upward increase tst and then decrease hst in abundance and maturity the condensed section can be distinguished from the overlying and underlying deposits by the higher concentration and maturity of glaucony allochthonous intrasequential parautochthonous glaucony can be present in the entire tst hst and lowstand systems tract lst generally showing lower concentration and maturity than its autochthonous counterpart allochthonous extrasequential detrital glaucony is present mainly in the lst its concentration and composition depending on the characteristics of the source horizon the associa ion between autochthonous and allochthonous intrasequential and extrasequential glaucony commonly exists in the lst and in the lower tst

evaporitic and biosiliceous cyclic sedimentation in the miocene of the gulf of suez depositional and diagenetic aspects abstract the middle to late miocene evaporite bearing formations which outcrop along the gebel zeit and gems highs in the southwestern gulf of suez egypt consist of thick calcium sulphate beds rhythmically interbedded with marlstones siltstones and claystones containing various amounts of biogenic silica as well as pure diatomites the calcium sulphate beds are composed mainly of gypsum and anhydrite subaqueous crustallisation in subpermanent brine ponds of marine origin predominated during deposition of the selenite and laminated gypsum early diagenetic interstitial growth of nodular anhydrite occurred episodically when the water level dropped in response to increasing salinity associated with the precipitation of halite in the deeper troughs nevertheless most of the nodular facies resulted from the burial conversion of gypsum to anhydrite which has been sometimes rehydrated into gypsum a last phase of gypsum dehydration has occurred at the surface related to the present hot and dry climatic conditions the biosiliceous deposits contain either well preserved opal a or diagenetically altered opal ct clinoptilolite quartz and even clays diatom frustules such diagenetic changes are commonly described in the oceanic biosiliceous deposits the fossil content of these diatomitic layers implies shallow marine conditions on the shelves of highs induced by block faulting the cyclic succession of evaporited and biosiliceous deposits recorded the alternation of high sea level stands associated with high organic productivity probably enhanced by seasonal input of nutrients and low sea level stands associated with hypersaline conditions and evaporite deposition locally the sharp contact between the diatomites and gypsum argues for a rapid evolution of salinity towards high concentration up to gypsum saturation and more the formation of finely laminated diatomitic sediments is known to require either high organic productivity or anoxic conditions in bottom intermediate waters and eventually both processes in the gebel zeit and gemsa areas a local association of the biosiliceous sediments with diagenetic carbonates and native sulphur resulting from processes of bacterial sulphate reduction confirms that anoxic conditions occurred in the deep water body or in the sediments large amounts of organic compounds were involved in these diagenetic processes immature organic matter was consumed during an early diagenetic stage of transformation it is assumed that this organic matter was supplied either by the biosilica rich interbeds or the organic rich laminated carbonates the initial organic content of the biogenic deposits was impoverished as early as the first stages of sedimentation and diagenesis although a large part of the organic matter could have been destroyed by these early diagenetic processes and further oxidation in outcrops these sediments can be considered as potential source rocks in nearby less exposed sequences

early cambrian back arc volcanism in the western taurides turkey implications for rifting along the northern gondwanan margin the lower cambrian tommotian go ebakan formation in western central anatolia is made up of slightly metamorphosed continental to shallow marine clastic rocks with pillowed and massive spilitic lavas and dolerite dykes spilitic lavas commonly amygdaloidal are albite and pyroxene phyric with the metamorphic mineral paragenesis albite calcite sericite epidote tremolite chlorite dolerite dykes mainly include plagioclase and pyroxene as primary minerals and tremolite epidote chlorite as low grade secondary minerals geochemical data show that the spilitic lavas and dolerite dykes are sub alkaline of oceanic tholeiitic basalt character and display a tholeiitic fractional trend characterized by an increase in feo mgo and zr and tio2 in variation diagrams they are characterized by relatively high zr y 2 4 5 relatively high th yb 0 15 1 0 and la nb 0 5 2 5 both show marked negative nb and ti anomalies relative to th and la ce implying a subduction related chemistry chondrite normalized ree patterns display slight enrichment of light ree spilitic lavas la yb n 0 79 1 56 dolerite dykes la yb n 0 89 3 50 fairly comparable with morb the geochemical similarity of the spilitic lavas and dolerite dykes suggests a co genetic origin la nb ratios of both types are slightly higher than average morb values and were possibly formed in the early stages of back arc basin development petrogenetic modelling suggests the mafic rocks of the formation were formed by 9 batch melting of spinel lherzolite in shallower depths c 60 km taken together the data suggest that the early cambrian mafic rocks of the taurus units were developed in a back arc basin along the northern edge of gondwana above the southward subducting oceanic lithosphere and may represent initial rifting that resulted in separation of the peri gondwanan terranes

run out distance and erosion of debris flows in the nile deep sea fan system evidence from lithofacies and micropalaeontological analyses abstract debrites with different volumes depositional periods and setting are observed in the nile deep sea fan system here we present debrites from four late quaternary environments i within the rosetta submarine channel at 1700 m ii within small basins created by salt tectonics in the eastern province at 1300 m iii on the open slope outside of channels at 2600 m and iv in the distal part of the fan fringe beyond channel terminations at 3050 m water depth the debrites comprise mud clasts in a generally ungraded muddy sand matrix they are relatively thin 20 150 cm in fan fringe in channel and salt tectonic basin settings and somewhat thicker 8 m in the open slope setting benthic foraminiferal assemblages and variation in the planktonic benthic foraminiferal ratios are considered as a useful tool for tentatively evaluating the origin of sediment in these debris flows and estimation of their run out distance similar microfaunal contents of clast matrix combinations document that the debrites in the rosetta channel and salt tectonic basin were locally sourced the debrite from the open slope travelled farther up to 150 km three separate debrites in a fan fringe core were deposited by debris flows that originated over 200 km away in water depths shallower than 1000 m these far travelled debris flows appear to have eroded remarkably little sediment as they travelled for 200 km across low 0 8 1 2 gradient seafloor this lack of erosion is attributed to hydroplaning or increasing pore fluid pressure at the base of debris flows this study confirms that remarkably mobile debris flows can travel long distances to produce thin debrites in the distal fringes of submarine fans

diagenesis of siliciclastic and volcaniclastic sediments in the cretaceous and miocene sequences of the nw african margin dsdp leg 47a site 397 abstract the lower cretaceous and miocene sequences of the nw african passive continental margin consist of siliciclastic volcaniclastic and hybrid sediments these sediments contain a variety of diagenetic carbonates associated with zeolites smectite clays and pyrite reflecting the detrital mineralogical composition and conditions which prevailed during opening of the north atlantic in the lower cretaceous siliciclastic sediments siderite 6 to 0 7 18 o pdb 19 6 to 0 6 13 c pdb was precipitated as thin layers and nodules from modified marine porewaters with input of dissolved carbon from the alteration of organic matter microcrystalline dolomite layers lenses nodules and disseminated crystals 3 0 to 2 5 18 o pdb 7 2 to 4 9 13 c pdb predominate in slump and debris flow deposits within the lower miocene sequence during the opening of the atlantic volcanic activity in the canary islands area resulted in input of volcaniclastic sediments to the middle and upper miocene sequences calcite is the dominant diagenetic carbonate in the siliciclastic bioclastic volcaniclastic hybrid and in the volcaniclastic sediments which commonly contain pore rimming smectite diagenetic calcite 22 to 1 6 18 o pdb 35 7 to 0 8 13 cpdb was precipitated due to the interaction of volcaniclastic and bioclastic grains with marine porewaters phillipsite is confined to the alteration of volcaniclastic sediments whereas clinoptilolite is widely disseminated occurring essentially within foraminiferal chambers and formed due to the dissolution of biogenic silica

modern estuarine siliceous spiculites tasmania australia a non polar link to phanerozoic spiculitic cherts biosiliceous sedimentary rocks are well known from the geologic record and many are correctly interpreted to have formed in deep water or cold water environments shallow non polar spiculites are also known from the rock record yet no modern analog has been documented for such environments bathurst harbour an estuarine system in southwest tasmania provides this much needed modern analog in this system a sharp halocline separates tannin rich low salinity surface waters from clear marine bottom waters tannins supply few nutrients and substantially reduce light penetration to bottom environments resulting in a thinned photic zone and the mixing of deeper water sub photic biotas of soft corals bryozoans and sponges with other organisms more typical of this temperate shallow water environment the well defined halocline allows a typically marine biota including echinoderms to live in bottom waters of this estuarine setting the bioclastic factory producing both carbonate and siliceous particles exists in marine subphotic bottom waters of incised channel and shallow rocky environments along the shoreline extensive organic rich soft sediments in protected embayments generate few bioclasts but contain allochthonous sponge spicules transported from the adjacent bioclastic factory trapping of organic material within the estuarine system lowers sediment ph and promotes dissolution of carbonate biofragments resulting in preferential preservation of siliceous sponge spicules this situation implies that many biosiliceous neritic deposits in the rock record may be the result of similar preferential preservation

eocene inversion history of the sandown pericline isle of wight southern england study of the composition and distribution of derived lithoclast and fossil suites collected from the selsey barton and becton formations in whitecliff bay isle of wight has enabled a detailed reconstruction of mid late eocene uplift of 500 m on the northern limb of the sandown pericline the stratigraphical distribution of clasts and fossils derived from older formations demonstrates the erosion of progressively older eocene palaeocene and cretaceous sediments during growth of the structure the presence of delicate reworked fossils and clasts together with limited palaeocurrent data support very local derivation from the south the preservational state of the derived materials is used to identify the diverse processes of erosion and transport two phases of uplift lutetian bartonian separated by a period of quiescence and peneplanation have been identified rates of eocene uplift of about 100 m ma 1 are postulated to have taken place

on the transfer of momentum from a granular landslide to a water wave abstract the momentum flux from a landslide at impact in a water body is the driving force behind the generation of landslide tsunamis analysis of this problem is presented and used to derive idealized theoretical relationships for the maximum wave amplitude in the near field zone this is accomplished for momentum transfer using both hydrostatic and hydrodynamic assumptions for rapidly evolving near field waves with a supercritical densimetric froude number the maximum wave amplitude is also constrained according to the fluid continuity equation simplification of the hydrostatic momentum equation is also presented by considering fluid acceleration resulting in an expression that is independent of length and time scales during wave generation the results of the novel momentum based equations are in agreement with laboratory data collected using high speed digital cameras for granular landslides and previously published experimental data used to develop a semi empirical equation furthermore the results provide new insight on the range of applicability of theoretical and semi empirical equations for predicting the maximum near field wave amplitude of landslide generated tsunamis

the norwegian greenland sea continental margins morphology and late quaternary sedimentary processes and environment the continental margins surrounding the norwegian greenland sea are to a large degree shaped by processes during the late quaternary the paper gives an overview of the morphology and the processes responsible for the formation of three main groups of morphological features slides trough mouth fans and channels several large late quaternary slides have been identified on the eastern norwegian greenland sea continental margin the origin of the slides may be due to high sedimentation rates leading to a build up of excess pore water pressure perhaps with additional pressure caused by gas bubbles triggering might have been prompted by earthquakes or by decomposition of gas hydrates trough mouth fans tmf are fans at the mouths of transverse troughs on presently or formerly glaciated continental shelves in the norwegian greenland sea seven tmfs have been identified varying in area from 2700 km2 to 215 000 km2 the trough mouth fans are depocentres of sediments which have accumulated in front of ice streams draining the large northwest european ice sheets the sediments deposited at the shelf break upper slope by the ice stream were remobilized and transported downslope mostly as debris flows the trough mouth fans hold the potential for giving information about the various ice streams feeding them with regard to velocity and ice discharge two large deep sea channel systems have been observed along the norwegian continental margin the lofoten basin channel and the inbis channel along the east greenland margin several channel systems have been identified the deep sea channels may have been formed by dense water originating from cooling sea ice formation and brine rejection close to the glacier margin or they may originate from small slides on the upper slope transforming into debris flows and turbidity currents

vertical extrusion and horizontal channel flow of orogenic lower crust key exhumation mechanisms in large hot orogens a large database of structural geochronological and petrological data combined with a bouguer anomaly map is used to develop a two stage exhumation model of deep seated rocks in the eastern sector of the variscan belt an early sub vertical fabric developed in the orogenic lower and middle crust during intracrustal folding followed by the vertical extrusion of the lower crustal rocks these events were responsible for exhumation of the orogenic lower crust from depths equivalent to 18 20 kbar to depths equivalent to 8 10 kbar and for coeval burial of upper crustal rocks to depths equivalent to 8 9 kbar following the folding and vertical extrusion event sub horizontal fabrics developed at medium to low pressure in the orogenic lower and middle crust during vertical shortening fabrics that record the early vertical extrusion originated between 350 and 340 ma during building of an orogenic root in response to se directed saxothuringian continental subduction fabrics that record the later sub horizontal exhumation event relate to an eastern promontory of the brunia continent indenting into the rheologically weaker rocks of the orogenic root indentation initiated thrusting or flow of the orogenic crust over the brunia continent in a north directed sub horizontal channel this sub horizontal flow operated between 330 and 325 ma and was responsible for a heterogeneous mixing of blocks and boudins of lower and middle crustal rocks and for their progressive thermal re equilibration the erosion depth as well as the degree of reworking decreases from south to north pointing to an outflow of lower crustal material to the surface which was subsequently eroded and deposited in a foreland basin indentation by the brunia continental promontory was highly noncoaxial with respect to the se oriented saxothuringian continental subduction in the early visean suggesting a major switch of plate configuration during the middle to late visean

on the frontal dynamics and morphology of submarine debris flows several submarine debris flows show an apparently chaotic frontal part with blocks of variable size from roughly tens to some hundreds of metres located some distance beyond the front of the main deposits this outrunner phenomenon was studied both in the field and in laboratory experiments depositional patterns in a field case finneidfjord northern norway are classified from the outer distal part of the debris flow to the outermost outrunner block similar patterns were found in experimental debris flows and we suggest that flow processes in the laboratory are applicable to the field example theoretical investigations are applied to assess frontal dynamics and especially the formation and motion of outrunner blocks as the front of the debris flow pushes through ambient water a combination of front pressure and lift force allows for intrusion of a water layer underneath the front hydroplaning this water layer reduces basal friction and induces tensile stresses farther behind the front leading to a possible detachment and decoupling with respect to the main slide body these outrunner blocks show an increased mobility compared to the main slide body and deposition of such blocks may occur far away from the main slide body

conversion of diatoms to clays during early diagenesis in tropical continental shelf muds in coastal muds downdrift from the amazon river mouth marine diatom frustules are rapidly converted to various forms of authigenic aluminosilicate phases during burial the dominant neoformed crystalline phases have a composition similar to k smectite yield electron diffraction patterns characteristic of clay minerals and exhibit a range of crystal sizes and morphologies including euhedral pseudohexagonal crystals and anhedral flakes replacing biogenic silica a poorly crystalline or microcrystalline k rich and fe rich aluminosilicate material also replaces the siliceous frustules the conversion process is not always complete leaving relics of the original frustule in the resulting authigenic aluminosilicate phases laboratory incubation experiments with cultured diatoms demonstrate that the conversion process occurs in 20 23 months the conversion of biogenic silica to authigenic clays occurs throughout the amazon deltaic deposits and presumably takes place in other comparable depositional settings biogenic silica alteration provides proof for a direct link between the biogeochemical cycle of silica in nearshore environments and the neoformation of cation rich aluminosilicate phases and it may prove to be important for oceanic geochemical cycles as a sink for si k and other elements incorporated in the authigenic aluminosilicates rapid formation of authigenic k smectite may also represent a reaction stage leading to eventual formation of illitic clays during later diagenesis

diagenesis of silica rich mound bedded chalk the coniacian arnager limestone denmark abstract the coniacian arnager limestone formation is exposed on the danish island of bornholm in the baltic sea it is composed of mound bedded siliceous chalk and x ray diffraction and scanning electron microscopy indicate a content of 30 70 insoluble minerals including authigenic opal ct quartz clinoptilolite feldspars calcite dolomite and barite opal ct and clinoptilolite are the most common and constitute 16 53 and 2 9 respectively the content of insoluble minerals varies laterally both within the mounds and in planar beds and the opal ct content varies by up to 10 vertically the mounds consist of two microfacies spiculitic wackestone and bioturbated spiculitic wackestone containing 10 22 and 7 12 moulds after spicules respectively subsequent to deposition and shallow burial dissolution of siliceous sponge spicules increased the silica activity of the pore water and initiated precipitation of opal ct the opal ct formed at temperatures around 17 c the precipitation lowered the silica activity and the si al ratio of the pore water resulting in precipitation of clinoptilolite feldspar and smectite calcite formed synchronously with the latest clinoptilolite minor amounts of quartz precipitated in pore water with low silica activity during maximum burial probably to depths of 200 250 m the dissolution of sponge spicules and decomposition of the sponge tissue also resulted in the release of ba2 sr2 mg2 ca2 and co32 facilitating precipitation of barite and dolomite precipitation of especially opal ct reduced the porosity to an average of 40 and cemented the limestone the study highlights the diagenetic pathways of bio siliceous chalk and the effects on preservation of porosity and permeability

identification and long range correlation of bentonites in turonian coniacian upper cretaceous chalks of northwest europe a geochemical and mineralogical study of thin 2 20 cm clay rich beds found in turonian coniacian chalks from the anglo paris basin has been undertaken on the basis of their rare earth element ree and mineralogical composition it is possible to subdivide beds into bentonites characterized by a negative eu anomaly and elevated smectite content and detrital beds characterized by a minimal or absent eu anomaly and a greater proportion of illite six beds are considered to be bentonites glynde 1 southerham 1 caburn bridgewick 1 lewes and shoreham 2 trace element discriminant diagrams add support as does comparison with similar studies undertaken in eastern england and northern germany geochemical evidence demonstrates that the tephra was variably acidic in composition rhyodacite rhyolite comendite pantellerite and was probably derived from crustal melting associated with initial rifting of the north atlantic correlation of bentonites between the anglo paris basin eastern england and northern germany can be demonstrated and independently tested establishing a tephro event stratigraphy across northwest europe for this period

late weichselian submarine debris flow deposits on the bear island trough mouth fan sedimentary processes on the bear island trough mouth fan during the last glacial were studied using high resolution reflection seismics and gravity cores the fan succession is dominated by large debris flow deposits of up to 24 km in width and 50 m thick debris lobes can be followed over 100 km downslope and the largest cover an area of 1880 km2 the large debris flows were generated when the barents sea ice sheet reached the shelf break glacigenic sediments transported to the grounding line were temporarily stored on the upper slope due to the high sedimentation rate the sediments were unstable and earthquakes oversteepening and or build up of excess pore pressure triggered sediment release generating large debris flows sediments were also eroded and incorporated during the downslope flow debris flows were the most important sediment distributing process due to the relatively high shear strength low flow mobility of the glacigenic diamicton and the low fan gradient the weichselian evolution of the fan was characterized by a relatively low sedimentation rate during the early and mid weichselian the barents sea ice sheet might have reached the shelf break twice during the late weichselian on average one large debris flow comprising 18 km3 of sediments was released between every 35 to 75 years during the last glacial maximum

numerical modeling of an underwater bingham plastic mudslide and the waves which it generates underwater landslides are a common source of tsunamis in coastal areas theoretical and experimental studies on this problem however are scarce because of the difficulties in modeling and observing a submarine slide and the associated tsunami to study this problem we present a numerical model that simulates the coupling of a bingham plastic mudslide on a gentle uniform slope with the surface waves which it generates a formulation of the dynamics of the problem is presented where the landslide is treated as an incompressible bingham plastic flow and the water motion is assumed irrotational the long wave approximation is adopted for both water waves and the mudslide dispersion of waves and potential turbulent mixing are not considered the resulting differential equations are solved by a finite difference method we present the numerical results for successive profiles of the mud surface the horizontal velocity distributions of the slide the evolution of the surface elevations and the distributions of the particle velocity of the water motion three major parameters dominate the magnitude of the waves if the volume of the mud is fixed the density of mud the yield stress of the mud and the depth of water at the mudslide site because of the yield stress the slides stop on the slope when the shear stress exerted on the bottom become smaller than the yield stress the bingham plastic behavior of the mud significantly reduces the extent and the speed of the mudslide and also the magnitude of the surface waves generated comparison of the solution of the bingham plastic mudslide model with a snow flow test is presented the solution of a viscous fluid model has been derived as a special case of the present solution

relics of an early panafrican metabasite metarhyolite formation in the brno massif moravia czech republic the brno massif in moravia czech republic is an important exposure of precambrian basement in central europe it includes large volumes of cadomian granitoids and a narrow fault bounded zone with metagabbros metadiorites and metabasalts this so called central basic belt also contains some metarhyolites one of these was dated by means of the zircon evaporation method at 725 15 ma chemical and isotope data show that the dated rock represents a mantle derived magma which is cosanguinous with surrounding morb type metabasites the data suggest that the brno massif hosts the oldest metabasite complex currently known in central europe its formation apparently coincides with the main period of ocean floor spreading and island arc formation in the panafrican orogens this lends further support to the theory that the brno massif is a gondwana derived element

authigenic zeolites in late pleistocene sediments of the south atlantic angola basin two types of authigenic zeolites from late pleistocene hemipelagic sediments of the south atlantic were examined by xrd and sem analysis the xrd characteristics and the thermal behaviour of the zeolites suggest that type 1 is composed of clinoptilolite type 2 was identified as mordenite based on morphological features and qualitative elemental composition their authigenic nature is suggested from the shape of the crystals and their growth on and within foraminifera tests volcanic ash material acting as precursor minerals to zeolite formation could not be found nor were the zeolites directly related to siliceous remains an authigenesis from pore waters must be assumed mineral stabilities for amorphous sio2 and zeolites were calculated with the computer program solmineq88 interstitial waters proved to be oversaturated throughout the core in respect to all zeolites considered biogenic opal represents the limiting solid phase for si concentrations in pore waters therefore the dissolution of opal is regarded as the main source of si for interstitial waters below 9 m core depth where opal is only present in traces detrital feldspars and the zeolites themselves are affected by dissolution this may indicate the metastable nature of the zeolites also corroborated by the presence of two almost isochemical members of the same zeolite group

eocene spiculites and spongolites in southwestern australia not deep not polar but shallow and warm siliceous spongolite and spiculite are generally interpreted as deep and or cold water deposits largely because modern analogs are found mostly in cold and or deep water environments however extensive shallow water biosiliceous accumulations are present in late eocene age deposits of southern western australia the attributes and paleoenvironmental setting of these accumulations frame the specific climatic and or oceanographic constraints that allow such shallow neritic sediments to form the generally fine grained siliciclastic biosiliceous sediments accumulated in a nearshore shallow water setting around numerous islands and offshore from a warm temperate rainforest covered upland sponges compose a lithistid hexactinellid assemblage of mesozoic tethyan affinity confined to deep water in the modern ocean that migrated into neritic paleoenvironments during late eocene time lithistids dominated shoreface environments and were reworked into sponge conglomerate beaches while hexactinellids flourished offshore in muddy subshoreface environments these deposits also contain common soft demosponge spicules and a rare but otherwise normal marine calcareous biota the biosiliceous sediments grade offshore into bryozoan rich marls and limestones sponges outcompeted the calcareous benthos in these inner shelf environments because of elevated amounts of land derived nutrients that included high dissolved silica and a calm hydrodynamic setting these deposits suggest that neither temperature nor water depth are critical factors for prolific sponge colonization the rarity of such deposits in the rock record likely reflects the necessity for the coincidence of all of these factors or they are misinterpreted

glaciomarine sedimentation in epicontinental seas exemplified by the northern barents sea abstract sediments on high arctic shelves result from modern processes and the effect of former glaciations based on data from the northern barents sea an area with input from large and numerous surging glaciers we define two principal zones with different environmental regimes and corresponding sedimentary facies 1 a glacier proximal zone influenced by grounding line processes and the immediately adjacent areas affected by glacial sediment input and 2 a glacier distal sea ice and current controlled zone which also includes a wide sediment starved region dominated by biogenic carbonate accumulation characteristic of the glacier proximal zone are glacial surges which affect sedimentation rates and leave a diagnostic pattern of sea floor morphologies extensive ice gouging causes a homogeneous sediment texture in the glacier distal zone fine grained mud supplied from sea ice and infrequent coarser material deposited from icebergs is reworked by modern oceanographic processes on shallow banks in 30 50 m of water carbonates accumulate from a prolific bottom fauna formed in response to extensive reworking and nutrient supply

neoproterozoic and cambro ordovician magmatism in the variscan klodzko metamorphic complex west sudetes poland new insights from u pb zircon dating the klodzko metamorphic complex kmc in the central sudetes consists of meta sedimentary and meta igneous rocks metamorphosed under greenschist to amphibolite facies conditions they are comprised in a number of separate tectonic units interpreted as thrust sheets in contrast to other lower palaeozoic volcano sedimentary successions in the sudetes the two uppermost units the orla gologlowy unit and the klodzko fortress unit of the kmc contain meta igneous rocks with supra subduction zone affinities the age of the kmc was previously assumed to be early palaeozoic devonian based on biostratigraphic findings in the lowermost tectonic unit our geochronological study focused on the magmatic rocks from the two uppermost tectonic units exposed in the sw part of the kmc two orthogneiss samples from the orla gologlowy unit yielded ages of 500 4 3 1 and 500 2 4 9 ma interpreted to indicate the crystallization age of the granitic precursors a plagioclase gneiss from the same tectonic unit intimately interlayered with metagabbro provided an upper intercept age of 590 1 7 2 ma which is interpreted as the time of igneous crystallization from the topmost klodzko fortress unit a metatuffite was studied which contains a mixture of genetically different zircon grains the youngest 207pb 206pb ages which cluster at ca 590 600 ma are interpreted to indicate the maximum depositional age for this metasediment the results of this study are in accord with a model that suggests a nappe structure for the kmc with a middle devonian succession at the base and upper proterozoic units at structurally higher levels it is suggested here that the kmc represents a composite tectonic suture that juxtaposes elements of pre variscan basement intruded by the lower ordovician granite against a middle palaeozoic passive margin succession the new ages combined with the overall geochemical variation in the kmc indicate the existence of rock assemblages representing a gondwana active margin the recognition of neoproterozoic subduction related magmatism provides additional arguments for the hypothesis that equivalents of the tepla barrandian domain are exposed in the central sudetes

the margins of laurussia in central and southeast europe and southwest asia the continuation of the laurussian margin into central and southeast europe and southwest asia is defined by the rheic suture which becomes harder to trace to the southeast because of complex post variscan strike slip displacements and tectonic stacking linked to the cimmerian and alpine cycles the uncertain extent of the neoproterozoic baikalian orogeny fringing baltica ambiguous early paleozoic paleobiogeographic data and strike slip activity complicate the distinction of the tornquist suture from the transeuropean suture zone there is growing evidence for the incorporation of the brunovistulian malopolska and west moesian terranes into the late neoproterozoic cambrian baltican margin the istanbul zonguldak terrane along with the bitesh and east moesia terranes may have been part of the avalonian terrane assemblage although an arabian nubian shield or baltica provenance cannot be excluded the terranes of the armorica terrane assemblage bordering the rheic suture include the outer carpathian tatra getic and balkan terranes in southeast europe and sakarya and the anatolide tauride terrane in turkey further east the rheic suture may be present in the caucasus in all probability between the greater caucasus and the scythian platform or alternatively between the greater caucasus and transcaucasia alborz in northern iran is interpreted as a distal part of transcaucasia the location of the rheic suture in the southeast part of the turan domain of central asia is poorly constrained

large scale sedimentation on the glacier influenced polar north atlantic margins long range side scan sonar evidence long range side scan sonar gloria imagery of over 600 000 km of the polar north atlantic provides a large scale view of sedimentation patterns on this glacier influenced continental margin high latitude margins are influenced strongly by glacial history and ice dynamics and linked to this the rate of sediment supply extensive glacial fans up to 350 000 km were built up from stacked series of large debris flows transferring sediment down the continental slope the fans were linked with high debris inputs from quaternary glaciers at the mouths of cross shelf troughs and deep fjords where ice was slower moving but still extended to the shelf break large scale slide deposits are observed where ice failed to cross the continental shelf during full glacials the continental slope was sediment starved and submarine channels and smaller slides developed a simple model for large scale sedimentation on the glaciated continental margins of the polar north atlantic is presented

submarine debris flow impact on pipelines part ii numerical analysis computational fluid dynamics cfd numerical analysis was employed to analyze the situations tested experimentally as described in part i the methodology and results of the cfd analyses are discussed and compared with the observations made from the experiments the numerical model performed satisfactorily with regard to obtaining the impact forces exerted on the model pipe as well as simulating the hydroplaning phenomenon and estimating slurry flow heights the experimental results were combined with the results of the cfd analyses to develop a practical method to compute the drag force caused by a submarine debris flow impact on a pipeline the cfd analyses provided some insight to the separated region characterization but the attempt to analyze the vortex shedding phenomenon as observed in the experiments was unsuccessful additional studies are required for better understanding of both the separated region characteristics and vortex shedding

long lasting cadomian magmatic activity along an active northern gondwana margin u pb zircon and sr nd isotopic evidence from the brunovistulian domain eastern bohemian massif manuscript published version available in international journal of earth sciences 2016 doi 10 1007 s00531 016 1416 y

hydroplaning of subaqueous debris flows and glide blocks analytical solutions and discussion 1 subaqueous debris flows often attain significantly higher velocities and longer run out distances than their subaerial counterparts in spite of increased viscous drag and reduced effective gravity due to buoyancy recent experimental research suggests that a basal lubricating layer of water associated with hydroplaning decouples the sediments from the bed resulting in a dramatic reduction of the basal shear stress hydroplaning thus provides an explanation for these observations the conditions for onset of hydroplaning are discussed in terms of critical densimetric froude number the stress reduction due to a lubricating layer of water or mud slurry is studied via equilibrium solutions for a two layer couette flow the calculations reveal that the stresses in both the low viscosity lubricating layer and the high viscosity deforming deposits below it are substantially reduced the principles of laminar boundary layers are used to develop an equilibrium solution for the steady motion of a hydroplaning debris glide block this adjusted version of lubrication theory properly accounts for hydroplaning associated with a dynamic pressure generated at the head of the block example calculations at both laboratory and field scale support the experimental results of reduced bed friction limited erosion sediment rheology independence and high velocities the results also reveal the possibility for a net up slope discharge in the lubricating layer

the effect of grain coating microquartz on preservation of reservoir porosity clay coatings have been widely accepted by many workers as an explanation for preserving high porosity in deeply buried sandstones but few workers have realized that similar effects can be produced by microcrystalline quartz coatings this phenomenon can be expected only under special circumstances but in such cases it can have profound consequences for exploration in the central graben area of the southern north sea unusually high porosity 20 27 and permeability 100 1000 md are found in certain zones in upper jurassic sandstones at depths of 3 4 4 4 km the porosity in these zones is 5 15 higher than expected based on average porosity depth trends from brent and haltenbanken sandstones we propose that the high porosity is due to continuous grain coatings of euhedral microcrystalline quartz crystals that are 0 1 2 m thick the distribution of microcrystalline quartz coatings is controlled by the presence of siliceous sponge spicules rhaxella which implies a sedimentological control on the reservoir quality we present a thermodynamic model showing how continuous microcrystalline quartz coatings inhibit development of no mal macrocrystalline quartz overgrowths sourced mainly from stylolites high porosities in parts of various upper jurassic oil fields ula and gyda have previously been explained by inhibition of quartz cementation by early hydrocarbon charge we suggest that the microcrystalline quartz coatings provide a more plausible explanation

heterogeneous extrusion and exhumation of deep crustal variscan assembly geochronology of the western tatra mountains northern slovakia abstract the nature and style of mid crustal assembly and exhumation during continental collision has been investigated in the tatra mountains of the western carpathians the pre alpine basement of the western carpathians represents the easternmost exposure of the variscan orogen in europe which marks the collision of laurasia with gondwanian affiliated terranes during the palaeozoic the tatric crystalline unit of the western tatra in northern slovakia displays an inverted metamorphic sequence where a high grade unit comprising migmatites with relicts of eclogite has been thrust over a lower grade mica schist unit new geochronological and thermochronological data together with published thermobarometry illuminate the metamorphic history of the western tatra the upper unit eclogites with occasionally preserved omphacite record near isothermal decompression from 1 6 gpa to 1 0 1 2 gpa at 750 800 c which lead to intensive re equilibration at high pressure granulite facies conditions comparable to the peak metamorphic conditions of the host migmatite both eclogite and migmatite shared a retrograde p t path following the insertion of the eclogite assemblage into the migmatites the metamorphic evolution of the lower unit mica schist is constrained to peak p t conditions of 0 6 0 8 gpa and 640 and 660 c followed by retrogression this suggests that different rock types of the western tatra metamorphic core shared only their exhumation path from mid crustal levels id tims sm nd dating of garnet from eclogite yields a whole rock garnet isochron age of 337 10 ma with an initial e nd isotopic composition of 8 3 in situ u pb dating of monazite from a migmatite surrounding the eclogite shows one age population of c 380 ma whereas monazite from a migmatite away from the eclogite preserves a robust 340 11 ma age which is indistinguishable from sm nd garnet age and u pb age of zircons in the anatectic leucosome of the migmatite 347 7 ma a younger monazite age population from the migmatite of 300 16 ma is consistent with 40 ar 39 ar mica ages of c 310 ma this argues for a contemporaneous and likely shared exhumation path of the assemblage pair in situ monazite total pb analyses from the lower unit mica schists yields xenocrystic and c 370 ma ages but no geochronologic evidence for peak variscan tectonism exhumation of the deep crustal root occurred most probably in a two stage process the timing of the high pressure eclogite facies metamorphism before the onset of exhumation into the mid crust was likely between c 380 ma and 360 ma subsequent exhumation into the middle crust was coeval with migmatite generation at c 340 ma and garnet diffusion modeling suggest 30 c ma cooling rates the exhumation was likely tectonically forced by the action of a rigid indentor which prompted the weak lower crust to be heterogeneously extruded to mid crustal levels at a time coeval with anatexis and subsequently extruded with mid crustal material to the upper crust

late quaternary sedimentation and glacial history of the western svalbard continental margin abstract glacigenic sediments recovered in shallow cores from the western svalbard continental slope are subdivided into five facies associations based on grain size sedimentary structure mineralogy petrography and geochemistry two diamicton facies are recognised one of which is interpreted as hemipelagic mud with variable amounts of ice rafted debris ird and the other as a product of mass movement the diamictons are associated with melting of icebergs during glacial melt events and debris flow deposition on the submarine fans during peak glaciation respectively laminated to layered mud and turbidites seem to be closely related to eustatic fall in sea level and erosion of banks located on the continental shelf resulting in accumulation of fine grained organic rich deposits and thin silt and sand layers on the continental slope middle weichselian was characterised by several phases of extensive iceberg production and input of ird the first phase 60 55 ka is correlated with a glacier advance on svalbard but the following phases 54 44 ka can not be correlated with glacier advances on land this demonstrates that there may have been more glaciations than recorded on svalbard and that ice sheets at high northern latitudes fluctuated more frequently than previously assumed the composition of the ird deposited after 54 ka suggests that the ice sheets during these advances were located in the eastern svalbard barents sea area the late weichselian growth of the svalbard barents sea ice sheet occurred probably in two steps nucleation of a continental based ice sheet between 27 and 22 5 ka followed by a rapid advance to the shelf edge when the ice margin reached the soft clay rich sediments on the continental shelf eustatic lowering of the sea level during the initial phase led to bank exposure and erosion bringing large quantities of fine grained organic rich sediments to the deep sea during peak glaciation glaciers provided a localised supply of sediments to the shelf troughs and the upper slope which were redistributed by debris flows the marine based svalbard barents sea ice sheet started to retreat around 14 5 ka through massive iceberg discharge the retreat was interrupted by a short lived advance accompanied by erosion of the shelf banks and redistribution of organic rich sediments to the continental slope the final ice recession started around 12 ka and ended close to 9 ka when the fjords of svalbard were essentially ice free large amounts of meltwater released during the removal of the svalbard barents sea ice sheet cooled down the surface waters of the norwegian greenland sea and formed a widespread sea ice cover between 12 and 8 ka input of terrigenous material was greatly reduced during the early part of holocene the present interglacial is characterised by erosion of the shelf and upper slope by bottom currents leaving a prominent lag deposit

petrogenesis and tectonic setting of cadomian felsic igneous rocks sandikli area of the western taurides turkey in the sandikli afyon region western taurides the late proterozoic rocks of the sandikli basement complex are composed of low grade meta sedimentary rocks guvercinoluk formation intruded by felsic rocks kestel cayi porphyroid suite kcps the kcps is a deformed and highly sheared dome shaped rhyolitic body with a granitic core quartz porphyry dikes intrude both the slightly metamorphic igneous and the sedimentary rocks of the basement complex both the quartz porphyries and rhyolites were converted into mylonites with relict igneous textures geochemical data show that these felsic igneous rocks are subalkaline and mainly granitic in composition with sio2 72 wt and al2o3 11 5 wt the chondrite normalized incompatible trace element patterns are characterized by distinct negative rb nb sr p ti and eu with enrichment in th u la ce nd sm and zr the ree patterns of the felsic rocks indicate a strong enrichment in lree but display slightly flat hree patterns according to geochemical characteristics and petrogenetic modeling extrusive and intrusive rocks of the kcps were probably derived from an upper continental crustal source partial melting of granites felsic rocks by 18 20 fractional melting plus 18 20 rayleigh fractional crystallization which seems to be the most effective igneous process during the crystallization of the kcps single zircon age data from the granitoids and fossils from the disconformably overlying sedimentary successions indicate that the metamorphism and the igneous event in the taurides are related to the cadomian orogeny based on the geological geochemical and petrogenetic correlation of the post collisional granitoids it is further suggested that the tauride belt in western central turkey was in a similar tectonic setting to the gondwanan terranes in north africa younger granitoids and southern europe spain france bohemia brno massifs during the late cadomian period

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

recurrent large scale landsliding on the west flank of la palma canary islands a large area of debris avalanche deposits has been discovered on the western submarine flanks of the island of la palma multibeam bathymetry and its derivative backscatter data towed ocean bottom instrument tobi sidescan sonar images and 3 5 khz and airgun seismic reflection data have been used to identify at least two and possibly as many as four major landslide events the youngest of the events the cumbre nueva debris avalanche extends onshore into the valleys bounded by the caldera de taburiente and cumbre nueva ridge which mark the degraded collapse scars radiometric dating of the volcanic flows in the headwall indicate an age of between 536 and 125 ka for this landslide the debris avalanche covers an area of 780 km2 has a maximum thickness of 500 m and has an estimated volume of 95 km3 older deposits collectively referred to as the playa de la veta debris avalanche complex are probably as the name indicates an amalgamation of at least two or three events rather than the result of a single catastrophic failure the playa de la veta debris avalanche complex is associated onshore with an unconformity dated as late matuyama 1 ma to 800 ka it covers an area of 1200 km2 has a maximum thickness of 1300 m and may represent a total volume of up to 650 km3 the greater thicknesses and limited areas occupied by debris avalanches on the western flank of la palma compared to other landslides in the canary archipelago suggest that the la palma landslide masses have relatively low mobility the different debris avalanche lobes formed by each landslide event are separated by channels 2 2 5 km wide the clear relationship between channel position and the boundaries of each debris avalanche lobe indicates that debris avalanches control later channel formation and pathways the relief of the submarine flanks of the la palma volcanoes in the areas of island slope unaffected by landslides is mainly the result of constructional volcanic processes however the older submarine slopes such as in the northern taburiente volcano may also have been modified by smaller scale submarine mass wasting and sediment flows

late cenozoic seismic stratigraphy and glacial geological development of the east greenland and svalbard barents sea continental margins abstract the european program on the late cenozoic evolution of the polar north atlantic margins ponam running from 1990 to 1994 resulted in a wealth of seismic data and sediment cores particularly from the svalbard and barents sea continental margin but also from areas of the east greenland margin deep sediment coring was undertaken on both margins during odp legs 152 and 162 this paper uses the ponam generated information as well as previous and subsequent seismic and core data to review our present understanding of the glacial geological development of these regions four main depositional facies have been identified these are represented by hemipelagic glaciomarine sediments sandy silty debris flows diamictic debris flows and tills deposited directly beneath grounded ice the temporal and spatial distribution of these four facies determines the architecture and seismic character of the two continental margins the two regions show significant differences with regard to both the timing of initial glaciation and the response of the ice sheets to climatic variability glacial deposition has taken place on the east greenland margin at least since 7 ma but apparently only since 2 5 ma on the svalbard barents sea margin significant glacial expansion across the continental shelf probably occurred in the early and late pliocene in east greenland whereas the glaciers on svalbard and the barents sea did not reach the shelf edge until the early pleistocene despite a shorter glacial period average glacial sedimentation rates are 2 3 times higher on the svalbard barents sea margin than on the studied parts of the east greenland margin the svalbard barents sea ice sheet has advanced and retreated much more frequently during the plio pleistocene than the greenland ice sheet glacial regime polar on greenland and polythermal to temperate in svalbard and the barents sea and the more easily erodible preglacial bedrock of svalbard and the barents sea are thought to be main factors responsible for the differences in ice sheet behavior and consequently glacial sediment production

scaling behaviour of clay rich submarine debris flows we perform a statistical study of submarine debris flows based on recent data from the storegga area off the western coast of norway due to the high quality of the data and the uniformity of materials the data from the storegga database are far less dispersed than world wide compilations available so far allowing for a fit with good statistical significance we find that both the run out and the ratio between fall height and run out are best described as a power law function of the volume for small to moderate volumes visco plastic models are able to reproduce the power law in contrast to granular frictional models however either progressive mixing of the shear layer with ambient water or hydro planing must be invoked in order to explain the extreme run out distances of larger debris flows

mass wasting processes in the western wilkes land margin possible implications for east antarctic glacial history abstract multichannel seismic data collected off western wilkes land east antarctica reveal widespread sediment mass movement events mainly in the form of mega debris flows deposited on the continental rise in places they have a seaward extent of more than 200 km and a thickness of up to 400 m debris flow units are commonly separated by thin deposits of well stratified facies interpreted as glaciomarine mixed contouritic and distal turbidite deposits possibly with some hemipelagic sediments these units due to a dominant contouritic component represent weakened layers and could then play a major role in the slope instability based on stratigraphic correlation with dsdp site 268 it is suggested that slope failures in the western wilkes land occurred mostly during the miocene inferred high sedimentation rates due to large amounts of sediment delivered from a temperate wet based ice sheet would have constituted a key factor in the sediment failures the distribution of mass wasting related features appears also strongly related to the amount of meltwater discharge the main trigger mechanism would probably have been earthquakes enhanced by isostatic rebounds following major ice sheet retreats

sediment mass flow processes on a depositional lobe outer mississippi fan abstract seamarc 1a sidescan sonar imagery and cores from the distal reaches of a depositional lobe on the mississippi fan show that channelized mass flow was the dominant mechanism for transport of silt and sand during the formation of this part of the fan sediments in these flows were rapidly deposited once outside of their confining channels the depositional lobe is formed of a series of long narrow sublobes composed of thin bedded turbidites normally graded siliciclastic sand and silt 20 cm thick on average debris flow deposits soft clay clasts up to 5 cm in diameter in a siliciclastic silt matrix 48 cm thick on average and background sedimentation hemipelagic muds the mass flows most likely originated from slope failure at the head of the mississippi canyon or on the outer ontinental shelf and flowed approximately 500 km to the distal reaches of the fan with debris flow being the dominant flow type an analysis that uses the geometry of the confining channels and strength properties of the debris flow material shows that these thin debris flows could have traveled hundreds of kilometers on extremely small sea floor slopes at low velocities if the flowing medium behaved as bingham fluids and were steady state phenomena

activity diagrams for clinoptilolite susceptibility of this zeolite to further diagenetic reactions clinoptilolite is the predominant zeolite in diagenetically altered volcanic rocks at yucca mountain nevada having formed by posteruptive reactions of ground water with vitric tuffs in the pyroclastic deposits compositional variations of clinoptilolites in the fractured and zeolitized tuffs not presently in contact with ground water and the vulnerability of zeolites to burial diagenesis raise questions about the long term stability of clinoptilolite equilibrium activity diagrams were calculated for clinoptilolite solid solutions in the seven component system ca na k mg fe al si plus h sub 2 o employing available thermodynamic data for related minerals aqueous species and water stability fields are portrayed graphically assuming the presence of potassium feldspar saponite and hematite and using ranges of activities for sio sub 2 and al sup 3 defined by the saturation limits for several silica polymorphs gibbsite kaolinite and pyrophyllite the clinoptilolite stability field broadens with increasing atomic substitution of ca for na and k for ca reaches a maximum for intermediate activities of dissolved al and decreases with increasing temperature the thermodynamic calculations show that ground water of the sodium bicarbonate type is approximately in equilibrium at 25c with calcite and several zeolites including heulandite and calcic clinoptilolite mg rich clinoptilolites are stabilized in ground water depleted in ca sup 2 the activity diagramsmore indicate that prolonged diagenetic reactions with ground water depleted in al enriched in na or ca and heated by the thermal envelope surrounding buried nuclear waste may eliminate sorptive calcic clinoptilolites in fractured tuffs and underlying basal vitrophyre less

submarine slope stability on high latitude glaciated svalbard barents sea margin abstract slope stability is evaluated at two locations on high latitude deep sea fans along the svalbard barents sea margin based on available samples and using an infinite slope analysis the stability evaluation uses the mohr coulomb failure criterion and a semi analytical approach based on gibson s formulation for determining the excess pore pressure build up due to sedimentation the main results are presented in the form of contour plots of slope safety factors in a diagram with axes of time and thickness of deposit the results show that during rapid sedimentation which mostly takes place during periods of maximum glaciation with the ice front located along the shelf edge slope failure will occur with a frequency varying between 95 and 170 years only part of the upper sedimented layer will be mobilised 10 30 m while the remaining thickness 40 70 m will remain at the initial sedimentation site these results may explain why the continental slope is characterised by relatively uniform sediment thickness from upper to lower slope

pipeline soil water interaction modelling for submarine landslide impact on suspended offshore pipelines the submarine landslide is one of the major geohazards in deep water oil and gas developments the impacts of glide blocks or out runner blocks which carry the geotechnical properties of the paren

clinoptilolite heulandite nomenclature heulandite was first named in 1822 for the english mineral collector j h heuland see dana 1914 p 574 576 although it is typically found as macroscopic commonly 0 2 2 cm in size crystals in cavities in mafic igneous rocks and is volumetrically minor on the earth s surface heulandite also occurs in larger amounts in some sedimentary deposits often in association with clinoptilolite due to the large size of typical heulandite crystals its chemical composition and crystallographic and optical properties were easily characterized mineralogists recognized early that heulandite is monoclinic and that heating changes its optical properties in a predictable manner slawson 1925 unlike heulandite the mineral known today as clinoptilolite typically occurs as microscopic crystals commonly 2 20 m in size and commonly intimately admixed with other fine grained minerals although clinoptilolite is known today as the most common natural zeolite occurring in large amounts millions of tons in altered volcanic tuffs and saline alkaline lake deposits it is generally mentioned only in passing in beginning mineralogy texts clinoptilolite was not described as a distinct mineral species until 1932 schaller 1932 prior to that time the platy material described by pirsson 1890 in amygdules in weathered basalt from the hoodoo mountains wyoming had been classified as mordenite based primarily on its chemical similarity with mordenite from nova scotia in spite of the chemical similarities pirsson did recognize the crystallographic similarity between the wyoming mordenite and heulandite dana s sixth edition 1914 p 572 573 lists both ptilolite and mordenite as members of the mordenite group ptilolite which we now recognize as mordenite is listed by dana as commonly occurring in aggregates of needles having parallel extinction but mordenite is reported by dana to be monoclinic having a form closely approximating that of heulandite schaller 1932 proposed the name clino ptilolite based on the chemical

cenozoic sedimentation and clay mineralogy in the northern part of the magellan trough central pacific basin abstract assemblages of clay sized minerals in twelve deep sea cores from the northern part of the magellan trough in the central pacific basin clearly show that authigenic smectite together with clinoptilolite formed subsea in situ and predominated throughout palaeogene time clastic clay minerals such as chlorite illite and kaolinite increased at the expense of smectite in sediments deposited since the pliocene most of the authigenic smectites are of the di octahedral iron rich type the most probable origin of the authigenic smectites is formation from precursors such as volcanic glass as part of this process biogenic silica evidently contributed to the formation of smectite and zeolites as clinoptilolite the presence of a tri octahedral saponite and the tem morphology of some smectites on the other hand suggests that not all of the smectite studied was formed subsea in situ but that some had an allogenic origin systematic vertical changes in the assemblage of clay sized minerals suggest that the authigenesis of submarine smectite and clinoptilolite prevailed in conditions of reduced aridity and weak wind activity throughout the palaeogene in the study area however allogenic clay minerals such as chlorite and illite increased since the olduvai event under conditions of severe aridity and strong wind activity caused by global climatic change the west northwest movement of the pacific plate must have partly played a role in deposition of the clastic clay sized minerals from the asian continent by westerlies in the study area the widespread occurrence of cenozoic hiatuses in the study area is attributed to the influence of antarctic bottom water aabw the latter must have influenced non deposition of the clay sized minerals at times during the cenozoic

late neoproterozoic to early palaeozoic palaoegeography of the holy cross mountains central europe an integrated approach study of geochemistry examination of isotope ages of detrital minerals palaeomagnetic analysis and a study of the trilobites were performed to provide constraints on the palaeogeographical position of the holy cross mountains in late ediacaran early palaeozoic time the geochemical results indicate an active continental margin or continental island arc provenance of the ediacaran sediments sediments from a passive continental margin were deposited here during the cambrian and ordovician the palaeomagnetic pole isolated from cambrian rocks of the malopolska region of the holy cross mountains corresponds to the cambrian segment of the baltic apparent polar wander path isotope age estimations indicate that cambrian sediments of the malopolska region contain detritus not only from a latest neoproterozoic source but also from sources with ages of c 0 8 0 9 ga 1 5 ga and 1 8 ga the malopolska brunosilesia dobrugea and moesia terranes which originally developed near the present southern edge of baltica and were partly involved in the cadomian orogen were dextrally relocated along its trans european suture zone margin the first stage of this movement took place as early as latest ediacaran time while baltica rotated anticlockwise anticlockwise rotation of baltica at the cambrian ordovician boundary implies further dextral movement of the malopolska block

petrology and palaeoenvironmental significance of glaucony in the eocene succession at whitecliff bay hampshire basin uk following the investigations of odin and others into the distribution of green granules glaucony has been widely assumed to be a reliable indicator of a fully marine open shelf environment with a low sedimentation rate we have investigated the value of glaucony as a palaeoenvironmental indicator through an investigation of the pellets and their distribution and reworking in the predominantly brackish to shallow marine tertiary sediments of the hampshire basin together with a re evaluation of the sedimentology glaucony has apparently formed in situ in all lithofacies from shallow marine to estuarine of the three highest glaucony concentrations all dominated by in situ glaucony two occur within highstand system tracts the third is at a sequence boundary several important surfaces do not have more than a few percent glaucony with very variable proportions of mature and in situ pellets the correlation between glaucony concentration and sequence stratigraphy is most obvious in the london clay and wittering formations where least reworking of pellets has occurred in the barton group there are no major concentrations of glaucony at any of the important stratal surfaces we believe this more random glaucony distribution is due to limited glaucony formation and reworking of older glaucony in these sediments ideal conditions for glaucony formation are interpreted to have been fully marine 10 30 m water depth a warm temperature plus low sedimentation rate with periodic winnowing to concentrate the pellets although most of these conditions for glaucony formation occurred in the selsey formation and barton group a factor or factors mitigated against glauconitization we suggest that this was lowering of the water temperature the london clay and wittering formations were deposited relatively rapidly 50 60 m ma 1 and include intervals of estuarine sedimentation both factors that we believe inhibited glaucony formation glaucony maturity reflects the minimum length of time spent in surface sediments close to the oxic sub oxic interface point count data and chemical data for glaucony indicate widespread reworking and an overall increase in reworking with time possibly due to uplift on the isle of wight monocline the apparently wide range of conditions in which glaucony will form and the frequency with which it is reworked suggest that it is a less useful indicator palaeo environmental indicator than is commonly supposed

chronological constraints on the pre orogenic history burial and exhumation of deep seated rocks along the eastern margin of the variscan orogen bohemian massif czech republic key lithological units of the high grade eastern margin of the bohemian massif were dated using the u pb and pb pb methods on zircons in order to establish a chronological framework for the geodynamic evolution of the variscan orogenic root the protolith ages for metagranitoids orthogneisses and granulites of thickened lower and middle crust reveal the existence of magmatic activity that occurred over a 100 million year time interval from cambro ordovician to early devonian times probably related to discontinuous intracontinental rifting of neoproterozoic crust our geochronological data suggest that the eastern part of the orogenic root represents thermally softened and rifted neoproterozoic crust preserved farther to the east as the brunia microcontinent zircon ages for felsic granulites high grade gneisses of the lower crust and of a syn convergence granodioritic intrusion in the upper crust indicate that thickening and exhumation of the crust occurred during a narrow time interval between 370 and 340 ma exhumation of the lower crust to mid crustal levels was a localized process that occurred at 340 ma and was associated with crustal scale folding in the internal part of the root as well as orogenic channel flow along the eastern collisional margin both types of exhumation mechanisms were driven by deep level wedging indentation of the easterly brunia continent followed by deposition of heavy minerals and pebbles derived from high pressure rocks in the adjacent foreland basin final orogenic development was characterized by ne sw dextral transpressive shearing parallel to the brunia margin as well as dextral trans tension associated with activity along the elbe lithospheric fault these processes affected the marginal parts of the orogenic root and were accompanied by 330 to 325 ma old syntectonic granitoid intrusions along reactivated lithotectonic boundaries rotation of the assembled orogenic belt accompanied by lithospheric faulting driven by westerly subduction roll back may be the most plausible model to explain late deformation of the orogenic root

the mineralogy and origin of some silurian bentonites welsh borderland u k thirty clay rich horizons from the wenlock and ludlow series of the welsh borderland were analysed to investigate their mineralogy and possible origins two mineralogical assemblages were determined an assemblage of illite smectite and kaolinite of volcanic origin which was associated in many samples with an assemblage of illite and chlorite of detrital origin immobile chemical discriminants zr tio2 versus nb y infer an originally rhyolitic ash composition with a possible temporal progression from the wenlock to ludlow to more differentiated compositions the thin nature of the bentonites and lack of juxtaposed subduction related calc alkaline magmatism suggests that the tuffs were derived from distant explosive eruptions from volcanic centres possibly in ne europe

the morphology setting and processes of the afen slide abstract identified in 1996 during an environmental survey for the atlantic frontiers environment network the afen slide lies around 95 km northwest of the shetland islands the head of the slide is at a water depth of 830 mbsl and the debris lobe stretches to over 1120 mbsl along a slope varying from around 0 7 to 2 5 the overall length head scarp to toe of lobe of the slide is in excess of 12 km and the maximum width attained is around 4 5 km the relative timing of the various phases can be determined from the morphology imaged using seabed picks from 3d exploration seismics and high resolution deep tow boomer data these seem to show at least four major phases of failure and several distinct modes of sediment transport ranging from hydroplaning to block sliding the most likely trigger for the failure is a seismic event focused on the nearby victory transfer zone sensitising factors include the presence of contouritic sands directly beneath the surface of rupture these would serve as a plane of weakness and under seismic loading may further weaken due to liquefaction indeed previous studies have shown that the slope in this area is stable in the absence of external triggers the processes of sediment transport subsequent to failure are also investigated using sediment cores as well as the 2d and 3d seismic and appear to indicate that flow transformation occurred in at least the first phase of mass movement

illite distribution and morphology explaining basinal variations in reservoir properties of upper jurassic sandstones danish north sea abstract growth of fibrous illite may destroy an otherwise promising sandstone reservoir even sandstones characterized by microquartz coatings therefore detailed petrographical and diagenetic investigations were performed in order to understand the factors that control illite precipitation and other factors affecting the reservoir properties in the upper jurassic heno formation the heno formation is encountered in large parts of the danish central graben where its lower part the gert member was mainly deposited in back barrier environments and its upper part the ravn member was deposited in a shoreface environment in total 215 core samples from 15 wells were investigated petrographically by optical and scanning electron microscopy this was supplemented by plug porosity and permeability measurements and x ray diffraction of bulk and clay fraction the investigations show among other things that microquartz coatings may help to preserve porosity and permeability whereas the permeability is reduced when microquartz occurs combined with fibrous illite illite precipitation is largely governed by the amounts of k feldspar present during burial consequently the initial abundance of k feldspar in the sediment source area and its alteration during and immediately after deposition in particular during subaerial exposure at sequence boundaries has a major influence on the final reservoir properties of the sandstones the risk of illite precipitation can largely be predicted from the available sediment source material depositional environment and burial depth

geology and geochemistry of the pre early cambrian rocks in the sandikli area implications for the pan african evolution of nw gondwanaland abstract the pre early cambrian sandikli basement complex in western central anatolia comprises a low grade meta sedimentary succession guvercinoluk formation and meta rhyolites intruded by meta quartz porphyry rocks kestel cayi porphyroid suite the guvercinoluk formation consists of alternation of meta siltstones and meta sandstones with olistostromal conglomerates rare black chert and cherty meta dolomite lenses the kestel cayi porphyroid suite is a deformed highly sheared dome shaped rhyolitic body with quartz porphyry rocks quartz porphyry dykes intrude both the volcanic carapace and the meta sedimentary rocks of the guvercinoluk formation both the meta quartz porphyry rocks and meta rhyolites are typically mylonitic with relict igneous textures geochemical data indicate that the felsic rocks of the kestel cayi porphyroid suite are subalkaline and display characteristic features of post collisional i type granitoids the basement complex is unconformably overlain by variegated conglomerates mudstones and arkosic sandstones with andesitic lavas followed by siliciclastic rocks and carbonates that yielded early middle cambrian fossils based on the geochemical characteristics of the felsic rocks of kestel cayi porphyroid suite and the depositional features of the associated sediments it is suggested that the sandikli basement complex is related to a post collisional extension event in nw gondwanaland similar occurrences elsewhere have been related to a transition from continental plate convergence to continental plate divergence along the pan african belt

early cambrian location and affinities of the brunovistulian terrane central europe in the light of palaeomagnetic data the brunovistulian was one of the first tectonic units of central europe to be defined as a terrane in spite of extensive studies the early palaeozoic palaeogeographical position and provenance of this unit remains unclear a palaeomagnetic study of the lower cambrian red beds and a study of the trilobite fauna were performed to provide constraints on the palaeogeographical position of the terrane in early cambrian time good quality palaeomagnetic data obtained from the lower cambrian red beds suggest the mixed nature of the early cambrian geomagnetic field and a nearly equatorial position a palaeolatitude of c 7 of the brunovistulian terrane in the early cambrian comparison of this palaeolatitude with existing palaeogeographical models leads to the conclusion that at this time the brunovistulian terrane was separated by a great distance from the avalonian margin of gondwana the terrane was located within the cadomian belt occupying a position north of the present day northern margin of africa it was coupled to the present day southern margin of baltica during the cambrian when baltica moved along the cadomian margin of gondwana another possibility is that the brunovistulian terrane could have remained near this margin of baltica since grenvillian time and was incorporated into the cadomian orogen

estimation of soil strength in fine grained soils by instrumented free fall sphere tests the dynamic response of a sphere in soft clay is considered through field tests in which a 0 25 m dia steel sphere was allowed to free fall in water and dynamically penetrate the underlying soft soil the test data collected in a lake and a sea environment relate to sphere velocities of up to 8 m s reaching sphere invert embedments close to ten diameters an inertial measurement unit located within the sphere measured the motion response of the sphere during free fall and penetration in soil the resulting acceleration data were used within a simple framework that accounts for both geotechnical shearing resistance and fluid mechanics drag resistance but cast in terms of a single capacity factor that can be expressed in terms of the non newtonian reynolds number the merit of the framework is demonstrated by using it as a forward model in a series of inverse analyses that calculate the undrained shear strength profile from acceleration data measured in free fall sphere tests the good match between th

authigenic zeolites and their relation to silica diagenesis in odp site 661 sediments leg 108 eastern equatorial atlantic at odp site 661 from the continental margin of northwest africa authigenic clinoptilolites were investigated in detail based on chemical data crystal size and shape and their intergrowth with associated mineral phases two types of clinoptilolite type a and b occur representing different diagenetic conditions under which the formation of zeolites took place clinoptilolite type a was found in a sediment section comprises numerous hiatuses and stratigraphically condensed sediments and could have been formed during early diagenesis in contrast clinoptilolite type b was precipitated in campanian sediments during later diagenesis after the transformation from opal a to opal ct had taken place at site 661 the silica source for the authigenesis of both clinoptilolite types is biogenic opal volcanic ash material occurs but in low amounts and thus is not a prerequisite for the formation of clinoptilolite at site 661

rare earth element geochemistry of standard sediments a study using inductively coupled plasma spectrometry the rare earth elements ree and y have been determined in 15 international standard sediments from france german democratic republic canada and the u s a samples were prepared using conventional rock dissolution techniques and the ree and y were separated from other constituents using cation exchange chromatography the ree la ce pr nd sm eu gd dy ho er yb lu and y were analysed simultaneously by inductively coupled plasma atomic emission spectrometry results indicate that u s g s standard shale sco 1 cody shale is a good reference material to use for the normalisation of the ree distributions of sediments data normalised to sco 1 are more readily interpreted than those normalised to existing estimates of average shale the ree patterns of standard sediments vary considerably in shape span an order of magnitude in absolute concentration and provide valuable reference values for the ree analysis of other sedimentary materials

fate of silicate minerals in a peat bog an investigation of silicate weathering in a minnesota mire indicates that quartz and aluminosilicates rapidly dissolve in anoxic organic rich neutral ph environments vertical profiles of ph dissolved silicon and major cations were obtained at a raised bog and a spring fen and compared profiles of readily extractable silicon diatom abundance ash mineralogy and silicate surface texture were determined from peat cores collected at each site in the bog normally a recharge mound dissolved silicon increases with depth as ph increases exceeding the background silicon concentration by a factor of two silicate grain surfaces including quartz are chemically etched at this location despite being in contact with pore water at neutral ph with dissolved silicon well above the equilibrium solubility of quartz the increasing silica concentrations at circum neutral ph are consistent with a system where silicate solubility is influenced by silica organic acid complexes silica organic acid complexes therefore may be the cause of the almost complete absence of diatoms in decomposed peat and contribute to the formation of silica depleted underclays commonly found beneath coal

origin of zeolite cements in the miocene sandstones north tejon oil fields california zeolite cement zoning from heulandite via heulandite laumontite to laumontite is found in miocene volcaniclastic sandstones at the north tejon oil field southern san joaquin basin california the zeolite transition occurs at the depth range from 2703 2743 m present temperature range 90 92 degrees c heulandite and minor smectite forms together from the dissolution of volcanic glass during early diagenesis at depths shallower than 2743 m early laumontite forms directly at the expense of heulandite by a reaction of the form 1250 cc 1470 cc ca sub 3 75 al sub 7 5 si sub 28 5 o 72 24h 2 o 3 35ca super 2 6 7al oh 4 super 7 1caal 2 si 4 o 12 4h 2 o 9h 2 o heulandite laumontite this reaction is based on the volumetrical relation between both zeolites and the absence of quartz cements during the zeolite transition the sources of the ca and al appear to be partial dissolution of plagioclase and smectite occurring prior to the above reaction and incorporation of residual smectite coatings at that reaction time active albitization and late laumontite formation begin to occur in the laumontite bearing sandstones at depths greater than 2743 m present temperatures greater than 94 degrees c this albitization reaction accompanying the late laumontite is as follows 100 cc 70 cc 62 cc na sub 0 7 ca sub 0 3 al sub 1 3 si sub 2 7 o 8 0 6h 4 sio 4 0 7naalsi 3 o 8 0 3caal 2 si 4 o 12 4h 2 o plagioclase albite lumontite clay mineral transitions from smectite via mixed layer clay minerals c s or i s to chlorite or illite probably produced the h 4 sio 4 necessary for the above reaction in addition to the albitization the source of late laumontite was derived in part from a mass transfer from outside during the late laumontite formation calcite locally forms and acts as an additional sink for ca immediately adjacent to deformed biotite flakes

catastrophic collapse of the volcanic island of hierro 15 ka ago and the history of landslides in the canary islands landslides play an important role in the evolution of many volcanic islands producing huge fields of blocky volcanic debris on their submarine slopes sidescan sonar images presented in this paper provide evidence for a large debris avalanche el golfo on the northern flank of hierro island in the canary islands angular blocks as much as 1 2 km across and 200 m high cover the debris avalanche surface el golfo avalanche is related to both the canary debris flow and a volcaniclastic turbidite found in the madeira abyssal plain 600 km west of the canaries dating of the turbidite and the failure scarp onshore indicates that the failure probably occurred between 13 and 17 ka there appears to be a general correlation between volcaniclastic turbidites in the abyssal plain sequence and landslides in the canaries during the past 750 ka tentatively this correlation suggests that seven major landslides have affected the canaries in that time

the storegga slides evidence from eastern scotland for a possible tsunami abstract the second storegga slide on the continental slope off western norway has been dated at between 8000 and 5000 yrs b p a prominent sand layer in flandrian holocene deposits along the coast of eastern scotland and dated at approximately 7000 yrs b p may have been deposited by a tsunami generated by the slide the altitude and stratigraphy of the layer allow estimates to be made of the magnitude of the earthquake which initiated the slide

slope failure dynamics and impacts from seafloor and shallow sub seafloor geophysical data case studies from the costa project holocene and slightly pre holocene submarine landslide are found both in high latitude glacial dominated margins and in lower latitude river dominated margins this paper constitutes a major assessment on some of the best studied submarine instabilities in the world we review and update from original data and literature reports the current state of knowledge of storegga traenadjupet and finneidfjord slides from the mid norwegian margin afen slide from the faeroe shetland channel big 95 slide and central adriatic deformation belt cadeb from continental slope and inner continental shelf settings off the ebro and po rivers in the mediterranean sea canary slide west of the westernmost youngest canary islands and gebra slide off the northern tip of the antarctic peninsula in the southern hemisphere i e those studied in the continental slope stability costa project the investigated slides range in size from the gigantic 90 000 km2 and almost 3000 km3 storegga slide to the tiny 1 km2 and 0 001 km3 finneidfjord slide not only do individual submarine landslides rarely involve processes precisely fitting with pre established categories mostly based on subaerial research but also they display complex mechanical behaviors within the elastic and plastic fields individual events can involve simultaneous or successive vertical to translational movements including block detachment block gliding debris flow mud flow and turbidity currents the need for an in depth revision of the classification criteria and eventually for a new classification system based on the new imaging capabilities provided by modern techniques is more than obvious we suggest a new system which for the moment is restricted to debris flows and debris avalanches volume calculation methods are critically reviewed and the relations between some key geomorphic parameters are established for the selected slides the assumed volume missing from scar areas does not necessarily match the actual volume of sediment remobilised by an individual event since in situ sediment can be remoulded and eventually incorporated during the slide downslope journey cadeb a shore parallel prodelta detached from its source is the exception to the good correlation found between across slope width and alongslope length with slide area height drop measured from the headwall upper rim to its foot correlates with the debris deposit maximum thickness unless the slide moves into restricted areas which prevent farther forward expansion of the deposit such as gebra and big 95 in such cases over thickened deposits are found a particularly loose and fluid behavior can be deduced for slides showing an over thinned character such as the canary slide that traveled 600 km scar areas and slip planes have been investigated with particular emphasis although slide headwalls might present locally steep gradients up to 23 for storegga slide the slope gradients of both the failed segment margins and the main slip planes are very low max 2 and usually around 1 and less an exception is the finneidfjord slide 20 5 that occurred in 1996 because of a combination of climatic and anthropogenic factors leading to excess pore pressure and failure mechanically distinct low permeable clayey weak layers often correspond to slip planes beyond the slide headwall since not only formation of these weak layers but also sedimentation rates are climatically controlled we can state that slide pre conditioning is climatically driven too run out distances reflect the degree of disintegration of the failed mass of sediment the total volume of initially failed material and transport mechanisms including hydroplanning commonly specific run outs could be attributed to distinct elements such as cohesive blocks and looser matrix as nicely illustrated by the big 95 slide total run outs usually correspond to matrix run outs since the coarser elements tend to rest at shorter distances outrunner blocks are finally a very common feature proving the ability of those elements to glide over long distances with independence of the rest of the failed mass in addition to pre conditioning factors related to geological setting and sedimentation conditions a final trigger is required for submarine landslides to take place which is most often assumed to be an earthquake in high latitude margins earthquake magnitude intensification because of post glacial isostatic rebound has likely played a major role in triggering landslides although it cannot be totally ruled out there is little proof at least amongst the costa slides that gas hydrate destabilisation or other processes linked to the presence of shallow gas have acted as final triggers

regional assessment of mass failure events in the baie des anges mediterranean sea abstract pliocene and quaternary surficial sediments of the baie des anges are commonly affected by instability laboratory analyses of sediment samples provide information about the physical properties of these sediments including consolidation state and mechanical behaviour some of these physical properties specifically undrained shear strength values s u have been calibrated by a few in situ measurements the results show that sediments deposited on the slope and on the shelf are mainly homogeneous silty clays whereas those deposited on the floor of canyons are coarser possible grain flow deposits by using s u measurements we have classified the silty clays into four geotechnical types and constructed a geotechnical map of undrained slope stability analysis infinite slope analysis provides an assessment of the possible instabilities under both drained and undrained conditions a regional hazard offshore map is presented including areas sensitive to earthquake induced sliding two potential types of failure are likely to occur in the bay shallow failures which are low volume slides involving underconsolidated near surface sediments and deeper failures which may occur on the flanks of the ridges and may be preferentially triggered by earthquakes these sliding processes involve a large volume of normally consolidated or overconsolidated sediments and may evolve into turbidity currents such as the 1979 nice slide even if it was not an earthquake induced slide channelled by the var or the paillon canyons for more than 100 km our study indicates that future development projects within the baie des anges must address offshore hazards

risk faults in stable crust of the eastern bohemian massif identified by integrating gnss levelling geological geomorphological and geophysical data abstract it is difficult to identify and assess the recently active faults representing a risk factor for key human activities in the areas of stable crust with slow tectonic deformation and reduced seismicity we face the problem in the eastern bohemian massif central european variscides at a contact with the eastern alpine western carpathian orogenic belt through building its integrated geodynamic model based on the long term gnss data cross checked with the results from existing levelling geological surveys geophysical surveys and a new geomorphological analysis the model shows differently moving crustal blocks determining the intervening boundary zones as the main risk regions where weak earthquakes are also usually concentrated primarily diendorf cebin tectonic zone nectava konice fault hana faults b la fault and bulhary fault shear zone the maximum horizontal gnss differential velocities in the exposed bohemian massif reach up to 1 5 2 0 mm yr 1 the up thrusted segments of the western carpathians move individually 2 mm yr 1 the integration of a number of full area datasets corresponding to various dimensions and depth levels of crustal processes allowed us to highlight the important fault zones as driving elements of regional geodynamics

brunovistulian terrane bohemian massif central europe from late proterozoic to late paleozoic a review the brunovistulian terrane represents a microcontinent of enigmatic proterozoic provenance that was located at the southern margin of baltica in the early paleozoic during the variscan orogeny it represented the lower plate at the southern margin of laurussia involved in the collision with the armorican terrane assemblage in this respect it resembles the avalonian terrane in the west and the istanbul zone in the east there is a growing evidence about the presence of a devonian back arc at the margin of the brunovistulian terrane the early variscan phase was characterized by the formation of devonian extensional basins with the within plate volcanic activity and formation of narrow segments of oceanic crust the oldest visean flysch of the rheic rhenohercynian remnant basin protivanov andelska hora and horni benesov formations forms the highest allochthonous units and contains together with slices of silurian bohemian facies clastic micas from early paleozoic crystalline rocks that are presumably derived from terranes of armorican affinity although provenance from an active brunovistulian margin cannot be fully excluded either the development of the moravo silesian late paleozoic basin was terminated by coal bearing paralic and limnic sediments the progressive carboniferous stacking of nappes and their impingement on the laurussian foreland led to crustal thickening and shortening and a number of distinct deformational and folding events the postorogenic extension led to the formation of the terminal carboniferous early permian boskovice graben located in the eastern part of the brunovistulian terrane in front of the crystalline nappes the highest allochthonous westernmost flysch units locally with the basal slices of the devonian and silurian rocks thrusted over the silesicum in the nw part of the brunovistulian terrane may share a similar tectonic position with the giessen harz nappes the silesicum represents the outermost margin of the brunovistulian terrane with many features in common with the northern phyllite zone at the avalonia armorica interface in germany

quaternary seismic stratigraphy of the north sea fan glacially fed gravity flow aprons hemipelagic sediments and large submarine slides abstract approximately 1000 km of high resolution sleeve gun array transects on the north sea fan located at the mouth of the norwegian channel reveal three dominant styles of sedimentation within a thick 900 m quaternary sediment wedge comprising numerous sequences these are interpreted as terrigenous hemipelagic sedimentation large scale translational slides and aprons of glaciogenic debris flow deposits contributing to considerable fan construction four large buried translational slides involved sediment volumes upwards of 3000 km 3 each and preceded the similarly dimensioned first storegga slide on the ne fan flank several thick 100 m terrigenous hemipelagic deposits apparently represent long lived 150 200 kyr periods of sedimentation whose distribution indicates fan input via the norwegian channel the upper sequences are each made upper sequences are each made up of one or several thick 100 m aprons comprising stacked lensoid and or lobate forms which range from 2 to 40 km in width and 15 to 60 m in thickness they characterize debris flows attributed to periodic input from several phases of a norwegian channel ice stream reaching the shelf edge subsidence in the outer norwegian channel allowed preservation of several glaciation cycles represented by sheet erosion bounded tills and progradational units much of the shelf slope transition has been preserved allowing a preliminary chronology of the fan sequences through correlation with borehole sediments in the norwegian channel debris flows which signal the initial shelf edge glaciation are not recognized from the initial glaciation in the channel 1 1 myr but are associated with a middle pleistocene and all following glacial erosion surfaces ges in the outer norwegian channel this was followed by six further sequences probably totalling over 13 000 km 3 of sediment at least four of these were shelf edge ice maximum events the last of which was late weichselian age 14 c ams considering earlier glaciation related hemipelagic sedimentation material since removed by the large slides and extensive unmapped areas total quaternary fan sedimentation was in the vicinity of 20 000 km 3

diagenetic clinoptilolite and opal ct from the middle eocene wittering formation isle of wight u k abstract thinly interbedded estuarine sandstones and mudstones in the middle eocene wittering formation bracklesham group isle of wight contain authigenic clinoptilolite opal ct and possibly authigenic smectite over a thickness of 8 5 m the clinoptilolite and opal ct cements have resulted in these beds being the only ones tightly cemented in the wittering formation the rest being soft sands and muds the unit contains abundant siliceous sponge spicules many of which are preserved as voids and were the likely source of the opal ct the presence of an organic rich rooted paleosol histosol immediately overlying the unit is believed to have contributed significantly to the early diagenetic history of the estuarine sediments in particular the formation of zeolite although the ph and dissolved silica of unmodified seawater are too low for zeolite formation high concentrations of dissolved silica are believed to have resulted from dissolution of siliceous sponge spicules opal a and formation of silica organic acid complexes organic acid dissolution of feldspars absent from the zeolite bearing interval is the most probable source of alumina and cations for zeolite formation ree data show that volcanic ash was never present and cannot therefore have been the source of the zeolite this investigation therefore demonstrates a novel route by which the pore fluid chemistry required for zeolite formation can be achieved

quartz types authigenic and detrital in the upper cretaceous eagle ford formation south texas usa abstract lithologic heterogeneity of the eagle ford formation in south texas arises from mixing of extrabasinal grains of siliciclastic composition with intrabasinal grain assemblages composed dominantly of marine carbonate with a lesser component of biosiliceous debris detrital quartz in particular is derived from both extrabasinal and intrabasinal sources posing a challenge for the use of bulk compositional data for mudrock classification extrabasinal detrital quartz supplied along a major axis of siliciclastic influx the woodbine depositional system of east texas is reduced to a minor part of the grain assemblage in south texas petrographic evidence and point count results indicate that around 85 percent of total quartz in these rocks equal to about 12 6 volume percent is authigenic thus significant quantities of authigenic silica are not restricted to siliceous mudrocks but can be found in carbonate rich mudrocks as well formerly opaline skeletons of radiolaria the dominant source of silica for authigenic quartz precipitation are only poorly preserved by replacements including calcite dolomite pyrite and quartz dissolved silica released by dissolution of radiolarians and perhaps also by volcanic glass dissolution is re precipitated in a variety of forms including matrix dispersed microquartz cement fillings within primary intragranular pores and grain replacement of both calcareous and siliceous allochems the mass balance of dissolved silica mobilized from radiolarians and other reactive silicates and the precipitation of authigenic quartz is uncertain because the initial volumes of now dissolved detrital material versus the final volume of authigenic material quartz and other authigenic silicates cannot be determined with accuracy

magnetic and calcareous nannofossil stratigraphy of the lower palaeogene formations of the hampshire and london basins a magnetostratigraphic study of the lower palaeogene formations exposed in the hampshire and london basins southern uk has led to the identification of eight stratigraphically distinct normal polarity magnetozones within an otherwise reverse polarity sedimentary sequence which spans the late palaeocene to middle eocene a complementary study of the calcareous nannofossil biostratigraphy of these sections and related sections elsewhere in nw europe allows a correlation of this succession of normal polarity magnetozones with the biostratigraphically calibrated geomagnetic polarity timescale based on marine magnetic anomalies it is concluded that the normal polarity chrons corresponding to anomalies 20 21 and 23 are recorded within the huntingbridge earnley and wittering divisions of the bracklesham group respectively that anomalies 24a and 24b are represented within divisions d to b2 of the london clay and anomaly 26 is represented in the lower part of the thanet beds an additional normal polarity magnetozone within the oldhaven beds is believed to represent a short normal polarity event between anomalies 24b and 25 anomalies 22 and 25 appear not to be represented in the uk lower palaeogene succession because of major unconformities at the early middle eocene boundary within the wittering division of the bracklesham group and within the late palaeocene respectively the former appears to correlate with a widespread erosional event in the oceans identified from seismic records vail et al 1979 and interpreted as reflecting a major eustatic sea level fall

shingled quaternary debris flow lenses on the north east newfoundland slope debris flow deposits are the principal component of quaternary continental slope sediments between the north east newfoundland shelf and central orphan basin in seismic profiles these deposits occur as shingled elongate acoustically transparent lenses with their long axes orientated downslope deposits of individual flows form positive mounds on the sea floor subsequent flows were diverted by the pre existing topography into bathymetric lows between older debris flow deposits these deposits show a large variation in the area of sea floor covered by individual flows about 60 1000 km2 average thickness of deposits 9 37 m and volume of sediment displaced 1 27 km3 the ratio of average thickness to a measure of deposit diameter termed the aspect ratio has a threefold variation from 0 0006 to 0 0021 very low depositional slopes and low aspect ratios suggest relatively low viscosities probably due to inmixing of water during downslope transport stratified sediments form three distinct horizons and are locally interbedded with the debris flow deposits these are mainly hemipelagic deposits the slope and rise to the west of the orphan basin are constructional in character the apparent absence of upper slope erosional features and the abundance of debris flow deposits on the slope suggest that the supply of sediment to the continental slope occurred predominantly during times of maximum extent of quaternary glacial ice the ice sheet grounding line during several glacial maxima must have been situated at or near the present shelf break supplying vast amounts of sediment directly to the upper slope oversteepening and subsequent slope failures fed material into deeper water

geochemistry of early siderite cements from the eocene succession of whitecliff bay hampshire basin u k abstract siderite cements in the eocene of whitecliff bay hampshire basin u k occur in a range of depositional facies and morphological associations most siderites are associated with in situ glaucony or occur beneath conspicuous lithological breaks these associations illustrate the importance of slow deposition for early diagenetic carbonate precipitation siderite in the eocene sediments of whitecliff bay is impure and in many cases comprises zoned crystals with an overall decrease in substitution of ca mg and mn for fe from crystal core to rim trends in ca mg and mn from early to later siderite vary between samples with no evident environmental control siderite concretions without calcite cement occur only beneath lithological breaks where meteoric water may have been introduced precipitation temperatures have been calculated from siderite 18o data and are based on the assumption that precipitation occurred from seawater these temperatures are reasonable for typical microbial siderite precipitated in marine sediment but are slightly low for marine siderite where there may have been meteoric overprinting if the precipitation temperature for siderite cements is assumed from 18o data for time equivalent biogenic carbonate rather than the composition of the precipitating fluid the calculated isotopic composition of the precipitating fluid is generally compatible with the inferred marginal marine depositional environments