the importance of upper mantle heterogeneity in generating the indian ocean geoid low one of the most pronounced geoid lows on earth lies in the indian ocean just south of the indian peninsula several theories have been proposed to explain this geoid low most of which invoke past subduction some recent studies have also argued that high velocity anomalies in the lower mantle coupled with low velocity anomalies in the upper mantle are responsible for these negative geoid anomalies however there is no general consensus regarding the source of this particular anomaly we investigate the source of this geoid low by using models of density driven mantle convection our study is the first to successfully explain the occurrence of this anomaly using a global convection model driven by present day density anomalies derived from tomography we test various tomography models in our flow calculations with different radial and lateral viscosity variations some of them produce a fairly high correlation to the global geoid but only a few smean2 gypsum semucb and llnl jps could match the precise location and pattern of the geoid low in the indian ocean the source of this low stems from a low density anomaly stretching from a depth of 300 km down to similar to 900 km in the northern indian ocean region this density anomaly potentially originates from material rising along the edge of the african large low shear velocity province and moving toward the northeast facilitated by the movement of the indian plate in the same direction plain language summary one of the lowest geoid anomalies on earth lies in the indian ocean just south of the indian peninsula several theories have been proposed to explain this gravity low most of these theories try to explain the existence of this anomaly with the help of cold dense oceanic plate that sank into the mantle in the past and which could potentially be present below the indian ocean at depths greater than 1 000 km however there is no general consensus regarding the source of this particular negative geoid anomaly we investigate the source of this low by using models of density driven mantle convection our study finds that the source of this low stems from a low density anomaly stretching from a depth of 300 km down to similar to 900 km in the northern indian ocean region this density anomaly potentially originates from hot buoyant material rising from deep mantle beneath africa and moving toward the northeast facilitated by the movement of the indian plate in the same direction our study is the first to successfully explain the occurrence of this geoid low using present day density anomalies

abrupt change in slope causes variation in the deposit thickness of concentrated particle driven density currents abstract abrupt changes in slope occur frequently in some marine environments laterally confined laboratory experiments show that when dense surge like particulate flows travel over abrupt slope reductions their deposits may have an asymmetric bell shaped thickening near the break of slope this thickening is herein called a slope break deposit and is related to the change in kinetic energy of the flow slope break deposits are particularly pronounced under relatively high velocity flows in our experiments these are flows with high particle concentrations c 5 10 by volume silicon carbide moving down slopes steeper than 3 the experiments were designed such that currents generated by a lock exchange mechanism flowed down a slope variable slope angle onto a flat surface the bodies of the flows became thicker and slower just downstream of the slope break because the flow body slows very rapidly particles are dumped forming the slope break deposit the peak in sediment thickness of the slope break deposit is downstream of the break in slope because falling particles continue to move forward in the flow during settling the slope break deposits may be several tens of percent thicker than deposits from an equivalent flow in which no change in slope occurred the parameters of the slope break deposit correlate with slope angle change

search for milankovitch patterns among oolitic ironstones the stratigraphic record of about 175 oolitic ironstones is sparse yet it portrays several meaningful patterns repeated ironstone episodes occurred in only about 10 major sedimentary basins which were marked by relative tectonic stability or subdued orogeny intervals between episodes varied but were mostly a few to several million years long repetitions on this scale are commonly construed as global rise and fall of sea level the pattern persisted for a few tens of million years in fore deeps several tens of million years on unstable cratons and microcontinents and more than 100 m y in intracratonic basins within the congenial habitats an ironstone developed locally between each of several successive shallow marine upward shoaling detrital sequences these asymmetric units normally a few meters to a few tens of meters thick recurred on average every 250 to 500 kyr commonly fewer than 10 ironstone bearing sequences are involved during a very long lapse in normal sedimentation between such sequences stacked ironstones accumulated on the same short time scale speculation about short time scale patterns is poorly constrained but several other repetitive stratigraphic successions with a several hundred thousand year cadence have been attributed tentatively to the 400 000 year milankovitch climate cycle it is unclear how this would exert a eustatic control without the waxing and waning of continental glaciers

an early holocene submarine slide in boknafjorden and the effect of a slide triggered tsunami on stone age settlements at rennesoy sw norway abstract multibeam bathymetry and seismic data disclose three submarine slides in the outer boknafjord area sw norway the largest slide arsneset slide has a volume of ca 28 10 6 m 3 the scar of this slide is 15 30 m high and it covers an area of ca 1 4 10 6 m 2 seismic data on sediment thicknesses and sedimentation rate estimates from radiocarbon dating indicate that this slide occurred ca 10 000 14 c yr bp 2d and 3d simulations of the tsunami generated by the slide indicate run up heights on the neighbouring galta peninsula of 2 5 4 m at a slide velocity of 25 m s 1 possible higher slide velocities would have caused waves reaching higher areas an archaeological excavation on the galta peninsula at rennesoy yielded approximately 17 500 flint artefacts of late palaeolithic early mesolithic age in an up to 1 m thick beach sediment sequence the archaeological material combined with sedimentological and shoreline displacement data limit the occupation time of the settlements to approximately 10 000 9700 14 c yr bp which makes them to one of the oldest known stone age settlements in southern norway there is no evidence of transgressions between 10 200 and 9500 14 c yr bp which could explain erosion of settlements and the presence of flint artefacts within the beach sediment sequence it is thus possible that the oldest settlements were flooded and eroded away by a slide generated tsunami artefacts and sediments were transported downslope into the sea and were subsequently reworked by waves during continued isostatic uplift

clean periodicity in secular variations of dolomite abundance in deep marine sediments abstract secular variations in dolomite abundance in deep marine sediments dadms indicate changing bio geochemical and sedimentary environments of deposition increasing dolomite abundances of the past indicate that past is the key to the present in this case spectral analyses of best available dadms record for the past 140 million years m y using a powerful clean spectral algorithm for the first time reveal a clean and statistically significant at 95 cl periodicity of about 24 5 1 5 m y maximum entropy spectral analysis mesa of the dadms record further confirms the above finding these results reinforce the general belief that changes in the earth s processes occurred in a cyclic manner interestingly 24 5 1 5 m y periodicity in the dadms record also compares extremely well within error limit with the marine mass extinction cycle 26 m y and lends credence to the cyclicity of marine processes it may be inferred that quasi periodic terrestrial records of sealevel climate and environmental changes coupled with some modest bio geochemical variations may have stimulated quasi periodic variations of dolomitization

the age and emplacement of obducted oceanic crust in the urals from smnd and rbsr systematics the urals contain a 2000 km belt of mafic ultramafic bodies the sm nd and rb sr systematics of two of these bodies the kempersai massif in the south ural mountains and the voykar syninsky ophiolite complex in the polar ural mountains have been examined these data confirm the hypothesis that these bodies represent fragments of pre collision oceanic crust and establish constraints on the nature and timing of events in the uralian orogeny two kempersai gabbros define sm nd internal isochrons of 397 20 my and 396 33 my with e nd t 8 7 0 6 and 8 4 1 3 respectively whole rock samples of pillow basalt diabase gabbros troctolite and a metasediment give sm nd values which lie on this isochron indicating that these rocks are genetically related and have an igneous crystallization age of 397 my whole rock samples of voykar syninsky diabase gabbros and clinopyroxenite give sm nd values which lie on or within 1 e unit of this isochron indicating an age and e nd t virtually identical to those of kempersai e nd t for the kempersai and voykar syninsky mafic samples range from 7 3 to 9 0 with an average value of 8 4 this indicates that the urals ophiolites are derived from an ancient depleted mantle source and are most plausibly pieces of the oceanic crust and lithosphere the fact that a metasediment has the same e nd 397 my as the other samples indicates derivation from an oceanic source with negligible continental input e nd t for the massifs is 1 5 e units lower than the average for modern morbs this may be due to the differential evolution of the morb source over the past 397 my and in conjunction with data for other ophiolites and mesozoic morb suggests that over the past 750 my the source for morb has evolved at a rate less than or equal to its rate of evolution averaged over the age of the earth initial 87 sr 86 sr ratios are highly variable ranging from e sr t 25 2 for a gabbro to 70 3 for a highly serpentinized harzburgite this reflects the effects of seawater alteration which is particularly strong on ultrabasic rocks we conclude that the long belt of mafic ultramafic rocks in the urals which includes the kempersai and voykar syninsky massifs represents segments of siluro devonian oceanic crust our igneous age for kempersai in conjunction with other age constraints suggest that these segments of oceanic crust formed at least 80 my before the collision that produced the urals

magnetostratigraphy susceptibility of the přidolian lochkovian silurian devonian gssp klonk czech republic and a coeval sequence in anti atlas morocco abstract the magnetosusceptibility event and cyclostratigraphy msec record for the p idolian lochkovian silurian devonian global boundary stratotype section and point gssp klonk prague basin czech republic is described and used to establish a magnetostratigraphy susceptibility profile for the gssp gssp msec data are summarized into three magnetozones msz the tma msz late p idolian with 13 msszs mssz the klonk msz latest p idolian and earliest lochkovian with 17 msszs and the voskop msz early lochkovian with 7 msszs the base of klonk mssz 2 is coincident with the base of lochkovian and the devonian the proposed magnetostratotype for the p idolian lochkovian boundary is supported by ms data from a nearby core through the gssp sequence and into the upper ludlow three additional mszs are recognized for the portion of the core sequence older than the gssp boundary sequence the extension of the mszs and msszs away from the proposed magnetostratotype is tested by comparison with a lochkovian sequence in the western sahara of southeastern morocco mszs are the result of global sea level fluctuations that alter base level and the pattern of erosion and influx of detrital paramagnetic mineral components into the marine environment large scale transgressive and regressive patterns interpreted from the msec data establish that the silurian devonian boundary in the barrandian region falls between a short lived transgressive pulse in the latest p idolian and an equally short lived regressive pulse in the earliest lochkovian msszs identified in the gssp and core sequences are the result of variation in climate cycles and the resulting periodicity can explained by either the 38 9 ka silurian and devonian equivalent of the modern 54 ka obliquity cycle or the eccentricity cycle of 106 ka periodicity use of the obliquity periodicity gives a duration for the barrandian lochkovian of 4 46 ma which agrees with the most recent geochronometric estimate of 4 5 ma for the lochkovian use of the eccentricity periodicity gives a duration for the barrandian lochkovian of 12 16 ma which agrees with the previous geochronometric estimates of 12 2 and 12 5 ma for the lochkovian in any case the cyclic nature of the msec data established by the msszs can be explained by variations in the rate of supply of weathered terrigenous paramagnetic grains to the marine system these variations in supply occurred due to climate changes resulting from the either the obliquity or eccentricity of the earth s orbit knowledge of the periodicity of lochkovian cycles in the barrandian area allows estimation of the rates of sediment accumulation the duration of fossil ranges and the rates of evolution depending on the choice of obliquity or eccentricity to explain the cyclicity in the barrandian lochkovian the estimated rate of sediment accumulation in the gssp outcrop averaged either 51 or 140 ka m the range of the graptoloid monograptus uniformis angustidens wholly contained within the lochkovian sequence at the gssp is also estimated at either 51 or 140 ka

landscape evolution and slide processes in a glacioisostatic rebound area a combined marine and terrestrial approach thick fine grained nonuniformly stratified deposits along a 20 km stretch coastline have been investigated using a combined marine and terrestrial approach the sediments were deposited rapidly in glaciomarine marine and submarine ice contact environments during the allerod and younger dryas periods rapid glacioisostatic rebound caused extensive modification of the landscape mainly by sliding slides in the area were affected by the bedrock morphology location and sedimentation rate of the glaciomarine sediments isostatic rebound presence of gas fluids in marine sediments and later river incision tides and groundwater flow spatial and temporal distribution of slide deposits in the marine stratigraphy and morphology of submarine and terrestrial features give detailed information of landscape evolution through time this is illustrated by conceptual profiles from three areas that explain the landscape evolution and changing processes during the rebound the most intensive slide activity both in frequencies and volumes and hence the most considerable landscape modification occurred early in the holocene period i e when the relative sea level fell most rapidly

a depositional record of deglaciation in a paleofjord late carboniferous pennsylvanian of san juan province argentina the role of catastrophic sedimentation the combination of high sediment supply rates and ample accommodation within fjords provides high resolution records of deglaciation ancient fjord fills provide the potential for three dimensional views of the evolution of depositional environments in response to changing sediment supply and base level through the deglacial process we describe the fill jejenes formation of a well exposed late carboniferous pennsylvanian glacial valley and its tributaries these deposits record the progressive marine flooding and infilling of topography by glacially derived sediments the geometry of the valley and its tributaries is controlled by the underlying lower paleozoic lithologies a deep valley with steep sides exists where the bedrock is massive limestones and a broader shallower valley exists where the bedrock is generally a fine grained olistostrome the valleys are locally floored with diamictites including both in situ tillites and remobilized diamictites in the trunk valley these are locally overlain by a small shallow water delta the major part of the valley fill consists of a 150 m thick mudstone dominated succession probably generated by plumes of glacial outwash containing numerous dropstones that decrease in abundance down the fjord the mudstones contain numerous thin sandstone and conglomerate turbidites that were supplied laterally via subaqueous gravel fans feeding in from the tributary valleys each of which has a distinctive clast suite related to the local subcrop the entire succession is overlain by 300 m of sandy turbidites of which the upper part includes large mass transport complexes intercalated within the succession in the trunk valley are structureless graded silty mudstones lacking dropstones but with abundant large wood fragments close to the steep western margin of the trunk valley each of these massive mudstones is underlain by a slump or debris flow locally containing meter scale blocks of ordovician limestone from the valley side we interpret these as a consequence of rockfalls from the steeper valley sides triggering debris flows on the subaqueous fjord slopes we suggest that large solitary waves were generated as the rockfalls entered the water traveling along the fjord and stripping vegetation from the shoreline large amounts of mud and silt were thrown into suspension during these events and subsequently settled from suspension to form the structureless graded beds these deposits and other mass flow deposits within the succession emphasize the potential importance of catastrophic sedimentation within deglacial successions

opening of the grenada back arc basin and evolution of the caribbean plate during the mesozoic and early paleogene abstract geological and geophysical data indicate that the grenada basin was presumably created during the paleocene by sundering of a proto eastern caribbean arc into a remnant arc to the west aves swell and an active arc to the east lesser antilles ridge grenada basin spreading is thought to have been penecontemporaneous with the creation of the yucatan basin located at the opposite side of the caribbean sea i suggest that a continuous mesozoic caribbean arc m c a including the greater antilles the aves lesser antilles system and the aruba blanquilla chain netherland venezuelan antilles was initiated in the pacific probably about 130 120 ma ago its arrival in front of and its subsequent motion inside the central atlantic tethyan seaway caused the opening of both yucatan and grenada basins which occurred at the two initial points of contact with the north and south american cratons in contrast to the style of many other island arcs this back arc spreading event occurred only once in the long history of the m c a the lesser antilles appear to be the oldest currently active intra oceanic island arc

age and geochemistry of late precambrian sediments of the hammamat series from the northeastern desert of egypt willis k m stern r j and clauer n 1988 age and geochemistry of late precambrian sediments of the hammamat series from the northeastern desert of egypt precambrian res 42 173 187 late precambrian crustal evolution in the northeastern desert of egypt culminated in a major episode of strong extension accompanied by bimodal igneous activity and deposition of clastic sediments in restricted terrigenous basins these sediments known as the hammamat series record the uncovering of the evolving crust of the region we have undertaken petrographic geochemical and rb sr and k ar geochronologic studies of hammamat samples collected along a single traverse the lower half of a 400 m thick section consists of coarse detritus shed from nearby ensimatic terranes while the upper half was derived from rapid reworking of bimodal igneous rocks similar to those of the dokhan volcanics and pink granites units that are preserved within the region rb sr whole rock analyses give an 8 point isochron age of 585 15 ma with an initial stsr sr of 0 70323 0 00013 interpreted to approximate closely the time of sedimentation this is very similar to the k ar ages of the coarser clay fractions 2 0 5 m 588 567 ma this result is consistent with stratigraphic considerations and other geochronological studies indicating that hammamat deposition occurred at 590 ma rb sr analyses of leached and unleached size fractions indicate thermal resetting at 524 17 ma accompanied or followed by fluxing of a radiogenic sr rich pore fluid stsr s sr 0 7124 this is further indicated by k ar ages of the 0 2 0 5 ttm size fraction of 542 532 ma

early cretaceous uplift in the ellsworth mountains of west antarctica apatite fission track analysis of samples covering a 4 2 kilometer vertical section from the western flank of vinson massif antarctica s highest mountain indicates that the ellsworth mountains were uplifted by 4 kilometers or more during the early cretaceous following the initial separation of east and west gondwana and accompanying the opening of the weddell sea relief of at least 1 8 kilometers has persisted in the ellsworth mountains since the early cretaceous and a maximum of 3 kilometers of uplift has occurred since that time

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

palynology and geochronology of eocene beds from cheslatta falls and nazko areas central british columbia early tertiary lavas and sediments were collected from two areas west and south of prince george british columbia and processed for k ar dating and palynoassemblages samples from cheslatta falls gave k ar dates of 36 5 and 37 7 ma and yielded a palynoassemblage very similar to that from the jackson group in alabama and mississippi this late eocene assemblage is interpreted as having developed in a humid subtropical environment prior to a climatic cooling that we believe should be assigned to early oligocene time the tertiary lavas and sediments from the nazko area west of quesnel gave three middle eocene dates and over 60 species of palynomorphs these correlate with other rocks and palynoassemblages of kamloops group equivalents that occur southward across the international boundary and north to latitude 55 n the paleoclimate was wet and in the range of very warm temperate to humid subtropical

a petrologic comparison of triassic plutonism in the san gabriel and mule mountains southern california triassic magmatism in the southwest u s cordillera forms a semicontinuous magmatic arc extending from northwestern nevada to southeastern california quartz monzodioritic and quartz monzonitic rocks and associated diorites and granites are widespread in southeastern california and we suggest that these rocks represent exposure of a structurally deeper part of the triassic arc where it was emplaced into comparatively thick proterozoic crust elemental and isotopic data suggest that triassic quartz monzodiorites and quartz monzonites in the mule and san gabriel mountains were derived from a relatively undepleted nonradiogenic mafic lithospheric source with virtually no upper crustal interaction very limited data for associated triassic diorites indicate a wide range in composition and a surprisingly radiogenic isotopic signature younger triassic granites record a strong geochemical signature of interaction with continental crust including inherited zircon and high initial sr ratios but comparatively less radiogenic pb isotopic compositions the major and trace element geochemistry of late triassic plutonic rocks in southeastern california is similar in many respects to alkalic components of the triassic arc in the mojave desert however contemporaneous rocks farther north have a calc alkalic signature perhaps reflecting the variation in age and composition of lithosphere across which the triassic arc was constructed

quaternary erosion and depositional processes western norwegian fjords norwegian channel and north sea fan abstract the southern norwegian fjords the northern north sea and north sea margin represent major pathways of sediment flux from the southern part of fennoscandia to the deep sea basin volumes genesis and chronology of the temporary and semi permanent quaternary sediment repositories are reviewed the fjord infill is dominated by sediments from the last deglaciation 150 km 3 the norwegian channel is occupied by tills and glaciomarine marine sediments 5000 km 3 the north sea fan comprises glacially fed debris flow fingers lobes constituting 80 of deposits in the mid to late pleistocene together with hemipelagic and mass transport slide sediments totalling 15 000 km 3 the norwegian channel represents a dynamic transport conduit whereby during peak glaciation a fast flowing ice stream has drained large parts of the southern fennoscandian ice sheet several times the sediment flux to the deep sea is temporarily interrupted between glacials when stored in the channel but under glacial maxima the channel is probably largely bypassed with material transported as subglacial load and deposited as debris flows on the north sea fan sediments on the fan have a much longer storage time numerous glaciation cycles but are further transported to the deep sea in large slide events the volume of quaternary sediments found along this sediment pathway plus that which slid to the deep sea total at least 25 000 km 3 corresponding to an averaged 120 m of erosion across southern norway

40ar 39ar mineral ages from the oki metamorphic complex oki dogo southwest japan implications for regional correlations abstract the oki metamorphic complex exposed in the oki dogo islands consists predominantly of psammitic and pelitic gneisses with subordinate amphibolite and rare calcareous gneiss the oki gneisses were regionally metamorphosed to general amphibolite facies conditions with local development of granulite facies assemblages peak metamorphic conditions of c 800 c have been suggested hornblende concentrates from amphibolites collected within the oki metamorphic complex record 40 ar 39 ar isotope correlation ages of 199 192 ma these are interpreted to date the post metamorphic cooling through temperatures required for intracrystalline retention of argon c 500 c muscovite concentrates record 40 ar 39 ar plateau ages of 167 168 ma these are interpreted to date post metamorphic cooling through appropriate closure temperature of muscovite c 400 375 c combined with the previously reported geochronological data the oki metamorphic complex appears to have experienced peak metamorphic conditions at c 250 ma subsequently it cooled and was exhumed at the earth s surface at c 90 ma with cooling rate of c 5 c ma the oki metamorphic complex records a similar prograde metamorphic event as the hida metamorphic complex exposed in central japan the cooling and exhumation rates of the hida metamorphic complex were significantly more rapid compared with the oki metamorphic complex and they were exhumed with extensively intruded jurassic granites funatsu granites

approximate paleomagnetic poles for some of the new england seamounts abstract paleomagnetic pole positions were estimated for several of the new england seamounts by a simple dipole method computer poles are in agreement with poles determined by others for several seamounts in the chain using three dimensional modeling collectively the poles plot in a swath which follows the late mesozoic polar wander path across northern siberia to the bering strait it is shown that for relatively simple seamount geometries and dipole like magnetic anomalies inclinations and declinations determined by the dipole method agree within a few degrees with those found by three dimensional methods paleopole determinations by either method may be degraded by interfering neighboring anomalies and other effects but the five poles considered best determined are consistent with the overall distribution of poles the distribution is not consistent with a model involving a hot spot origin or with geologic evidence suggesting origin during a brief time within the cretaceous normal interval statistically the poles are in much better agreement with the hypothesis that the seamounts are the same age as the sea floor underlying them

high resolution local moho determination using gravity inversion a case study in sri lanka the seismic data incorporated in global moho models are sparse and therefore the interpolation of global moho depths on a local area may give unrealistic results especially in regions without adequate seismic information gravity inversion is a useful tool that can be used to determine moho depths in the mentioned regions this paper describes an interactive way of local moho depth determination using the gravity inversion method constrained with available seismic data before applying inversion algorithms the bouguer gravity data is filtered in various stages that reduce the potential bias usually expected in moho depth determination using gravity methods with constant density contrast assumption a test area with reliable seismic data is used to validate the results of moho computation and subsequently the same computation procedure is applied to the sri lankan region the results of the test area are in better agreement with seismically determined moho depths than those obtained by global moho models in the sri lankan region moho determination reveals a fairly uniform thin crust of average thickness around 20 km the overall result suggests that our gravity inversion method is robust and may be suitable for local moho determination in virgin regions especially those without sufficient seismic data

submarine slides in glaciomarine sediments in some western norwegian fjords abstract submarine slides from four western norwegian fjords fjaerlandsfjord and ardalsfjord in the sognefjord and nordfjord and romsdalsfjord are studied sparker and high resolution seismic profiles are used to illustrate the thickness morphology and internal structure of the primary material as well as of the accumulated slides sediment cores are studied to calibrate the acoustic signals acoustic lamination is thought to represent sequences of variable density or some of the zones of fine sand and silt laminae which have acted as sliding planes these rapidly deposited layers constitute underconsolidated zones that are susceptible to liquefaction causing sliding of the overlying material along bedding planes or faults the morphology and structure of the slides are in some cases very similar to that of the mass movements described from continental slopes a 25 m deep and 1 km 2 wide plunge pool is formed in the sognefjord at the bottom of a 800 m high and 25 steep slide path down from the fjaerlandsfjord most of the slides are ancient but one slide increasing the fjord depth in an area of the inner nordfjord by 55 m most probably took place in 1967 the volumes of the slides are in the order of 3 30 10 6 m 3

dating transcurrent terrane accretion an example from the meguma and avalon composite terranes in the northern appalachians the polygenetic minas geofracture separates the meguma and avalon composite terranes of the maritime appalachians dynamically recrystallized muscovite and biotite occur within d3 shear zones which developed during dextral movement along the geofracture these record 40ar 39ar plateau ages between circa 360 and 370 ma comparable plateau ages are recorded by micas within undeformed portions of granitic plutons and their low pressure contact metamorphic aureoles these are similar to u pb ages previously reported for igneous monazite therefore indicating relatively rapid postmagmatic cooling at shallow crustal levels the d3 fabrics were superimposed on earlier s1 structures which formed during initial amalgamation of the meguma and avalon composite terranes whole rock slate phyllite samples collected outside high temperature portions of the plutonic contact aureoles yield 40ar 39ar plateau ages which correspond to groupings of circa 400 395 ma 390 385 ma and 380 375 ma these are interpreted to date diachronous formation of the s1 fabrics and concomitant low grade regional metamorphism in the circa 25 ma between initial amalgamation and granitic plutonism it is inferred that there was a slow rise of isotherms through the crust as a result of overthrust tectonic thickening this led to crustal melting and the production of widespread granitic magmas which were emplaced immediately prior to d3 dextral shearing

the indian ocean gravity low evidence for an isostatically uncompensated depression in the upper mantle the broad gravity low in the equatorial indian ocean south of sri lanka is the largest and most striking feature in the gravitational field of the earth the most negative long wavelength free air gravity anomalies are found there and the sea surface geoid lies more than 100 meters below the best fitting ellipsoid we propose a model of the lithosphere and upper mantle which accurately predicts the observed free air gravity and geoid elevation this model is consistent with bathymetry and sediment thickness data and suggests that the crust south of india currently floats as much as 600 meters lower than would be expected if the region were isostatically compensated this residual depression of the crust is apparently confirmed by observations of ocean depth an uncompensated depression is consistent with the downgoing arm of a convection cell and also with the presence of a mechanical wake left in the upper mantle behind india as it traveled toward asia

fjord stratigraphy and processes evidence from the ne atlantic fensfjorden system fjords commonly hold sediment basins with high temporal resolution that mirror land and marine based processes and depositional environments during a glacial interglacial cycle here we present topas seismic profiles with a vertical resolution of 30 cm bathymetric records and a gravity core from fensfjorden west norway which allow a detailed study of sedimentary processes and depositional environments in a ne atlantic fjord system fensfjorden hosts a sediment volume of 0 70 km3 and the sediment basins evolved reach a maximum thickness of 100 m the basins are characterized by a lower acoustically well laminated glacimarine unit of allerod and younger dryas age this unit is overlain by several acoustically transparent lenses interpreted to be slide debrites we suggest these slide debrites to be a result of recurrent mass failures that occurred between 11 500 and 2100 cal a bp a thin late holocene hemipelagic unit drapes the slide debrites during the late holocene the sedimentation rates in fensfjorden decreased from 0 110 to 0 040 cm a 1 and two turbidity currents occurred in the 2040 1190 cal a bp time period this ability to map fjord processes in more detail has furthermore made it possible to revise the established stratigraphical framework for ne atlantic fjords copyright 2013 john wiley sons ltd

geologic framework of the offshore region adjacent to delaware abstract several multichannel common depth point cdp seismic reflection profiles concentrated in the area of the entrance to delaware bay provide a tie between the known onshore geology of the coastal plain of delaware and the offshore geology of the baltimore canyon trough the data provide a basis for understanding the geologic framework and petroleum resource potential of the area immediately offshore delaware our research has focused on buried early mesozoic rift basins and their geologic history assuming that the buried basins are analogous to the exposed newark supergroup basins of late triassic early jurassic age the most likely possibility for occurrence of hydrocarbon source beds in the area of the landward margin of the baltimore canyon trough is presumed to be lacustrine organic rich shales probably present in the basins although buried basins mapped offshore delaware are within reach of drilling no holes have been drilled to date therefore direct knowledge of source reservoir and sealing beds is absent buried rift basins offshore delaware show axial trends ranging from nw se to nne ssw seismic reflection profiles are too widely spaced to delineate basin boundaries accurately isopleths of two way travel time representing basin fill suggest that structurally the basins are grabens and half grabens as shown on seismic reflection profiles bounding faults of the basins intersect or merge with low angle fault surfaces that cut the pre mesozoic basement the rift basins appear to have formed by mesozoic extension that resulted in reverse motion on reactivated basement thrust faults that originated from compressional tectonics during the paleozoic computer plotted structure contour maps derived from analysis of seismic reflection profiles provide information on the burial history of the rift basins the postrift unconformity bevels the rift basins and in the offshore area mapped ranges from 2000 to 12 000 m below present sea level the oldest postrift sediments that cover the more deeply buried rift basins are estimated to be of middle jurassic age bajocian bathonian the probable time of opening of the atlantic ocean basin and onset of continental drift about 175 180 m y ago by late oxfordian early kimmeridgian time the less deeply buried basins nearshore delaware had been covered a time temperature index of maturity plot of one of the basins indicates that only dry gas would be present in reservoirs in synrift rocks buried by more than 6000 m of postrift sediments and in the oldest bathonian callovian postrift rocks less deeply buried synrift rocks landward of the basin modeled might still be within the oil generation window

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

occurrence and origin of submarine plunge pools at the base of the us continental slope high resolution bathymetric data from the new jersey and californian continental margins show a marked depression running along parts of the base of the continental slope detailed analysis reveals that the depressions are a series of discrete plunge pools with associated downslope topographic ramparts we have used new bathymetric data to create our own data base of over 150 examples and systematically analyse plunge pool morphology and location previous observations of plunge pools have been sparse plunge pools are up to 1100 m wide and 75 m deep with a mean diameter of 400 m and a mean depth of 21 m plunge pools only occur where there are sharp decreases in slope of more than 4 and are well developed where changes in slope exceed 15 we propose plunge pools can be created by two mechanisms firstly they may be due to reduced bed shear stress downstream of hydraulic jumps in submarine sediment laden density flows that causes the deposition of bedload and the creation of a sediment bar this bar then defines the downslope margin of a pool secondly the impact of high momentum sediment laden density flows can excavate a depression as has been observed for subaerial snow avalanches sediment deposited downslope of these impact pools is very poorly sorted and partly derived from erosion within the pool both mechanisms influence whether turbidity currents are generated from high density sediment laden density flows influence whether depositional flows are channelised and have implications for base of slope facies models

western norwegian fjord sediments age volume stratigraphy and role as temporary depository during glacial cycles abstract the sediments in the western norwegian fjords are described chronologically qualitatively and quantitatively by means of seismic profiling and correlation with dated terrestrial sediments along the fjords five chronostratigraphic units i v are proposed for the fjord sediments using the well established quaternary stratigraphy in the area sediment volumes of the main fjords are calculated using a dense seismic grid combined with map analyses approximately 150 km 3 of sediments are present in the fjords between 59 63 n ninety percent of this material is considered to be deposited during deglaciation of the last weichselian ice sheet less than ten percent of the fjord sediments in this area is older than the last glacial weichselian maximum both glacial and glaciofluvial processes are active in emptying the fjord basins and transporting the sediments to the continental shelf and slope during glaciations

mass accumulation rates in asia during the cenozoic summary this work establishes estimates of mass accumulation rates in 18 mostly offshore sedimentary basins in asia since the beginning of the cenozoic 66 ma the estimates were derived from isopach maps cross sections and drill holes or stratigraphic columns assuming regional similarity of the strata average solid phase volumes and accumulation rates were calculated for nine epochs approximately corresponding to geological periods palaeocene 66 58 ma eocene 58 37 ma oligocene 37 30 and 30 24 ma miocene 24 17 17 11 and 11 5 ma pliocene 5 2 ma and quaternary 2 0 ma these rates shed new light on the geological history of asia since the onset of the collision of india with asia 50 ma the overall average accumulation rates curve for asian sedimentary basins since the beginning of the tertiary shows an exponential form with slow accumulation rates less than 0 5 106 km3 myr 1 until the beginning of the oligocene more than 15 myr after the onset of the collision from the oligocene onwards rates increase quickly in an exponential manner reaching their maximum values in the quaternary more than 1 5 106 km3 myr 1 from these observations we suggest that extrusion and crustal shortening are complementary processes that have been successively dominant throughout the india eurasia collision history at smaller scales one may distinguish between independent histories at the subcontinental and basin scales this permits a comparison of the relative importance of tectonic and climatic erosion processes affecting the different mountain belts of asia during the cenozoic

episodic nature of the cenozoic marine record various suggestions of a geological periodicity of 2 7 m y have been made in the literature if such periods exist they fall between the earth orbital milankovitch periods and the solar system s galactic oort periods and have no known internal or external source to study the period range 1 10 m y four types of cenozoic marine data were subjected to formal time series analysis no significant periodicities were found and only a mean interval between global marine episodes 5 2 m y could be defined possible causes of the variability are discussed

morphometric analysis of plunge pools and sediment wave fields along western great bahama bank abstract a systematic assessment of morphometric parameters of over 200 plunge pools along the steep escarpment base of western great bahama bank and 2000km2 of sediment wave fields of upslope migrating cyclic steps documents the importance of cascading density currents for sedimentation on the slope the abrupt downslope termination of the holocene mud wedge with the cyclic steps shows that strike parallel bottom currents interacting with the off bank currents are responsible for slope sediment distribution the plunge pools and sediment waves were generated by density cascading and both are related to a hydraulic jump caused by two gradient changes along the slope profile the bedforms highlight both the erosional and depositional nature of this current regime which is controlled by slope gradient and the directional confinement by either grooves on the steep escarpment or gullies on the middle to lower slope the 20 m deep plunge pools are ellipsoidal with an average width of 211 m and length of 283 m but variations between 80 360 m and 100 650 m for width and length occur they are caused by an average gradient break of 16 on the cemented upper slope gradient breaks of as low as 2 are reported to be sufficient to scour a plunge pool like the ones in the study area but higher gradient breaks between 10 and 20 are quite common for consistent plunge pool development a second gradient break further down slope changes flow conditions for the generation of cyclic steps with asymmetric waveforms of 4 m high average in large wave fields in the entire the study area orientation is mainly orthogonal to the main slope direction but wave lengths and sinuosity vary depending on the morphologic location of the wave field the comparison with sediment wave fields with similar geometries or in similar environments shows that flow reconstruction based on the wave height and wave length alone along with a characterization of sediment grain size however yields non unique results and is site specific

a high resolution seismic stratigraphy from a scottish sea loch and its implications for loch lomond stadial deglaciation a detailed high resolution seismic stratigraphy calibrated by core data and terrestrial geomorphological mapping has been constructed for loch ainort isle of skye this study has provided a palaeoenvironmental history of the area as well as important corroborative evidence for the stepped deglaciation of the loch lomond stadial ice field on skye the ainort glacier reworked pre loch lomond glacial deposits terminating in a grounded tidewater ice front potentially 800 m beyond the previously extrapolated limit the first stage of deglaciation was characterised by the formation of de geer moraines indicative of a period of interrupted retreat the second phase by contrast produced hummocky relief with sporadic linear moraines suggesting periods of uninterrupted retreat with occasional stillstands readvances paraglacial reworking of terrestrial slopes resulted in the deposition of thick subaqueous debris flows which graded into fluvioglacial dominated sediments and ultimately modern fjordic deposits the identification of an initial period of active retreat punctuated by numerous readvances correlates directly with the terrestrial record however the offshore stratigraphy suggests that although the second phase was dominated by uninterrupted retreat occasional stillstands readvances did occur

modern deposition rates and patterns of organic carbon burial in fiordland new zealand fjords are disproportionately important for global organic carbon oc burial relative to their spatial extent and may be important in sequestering atmospheric co2 providing a negative climate feedback within fjords multiple locally variable delivery mechanisms control mineral sediment deposition which in turn modulates oc burial sediment and oc sources in fiordland new zealand include terrigenous input at fjord heads sediment reworking over fjord mouth sills and landslide events from steep fjord walls box cores were analyzed for sedimentary texture sediment accumulation rate and oc content to evaluate the relative importance of each delivery mechanism sediment accumulation was up to 3 4 mm yr in proximal and distal fjord areas with lower rates in medial reaches x radiograph and 210pb stratigraphy indicate mass wasting and surface sediment bioturbation throughout the fjords sediment accumulation rates are inversely correlated with oc spatial heterogeneity in sediment depositional processes and rates is important when evaluating oc burial within fjords

late cenozoic tectonic evolution of southwestern california we synthesize available geologic and geophysical data from southern california and adjoining areas in order to develop a reconstruction of the tectonic evolution of the southern coast ranges western transverse ranges and borderland regions of california since 30 ma premises include specified relative plate motions for times prior to 10 5 ma and after 3 ma a mid tertiary bight in the continental margin of southern california midcrustal detachment faults under much of california and adjoining regions rotation of the western transverse ranges about an eastern pivot and specified fault displacement histories prior to 18 ma about 90 of the tangential component of pacific north america relative motion was accommodated on an offshore dextral fault system near the toe of the continental slope from 18 ma to 5 5 ma dextral slip was accommodated predominantly on the offshore system but also on a second inboard system that included the san andreas fault fault bounded crustal blocks between the offshore and inboard fault systems underwent translation rotation and extension from 18 ma to 11 5 ma but not from 11 5 ma to 5 5 ma since 5 5 ma dextral slip has been accommodated predominantly on the inboard fault system dextral slip ceased on the offshore fault system north of the transverse ranges but continues on faults west of or within baja california the san gregorio san simeon hosgri fault system has accommodated less than 5 km of the late cenozoic dextral slip the distribution of dextral displacement in the plate boundary zone has been controlled by abrupt jumps of the position of a southern triple junction and to a lesser degree changes in magnitude of pacific north america relative motion based on our reconstuction the tangential component of pacific north america relative motion was 90mm yr for the period 10 5 ma to 5 5 ma and 60mm yr for the period 5 5 ma to 3 ma

impact of synsedimentary metre scale normal fault scarps on sediment gravity flow dynamics an example from the gres d annot formation se france abstract synsedimentary faults result in the direct interaction between tectonic and sedimentary processes at similar spatio temporal scales sedimentological analysis of sediment laden gravity flows in the northern part of the gres d annot formation sanguiniere sub basin col de la moutiere tete ronde has revealed the presence of fault scarps of metre scale height these synsedimentary fault scarps were sufficient to disturb the sediment gravity flow dynamics resulting in i a strong variation of the erosive behaviour of a concentrated flow and ii the transformation of a strongly stratified laminar hyperconcentrated flow into a turbulent flow in short distance less than 500 m these disturbances develop without the flows being deviated by the fault scarps but produce great facies heterogeneity the least homogeneous facies mixing sand and clay being localized on the upstream obstacle side the most homogeneous massive sand downstream

evidence for an earthquake triggered basin collapse in saguenay fjord canada abstract on february 5 1663 perhaps the largest earthquake ever witnessed in eastern north america struck the saguenay fjord basin with such force that landslides and submarine slides were triggered over a wide region over 3 km 3 of clayey holocene sediments collapsed from the margins of the fjord resulting in amalgamated debris flow and slide deposits that covered much of the basin floor these deposits reached thicknesses of up to 100 m and extended over an area of 100 km 2 the ambient seafloor was compressed under the impact and load of these debris masses and or liquefied under the cyclic stress of the seismic wave a 0 2 km 3 landslide also occurred at this time blocking the saguenay river and possibly facilitating an extra large spring freshet discharge biotracers planktonic and benthic foraminifera arcellaceans pollen and wood in conjuction with mass physical properties of sediment cores and high resolution seismic and sidescan profiler data have been used to identify local and distal sediment sources including their original water depth of deposition and their subsequent mode of mass gravitational transport the landslide material was eroded by the river and super elevated sediment concentrations are considered responsible for a long lasting 28 days turbidity current that entered the saguenay fjord depositing a single 0 3 km 3 turbidite the 2 to 10 m thick turbidite is considered to have been self igniting having eroded into the surface of the collapsed basin debris paleo hydraulic calculations suggest that this turbid flow averaged 0 45 m s and reached a flow thickness of 30 m

post glacial depositional environments in a mid high latitude glacially overdeepened sea loch inner loch etive western scotland abstract a high resolution seismic and gravity coring survey has been conducted on inner and part of outer loch etive a 30 km long 150 m deep sea loch on the west coast of scotland the seismic reflection profiles reveal a 30 60 m thick sediment pile that has accumulated on the floor of the loch since the last younger dryas stadial glacial re advance 11 10 ka bp four seismic facies have been identified grouped into two seismic sequences a and b which are separated by a distinct reflector termed e1 a highly reflective facies is interpreted as direct river input an acoustically well laminated draped facies interpreted as fine grained river sediments and a well laminated to transparent facies interpreted as glaciomarine and glaciolacustrine throughout the loch methane gas rich sediments occur producing a chaotic seismic facies the transition from glacially influenced to river dominated deposition is displayed by the seismic reflector e1 core analysis identified eight lithofacies the oldest sediments are grey muddy sands and olive sandy silts overlain by younger laminated greeny grey muddy sand and greeny grey and greeny black homogeneous watery sandy mud abundant shell material is present throughout notably the bivalve arctica islandica from which a 14 c age of 9490 90 yr bp was obtained from the laminated greeny grey muddy sands the sediments are interpreted as being of glaciomarine and glaciolacustrine younger dryas to early mid holocene and more modern riverine derived origin mid latest holocene

stratigraphic implications of palaeomagnetic data from honduras summary palaeomagnetic results from mainly cretaceous rocks in honduras delineate a distinctive apparent polar wander path apwp which is well suited for magnetostratigraphy the apwp is based on palaeomagnetic data from palaeontologically dated units in the established stratigraphic column and three radiometrically dated intrusions the ages and stratigraphic positions of sedimentary units whose stratigraphic assignments have been debated can be inferred by comparing their palaeornagnetic pole postion with the known apwp the results demonstrate the usefulness of magnetostratigraphy for resolving stratigraphic problems in the absence of fossils or marker beds and for areas of discontinuous exposures for regional interpretations the most important conclusion is that strata in honduras that have been assigned to the todos santos formation were not deposited on the same tectonic plate as the todos santos formation of guatemala and southern mexico there is no evidence that the honduran todos santos strata are depositionally related to the true todos santos formation the name todos santos formation should be abandoned in honduras and for the entire chortis block

holocene mass transport activity and climate in outer isfjorden spitsbergen marine and subsurface evidence the analyses of high resolution seismic data swath bathymetry data and sediment cores from the basin svensksunddjupet in isfjorden spitsbergen reveal the deposits of repeated slope failures most of the slope failures occurred during three periods at c 9650 cal bp 8350 8200 cal bp and 3000 cal bp suggested factors causing instability of the slopes include earthquake activity resulting from rapid isostatic uplift excess pore pressure caused by relative sea level fall and or the presence of gas as well as climatic changes mass transport deposits at the mouth of an incision at the southern slope of svensksunddjupet are suggested to mainly relate to runoff from the land based glacier vardebreen the increase of the mass transport activity may indicate that vardebreen either formed or increased in size at c 7000 cal bp

new paleomagnetic results from northern china collision and suturing with siberia and kazakhstan abstract we report new results from our paleomagnetic studies of the inner mongolia autonomous region in northeastern china and the xinjiang autonomous region in northwestern china primary magnetizations are isolated in tertiary cretaceous late jurassic and late permian rocks and secondary components of magnetization of late jurassic and recent ages are seen in strata of inner mongolia western junggar basin and part of the tarim block suffered widespread complete tectono thermal remagnetization at about 280 ma permian the paleomagnetic evidence suggests that the sampled areas in inner mongolia have been part of the north china block at least since late permian time and the junggar block collided with the tarim block by late permian time our own paleomagnetic results together with available data from other parts of eastern eurasia suggest a tectonic model in which kazakhstan europe and siberia collided with each other and formed the europe siberia kazakhstan plate eur sib kaz in late permian time to the east mongolia outer mongolia inner mongolia and the north china block were also wedged together forming the mongolia north china plate mon nc by this time these two composite continental plates were not a stable unit in the late permian the geometrical relationship of the paleomagnetic poles for these two plates suggests that collision initially occurred in the late permian near the western end 50 n 75 e of the southern siberian fold belt and progressed eastward as the mon nc plate rotated and clockwise about 117 relative to the eur sib kaz plate during the early mesozoic suturing and rotation were probably complete by the late jurassic significant relative motion between the tarim and siberia blocks continued from early triassic to late jurassic as tarim moved northeastward 1400 km relative to siberia

heat flow in jane basin northwest weddell sea the jane basin is a marginal basin situated immediately to the east of the south orkney microcontinent in the northwest section of the weddell sea thirty five heat flow measurements made in the jane basin ranged in value from 67 5 4 3 to 92 1 3 0 mw m2 excluding values that were corrected for tilting or were on the very edge of the basin the remaining 28 values range between 75 0 8 0 and 84 6 9 1 mw m2 magnetostratigraphy on the recovered core from ocean drilling program hole 697 which was drilled in jane basin to a depth of 322 m allowed sedimentation rates to be calculated back to 4 5 ma single channel seismic reflection data from rss shackleton allowed estimations of total sediment thickness for the jane basin to be made we calculate that the measured heat flow is only 86 89 of the actual heat flow as a result of sedimentation heat generation in the sediments contributes 1 5 1 9 mw m2to the total heat flow the corrected heat flow gives an age for the jane basin of between 25 and 32 ma from age versus heat flow comparisons similar to the age determined from basement depth the scotia sea located to the north of jane basin and the south orkney microcontinent has been dated as anomaly 10 30 ma and younger our calculated age for the jane basin would indicate that it may have been created prior to the initiation of seafloor spreading in the scotia sea evidence from major plate motions indicate that antarctica began to rotate clockwise away from south america at about 65 ma such motion may have triggered subduction along the southeast side of jane bank and the opening of jane basin as a back arc basin subduction at jane bank ended at anomaly 6a time 22 ma as evidenced by the age of the identified magnetic anomalies on the antarctic plate found immediately to the east of jane bank we conclude that jane basin opened prior to the opening of the scotia sea and that the spreading center that opened jane basin may have jumped to the scotia sea and produced the seafloor spreading there

polyorogenic 40ar 39ar mineral age record within the kalak nappe complex northern scandinavian caledonides the kalak nappe complex is composed of variably retrogressed middle proterozoic basement and imbricated polydeformed metasedimentary cover successions which at least in part appear to have originated within the late proterozoic early palaeozoic baltoscandian miogeocline mafic alkaline plutons seiland igneous suite occur within uppermost structural units of the nappe complex 40 ar 39 ar incremental release mineral ages suggest local differences in tectonothermal evolution within the kalak nappe complex post metamorphic cooling dates of c 490 ma are locally recorded by hornblende within the structurally highest tectonic unit suggesting significant orogenic activity occurred during and or immediately prior to the arenig a distinctly later metamorphic overprint occurred in the silurian and was of sufficient magnitude to everywhere rejuvenate ar systems in muscovite and nepheline and locally in hornblende this was followed by relatively rapid post metamorphic cooling through hornblende and muscovite ar closure temperatures between c 425 and 415 ma the complex tectonic history suggested for the kalak nappe complex is generally similar to that previously outlined for the central swedish caledonides together 40 ar 39 ar mineral ages from these widely separated areas indicate that significant tectonothermal activity occurred along the baltoscandian margin prior to the silurian this activity appears at least in part to have been associated with formation of a late cambrian early ordovician accretionary wedge over a westward dipping subduction zone during initial closure of the iapetus ocean

sedimentary processes and depositional environments in glaciated fjord systems evidence from nordfjord norway abstract fjords situated in past or present glacial regimes represent important repositories between land masses source systems and the open oceans sink systems newly collected topas high resolution seismic profiles from the previously glaciated nordfjord system on the west coast of norway reveal sedimentary processes and depositional environments within fjords in more detail than before the seismic data show that the fjord basins are characterised by a well laminated lower unit that is overlain by acoustic transparent lensoidal bodies we infer the lower unit which is up to 350 m thick to be composed of glacimarine sediments the transparent bodies represent up to 0 25 km 3 large slide debrites that comprise 14 c yr bp c 15 000 cal yr bp during the last deglaciation the entire nordfjord system was ice free for a short time period before the 1000 year long younger dryas readvance halted the main fennoscandian deglaciation and over ran the eastern part of nordfjord in contrast to the last glacial maximum we suggest that the sediments in the ice covered fjord basins were preserved during younger dryas the rapid isostatic adjustments accompanying the withdrawal of the younger dryas ice sheet promoted conditions for failures we relate the identified nordfjord slide bodies to this paraglacial environment this implies that the acoustic well laminated glacimarine fjord unit has been deposited in about 2000 yr and that sediment rates as high as 20 cm yr have existed during deposition

seismic refraction crustal study along the sognefjord south west norway employing ocean bottom seismometers summary this paper presents a crustal structure model derived from an extensive oceanbottom seismographic refraction experiment conducted on a 150 km profile line along the sognefjord south west norway the main part of the profile was located in the western gneiss region wgr which is characterized by deformation and metamorphic overprinting during the caledonian orogeny the western and eastern ends of the profile crossed the solund devonian basin and the allochthonous unit of the jotun nappe respectively within the wgr the fjord bottom is covered with 200 250m thick glacial sediments with a low p wave velocity 1600m and a high poisson s ratio 0 48 0 49 the p wave velocity and velocity gradient of the uppermost crystalline basement is 6 05 km s and 0 03 s respectively the poisson s ratio within the upper 12 km crust has an almost constant value of 0 26 in spite of the westward increase in the caledonian metamorphism this may indicate that the uniform bulk composition of the wgr is the predominant factor on the seismic wave velocities rather than the fossil caledonization the p wave velocity and the poisson s ratio in the lower crust deeper than 19 20 km are 6 6 7 0 km s and 0 27 respectively which are comparable to those for an amphibolitic granulitic rock type the moho gently deepens eastward from 31 to 36km the velocity contrast at the moho is large 1 0 1 2kmsp1 as seen in the other areas of the wgr at the eastern end of the profile the jotun nappe the p wave velocity at the uppermost basement shows a higher value 6 20 km s than that within the wgr 6 05 km s representing relatively mafic rock components in the jotun nappe such a lateral velocity change becomes obscure at depths deeper than 6 7km which indicates that the detachment between the wgr and the jotun nappe is situated at a very shallow depth this strengthens the hypothesis that the wgr is a westward extension of the precambrian baltic shield buried beneath the caledonian nappes a mid crustal interface with a velocity jump of 0 2 0 3 km s was observed at a depth of 19 20 km this interface disappears under the western part of the profile indicating the intense deformation of the wgr during the caledonian orogeny

can depression of the core mantle interface cause coincident magsat and geoidal lows of the central indian ocean abstract according to hide undulations at the core mantle interface distort geopotential fields that can be observed in lower order harmonics hide and malin obtained a significant correlation between long wavelength gravity and non dipole magnetic fields when the latter is displaced in longitude by 160 the central indian ocean is characterised by the largest geoidal low which correlates well with the magsat component low without any longitudinal displacement an integrated interpretation of geoidal and magnetic anomalies suggests that the source of these anomalies should be the same and may originate at the depression of the core mantle boundary the shallow curie isotherm the matching of the long wavelength of the geoidal anomaly with the vertical magsat anomaly and the identical location of the centres of the anomalies provide an excellent confirmation of hide s hypothesis but contradicts earlier geoidal low interpretations of mass deficiency in the earth s crust and mantle

complexities in eolian and marine interactions processes and eustatic controls on erg development abstract the interplay between eolian and marine realms includes process interactions cycles of transgression and regression and possible inland effects of marine coastal events process interactions are geologically common and most obvious where eolian and marine environments are adjacent these interactions include sediment exchange between the two environments the supply of marine ions to the erg for surface and near surface cementation and the control directly or indirectly of marine events on the sediment budget of an erg regression accompanied by erg progradation over marine deposits occurs with both onshore and offshore winds marine transgression of ergs varies from producing a planar marine scoured surface to a planar deflation surface that precedes the transgression to varying degrees of paleotopographic dune preservation and a variety of transitional facies the extent of paleotopographic dune preservation is largely a function of the energy level of the transgressing marine realm the rate of the transgression and potential for early dune cementation general correlations between ergs and global eustatic sea level and coastal onlap curves occur for coastal and near coastal cyclic erg sequences eustatic control of inland ergs exists to the extent that sea level controls in large measure the extent of the basin exposed to subaerial processes i e regional base level and probably to a lesser extent the sediment supply to the erg direct correlation of inland erg events to coastal onlap curves is dubious at present but an indirect relationship may exist

middle paleozoic paleomagnetism of east kazakhstan post middle devonian rotations in a large scale orocline in the central ural mongol belt abstract in order to test different hypotheses concerning the paleozoic evolution of the ural mongol belt umb and the amalgamation of eurasia we studied middle devonian basalts from two localities 11 sites and lower silurian volcanics redbeds and intra formational conglomerates from three localities 20 sites in the chingiz range of east kazakhstan the devonian rocks prove to be heavily overprinted in the late paleozoic and a high temperature presumably primary southerly and down component is isolated at only four sites from a homoclinal section most silurian redbeds are found to be remagnetized in the late paleozoic in contrast a bipolar near horizontal remanence isolated from silurian volcanics is most probably primary as indicated by positive tilt and conglomerate tests analysis of paleomagnetic data from the chingiz range shows that southward pointing directions in ordovician silurian and devonian rocks are of normal polarity and hence indicate large scale rotations after the middle devonian the chingiz paleomagnetic directions can be compared with paleozoic data from the north tien shan and with the horseshoe shaped distribution of subduction related volcanic complexes in kazakhstan both paleomagnetic and geological data support the idea that today s strongly curved volcanic belts of kazakhstan are an orocline deformed mostly before mid permian time despite the determination of nearly a dozen new paleozoic paleopoles in this study and other recent publications by our team significant temporal and spatial gaps remain in our knowledge of the paleomagnetic directions during the middle and late paleozoic however the paleomagnetic results from the chingiz range and the north tien shan indicate that these areas show generally coherent motions with siberia and baltica respectively

storm effects on siliciclastic and carbonate shelf sediments in the medial silurian succession of pennsylvania abstract upper llandoverian through wenlockian strata in the pennsylvania part of the northern appalachian basin formed on a gentle epeiric ramp that extended from marginal tidal flats through coarser grained mid shelf shoals to a muddy basin center over approximately 10 million years the composition of the accumulating sediment evolved from siliciclastic to carbonate while the ramp maintained a relatively similar configuration and position below sea level and while storm generated processes continued as the major producers of sediment characteristics in both siliciclastic and carbonate parts of the succession sedimentary structures and their sequences are generally similar with only a small number of dissimilar features resulting from the differences in composition small scale coarsening and shallowing upward sequences are present in both mid shelf bar and basin transition deposits although specific sequence characteristics are different in siliciclastic and carbonate parts such sequences record cyclic fluctuations of relative sea level while the composition of the sediment evolved over this extended period the gentle ramp gradient was maintained largely by the processes generated by storms such processes were more effective because of the fluctuations of relative sea level

the middle triassic magnetostratigraphy from the peri tethys basin in poland abstract the paper presents the first complete magnetic polarity scale obtained for the middle triassic of the northern peri tethys area the roetian and muschelkalk deposits of southern poland upper silesia the holy cross mountains were studied paleomagnetically the obtained paleopole a 52 n 143 e fits well to the middle triassic ca 240 ma segment of the stable european apwp a set of various quality characteristic directions isolated in 106 samples was used for construction of the composite polarity scale this peritethyan scale has been tied with conodont zonation and referred to the scale erected earlier in the tethyan realm comparison of both scales indicates that the whole roetian succession in the southern polish basin should be correlated with the latest olenekian the normal marine sedimentation ceased in the polish basin as early as in the late fassanian time the obtained magnetostratigraphic scale combined with the sequence stratigraphic framework enables a reliable chronological correlation of the late olenekian ladinian succession over the entire peri tethys basin

a short interval of jurassic continental flood basalt volcanism in antarctica as demonstrated by 40ar39ar geochronology a continental flood basalt province the ferrar group kirkpatrick basalt and ferrar dolerite crops out along 3000 km of the transantarctic mountains in antarctica and is temporally related to the break up of gondwanaland although a wide range of dates between 90 and 193 ma have been published for the kirkpatrick basalt it is now recognized that the young dates reflect non ideal behavior of ar in the matrix in order to refine the geochronology feldspar separates have been analyzed by the 40ar39ar incremental heating method the main objectives are to constrain the duration of extrusive activity and the timing of volcanism along the outcrop belt basalt samples have been studied from the three principal outcrop areas yielding the following apparent ages central transantarctic mountains 176 8 0 5 ma south victoria land 176 4 0 4 ma north victoria land 176 6 0 7 ma ages from different stratigraphic levels within each area and from the three different areas are not analytically distinct the data imply that the eruptive activity which produced the kirkpatrick basalt occurred within a short interval of less than about 1 m y at 176 6 1 8 ma over an area which included more than 1200 km of the transantarctic mountains the jurassic volcanism in antarctica represents a short episode of magmatism comparable in duration with other well dated continental flood basalt provinces the linearly extensive outcrop of the ferrar province and the rapid eruption of the lavas suggests that lithospheric stretching exerted a major control on magmatism the poorly constrained age of the bajocian bathonian boundary makes the previously suggested connection between ferrar volcanism and an extinction event at that boundary uncertain

paraglacial slope instability in scottish fjords examples from little loch broom nw scotland lateglacial holocene fjord sediments in little loch broom preserve evidence of extensive slope instability the major area of reworking is in the outer loch and mid loch sill region where ice contact ice proximal deposits of the lateglacial assynt glacigenic formation have been disrupted by sliding and mass flow processes linked to the little loch broom slide complex and the adjacent badcaul slide mass failure was instigated about14 13 ka bp and is probably the response of the landscape to deglaciation immediately following the removal of ice support during glacial retreat an initial phase of translational sliding was followed by rotational sliding as revealed by the superimposition of scalloped shaped slumps on a larger scale rectilinear pattern of failure paraglacial landscape readjustment may have also been enhanced by episodic seismic activity linked to glacio isostatic unloading in the inner fjord evidence of holocene mass failure includes the ardessie debris lobe and a discrete intact slide block preserved within the postglacial basinal deposits the former is a localised accumulation linked to a fluvial catchment on the adjacent an teallach massif these mass transport deposits may represent an ongoing response to paraglacial processes albeit much reduced relative to the major slides in terms of sediment supply to the fjord

magmatism and continental break up in the south atlantic high precision40ar 39ar geochronology abstract a detailed ar ar study of the parana etendeka continental flood basalts cfb has been undertaken using laser spot analysis data provide information not only on the age of the samples but also on the variability of the non radiogenic ar component and state of alteration the results indicate the parana etendeka cfb were erupted over 10 million years between 137 and 127 ma providing a minimum overall eruption rate of 0 1 km3 yr 1 this is an order of magnitude less than that previously proposed for this the deccan and siberian cfb provinces but it is similar to estimates for hawaii iceland and the columbia river cfb in detail the new ar ar analyses indicate that magmatism within the parana etendeka province migrated from nw to se prior to and during the opening of the south atlantic providing an explanation for the asymmetry of the cfb lavas about the south atlantic moreover chemically defined magma types were erupted at different times in different places and so within the paranathey may not be used as reliable chronostratigraphic units rather such magmatic units may reflect the extent of compositionally distinct source regions in the uppermost mantle and indicate that partial melting took place over a wide area under the paranabasin the nw se migration of the onset of magmatism might be interpreted as a plume trace but the inferred rate of movement is 3 times faster than that inferred from subsequent magmatism on the rio grande rise it is argued that the onset of magmatism reflected extensional tectonics normal to the ponta grossa dyke swarm given that magmatism preceded the main phase of rifting and that extension across the ponta grossa was moderate current plume models have difficulty in predicting sufficient melting within the asthenosphere

structure and dating errors in the geologic time scale and periodicity in mass extinctions structure in the geologic time scale reflects a partly paleontological origin as a result ages of cenozoic and mesozoic stage boundaries exhibit a weak 28 myr periodicity that is similar to the strong 26 myr periodicity detected in mass extinctions of marine life by raup and sepkoski radiometric dating errors in the geologic time scale to which the mass extinctions are stratigraphically tied do not necessarily lessen the likelihood of a significant periodicity in mass extinctions but do spread the acceptable values of the period over the range 25 27 myr for the harland et al time scale or 25 30 myr for the dnag time scale if the odin time scale is adopted acceptable periods fall between 24 and 33 myr but are not robust against dating errors some indirect evidence from independently dated flood basalt volcanic horizons tends to favor the odin time scale

palynology paleoclimatology and correlation of middle miocene beds from porcupine river locality 90 1 alaska abstract beds in the upper ramparts canyon of the porcupine river alaska 67 20 n 141 20 w yielded a flora rich in pollen of hardwood genera now found in the temperate climates of north america and asia the beds are overlain or enclosed by two basalt flows which were dated to 15 2 0 1 ma by the 40 ar 39 ar method fixing the period of the greatest abundance of warm loving genera to the early part of the middle miocene the assemblage is the most northern middle miocene flora known in alaska organic bed 1 underlies the basalt and is older than 15 2 ma but is of early to middle miocene age the pollen assemblage from organic bed 1 is dominated by conifer pollen from the pine and redwood cypress yew families with rare occurrences of temperate hardwoods organic bed 2 is a forest floor containing redwood trees in life position engulfed by the lowest basalt flow a pine log has growth rings up to 1 cm thick organic beds 3 and 4 comprise lacustrine sediment and peat between the two basalt flows their palynoflora contain conifers and hardwood genera of which about 40 have modern temperate climatic affinities hickory katsura walnut sweet gum wingnut basswood and elm pollen are consistently present and beech and oak alone make up about 20 of the pollen assemblage a warm high latitude climate is indicated for all of the organic beds but organic bed 3 was deposited under a time of peak warmth climate data derived by comparison with modern east asian vegetation suggest that at the time of deposition of organic bed 3 the mean annual temperature mat was ca 9 c the warm month mean temperature wmmt was 20 c and the cold month mean temperature cmmt was ca 2 c in contrast the modern mat for the region is 8 6 c wmmt is 12 6 c and cmmt is 28 c organic beds 3 and 4 correlate to rocks of the middle miocene late seldovian stage of cook inlet and also probably correlate to and more precisely date the lower third of the suntrana formation in the alaska range beds at unalaklect part of the upper mackenzie bay sequence in the beaufort mackenzie basin and the mary sachs gravel of banks island this suggests that forests with significant percentages of temperate deciduous angiosperms existed between latitudes 60 and 72 n during the early middle miocene

timing the end triassic mass extinction first on land then in the sea the end triassic marks one of the five biggest mass extinctions but current geologic time scales are inadequate for understanding its dynamics a tuff layer in marine sedimentary rocks encompassing the triassic jurassic transition yielded a u pb zircon age of 199 6 0 3 ma the dated level is immediately below a prominent change in radiolarian faunas and the last occurrence of conodonts additional recently obtained u pb ages integrated with ammonoid biochronology confirm that the triassic period ended ca 200 ma several million years later than suggested by previous time scales published dating of continental sections suggests that the extinction peak of terrestrial plants and vertebrates occurred before 200 6 ma the end triassic biotic crisis on land therefore appears to have preceded that in the sea by at least several hundred thousand years

submarine slide scars and mass movements in karmsundet and skudenesfjorden southwestern norway morphology and evolution abstract shallow seismic sections multibeam bathymetric images and geotechnical investigations of the seafloor in karmsundet and skudenesfjorden sw norway have revealed the occurrence of large slide scars and associated mass movement deposits the slide escarpments are up to 30 40 m high and 8 km long with up to 20 10 6 m 3 of sediment released during a single event of retrogressive sliding the slide scars show a range of associated seafloor topography reflecting various modes of sediment displacement the variation in the escarpment morphology and sediment deformation style can be attributed to the varied intensity of liquefaction sliding involved mud deposits of allerod younger dryas to early holocene age but partly also deposits older than ca 12 000 14 c years bp the sediment failures were probably triggered by seismic reactivation of a local fault by postglacial regional isostatic rebound prior to failure the seafloor deposits were undercompacted and metastable due to high pore pressure the presence of shallow gas and the relatively steep local slope created by the formation of a major scour trough by sea currents minor gravitational sliding may still occur along some of the escarpments although engineering slope stability analysis indicates that the deposits can be regarded as stable in the present day conditions of static load and the anticipated weak sporadic earthquakes with an occurrence likelihood of 10 4 year and a peak acceleration of 0 25 g

the tertiary and the quaternary are here to stay in 1989 and 2000 the international commission on stratigraphy ics published geologic time scales in which the term tertiary had been eliminated in the time scales published by the ics in 2004 the term quaternary was also eliminated the cenozoic shown as composed of two systems the paleogene and the neogene the neogene extending to the present was there any logical basis for these changes a review of the geologic literature since 1980 19 journals of extensive distribution and a considerable number of geologic maps time scales and stratigraphy textbooks as well as the georef clearly indicates that the tertiary and the quaternary have long been and are now in widespread use by geologists the world over and that their use has not declined at all during the last 25 yr they are very useful terms in geologic work essential for clear communication among geologists paleogene and neogene have received increasing use during the last 10 yr because they are also useful terms quaternary is probably the stratigraphic term most frequently used in the geologic literature tertiary is used as the pre quaternary part of the cenozoic by most geologists some however prefer to use paleogene and neogene instead of tertiary but it should not be a question of either tertiary or paleogene and neogene all three are needed as are cenozoic paleocene eocene oligocene miocene and pliocene to express various degrees of precision in stratigraphic assignation and dating all should be recognized as units of a standard geologic time scale geologists should retain a choice of what they think better fits their needs the preferred time scale therefore should have the cenozoic erathem comprising the tertiary and quaternary systems and the tertiary including the paleogene and neogene subsystems past attempts to eliminate the tertiary and quaternary have been ignored recent attempts will not succeed either the tertiary and the quaternary are here to stay certainly as long as geologists continue to use them as they have and continue to oppose the ill advised efforts to discard them from the geologic time scale

the record of middle jurassic volcanism in the carmel and temple cap formations of southwestern utah altered volcanic ash beds in the middle jurassic temple cap and carmel formations in southwestern utah record a pulse of active arc related volcanism between 166 and 171 ma a second pulse between 148 and 155 ma has previously been documented in the upper jurassic morrison formation volcanic and volcaniclastic rocks of these same ages have also been identified closer to or within the arc in california in the inyo mountains the cowhole mountains the palen mountains and the central mojave desert the upper part of the volcaniclastic mount wrightson formation and the strata of cobre ridge in southern arizona are ca 170 ma in age and appear to be time correlative with the middle jurassic formations in southwestern utah the altered ash beds found in the temple cap and carmel formations typically contain phenocrysts of sanidine quartz biotite apatite zircon and titanite plagioclase was likely present originally in all of the ashes but was removed by alteration and is now found only in the temple cap red beds quartz and sanidine are absent in two crystal poor ash beds that contain two pyroxenes hornblende and biotite although major and trace element concentrations in the ash beds have been substantially modified compositions of relict phenocrysts reveal that the magmas were calc alkaline rhyolites to andesites two pyroxene two feldspar biotite and biotite apatite thermometers suggest that crystallization occurred at temperatures ranging from 740 to 910 8c hornblende geobarometry yields pressures of 1 2 kilobars for the two ash beds that contain the appropriate buffer assemblage the mafic silicates all have moderately high mg fe ratios this fact combined with the presence of hornblende biotite and titanite suggests that the phenocrysts crystallized at high oxygen fugacities similar to those of the granites of the batholiths of california the ash probably erupted from a low lying arc cut by strikeslip faults in what is now southern california and western nevada major jurassic unconformities occur near or within the ash bearing formations in southwestern utah laser fusion singlecrystal 40 ar 39 ar measurements have defined the ages of the unconformities and the associated volcanism the age of the j 1 unconformity found at the base of the temple cap formation in southwestern utah is older than ca 170 5 ma the j 2 unconformity which lies between the temple cap and carmel formations formed between ca 169 and 168 ma the origin of these unconformities is still unclear but may be related to the middle jurassic pulse of magmatism and the oblique plate convergence along the western margin of north america the age range of ash beds in the carmel formation between 166 3 and 168 0 6 0 5 ma is consistent with a bajocian bathonian boundary of ca 166 ma

pollen and spores date origin of rift basins from texas to nova scotia as early late triassic palynological studies of the nonmarine newark supergroup of eastern north america and of rift basins in the northern gulf of mexico facilitate correlation with well dated marine sections of europe new information emphasizes the chronological link between the newark basins and a gulf of mexico basin and their common history in the rifting of north america from pangea shales from the subsurface south georgia basin are shown to be of late karnian age early late triassic the known time of earliest sedimentation in the culpeper basin is extended from norian late late triassic to mid karnian and the date of earliest sedimentation in the richmond and deep river basins is moved to at least earliest karnian perhaps ladinian the subsurface eagle mills formation in texas and arkansas has been dated palynologically as mid to late karnian the oldest parts of the newark supergroup and the eagle mills formation mostly began deposition in precursor rift basins that formed in ladinian to early karnian time in the southern newark basins sedimentation apparently ceased in late karnian but continued in the northern basins well into the jurassic until genesis of the atlantic ended basin sedimentation

petroleum geology of the upper jurassic and lower cretaceous baltimore canyon trough western north atlantic ocean numerous hydrocarbon shows including a noncommercial gas and gas condensate accumulation occur in the baltimore canyon trough within sandstone units deposited in prograding coastal plain and transitional marine environments located updip of an oxfordian kimmeridgian carbonate shelf edge the coastal plain and transitional marine facies are overlain by a fine grained deltaic complex dominated by delta plain shales which collectively form a regionally extensive top seal unit this deltaic complex prograded into a back reef lagoon during aggradation of lower kimmeridgian through berriasian shelf margin carbonates wells drilled seaward of the continental shelf edge 1500 m water depth tested large structural stratigraphic closures along the downdip termination of the upper jurassic lower cretaceous carbonate shelf edge but encountered no significant hydrocarbon shows reservoir rocks in these wells consist of 1 oolite grainstone which was deposited within a shoal water complex located at the aptian shelf edge and 2 coral stromatoporoid grainstone and boundstone which formed an aggraded shelf margin complex located at the late kimmeridgian through berriasian shelf edge structural closures having reservoir and top seals are present in both updip and downdip trends hydrocarbon shows in wells along the shelf interior trend indicate the presence of mature source beds at least locally the absence of hydrocarbon shows in downdip carbonate reservoirs and around the schlee dome however suggests charge migration mechanisms within the fetch areas of these objectives have failed failure of charge can be due to 1 absence of mature source rocks 2 absence of migration pathways from source rocks to reservoirs and or 3 absence of top seals at the time of hydrocarbon migration continued development of play concepts in the baltimore canyon trough therefore requires identification and mapping of potential source rock intervals and construction of hydr carbon expulsion models to time hydrocarbon generation relative to trap formation

natural vs human induced facies changes in recent shallow fjord sediments of the store lungegardsvannet in bergen western norway a basin wide change from an older homogeneous bioturbated to a younger laminated facies occurs in sediments from the 26 m deep permanently anoxic store lungegardsvannet fjord the younger facies consists of alternating packages of light and dark layers each containing millimetre scale laminae the composition of the dark layers differs from that of the light layers in the occurrence of predominantly marine benthic diatoms larger grain size lower loss on ignition loi and lower trace metal cu pb zn concentrations total trace metal concentrations correlate with the redox sensitive trace elements mo and v r 0 8 and with loi r 0 6 the correlation of the minerogenic matter and the grain size related elements al and li is poor r 0 2 the shoaling of the sill depth and reduction of the fjord area resulting in the reduction of bottom water exchange accounted for the shift from bioturbated to laminated sediments during the end of the last century the alternating changes within the laminated facies are the result of alternating wind forces during years of calm wind conditions 1908 1919 and 1945 1961 undisturbed sedimentation of organic matter from primary production and an associated accumulation of trace metals prevail years of high wind force 1919 1945 and 1961 1991 trigger shore erosion and an increased influx of minerogenic matter

global tectonics since the breakup of pangea 180 million years ago evolution maps and lithospheric budget abstract pangea the earth s youngest single supercontinent broke up 180 million years ago tectonic plates were subsequently formed by dispersal of the continental fragments and accretion of new oceanic lithosphere the configurations of all the major lithospheric plates at 0 20 65 95 140 180 ma bp are reconstructed on six globes of the earth each with a radius of 10 cm it appears that plate boundaries maintain a remarkably close fit on model globes of constant radii if the reconstructions include the recovery of subducted spreading patterns this is illustrated with maps in equatorial orthographic oblique orthographic and transverse hammer aitoff projections the snug fit of the tectonic plates at every tested time since the breakup of pangea 180 ma bp is consistent with the theory of plate tectonics on a non expanding earth and contradicts rapidly expanding earth models the areas of oceanic lithosphere produced and consumed during the past 180 ma bp are estimated from surface measurements of the globes reconstructed on the basis of particular assumptions these measurements suggest a consistent increase in the production rate of oceanic lithosphere during the past 140 ma it was decided to revise the assumptions and see if alternative reconstructions of the ancient spreading patterns on the floors of the tethys and eo pacific oceans could avoid implying an increase of lithospheric production rates with time this appeared to be possible the revised maps suggest that ophiolites older than 180 ma bp may have been obducted in cenozoic collision zones of the himalayas andes rockies and the western part of the banda arc timor new guinea estimates of the ocean floor production and consumption budget appear to be quite similar for both map series and only the possible ranges are summarized here time averaged for the past 180 ma world wide production and consumption of oceanic lithosphere appears to have varied between 2 6 and 3 5 km2 a 1 at most the mean of world wide spreading velocities ranges between 2 4 and 3 5 cm a 1 and world wide means of subduction velocities lie between 4 2 and 6 3 cm a 1 more accurate estimates are possible on the basis of particular assumptions and have been specified for the various time intervals distinguished i e the neogene 0 20 ma bp palaeogene 20 65 ma bp upper cretaceous 65 95 ma bp lower cretaceous 95 140 ma bp and middle and upper jurassic 140 180 ma bp

a submarine landslide source for the devastating 1964 chenega tsunami southern alaska abstract during the 1964 great alaska earthquake m w 9 2 several fjords straits and bays throughout southern alaska experienced significant tsunami runup of localized but unexplained origin dangerous passage is a glacimarine fjord in western prince william sound which experienced a tsunami that devastated the village of chenega where 23 of 75 inhabitants were lost the highest relative loss of any community during the earthquake previous studies suggested the source of the devastating tsunami was either from a local submarine landslide of unknown origin or from coseismic tectonic displacement here we present new observations from high resolution multibeam bathymetry and seismic reflection surveys conducted in the waters adjacent to the village of chenega the seabed morphology and substrate architecture reveal a large submarine landslide complex in water depths of 120 360 m analysis of bathymetric change between 1957 and 2014 indicates the upper 20 50 m 0 7 km3 of glacimarine sediment was destabilized and evacuated from the steep face of a submerged moraine and an adjacent 21 km2 perched sedimentary basin once mobilized landslide debris poured over the steep 130 m high face of a deeper moraine and then blanketed the terminal basin 465 m water depth in 11 5 m of sediment these results combined with inverse tsunami travel time modeling suggest that earthquake triggered submarine landslides generated the tsunami that struck the village of chenega roughly 4 min after shaking began unlike other tsunamigenic landslides observed in and around prince william sound in 1964 the failures in dangerous passage are not linked to an active submarine delta the requisite environmental conditions needed to generate large submarine landslides in glacimarine fjords around the world may be more common than previously thought

late glacial to holocene environmental changes and climate variability evidence from voldafjorden western norway sedimentological micropalaeontological benthic foraminifers and dinoflagellate cysts stable isotope data and ams 14c datings on cores and surface samples in addition to acoustic data have been obtained from voldafjorden western norway based on these data the late glacial and holocene sedimentological processes and variability in circulation and fjord environments are outlined glacial marine sedimentation prevailed in the voldafjorden between 11 0 kyr and 9 2 kyr bp radiocarbon years in the later part of the allerod period and for the rest of the holocene there was deposition of fine grained normal marine sediments in the fjord basin turbidite layers recorded in core material and on acoustic profiles dated to ca 2 1 6 9 7 6 ca 9 6 and ca 11 0 kyr bp interrupted the marine sedimentation the event dated to between 6 9 and 7 6 kyr bp probably corresponds to a tsunami resulting from large scale sliding on the continental margin off norway the storegga tsunami during the later part of the allerod period voldafjorden had a strongly stratified water column with cold bottom water and warm surface water reaching interglacial temperatures during the summer seasons during the younger dryas cold event there was a return to arctic sea surface summer temperatures possibly with year round sea ice cover the entire benthic fauna being composed of arctic species the first strong holocene warming observed simultaneously in bottom and sea surface temperature proxies occurred at ca 10 1 kyr bp bottom water proxies indicate two cold periods possibly with 2 c lowering of temperatures at ca 10 0 pbo 1 and at 9 8 kyr bp pbo 2 these events may both result from catastrophic outbursts of baltic glacial lake water the remainder of the holocene experienced variability in basin water temperature indicated by oxygen isotope measurements with an amplitude of ca 2 c with cooler periods at ca 8 4 9 0 5 6 5 2 4 6 4 2 3 5 2 2 1 2 and 0 4 0 8 kyr bp changes in the fjord hydrology through the past 11 3 kyr show a close correspondence both in amplitude and timing of events recorded in cores from the norwegian sea region and the north atlantic these data suggest a close relationship between fjord environments and variability in large scale oceanic circulation copyright 2001 john wiley sons ltd

quartz arenites review and interpretation abstract quartz arenites orthoquartzites are exceptional sands pettijohn et al 1972 that in the past have formed extensive and commonly thick formations they are somewhat enigmatic in that they do not appear to be forming at the present time this paper examines the origin of quartz rich sands documents the range of environments in which they are found and suggests a model for their genesis quartz sand is most commonly formed by tropical weathering of coarse grained quartz bearing rocks such as granite it may be deposited as texturally immature fluvial sandstones generally under a humid climate with drying of the climate quartz rich bauxitic soils and sandy alluvium can be a substantial source of poorly rounded dune sands for major deserts quartz sand when transported into shallow marine environments becomes very well rounded through reworking by tidal currents such sand may spill into deep oceanic environments and by sedimentary or tectonic transport may come to rest in both stable and active tectonic settings quartz rich sandstones can also be formed by diagenetic destruction of labile framework grains of immature sandstones precambrian orthoquartzites are commonly thick and widespread when compared to younger examples the thinness of post silurian quartz arenites may be largely due to the trapping effect of land vegetation and solution of quartz by organic acids in weathering profiles there is an abundance of shallow marine and fluvial quartz arenites in the early paleozoic and the cretaceous this is due to widespread continental flooding and a humid world climate following the disintegration of supercontinents the shallow marine examples are commonly associated with bituminous sometimes phosphatic shale glauconite and possibly chamositic ironstone there is an abundance of eolian quartz arenites in the permo triassic this is related to a widespread dry continental climate during assembly of the pangean supercontinent

tracking an upper limit of the carnian crisis and or carnian stage in the western carpathians slovakia the late triassic timescale especially the carnian norian boundary is poorly constrained mainly due to a paucity of high precision radio isotopic ages that can be related accurately to contradictions between the biostratigraphic and magnetostratigraphic correlations la icp ms dating of detrital zircons from five samples of the lunz formation the upper triassic siliciclastic sediments from the western carpathians slovakia provided a wide spectrum of ages that vary from late archaean ca 2582 ma to triassic ca 216 ma these marine delta sediments represent a typical product of the carnian crisis a major climate change and biotic turnover that occurred during the carnian stage in the tethys ocean within the carbonate shelf and intrashelf basins in the northern calcareous alps and the western carpathians the supply of clastic material in the studied lunz formation was derived from several sources especially i from the recycled variscan orogen ii from the remote east european platform and iii from the contemporaneous triassic volcanic sources syn sedimentary volcanic zircons with a concordia age of 221 2 1 6 ma calculated from 12 single analyses represent the maximum age of deposition of the lunz formation and demonstrate that the upper limit of the carnian crisis and or the carnian stage in the alpine carpathians realm is younger than the current age of the carnian norian boundary at ca 227 ma listed on the international chronostratigraphic chart international commission on stratigraphy 2016 12 edition

cretaceous plate tectonic reconstructions abstract plate tectonic reconstructions for each cretaceous stage are produced as base maps for cretaceous paleogeography and for oceanic and continental data both geologic and geophysical data are utilized to determine the relative rotations of cretaceous plates with respect to north america a sea floor spreading history is generated from the relative rotations this history is consistent with data from the deep sea drilling project paleolatitude lines are derived using average paleomagnetic pole positions these reconstructions are significantly more comprehensive than previous global reconstructions although there are still many areas which remain controversial

relative sea level changes during the cretaceous in israel detailed lithologic microfaunal and biometric investigations using relative abundances diversity indexes and duration charts of ostracods and foraminifera allowed the recognition of sea level changes during the cretaceous of israel three major transgressive regressive sedimentation cycles occur on the northwest margins of the arabian craton these cycles are the neocomian aptian which is mostly terrigenous sediments the albian turonian which is basin marls and platform carbonates and the senonian which is uniform marly chalks the cycles are separated by two major regional unconformities the aptian albian and turonian coniacian boundaries the sedimentary cycles are related to regional tectonic and volcanic events and eustatic changes the paleodepth curve il ustrates the gradual sea level rise reaching its maximum during the late cretaceous with conspicuous advances during the late aptian late albian cenomanian early turonian early santonian and early campanian major lowstands occur at the aptian albian cenomanian turonian turonian coniacian and campanian maastrichtian boundaries this model for israel agrees well with other regional and global sea level fluctuations four anoxic events black shales accompanying transgressions correspond to the cretaceous oceanic record we hypothesize the presence of mature oil shales in the present day eastern mediterranean basin close to allochthonous reef blocks detached from the cretaceous platform

high resolution 40ar 39ar chronostratigraphy of the late cretaceous el gallo formation baja california del norte mexico laser probe 40ar 39ar analyses of individual sanidine grains from four tuffs in the alluvial late cretaceous campanian el gallo formation yield statistically distinct mean dates ranging from 74 87 0 05 ma to 73 59 0 09 ma the exceptional precision of these dates permits calculation of statistically significant sediment accumulation rates that are much higher than passive sediment loading would cause implying rapid tectonically induced subsidence the dates bracket tightly the age of important dinosaur and mammalian faunas previously reported from the el gallo formation the dates support an age less than 73 ma for the campanian maastrichtian stage boundary younger than indicated by several currently used time scales further application of the single grain 40ar 39ar technique may be expected to greatly benefit stratigraphic studies of mesozoic sedimentary basins and contribute to calibration of biostratigraphic and magnetostratigraphic time scales

lower jurassic navajo aztec equivalent sandstones in southern arizona and their paleogeographic significance thick sequences of lower jurassic rhyolitic and andesitic volcanic rocks in several mountain ranges of southern arizona contain interbedded quartzarenites locally up to 250 m thick these sandstone lenses composed of well sorted and well rounded quartz grains commonly contain large scale cross stratification and are considered to be eolian sand deposits the eolian sands were blown up against the continental side of the early jurassic volcanic arc that trended northwest southeast across the southwestern margin of the north american continent and or plate at that time paleocurrent data suggest southerly eolian transport of the sands from the colorado plateau area correlation of these sandstones with the lower jurassic navajo and aztec sandstones is indicated by the pa eocurrent data as well as radiometric dating of the interbedded volcanics eolian sand transport southward across central arizona in the early jurassic indicates that the mogollon highlands either did not then exist or were merely low discontinuous inselbergs on a broad back arc ramp more appropriately called the mogollon slope