sector collapse sedimentation and clast population evolution at an active island arc volcano stromboli italy sciara del fuoco is the subaerial part of a partially filled sector collapse scar that extends to 700 m below sea level on stromboli volcano the collapse occurred 2200 m and 10 km from the shore to the nnw a fan shaped mounded feature comprises debris avalanche deposits 4 km3 from two or more sector collapses volcaniclastic density currents originating from sciara del fuoco follow the topographic margin of the debris avalanche deposits although overbank currents and other unconfined currents widely cover the mounded feature with turbidites historical recorded eruptive activity in sciara del fuoco is considerably less than that which occurred earlier and much of the partial fill may have formed from eruptions soon after the sector collapse it is possible that a mass of eruptive products similar to that in the collapse scar is dispersed as volcanogenic sediment in deep water of the tyrhennian basin evidence that the early post collapse eruptive discharge was greater than the apparent recent flux 2kg s counters suggestions that a substantial part of stromboli s growth has been endogenous the partial fill of sciaria del fuoco is dominated by lava and spatter layers rather than by the scoria and ash layers classically regarded as main constituents of strombolian cinder cones much of the volcanic slope beneath the vents is steeper than the angle of repose of loose tephra which is therefore rapidly transported to the sea delicate pyroclasts that record the magmatic explosivity are selectively destroyed and diluted during sedimentary transport mainly in avalanches and by shoreline wave reworking and thus the submarine deposits do not record well the extent and diversity of explosive activity and associated clast forming processes considerable amounts of dense non vesicular fine sand and silt grains are produced by breakage and rounding of fragments of lava and agglutinate the submarine extension of the collapse scar and the continuing topographic depression to 2200 m below sea level are zones of considerable by passing of fine sand and silt which are transported in turbidity currents evidently volcanogenic sediments dispersed around island volcanoes by density currents are unlikely to record well the true spectrum and relative importance of clast forming processes that occurred during an eruption marine sedimentary evidence of magmatic explosivity is particularly susceptible to partial or complete obliteration unless there is a high rate of discharge of pyroclastic material into the sea

a revised chronology for the growth and demise of loch lomond readvance younger dryas ice lobes in the lochaber area scotland abstract we present a revised varve chronology for the duration of ice dammed lakes that formed in the lochaber district scotland during the loch lomond younger dryas stadial we analysed new varved sequences and combined them with existing varve records to develop the lochaber master varve chronology 2019 lmvc19 published here for the first time it spans an interval of 518 18 vyrs and is considered more secure than its predecessors because i it is anchored by a more robust record of the vedde ash which is dated to 12 043 43 cal yr bp and ii it provides revised estimates of the timings of key regional palaeoclimatic shifts that are fully compatible with those inferred from independently dated non varved records obtained from neighbouring sites the new results indicate that the lochaber ice dammed lakes existed between 12 135 and 11 618 61 cal yr bp but the pattern of glacier advance that led to lake formation was more complex than previously assumed with some ice fronts reaching their maximal positions 300 years before others initiation of ice retreat at 11 800 cal yr bp appears to have coincided with a rise of 2 c in mean july temperatures inferred from chironomid data obtained from the abernethy forest site in the eastern highlands this local climatic shift is thought to have been a delayed response by up to 335 years to a mid stadial northward migration of the north atlantic polar front the delay probably due to the influence of the sw highland icefield subsequent retreat that led to the formation of ice stagnation features throughout large parts of the area was initiated by a further rise in summer air temperature of 3 c at the start of the early holocene final drainage of the lake system occurred 190 years after the initiation of ice retreat while it took a further 200 years for the ice to vacate the rannoch plateau a nearby upland glacial source

a refined understanding of the paleoenvironmental history recorded at the okanagan centre section an mis 4 stratotype south central british columbia canada the okanagan centre section is the stratotype for marine oxygen isotope stage mis 4 sediments okanagan centre drift in the southern interior of british columbia canada previous work suggested that these sediments record two glacial and two interglacial cycles this study reports on detailed sedimentological and geochronological investigations of lithostratigraphic units comprising the okanagan centre sequence revealing successive deposition of subaqueous and subaerial outwash a subglacial till and glaciolacustrine sediments during mis 4 a limiting optical age of 113 8 ka defines the base of this sequence sedimentological paleopedological optical dating and tephrochronological data from sediments near the middle of the sequence reveal soil development mis 3 in eolian sediments deposited on a river terrace overlying a deglaciated surface within these sediments identification of mt st helens set c tephra suggest sedimentation between 50 and 35k 14c a bp optical dating corroborates the tephrochronology and suggests that this surface formed after 52 7 ka the record of mis 2 glaciation is restricted to deglaciation and overlies mis 3 sediments above an unconformity possibly related to regional subglacial meltwater erosion eolian sediments containing mt mazama set o tephra 7 62k cal a bp cap the sequence

the transition from calc alkaline to potassic orogenic magmatism in the aeolian islands southern italy the aeolian volcanic arc displays a wide range of magmatic products mafic lavas range from hypersthene normative calc alkaline basalts to silica undersaturated potassic absarokites although the former are spatially and temporally dominant consistent with the subduction zone tectonic setting in addition intermediate and acidic members of the various fractionation series may be recognised large variations in trace element and isotope ratios accompany the rapid calc alkaline to potassic transition and it is argued that these may be largely explained in terms of subduction zone mantle enrichment involving components derived from both basaltic ocean crust and subducted sediments in addition it seems that the mantle wedge itself was substantially heterogeneous prior to the onset of subduction zone processes not only are these subduction components similar to those proposed in a number of island arcs but they also resemble those recognised in the ultra potassic lavas of the roman province supporting recent subduction related petrogenetic models of the roman magmatism although subducted sediment plays an important role in the generation of some potassic magmatism it is not uniquely responsible for k2o rich lavas which are also produced without a large sediment contribution

genesis and diagnostic value of soft sediment deformation structures a review abstract soft sediment deformation structures are recognized as important diagnostic features in the rock record for determination of depositional environments and slope processes the diagnostic value of these structures is reevaluated by analysis of the parameters controlling sediment deformation soft sediment deformation is contemporaneous with deposition and occurs dominantly in course silt to fine sand the high depositional rate low permeability and low shear strength of grains within this sediment range maximize the occurrence of deformation the dominant mechanisms responsible for sediment deformation include 1 liquefaction or fluidization 2 reverse density gradation 3 slumping or slope failure and 4 shear stress in most cases a combination of these mechanisms occurs the processes function in a continuum producing features that are microscopic to megascopic in scale it is shown that the processes and thus the structures are not environment specific the true diagnostic value of the structures may be in defining hydrodynamic conditions and in interpreting paleocurrents and paleoclimatic and paleoseismic events ultimately for the best diagnostic results soft sediment deformation structures should be studied in association with all other available lithologic structural and paleontological information

jet efflux deposits of a subaqueous ice contact fan glacial lake rinteln northwestern germany abstract the coarse grained ice contact porta subaqueous fan delta complex was deposited in glacial lake rinteln at the margin of the saalian ice sheet that advanced south of the weser chains nw germany the ice proximal depositional system was up to 15 km long and 10 km wide the present study deals with ice proximal subaqueous fan deposits which are interpreted as products of a subcritical plane wall outflow jet that periodically passed into a supercritical jet with hydraulic jump the proximal facies assemblage consists of the coarse clast supported gravelly deposits of a hyperconcentrated high density effluent and of related cohesionless debris flows attributed to the conduit or immediate proximal jet outflow zone of flow establishment the intermediate facies assemblage attributed to the outflow jet proximal zone of flow transition is dominated by normally graded and cross stratified gravels with scour structures at their bases these gravels were deposited by a high density effluent capable of forming mouthbar like features these deposits pass downcurrent into an assemblage of planar parallel stratified and planar and trough cross stratified sands and pebbly sands partially interpreted as antidunes with abundant scour structures and intercalated layers of fine sand silt and silty mud attributed to the jet distal zone of flow transition the distal facies assemblage consists of trough cross stratified sands and pebbly sands and is attributed to the outflow jet proximal zone of established flow the sedimentary succession as a whole has wedge shape geometry with a gentle fan shaped inclination of the bedding from the southeast to the southwest repeated vertical alternations of supercritical and subcritical deposits and muddy interlayers can be attributed to temporary fluctuations in the meltwater outflow whereas the overall upward fining of the succession indicates a net decline of meltwater discharges

archaean orogenic ultrapotassic magmatism an example from the southern abitibi greenstone belt the clericy pluton in the southern abitibi greenstone belt of quebec is a syenitic intrusion cross cut by nordmarkitic dykes it is probably one of the oldest known ultrapotassic intrusions about 2 7 ga it crystallized in a crustal environment under low ph20 2 5 kbar and low fo2 conditions most trace elements behaved as compatible elements suggesting that sphene and apatite were involved together with clinopyroxene during low pressure crystal fractionation the large range of initial isotopic ratios calculated for 2 68 ga nd 1 9 to 2 3 as well as the trace element distribution suggest that the syenitic pluton is the product of differentiation from a parental magma with a composition similar to that of timiskaming type archaean shoshonites contaminated by a crustal component on the other hand the nordmarkitic dykes are probably the result of crustal anatexis of metasedimentary rocks and some addition of the syenitic magma the clericy peralkaline syenite differs chemically from typical intraplate syenites in being saturated with respect to quartz and displaying lower ti and hfse contents it is related to an ultrapotassic volcano plutonic event which characterized the last 20 ma of igneous activity in the abitibi greenstone belt it may represent an increased rate of convergence of small heterogeneous plates during a subduction driven accretion tectonic event which possibly marked the culmination of the kenoran orogeny in the superior province of the canadian shield

ree geochemistry of late permian shoshonitic lavas from the sydney basin new south wales australia abstract nine late permian shoshonitic lavas from the southern sydney basin have moderately fractionated rare earth element ree patterns and are enriched in light ree lree petrographic and geochemical data accord with the lavas being related by low pressure fractionation of plagioclase olivine and clinopyroxene trace element modelling on the basis of published partition coefficients and possible source compositions suggests that the shoshonitic magmas were generated by 10 15 partial melting of spinel lherzolite which had been enriched previously in lree generation of the shoshonitic lavas in the sydney basin was not related directly to benioff zone magmatism but the enrichment of the source region in lree may have been related to a pre late permian subduction event a compilation of ree data for shoshonitic volcanic rocks from a variety of geographic and tectonic settings indicates that there is no simple relationship between ree content and the thickness of continental crust above the source region

evidence for rapid sedimentation in a tunnel channel oak ridges moraine southern ontario canada abstract in south central ontario a late wisconsinan regional unconformity consisting of tunnel channels and drumlinized till crops out north of lake ontario the tunnel channels are locally infilled and the unconformity buried by sediment of the oak ridges moraine based on seismic reflection profiling and drillcore the tunnel channels are known to continue beneath the moraine detailed sedimentological analysis of 300 m of continuous core from two drillholes located 7 km apart in subparallel tunnel channels identified three facies the gravel facies is 17 m thick and occurs in only one of the cores it directly overlies the unconformity and may include a number of upward fining units seismic reflection data suggests the gravel forms stacked gravel mesoforms or quasi horizontal gravel layers bed load sheets deposited from fluidal flows along the deep channel axis the graded massive sand facies up to 37 m thick is the most common facies and consists of silty medium sand with minor coarse sand strata are reverse graded normal graded or massive with isolated silt intraclasts and evidence locally for dewatering this facies is interpreted to have been deposited from hyperconcentrated dispersions downflow of a hydraulic jump or major channel confluence the third facies consists of medium scale and small scale cross stratified sand medium scale cross stratification occurs predominantly in the lower 37 m of the core and is interbedded with the graded massive sand facies small scale cross stratified sand is progressively more common upward in core medium and small scale cross stratified sands was deposited respectively by subaqueous dunes and ripples formed in dilute fluid flows the complete succession is interpreted to have been deposited very rapidly within a subglacial tunnel channel before discharge ceased along the channel deposition followed closely and in part coincided with rapid expansion of the channel by erosion in a hydraulic jump or at a major channel confluence along the grounding line of a subglacial lake scour into unconsolidated sediment contributed to the sediment flux and quickly overloaded the flow with suspended sediment which in turn resulted in extremely high rates of sedimentation immediately downflow such depositional conditions support the notion that tunnel channels in the study area formed and or served as conduits for subglacial jokulhlaup discharges and that the laurentide ice sheet most probably did not generally drain by steady state processes but instead by short lived catastrophic events

sedimentation in a subglacial lake enniskerry eastern ireland abstract field relationships between a subglacial lake fill from the enniskerry basin eastern ireland provide evidence for dynamic links between the sedimentary fill regional subglacial meltwater flow and regional ice dynamics the basin fill 6 7 km2 forms an integral part of an extensive 30 km subglacial meltwater system which developed parallel to north south ice flow along the western marginal sector of the late pleistocene irish sea glacier high magnitude sediment fluxes were directed into the subglacial lake southwards across the northern basin rim from two nye type channels and westwards by a rothlisberger type channel the resulting subaqueous fans typically consist of cones of coarse boulder gravels deposited by jet effluxes overlain by cross bedded sands and foreset gravels in places these are eroded and overlain by multistorey dish shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head a variety of gravelly and sandy bedforms indicate that sediment migrated over efflux cores towards deeper parts of the basin facies variability within the ice proximal fans and spreads record deposition from a wide range of high and low density turbulent flows traction currents density underflows suspension and sediment gravity flows a surficial drape of winnowed diamict is related to areal resedimentation as jet effluxes closed down at one site the gravelly sequence shows a largely conformable transition upwards into glaciotectonised gravel and basal till in the lee of the basin rim elsewhere the upper part of the sediment pile is occasionally deformed by the drag of the ice roof a series of sequential events is postulated for the evolution of the subglacial drainage system and subglacial lake development initially a rock ridge transverse to ice flow resulted in the development of a relatively low pressure lee zone along the northern margin of the basin ice sheet decoupling within the basin was enhanced by water migration into this low pressure lee zone which also melted an ice roof cavity closure and maintenance of the ice roof was prevented by a fast ice flux generated by intense marine downdraw in the main ice lobe centred in the irish sea basin regional ice directed meltwater pressure gradients and erosion enhanced subglacial lake development in the lowest topographic point of the system major inlet and outlet nye type channels incised transverse to the rims of the basin testify to the intensity of ice directed drainage along the marginal sector of the irish sea glacier in a wider context the concepts of high magnitude subglacial meltwater flow coupled with high rates of debris flux invoked for the subglacial basin fill are also necessary to explain the thick tidewater sequences present in adjacent sectors of the irish sea basin

clastic dykes of the devono carboniferous horton bluff formation nova scotia storm related structures in shallow lakes abstract clastic dykes are common in the late devonian to early carboniferous horton bluff formation of nova scotia where they occur in wave dominated shoreline deposits of lacustrine shoaling upward cycles the dykes typically less than 25 cm wide and 40 cm in vertical extent project downward into clayshale from broad loads at the base of elongate isolated lenses of hummocky cross stratified siltstone ptygmatic folding of the dykes reflects a shale siltstone compaction ratio of 2 3 times and maximum depth of dyke penetration prior to compaction was 1 m dyke orientation parallels the orientation of wave ripple crests and the elongation direction of the siltstone lenses dyke formation was penecontemporaneous with sedimentation dyke and load formation was probably initiated in shallow water during storms which promoted sediment failure through cyclic wave loading microseisms and rapid deposition of hcs bearing siltstone lenses reversed density gradient and uneven sediment loading from silt lenses probably promoted downward emplacement loads reflect ductile failure of surficial water rich mud whereas dykes reflect downward injection of silt following brittle failure of underlying more compacted mud the depositional slope provided a tensional stress that controlled the fracture direction orthogonal to the slope of the failed sediment

wind driven circulation in titan s seas circulation in titan s seas forced by wind is simulated by an ocean circulation model using surface wind data predicted by a global circulation model wind driven circulation is insignificant throughout much of the annual cycle but becomes significant from late spring to late summer when the wind stress becomes strong the large scale circulation in summer is predominantly southward near the sea surface and northward near the sea bottom the sea surface current can get as fast as 5 cms 1 in some areas titan s rotation affects the vertical structure of sea currents in the form of an ekman spiral if the wind is strong the maximum wind setup at the shores is of the same order of magnitude as the tidal range wind stirring may reduce thermal stratification in summer but may be unable to destroy stratification of methane rich liquids on top of ethane rich liquids that can result from imbalances between evaporation and precipitation

the depositional history of an esker near ottawa canada the 10 km long stittsville ridge trending parallel to the last direction of ice advance into the ottawa area is here classified as an esker the sediments of the ridge are interpreted as subaqueous outwash deposited from a subglacial or englacial meltwater conduit emptying into an inlet in the late wisconsin glacier front the ridge formed by the coalescence of subaqueous outwash fans as the ice retreated northward sedimentological variation along the ridge is attributed to a change in the morphology of the inlet as the ice front retreated from an initially narrow symmetrical shape to a broader and increasingly asymmetrical form

origin of volcanic rocks from stromboli italy abstract quaternary volcanic rocks of stromboli italy can be divided into older calc alkaline and younger shoshonitic series the sio2 contents of the rocks range from 50 to 61 but the majority of them are basalts the rocks show systematic variations in chemical composition which correlate with the volcanic stratigraphy such that at a given sio2 content k and other incompatible elements such as ree increase with decreasing age in addition the la yb ratio increases while the k rb k ba zr ce and zr nb ratios decrease towards the top of the volcanic pile on the other hand the abundances of transition elements v co sc and zn like most major elements are broadly similar in comparable rocks of different ages it is suggested that the parent magmas were derived by partial melting from upper mantle peridotite enriched in incompatible elements by fluids released from the descending oceanic lithosphere the temporal chemical variations may probably be related to the lengths of time during which fluids were in contact with the upper mantle source

soft sediment deformation in a tectonically active area the plio pleistocene zarzal formation in the cauca valley western colombia abstract the plio pleistocene zarzal formation corresponds to fluvio lacustrine sediments deposited in an intramontane depression within the colombian andes associated with the cauca romeral fault system it crops out mainly in the cauca valley where numerous field sections have permitted the mapping of the vertical and lateral lithological variations lacustrine deposits of sands silts clays and diatomites are interbedded with fluvial sand and gravel beds and fluvio volcanic mass flows derived from the volcanic central cordillera numerous soft sediment deformation structures are encountered in this formation particularly in fine to medium grained sands silts and clays load structures load casts flame structures pseudonodules water escape structures water escape cusps dish and pillar and pocket and pillar structures soft sediment intrusions clastic sills and dykes disturbed laminites convolute laminations slumps and synsedimentary faulting deformation mechanisms and driving forces are related essentially to gravitational instabilities dewatering liquidization and brittle deformations field and regional geological data show that most of these deformations are related to seismicity and can be interpreted as seismites this area has a geological and recent seismic history and outcrops show both syn and post depositional faulting related to the transpressional regime of this part of the colombian andes which generates strike slip faults and associated local normal faults the drainage pattern within the zarzal formation shows the signature of neotectonics moreover the fine to coarse grained sands of the zarzal formation are lithologies prone to liquefaction when affected by seismic waves the intercalation of the deformed intervals within undisturbed strata confirms the catastrophic nature of the events finally the large areal extent of the deformations and the type of structures are compatible with seismites consequently the existence of seismites in the zarzal formation represents corroboration of tectonic activity in this area during the pleistocene earthquakes with a magnitude higher than 5 can be postulated based upon the proximity of active faults and the types of deformations

petrological evolution of the crust and mantle in its simplest form crust mantle evolution can be thought of as a study of the processes by which material is lost from the mantle and forms new crust the overall goal is achievement of mass balance between the average composition of material known to have been added to the crust and the estimated average composition of the entire crust attainment of this goal for the earth has been elusive primarily because the materials available for study have generally been involved in several stages of evolution including fractionation within both the crust and mantle and recycling of material from crust to mantle thereby complicating the interpretation of available data although the overall composition of the continental crust generally has been modelled as andesitic taylor and mclennan 1981a the present upper continental crust is granodioritic and requires a more mafic lower crust it has been proposed taylor and mclennan 1981a that originally the archean crust had an andesitic composition throughout its volume and that partial melting in the lower crust developed more felsic melts that rose to enrich the upper crust leaving a more mafic residuum of lower crust this concept has been challenged by weaver and tarney 1981a who argue that the granulites of presumed lower crustal origin do not have the correct compositions for this model if one considers more recent additions to the crust from the mantle over the past several hundred million years it appears that these latest additions are basaltic with very little if any granitic additions in fact barker 1981 in his introduction to a special issue of jgr on granites and rhyolites states to date no one has demonstrated that such magmas may form in the mantle indeed much experimental and geochemical work indicates that such siliceous liquids cannot originate there therefore such magmas must be generated in the crust in island arc environments where the average composition of added material normally is thought to be andesitic a anderson 1982 has shown that the parent melt is basaltic not andesitic in addition kay 1980 has shown that the k content of the newly added material is less than the average k content of the previously existing crust in the oceanic crust the additions from the mantle are basaltic and according to o hara 1982 probably are derived from very mafic picritic melts as parents continental flood basalts which have also added material from mantle to crust also are clearly derived from basaltic parental melts basaltic volcanism study project 1981 thus the evidence for the nature of material subtracted from the mantle and added to the crust for the past several hundred million or perhaps a billion years points to very mafic melts this contrasts significantly with the overall andesitic composition of continental crust it implies furthermore that if the overall archean crustal composition was andesitic as estimated by taylor and mclennan 1981a then additions to the crust have become more mafic with time a concept in direct conflict with most models in which secular trends are from mafic to felsic with time veizer and jansen 1979 and mclennan et al 198o a question which is beginning to appear either explicitly or implicitly is whether crustal volcanic rocks or the crust as a whole really represents the parent melt that formed in the mantle a anderson 1982 o hara 1982 and nisbet and walker 1982

geochemistry of basalts from central and southern new hebrides arc implication for their source rock composition abstract the basaltic rocks from the central and southern islands of the new hebrides aneityum tanna erromango efate emae tongoa and epi have geochemical features typical of island arc volcanics they are enriched in lile and depleted in zr hf nb and ta compared to n type morb the rocks were derived from a similar upper mantle source as n type morb but with a higher degree of partial melting in addition their source was enriched in lile k rb sr ba and lree probably by migrating hydrous fluids released during the dehydration of the subducted oceanic slab the basalts from futuna island which is located farther from the trench display characteristics typical of calc alkaline rocks the futuna basalts were generated from a different lile enriched upper mantle source it seems that this upper mantle source was modified by interaction with partial melts from the subducted oceanic lithosphere

tectonic and volcanic evolution of panarea aeolian islands italy abstract based on new geophysical volcanological structural and radiometric data a morphological structural reconstruction of the submarine part of the panarea volcanic edifice is provided and a model for the evolution of the entire complex is proposed panarea is a small part of a much larger submarine edifice whose overall shape is one of a truncated cone with an eastern protrusion the base of the cone is about 1500 m below sea level it has a diameter of about 23 km and an area of 460 km2 several lobes are present on the steep eastern slopes of the cone and the wide submarine top is of a morphology which is more complex than previously thought the evolution of the panarea volcanic complex occurred in three stages 1 1 development of a central volcano in the western sector of the complex the island of panarea represents the top of this volcano 2 2 eastward shifting of volcanic activity producing development of the lobed eastern sector of the complex 3 3 extensive caldera collapse of the central part of the complex and emplacement within the collapsed area of domes and lava bodies of various affinities some of which are basaltic ne sw oriented structures seem to have had a fundamental role during the development of the panarea volcanic complex these structures have been active until recent times and are of regional significance indeed the evolution of nearby stromboli has been controlled by the ne sw trending structures panarea and stromboli also display similar magnetic anomaly trends geochemical affinities and temporal relationships in volcanism

glacial sediments and landforms of holderness eastern england a glacial depositional model for the north sea lobe of the british irish ice sheet abstract borehole records and exposures at coastal cliffs and inland quarries around holderness are used in a critical assessment of the glacial depositional environments that operated at the margin of the north sea lobe of the british irish ice sheet at the last glacial maximum four lithofacies associations lfa are recognized in the area lfas 1 and 4 are laminated to massive diamictons traditionally called the skipsea and withernsea tills members and display deformation structures indicative of stress from the ne attenuated rafts of soft bedrock lithologies ice bed separation canal fill features and pseudo stratification and clast macrofabric data predominantly indicate deformation only to low strains they are interpreted as subaqueous deposits subsequently deformed by glacier ice to create end products that lie on the glacitectonite continuum localized increases in strain signature are equated with the development of shear zones between onshore thickening wedges of deformed pre existing lake sediment lfa 2 comprises cross bedded clinoforms locally steepening into foresets at the core of linear hummocks along the central spine of holderness lfa 2a and rhythmically laminated silts and sands with dropstones lfa 2b these sediments are interpreted as coalescent glacilacustrine subaqueous outwash fans fining distally to lake bottom rhythmites and varves ice contact deposition is evident in compressional folding faulting and hydrofracture filling due to ice overriding and extensional faulting associated with localized ice melt out depressions produced by folding or sagging provided the accommodation space for the later deposition of lfa 2 and 3 through syntectonic sedimentation lfa 3 comprises flat lying beds of well to poorly sorted cross stratified sands and gravels interpreted as proximal proglacial braided outwash deposits laid down largely in ribbon sandar defined by the topography of abandoned ice contact glacilacustrine depo centres well developed ice wedge pseudomorphs in lfa 3 record permafrost conditions during ice sheet marginal recession indicating that north sea lobe oscillations may have been non climatic or surge related a depositional model is proposed in which advance and retreat phase tills glacitectonites and associated ice contact lake sediments are the geological imprint of a single glaciation the initial advance of the north sea lobe is recorded by a westerly thinning advance till lfa 1 later lfa 1 and 4 retreat tills are strictly glacitectonites and are thicker depositional units because later ice readvances encroached upon and cannibalized more substantial sequences of deglacial lake sediment and subaqueous ice contact fans lfa 2 similar regional till architectures will be manifest wherever the palaeogeography resulted in the onshore flow of ice and the concomitant production of glacitectonites from glacial lake sediments

geochemistry of coexisting alkaline and calc alkaline volcanic rocks from northern azerbaijan n w iran abstract the eocene volcanic rocks of northern azerbaijan n w iran are composed of four distinct associations strongly undersaturated alkaline shoshonitic and calc alkaline all four series are closely associated in space and time they show many features common with rocks of orogenic zones such as low tio 2 mgo nb and high k 2 o ba sr and light ree abundances the rocks within each series are predominantly related by fractional crystallization the contents of major and trace elements in the rocks are consistent with their derivation from an enriched upper mantle by variable degrees of partial melting it is suggested that this enrichment process is related to a subduction zone accompanying the closure of the south tethyan sea during the cretaceous while melting occurred along deep seated faults reactivated during early tertiary times

the glacial sedimentology and geomorphological evolution of an outwash head moraine dammed lake south island new zealand extensive exposures through the glacial landforms around southern lake pukaki new zealand comprise seven lithofacies lfs 1 7 lfs 1 3 are grouped together as lfa 1 pukaki member and record pulsed subaqueous grounding line fan progradation cohesionless debris flows underflow activity and rhythmite deposition by suspension settling iceberg rafting of dropstones and pulsed traction current activity localized disturbance of these deposits by glacitectonic deformation and multi generational hydrofracture fills records minor readvances by the glacier snout and the emplacement of a glacitectonite lf 4 derived from cannibalization of glacilacustrine sediments lfs 4 6 are grouped together as lfa 2 twizel member and record direct glacigenic deposition of glacitectonite lf 4 subglacial traction till lf 5 and supraglacially dumped boulder rubble lf 6 stratigraphic relationships between lfa 1 with lfa 2 record the oscillatory behaviour of the former tasman glacier snout when it formed a calving margin in a proglacial and locally supraglacial lake dammed by a glacitectonically disturbed outwash head and lateral moraine ridges this is entirely consistent with the landform sediment record of its coeval terrestrial margins where flutings and push moraines are diagnostic of active temperate glacier recession from a glacially overridden outwash head the latter being recorded by the vertically stacked sub horizontally bedded and coarse grained gravels of lf 7 waitaki member previous proposals that late pleistocene lake damming was initiated by an ice cored moraine arc appear unfounded because the glacilacustrine deposits only lie above the altitude of the outwash head lateral moraine arc in locations where they have been glacitectonically compressed alternatively it is proposed that the overdeepened subglacial topography was produced by the construction of an outwash head leading to a glacilacustrine sediment sink which operates at times when the expanded tasman glacier actively retreats from the outwash head apex the changing landsystem imprint related to the shrinkage of the tasman glacier records spatio temporal landsystem change involving evolution from a coupled landsystem to a moraine dammed to an uncoupled landsystem

deposition in an esker bead and fan complex lanark ontario canada abstract a glaciofluvial landform complex comprising a single esker ridge proximally multiple ridges and beads in the middle section and a complex of ridges and fans distally is mapped and described we present detailed successions in the associated sediment showing sedimentary structure grain size and palaeocurrent estimates sediment in the esker is mainly coarse grained and varies from boulders with a fine sand matrix deposited at maximum discharges to diamicton interpreted as a product of ice pressing under low discharges early stage deposition in the esker at high flow was from suspension and bed load intermediate stage deposition was mainly from bed load and late stage deposition was from hyperconcentrated suspension the esker rests in a bedrock channel which functioned as a nye channel prior to esker formation the channel surface carries a variety of fluvial erosional marks short distributary ridges of the ridges and beads complex contain mainly cobbles and boulders but beads are mainly in sand with rapid down flow fining and change in sedimentary structure faulting and overfolding of bead sediment suggest a subglacial origin deposition of the esker fan complex was highly variable in space and time down fan sedimentary changes with transitions from gravel to cross laminated fine sand in a few tens of metres indicate rapid loss in competence fan location lateral to the esker indicates a broadening of the zone of subglacial meltwater with time deposition from suspension and steep sided scours are interpreted to result from deposition and erosion by hyperconcentrated flows a model of underflows with submerged hydraulic jumps spilling laterally from the esker tunnel into subglacial cavities explains the morphological and sedimentary characteristics of the fans detailed analysis of small scale fining upwards sequences in the fans and beads indicates deposition by a large number of flow events these events are explained by glacier hydraulics whereby periodic separation of the glacier from its bed caused water with a high suspended sediment concentration to spill out from the esker tunnel into adjacent subglacial cavities evolution of the subglacial drainage system indicates a complexity of subglacial sedimentation near to a grounding line which is not readily apparent from observations at modern glaciers terminating in relatively deep water

eocene paleoseismic record of the green river formation fossil basin wyoming u s a implications of synsedimentary deformation structures in lacustrine carbonate mudstones abstract laterally extensive intervals containing sedimentary deformation features are identified in outcrops of lacustrine deposits of the eocene 52 51 ma green river formation in fossil basin southwestern wyoming fossil basin is the smallest of the paleo lakes in the green river system and is located in the sevier fold and thrust belt which was tectonically active during deposition deformation structures include convolute lamination load structures hybrid brittle ductile features sedimentary dikes microfaults fluid escape features such as cusps and pipes oil shale breccias and mass transport deposits in most cases these structures are hosted by finely laminated variably organic rich carbonate mudstones that accumulated in a low energy profundal lacustrine environment deformed intervals range from a few centimeters to 5 m in thickness and are bound above and below by undeformed strata of the same facies which demonstrates the early post depositional timing of deformation the distribution of these features indicates a primary control exerted by sediment rheology resulting from variation in grain size clay and organic content and degree of lithification which in turn were governed by the depositional environment and early diagenesis based on their morphological attributes lateral extent and recurrence at different stratigraphic levels along with their sedimentary environment and the tectonic setting of the basin the deformation structures are interpreted to be seismites i e the result of stresses induced by syndepositional earthquakes and other potential trigger agents are rejected moreover stratigraphic relationships indicate that these small scale deformation features as well as the mass transport deposits formed on a virtually flat lake floor ruling out instability caused by the gravitational regime syndepositional deformation in fossil basin points to tectonic activity along the nearby absaroka and or hogsback thrusts and related fault systems seismites point to possible tectonic forcing as a mechanism for changes in bathymetry and sedimentation in the green river formation and consequently demonstrate their potential for elucidating the tectonic history of other lacustrine and marine basins

aseismic controls on in situ soft sediment deformation processes and products in submarine slope deposits of the karoo basin south africa intervals of soft sediment deformation features including vertical fluid escape and load structures are common and well exposed in permian lower slope deposits of the tanqua depocentre karoo basin the structures mainly comprise elongated flames and load structures associated with ruptured sandstones and structureless siltstones observed over a range of scales the presence of an upper structureless siltstone layer linked to the flames interpreted as a product of the debouching of fine grained material transported through the flame onto the palaeo seabed together with the drag and upward folding of lower sandstone layers is evidence that the flames were formed in situ by upward movement of sediment rich fluids flames are oriented parallel to the deep water palaeoslope in lateral splay deposits between two major slope channel complexes statistical correlation and regression analyses of 180 flame structures from seven stratigraphic intervals suggest a common mechanism for the deformation and indicate the importance of fluidization as a deformation mechanism importantly deformation occurred in an instantaneous and synchronous manner liquefaction and fluidization were triggered by incremental movement of sediment over steeper local gradients that were generated by deposition of a lateral splay on an inherited local north west facing slope seismic activity is not invoked as a trigger mechanism because of the restricted spatial occurrence of these features and the lack of indications of earthquakes during the time of deposition of the deep water succession the driving mechanisms that resulted in the final configuration of the soft sediment deformation structures involved a combination of vertical shear stress caused by fluidization development of an inverse density gradient and a downslope component of force associated with the local slope ground penetrating radar profiles confirm the overall north east orientation of the flame structures and provide a basis for recognition of potential larger scale examples of flames in seismic reflection data sets

the origin of compositional variation in basalts recovered by submersible drill from mount glooscap mid atlantic ridge at 36 25 n a large peak in the crestal mountains of the mid atlantic ridge about 16 km west of the amar rift valley at 36 25 n was sampled for basalt with a submersible electric rock core drill on a comparable surficial scale as the famous area twenty eight basalt samples from seven drilling stations have been analyzed for major and trace elements many of the samples come from flows lying under a cover of carbonate rocks and therefore could not have been sampled by a submersible or a dredge through comparisons with published compositional data it appears that unlike famous generated basalts amar generated basalts are on average more evolved and are always lree enriched most of the in and between hole compositional variation can be accounted for by low temperature alteration accumulation of phenocrysts and low pressure relatively low temperature fractional crystallization a source heterogeneous in trace elements or undergoing variable degrees of partial melting is necessary to explain the remaining

distribution of soft sediment deformation structures in clinoform successions of the permian ecca group karoo basin south africa abstract the stratigraphic distribution of two groups of soft sediment deformation structures ssds detached dominated by lateral movement forming slides and slump deposits and debrites and in situ dominated by vertical movement forming flame structures pseudonodules and ball and pillow structures are compared in two permian successions in the tanqua and laingsburg depocentres of the karoo basin ssds occur in a series of well exposed 40 to 55 m thick sedimentary cycles cycle thicknesses decrease upwards and the proportion of deformed strata is around 30 in both successions each flooding surface bounded cycle is characterized by a lower unit dominated by thin bedded turbidites overlain by an intermediate section dominated by soft sediment deformed facies above which are undeformed thick bedded mouthbar and shoreface sandstones the upper part of each cycle fines upwards into thin bedded turbidites which are overlain by the cycle bounding flooding surface the cycles and the distribution of ssds are the response to delta outbuilding and retreat over a clinoform rollover and onto a clinoform slope repeatable trends in the distribution of ssds during the evolution of clinoforms in both depocentres indicate a level of stratigraphic organisation and predictability in the otherwise complicated record of processes around the clinoform rollover

a sequence of soft sediment deformation dewatering structures in late quaternary subaqueous outwash near ottawa canada abstract a sequence of soft sediment deformation structures occurs in late quaternary sediments near ottawa canada the sediments are attributed to deposition on subaqueous outwash fans in the champlain sea at the submerged front of the retreating wisconsin glacier in upward sequence the deformed units comprise convolute stratification ball and pillow structures and dish structures deformation is attributed to slumping on the subaqueous fans and or to the melt out of ice blocks which had been buried by fan sediments the sequence of structures is interpreted in terms of a series of events as follows 1 1 local fluidization of low permeability sediments formed convolute stratification disrupted anticlines acted as vertical diapirs through which fluidized sediment ascended 2 2 the diapirs penetrated overlying more cohesive sediments forming ball and pillow structures 3 3 dish structures formed in silty fine sand which had passed upward through the diapirs and between the ball and pillow structures in some cases the silty sand moved downslope as a liquefied sediment flow and dish structures were deformed to give oval plan forms with long axes normal to the local paleoslope