geology and tectonics of the betic zone se spain abstract the southern margin of the iberian continent comprises a complex geological history which can be traced back into the proterozoic when a gneissic basement was formed a cover of nevado filabride rocks was deposited onto this proterozoic basement during the palaeozoic the permian intrusion of the bedar granite suggests that the palaeozoic sedimentary rocks now exposed in the betic cordilleras have been affected by the hercynian orogeny similar to that of palaeozoic rocks in the adjoining ossa morena zone the hercynian basement was probably covered by alpujarride carbonates in the mesozoic when rifting opened tethys and intruded 140 ma old basic dyke swarms the palaeozoic basement of the betic cordilleras comprises a suture of late cretaceous subduction 80 85 ma b p this can be inferred from hp lt metamorphic facies obducted in coeval thrust slices of nevado filabride rocks the nevado filabride nappes include mesozoic carbonates transformed into marbles macael the suture was probably annnealed after the closure of tethys the mesozoic boundary between africa and europe and the rifting in tethys ceased during the palaeogene when the atlas mountains were formed 36 ma b p subsequently relative movements between africa and europe in the neogene were accommodated by strike slip faults these define the iberian microplate moving eastward by atlantic spreading and possibly subducting under italy neogene deformation of iberia is most intensive in southeastern spain due to emplacement of a mantle diapir under the alboran area this occurred early in the neogene aquitanian and caused nappe spreading involving alpujarride and malaguide rocks the subsequent neogene history has now been studied in great detail and is reviewed here it involves clear examples of calc alkaline volcanism most probably not related to subduction seismic motion along strike slip faults within the iberian microplate and syntectonic deposition in intermontane neogene basins

palaeoseismology review of the state of the art abstract historical seismicity provides only a partial indication of the seismotectonic character i e earthquake potential of a given region even in italy where a relatively long historical record exists available catalogues are generally unsatisfactory for this purpose fortunately strong earthquakes often leave geological evidence herein referred to as seismites that are mainly related to surface faulting folding or other deformation and occasionally to secondary ground failures e g landslides liquefaction features etc these features may be preserved and therefore palaeoseismological studies may detect and date them thereby permitting extension of knowledge beyond the local historical threshold up to 2000 years in the most fortunate cases this paper provides a summary of criteria which may aid in the identification of areas suitable for palaeo earthquake investigation historical seismicity and the presence of well developed tectonic geomorphic features are recognized as the most reliable criteria for identifying active faulting however lack of these characteristics cannot be considered conclusive evidence for lack of activity palaeoseismological techniques aim at identifying not only the obvious effects of surface faulting such as offset of young geologic units but also the more subtle tectonic or non tectonic features including liquefaction structures gravity features and coseismic uplift and or subsidence finally we discuss some questions that pertain to palaeoseismicity evaluation techniques among these are the reliability of the quaternary dating techniques the evaluation of the seismic energy released minimum magnitude and principally the unequivocal identification of a seismic origin for the considered geological structures

late mesozoic and cenozoic palaeomagnetism of australia i a redetermined apparent polar wander path summary palaeomagnetic measurements have been carried out on one cretaceous and five cenozoic sedimentary sequences of australia of those one is in the carnarvon basin of north western australia and the others are in the otway basin of south eastern australia the new results are used together with those published previously to define a revised late mesozoic cenozoic apparent polar wander path for australia this path differs from earlier basalt derived paths by the absence of a large westward excursion and zig zag irregularities it is characterized instead by a substantially straight cenozoic trajectory a sharp bend in the late cretaceous and a non uniform rate of apparent polar wander the early tertiary segment of the new path lies north of the original paths thus eliminating a discrepancy that has been noted previously between the indian and australian palaeomagnetic data luyendyk rennick peirce and klootwyk peirce a re examination of the original data suggests that this discrepancy as well as two others in the australian results may have been caused principally by incomplete time averaging of remanence directions because the volcanics on which the results were based had been extruded episodically

high frequency cyclicity in a vertical alternation of gilbert type deltas and carbonate bioconstructions in the late tortonian tabernas basin southern spain abstract the deltaic succession in the tabernas basin represents the first deposition of marine sediments deposited during the late tortonian transgression that linked the mediterranean sea to the atlantic ocean through the basins of the betic cordillera the 100 m thick succession consists of seven 5 to 20 m thick vertically stacked wave dominated gilbert type deltas towards the top of each unit coral reef patches overlie the delta plain and are in turn overlain by calcarenites formed by accumulation of branching red algae colonies locally the calcarenite deposits fill microkarst depressions developed on the reefal carbonates during emergence unlike the corals the red branching algae colonies grew at a few metres depth under low energy conditions below wave base the calcarenites derived from branching red algae colonies formed when the delta plain was drowned creating the new accommodation space needed for the progradation of the delta forming of the overlying unit the repeated alternation of coral reef carbonates tropical carbonates and carbonates with bryomol skeletal assemblages temperate carbonates in the deltaic succession is linked to relative sea level changes reflecting the sum of glacio eustatic sea level fluctuations and tectonic subsidence each delta unit is represented by a transgressive systems tract built by the stacking of distributary mouth bars capped by reef patches a maximum flooding surface represented by branching red algal calcarenites and a highstand systems tract consisting of progradational wave dominated gilbert type delta because of the general increase in accommodation space controlled by glacio eustatic sea level rise and tectonic subsidence beach topset strata and distributary mouth bars were preserved in the cases studied subsidence rates exceeded the glacio eustatic sea level lows preventing the development of normal lowstand systems tracts in the delta stack

modelling seismites with a digital shaking table abstract soft sediment deformation structures induced by seismically triggered liquefaction and or fluidization seismites have been reproduced with a digital shaking table we have used natural sediments with variable granulometric ranges clay silt and sand and an earthquake simulator that is able to reproduce real tridimensional seismograms acceleration and pore pressure recording allowed us to follow liquefaction and or fluidization processes in unconsolidated sediments during earthquakes different types of seismites were produced by variations in the tested sedimentary column

brunhes chron excursion polarity episode recorded during the late pleistocene albuquerque volcanoes new mexico usa summary all basaltic lava flows of the albuquerque volcanoes lat 35 2 n long 253 2 e albuquerque belen basin new mexico record a short excursion polarity episode k ar isotopic age determinations weighted average 155 f 47 ka and evaluation of soil profiles on flow surfaces suggest the late pleistocene circa between 250 and 80 ka as the time of extrusion results from 63 sites in a minimum of eight flows yield a mean direction of d 101 lo z 36 lo ag5 1 2 a 0 7 a 1 2 k 2219 n 8 flows and a corresponding virtual geomagnetic pole position vgp of 354 1 e 20 2 s dp 0 8 dm 1 4 a 0 5 1 4 and vgp angular standard deviation asd 1 8 the unusual magnetization in flows of the albuquerque volcanoes is carried by fine grained single domain sd and or pseudo single domain psd low ti magnetite and is apparently not a function of complex sub solidus alteration of magnetic phases underlying baked soils contain a relatively low coercivity magnetization with directions comprising two groups one is roughly antipodal to the lava remanence the other intermediate between the lava remanence and present field direction because all flows yield statistically indistinguishable directions a field directional path clearly cannot be defined at the precision level of our age determinations the albuquerque feature may correlate with other short polarity episodes or excursions of late pleistocene age e g blake or jamaica though characteristically limited in directional morphology well dated polarity episodes i e sub chrons and excursions recorded in volcanic rocks may provide information on the frequency of significant dynamo instabilities

syn tectonic sedimentation in a neogene strike slip basin containing a stacked gilbert type delta se spain abstract the pliocene sedimentation in the cerro blanco ei barranquete subbasin cbb subbasin that forms part of the larger almeria nijar carboneras basin anc basin is controlled by a releasing overstep and a restraining zone in the ne trending serrata strike slip fault zone the sedimentary development of this subbasin can be considered in three stages of a fault kinematic model during stage i a wave influenced shoaling zone was present in front of an emergent serrata cape to the ne with a basin to the sw and w uplift of the shoaling zone in a restraining n080e trending cerro blanco fault zone cb fault zone is evidenced by the following syn tectonic sedimentary phenomena a a rotational unconformity towards the nw b four deepening pulses in the shallow water zone c massflow deposits originating from a near coastal zone possibly triggered by tectonic pulses during stage ii the uplifted zone became increasingly shallow and finally emerged quartz pebbles in the sediments that indicate a land connection between the serrata cape and the metamorphic basement in the north differentiate this stage from the previous one prograding shoreline deposits marked the outbuilding of the serrata cape towards the sw an episodically subsiding zone due to a releasing overstep between the sinistral n040e trending nw serrata boundary fault nwsb fault and b fault during stage ila is indicated by a southwestward outbuilding fandelta during this stage there was only one depocentre during stage ilb the depocentre of the subsiding zone split up this shifting of depocentres is explained according to the releasing overstep model by an increase of the overlap between the nwsb fault and the b fault during stage iii the cbb subbasin became continental and was inverted as demonstrated by its present day relief the area was severely faulted by n040e trending r and y shears on a metre scale which led to an estimated cumulative sinistral displacement of 2 km since fandelta deposition the present day activity of the nwsb fault is shown by sinistrally deflected stream courses and pressure ridges

permo carboniferous paleoclimate of the congo basin evidence from lithostratigraphy clay mineralogy and stable isotope geochemistry abstract approximately 1000 m of strata in the upper paleozoic lukuga formation in the dekese core in the central congo basin provide lithostratigraphic mineralogical and isotopic evidence for substantial climatic variation within a long lived lacustrine basin lithostratigraphic indicators of cold climate include polymictic strata dropstone deposits and coupled laminations of fine clay size material and coarse silt glacial varves dropstones are concentrated in three stratigraphic zones in the lower 425 m of the lukuga formation and varved strata occur in two broad stratigraphic zones in the lower 700 m of the formation these sedimentological indicators suggest that the lower 2 3 of the lukuga formation was strongly influenced by frigid conditions and glacial like processes the clay size fraction of 97 samples is dominated by detrital minerals including quartz feldspar chlorite illite and poorly ordered expansible 2 1 phyllosilicates based on variation in the mineralogy of these samples the lukuga formation is divisible into three clay mineral zones cmzs numbered in ascending stratigraphic order cmz 1 and cmz 3 include several horizons of expansible 2 1 phyllosilicates that represent warmer wetter intervals intervening cmz 2 is a long 500 m zone of chlorite and illite with no expansible phyllosilicates and is interpreted as a continuous cold frigid interval there are numerous calcite cemented layers including spar filled veins that cross depositional bedding and represent postburial alteration radiaxial fibrous cements that displace detrital grains and micrite that crystallized near the time of deposition eighty two stable isotope analyses of micrite yield 13c values that range from 44 6 to 4 1 and 18o values that range from 20 0 to 5 0 vpdb the carbon isotope data likely reflect a range of local carbon sources derived from bacterial activity and are unrelated to paleoclimatic conditions in contrast stratigraphic patterns in the oxygen isotope data suggest five or six intervals of frigid conditions conducive to glacial processes

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

geochemical correlation in an exhumed submarine channel complex tabernas basin se spain comparison to sedimentological correlation at various length scales abstract whole rock inorganic geochemical data have previously been used to aid characterization and stratigraphic correlation of fossil poor clastic sedimentary deposits although this approach has not yet been calibrated by testing chemostratigraphic correlations against physical stratigraphic correlations from outcrop chemical data from a well exposed siliciclastic succession in a tortonian late miocene submarine slope channel system in the tabernas basin of southern spain were generated using x ray fluorescence supplemented by x ray diffraction sem analysis and light microscopy amongst the 60 elements measured nearly a quarter of them have proved to be useful or reliable for geochemically based correlation at the tested scales 10 m 50 m 100 m these elements are sio2 k2o al2o3 cao and tio2 as well as zr nb th rb cs as and the rare earth elements la nd and ce high resolution bed to bed geochemical correlation is feasible over short distances 10 m geochemical data from sections in beds that are traceable suggest that a given stratigraphic level seems to be geochemically homogeneous with respect to some key elements geochemical data also provide a useful aid for high resolution sedimentary correlation at distances of several tens of meters up to at least 100 m since each individual bed seems to be broadly homogeneous in composition at a larger scale it is possible to discern a provenance signal in geochemical data chemical stratigraphy thus seems to work even in stratigraphically complicated submarine channel complexes

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

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

gravity slide and resedimentation processes in a miocene carbonate ramp hyblean platcau southeastern sicily abstract more than twenty sharp based channel form structures occur in the miocene palazzolo formation carbonates within a distally steepened se sicilian miocene carbonate ramp contemporaneous biota indicate deposition in water depths of 70 150 m fully exposed structures commonly exceed one kilometre along palacostrike their bases are concordant with the host strata but these steepen to 15 in proximity of their margins internal bedding planes generally are concordant with the basal truncation surface the lithologies of the channel fills are similar to the host sediment there is little evidence that these structures are erosional since they contain neither breccias nor turbidites rather they are interpreted as the product of gravitational sliding involving thin detached sheets of consolidated ramp carbonates the resulting irregular topography was draped by redeposited fine grained carbonate sediments once healed and further oversteepened renewed gravity sliding occurred this resulted in a 250 m thick slide dominated succession in a zone 4 km wide located between the outer ramp apron comprised of coralline algal and foraminifera rich sediments and basin margin pelagic marls this phenomenon although unusual in shallow water settings is well known from modern continental slope environments sliding was probably triggered by seismicity in the region associated with two known mesozoic basement faults an alternative hypothesis involving pressure gradient build up along distally steepened ramp zones during storm surges is dismissed as a cause although this mechanism may have facilitated resedimentation of seafloor sediments over the slide zone

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

early post impact sedimentation around the central high of the mjolnir impact crater barents sea late jurassic abstract the mjolnir bolide created the 40 km diameter mjolnir crater when it impacted the black mostly anoxic clays of the hekkingen formation in the paleo barents sea about 142 2 6 million years ago the normally calm 300 500 m deep epicontinental depositional environment was suddenly disrupted by the dramatic effect of the impact resulting in a brief period of extreme sediment reworking and redeposition the hypoxic to anoxic depositional conditions characteristic of the hekkingen formation returned to the impact site soon after the collapse when the major modification phases of the mjolnir crater were completed we have studied a shallow core 121 m long retrieved from the flanks of the central high in the mjolnir crater the core shows a complex depositional succession of the ragnarok formation which is related to both the uplift and the subsequent collapse and drowning of the central high the basal part of the core consists of chaotically organised large folded slabs of pre impact substrate which we infer to be related to the rapid steepening of the slope of the central high during its rising shortly after the impact the slump deposits are overlain by a diamict which is interpreted to originate from debris flows that originate by liquefaction and subsequent remoulding and remobilisation of sediment from the collapsing central high the diamict is in turn covered by a brecciated graded mudstone that records the action of impact related tsunami and the subsequent submergence of the impact crater a sequence of mainly debris flow and turbidite deposits separates the impact related deposit from the overlying shelf sediments of the hekkingen formation and forms the last post impact sedimentary recorder of the presence of a central high in the crater

sandy gravelly mass flow deposits in an ice marginal lake saalian leuvenumsche beek valley veluwe the netherlands with emphasis on plug flow deposits abstract in three pits in the leuvenumsche beek valley near ermelo and elspeet massive and diffusely banded clean gravelly sands found in association with sandy sediments showing some similarities to the bouma sequence were interpreted as originating from sediment gravity flows the flows which came to rest on a ca 6 paleoslope probably originated from slumping of parts of the ice pushed ridges at either side of an ice marginal lake major characteristic features in the three sand pits studied are u shaped channel forms with a maximum depth and width of 10 25 rmm the fills consist of sand and gravels locally containing giant sand clasts the sediments just below the base of these channel forms are commonly distorted and folded especially the massive more sandy fills are surrounded by a finer grained diffusely bedded and inversely graded zone these sedimentary features suggest that rigid sediment plugs sheared downslope generating a finer grained shear zone around the plug scouring a slide scar till its present semi cylindrical form and preserving the steep sides exceeding the angle of repose of the channel form by freezing the u shaped channel forms plugged troughs are locally overlain by shallower gently sided trough structures with mainly diffusely banded infillings very shallow and often smaller troughs are found again on top of these massive and diffusely banded infillings the sediments in these troughs consist of repetitions of two types of microsequences 1 thickly bedded sequences of normally graded massive sands near horizontal stratifications plane beds and cross bedded sets and 2 thinly bedded sequences of relatively thick units t a and thin units t c and t d of the bouma sequence the repetitions of the microsequences are interpreted as flow pulsations upwards thinning of the sequence together with a finer grain size may point to waning flow conditions their association with plugged troughs is suggestive of retrogressive flow slides

mega debris flow deposits from the oligo miocene pindos foreland basin western mainland greece implications for transport mechanisms in ancient deep marine basins the turbidite dominated oligo miocene pindos foreland basin of western mainland greece contains two thick 60 72 m matrix supported conglomerates the conglomerates are ungraded and contain three clast types 1 polymict rounded extrabasinal clasts long axes 3 50 cm 2 tightly folded intrabasinal clasts long axes 1 10 m and 3 tabular largely undeformed intrabasinal blocks long axes 18 300 m clasts are isolated within a slit dominated matrix these chaotic matrix supported conglomerates are interpreted as mega debris flow deposits during transport extrabasinal clasts were supported by a combination of matrix cohesion and clast dispersive pressure folded intrabasinal clasts were supported by a combination of buoyancy archimedes principle and clast dispersive pressure the large tabular clasts were transported by gravity sliding gliding within the flow on films at high pore fluid pressure these different clast support mechanisms were active simultaneously within the pindos mega debris flow deposits as a result the deposits have no systemic vertical stratigraphy in contrast to many described large scale mass flow deposits the mega debris flow deposits are significantly thicker than most described ancient siliciclastic debris flow deposits and provide an ancient analogue for the thick recent siliciclastic debris flow deposits on continental margins

numerical models of the geodynamo and observational constraints 1 the past few years have seen the emergence of a large number of numerical simulations of the geodynamo in parallel both new and old geomagnetic archeomagnetic and paleomagnetic observations have been interpreted as actual geomagnetic features and used as constraints for dynamo models naturally model predictions should be tested against actual characteristics of the geomagnetic field despite huge differences sometimes in excess of a billion between the values of parameters used in the simulations and those estimated for the earth it is intriguing that many available simulations succeed in producing largely axial dipolar magnetic fields with weaker nondipolar structures in agreement with the first order characteristics of the geomagnetic field yet when considering finer characteristics there are significant differences and failures to actually produce a number of fundamental characteristic features in this presentation we first review numerical results obtained to date then we attempt to summarize which field characteristics derived from observational data sets can be considered robust on the basis of simple criteria used to evaluate the degree of confidence that can be placed in each datum we sort presumably characteristic geomagnetic features into three categories robust controversial and unlikely we conclude that numerical models should be illustrated with a number of key predictions averaged over at least 10 dipole diffusion times these predictions should be tested against the subset of robust observations only controversial observations should await additional confirmation

earthquakes as a triggering mechanism for debris flows and turbidites on the calabrian ridge abstract debris flows and turbidites have been described in piston cores bottom photographs and side looking sonar records from basin floors amid the rugged irregular topography of the calabrian ridge a sediment transport process is inferred which began with a rotational slump on the steep basin wall subsequently transformed into a debris flow and turbid cloud such events occurred approximately every 1500 years because the debris flow turbidite deposits are correlative between basins some relatively widespread mechanism such as an earthquake is required to initiate the slope failure the estimated intensity of ground shaking as a result of historical earthquakes on the nearby calabrian and hellenic arcs has been used to develop a relationship between frequency of occurrence and intensity of ground shaking extrapolation of this relation to infrequent large magnitude events shows that the 1500 yr event is small enough to be geologically plausible but large enough to cause slope failure on basin walls it is possible that the historical record fortuitously contains one of these large magnitude long repeat time events which may have caused the most recent of the observed debris flows in 1903

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

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

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

transitional field behaviour from southern hemisphere lavas evidence for two stage reversals of the geodynamo palaeomagnetic records from australasian basalts provide a rare view of transitional field behaviour as seen from mid southern latitudes these data suggest that a geomagnetic reversal is accomplished in two steps separated by an interval of relative dynamo quiescence a potentially long lived field configuration developed early is observed to be the stepping stone from which both successful and unsuccessful reversal attempts are made several aborted attempts involving the same intermediate field geometry may precede an actual polarity transition

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

basinal setting and origin of thick 1 8 km mass flow dominated grand conglomerat diamictites kamoa democratic republic of congo resolving climate and tectonic controls during neoproterozoic glaciations

dual polarity directions in basaltic andesitic dykes reversal record or self reversed magnetization summary rock magnetic analyses were performed on basaltic andesitic dyke samples from the lhasa block which were previously used for palaeomagnetic investigations of the india asia collision the aim of the study is to prove whether antipodal directions separated in these samples represent different polarities of the earth s magnetic field or a self reversal magnetization reflected light microscopy domain pattern observations and energy dispersive x ray analyses revealed two generations of titanomagnetite tm grains one consisting of largesized 20 m to more than 100 m and inhomogeneous ti poor tm and another with small smaller than 10 m and rather homogeneous ti rich tm grains partial thermoremant magnetization experiments and reflected light microscopy show that magnetostatic or superexchange interaction between these two phases is unlikely temperature dependence of saturation magnetization and low temperature curves of isothermal remanent magnetization disprove a possible n type behaviour of the samples a self reversal due to ionic reordering can be ruled out as it requires a high degree of oxidation of the ti rich tms which was not observed in summary a self reversal magnetization is very unlikely in the studied dyke samples and therefore the observed antipodal directions most probably represent a record of different polarity epochs of the earth s magnetic field this conclusion implies that the time of remanence acquisition in the studied dykes was sufficiently long to average out paleosecular variation supporting the significance and reliability of the palaeomagnetic results

seismites an attempt at critical analysis and classification abstract the main types of seismites are reviewed following the proposed classification and are illustrated by our own case studies the large variety of seismites depends on the sedimentologic hydrodynamic and diagenetic characters of the deposits subject to seismic shocks on a given site generally different types of seismites cane be related to the same seismic event these peculiar but widespread sedimentary structures are not always univocal and may often be related to different causes therefore the structures discussed must necessarily be placed in a detailed geological context

deciphering records of geomagnetic reversals polarity reversals of the geomagnetic field are a major feature of the earth s dynamo questions remain regarding the dynamical processes that give rise to reversals and the properties of the geomagnetic field during a polarity transition a large number of paleomagnetic reversal records have been acquired during the past 50 years in order to better constrain the structure and geometry of the transitional field in addition over the past two decades numerical dynamo simulations have also provided insights into the reversal mechanism yet despite the large paleomagnetic database controversial interpretations of records of the transitional field persist they result from two characteristics inherent to all reversals both of which are detrimental to an ambiguous analysis on the one hand the reversal process is rapid and requires adequate temporal resolution on the other hand weak field intensities during a reversal can affect the fidelity of magnetic recording in sedimentary records this paper is aimed at reviewing critically the main reversal features derived from paleomagnetic records and at analyzing some of these features in light of numerical simulations we discuss in detail the fidelity of the signal extracted from paleomagnetic records and pay special attention to their resolution with respect to the timing and mechanisms involved in the magnetization process records from marine sediments dominate the database they give rise to transitional field models that often lead to overinterpret the data consequently we attempt to separate robust results and their subsequent interpretations from those that do not stand on a strong observational footing finally we discuss new avenues that should favor progress to better characterize and understand transitional field behavior

remagnetization of lava flows spanning the last geomagnetic reversal large directional changes of remanent magnetization within lava flows that cooled during geomagnetic reversals have been reported in several studies a geomagnetic scenario implies extremely rapid geomagnetic changes of several degrees per day thus difficult to reconcile with the rate of the earth s core liquid motions so far no complete rock magnetic model provides a clear explanation we revisited lava flows sandwiched between an underlying reverse and an overlying normal polarity flow marking the last reversal in three distinct volcanic sequences of the la palma island canary archipelago spain that are characterized by a gradual evolution of the direction of their remanent magnetization from bottom to top cleaning efficiency of thermal demagnetization was not improved by very rapid heating and cooling rates as well as by continuous demagnetization using a triaxe magnetometer we did not observe partial self reversals and minor changes in magnetic grain sizes are not related to the within flow directional changes microscopic observations indicate poor exsolution which suggests post cooling thermochemical remagnetization processes this scenario is strongly reinforced by laboratory experiments that show large resistance to thermal demagnetization when thermoremanence was acquired over a long time period we speculate that in the present situation exsolution was reactivated during in field reheating and yielded formation of new magnetite yet magnetic domain state rearrangements could also play a role initial reheating when the overlying flow took place albeit moderate less than 200 300 c was enough to produce overlying components with significantly higher unblocking temperatures

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

the character of seismo turbidites in the s 1 sapropel zakinthos and strofadhes basins greece the early holocene s 1 sapropelic sequence in the northwest hellenic trench has been studied in six piston cores from the zakinthos and strofadhes basins the s 1 sequence 0 7 3 5 m thick consists principally of silt to mud turbidites with rare thick disorganized sandy turbidites these lithofacies are described and compared with fine grained turbidites from the literature petrographical data including the abundance of organic carbon and planktonic microfossils indicate that the principal source of sediment to the turbidites was from the continental slope on the basis of composition and texture five turbidite units can be correlated between the two basins these basins are fed by separate but adjacent drainage systems the apparently synchronous occurrence of turbidites in the two drainage systems suggests that the turbidity currents were seismically triggered some of the turbidites show poorly organized beds which may reflect the slump origin and the short 30 km distances of travel turbidites were deposited more frequently in the s 1 sapropelic interval than in the over and underlying sediments application of slope stability analysis shows that on the 8 slopes above the basins a 10 cm thick sapropel would have a factor of safety of about 2 and would fail with earthquake accelerations in excess of 0 08 g the frequency of earthquakes likely to produce such accelerations is similar to the observed frequency of turbidites the low strength of the sapropelic sediment makes it particularly susceptible to such failure similar thin skinned slumping may be an important process for the initiation of turbidity currents in other environments where there are steep slopes or high sedimentation rates

turbidites facies response to the morphological confinement of a foredeep cervarola sandstones formation miocene northern apennines italy

contained reflected turbidity currents from the middle ordovician cloridorme formation quebec canada an alternative to the antidune hypothesis the parautochthonous cloridorme formation is a syn orogenic flysch succession that was deposited in an elongate foredeep basin as mainly lower middle fan outer fan and basin floor deposits the basin floor deposits about 1 5 km thick are confined to members 1 2 and 1 and are characterized by graded thick 1 10 m mud rich calcareous greywacke beds previously interpreted as deposits of concentrated muddy unidirectional turbidity currents that locally generated backset antidune lamination in internally stratified flows the dominant flow directions were from east to west but west to east transport also occurred as seen in the orientation of ripples climbing ripples flutes consistently overturned flames and grain imbrication we believe that the flows that deposited these thick calcareous greywacke beds reversed by roughly 180 one or more times during deposition of the lower sandy part of the beds flow reversals are consistent with the sharp grain size breaks and mud partings within sandy divisions measurement of grain fabric relative to stratification in the most celebrated antidune bedforms indicates flow from west to east thus the bedforms were produced by west to east migration of megaripples not by the upcurrent migration of antidunes the thick muddy beds were deposited by large volume muddy flows that were deflected and reflected from the side slopes and internal topographic highs of a confined basin floor much like the contessa and similar beds of the italian apennines large quantities of suspended mud were ponded above the irregular basin floor and settled to produce the thick silty mudstone caps seen on each bed because of their mode of emplacement we propose that these beds be called contained turbidites