paleoenvironmental and temporal significance of variably colored paleozoic orthoconic nautiloid cephalopod accumulations abstract accumulations of orthoconic nautiloid cephalopods occur throughout the lower paleozoic from the ordovician to the carboniferous studies focused on unraveling the nature of their formation tend to be restricted both spatially and temporally to localized investigations of either the constituent faunas or the lithological successions within which they occur herein an innovative approach to determining common factors among these particular fossil rich beds is utilized whereby different color and taphonomic groupings are identified and classified for known world occurrences of orthoconic nautiloid cephalopod concentrations these groupings are related to inferred paleosettings and paleoenvironmental gradients those horizons with a predominantly black to gray color generally represent event beds and were frequently deposited together with black shales while those ranging from red brown green beige are prevalently accumulations associated with condensed sequences and discontinuity surfaces the findings are further used to identify time specific changes in orthoconic nautiloid accumulation processes

lateral velocity resolution from three dimensional seismic refraction data summary a method for estimating the lateral velocity resolution from 3 d seismic refraction traveltimes is presented the method is non linear in that synthetic data calculated from checkerboard models are inverted using an iterative tomographic approach incorporating smoothness constraints and updated ray paths at each iteration two applications are presented 1 real data from the faeroe basin experiment using the ray coverage and noise level of approximately 50 000 picks and 2 ideal data from the same experiment corresponding to 100 per cent data recovery equivalent to about three times as many ray paths the refraction data constrain the sedimentary and basement structure to approximately 12 km depth a comparison of the results from the two data sets provides a qualitative check on the resolution method illustrates the pitfalls of using ray coverage as an indicator of resolution and demonstrates the potential resolution of currently feasible 3 d refraction experiments 32 checkerboard models consisting of alternating positive and negative velocity anomalies superimposed on the preferred final model of the basin were tested each with a diverent cell size position or orientation the problem of ray bending associated with the 5 per cent checkerboard anomalies is shown to be small using models with four cell sizes allowed for resolution estimates from 3 to 15 km this range being imposed by the frequency content of the data and the areal dimensions of the study area 44 26 km an operator centred on each model node measures the local semblance between the known and recovered checkerboard models a determination of the smallest well resolved cell size at each model node is then made using a 0 7 semblance threshold to provide a spatially dependent lateral resolution estimate resolution for the real data set varies from an average of just over 3 km at 2 km depth to 10 km at 10 km depth where there is a local maximum in ray coverage due to a concentration of ray bottoming points for the ideal data set the average lateral resolution drops ov roughly linearly from better than 3 km at 2 km depth to 6 3 km at 10 km depth the largest diverence between the resolution associated with the ideal and real data occurs at 7 2 km depth where it averages 4 6 km for the former and 10 8 km for the latter due to the near absence of ray bottoming points between 7 and 9 km the results show that the final model for the faeroe basin obtained by regularized inversion with smoothness constraints is consistent with the resolution estimates in the sense that the model does not contain structure with a wavelength smaller than the resolution estimate at any point the results for the ideal data show that good quality 3 d refraction experiments can provide a lateral resolution of no worse than the receiver spacing shot spacing for land data throughout most of the sampled volume

growth and destruction of gran canaria deduced from seismic reflection and bathymetric data the morphology and structure of the submarine flanks of gran canaria have been mapped using hydrosweep swath bathymetry and high resolution reflection seismic data the growth and destruction of the island has been characterized previously by three major periods of volcanic activity 16 9 ma 4 5 3 5 ma younger than 3 ma separatedby erosional intervals two major sector collapses along the west coast inferred from the coastal morphology are believed to have formed at the end of the shield building phase one is characterized by a 19 km wide reentrant along the northwestern coast that may have formed synchronously with the formation of the 20 km diametermiocene tejeda caldera high sedimentation rates around gran canaria 50 m myr tend to cover and bury major landslide blocks ssw off the island several canyons continue seaward into a major sediment fan a 9 5 km wide volcaniclastic ridge in this fan is interpreted to represent deposits of the pliocene subaerial roque nublo debris avalanche we tentatively interpret the slope break at a depth of 600 800 m as the transition between subaerial and subaqueous chilled lavas at the end of the shield building phase the subsidence caused by the volcanic load 30 000 km3 on the lithosphere may thus amount to no more than 800 m several canyons on the island can be traced down the submarine flanks to a depth of 3 5 km indicating that at least deeper portions below the level of subsidence were eroded by mass flows continuing seaward from the subaerial canyons four submarine volcanoes were identified west and northeast of the island

cone sheet formation and intrusive growth of an oceanic island the miocene tejeda complex on gran canaria canary islands more than 500 trachytic to phonolitic cone sheet dikes hypabyssal syenite stocks and subordinate radial dikes form a 20 km diameter intrusive complex in the volcaniclastic fill of the miocene tejeda caldera 20 35 km on gran canaria canary islands the dikes intruded concentrically around a central axis of radial symmetry and dip uniformly an average of 41 toward the center single crystal 40ar 39ar ages of dikes and syenite stocks ranging from 12 3 0 1 to 7 32 0 05 ma suggest more or less continuous intrusive activity during both volcanically active and inactive phases intrusions were emplaced at average intervals of 5 10 k y while explosive eruptions took place at 50 k y intervals the estimated aggregate volume of evolved cone sheet magma added at shallow level 2000 m below sea level amounts to 250 km3 compared to 500 km3 of evolved extrusive volcanics erupted during the same period formation of the tejeda cone sheets most likely resulted from deformation processes due to resurgent doming initiated by the recurrent replenishment of a flat laccolith like shallow magma chamber magma supply exceeding the volume that could be compensated for by updoming of the overlying caldera fill resulted in the formation of cone shaped fractures

the role of partial melting in the 15 ma geochemical evolution of gran canaria a blob model for the canary hotspot the subaerial portion of gran canada canary islands was built by three cycles of volcanism a miocene cycle 8 5 15 ma a pliocene cycle 1 8 60 ma and a quaternary cycle 1 8 0 ma only the pliocene cycle is completely exposed on gran canaria the early stages of the miocene cycle are submarine and the quaternary cycle is still in its initial stages during the miocene sio2 saturation of the mafic volcanics decreased systematically from tholeiite to nephelinite for the pliocene cycle sio2 saturation increased and then decreased with decreasing age from nephelinite to tholeiite to nephelinite sio2 saturation increased from nephelinite to basanite and alkali basalt during the quaternary in each of these cycles increasing melt production rates sio2 saturation and concentrations of compatible elements and decreasing concentrations of some incompatible elements are consistent with increasing degrees of partial melting in the sequence melilite nephelinite to tholeiite the mafic volcanics from all three cycles were derived from co2 rich garnet lherzolite sources phlogopite ilmenite sulfide and a phase with high partition coefficients for the light rare earth elements lree u th pb nb and zr possibly zircon were residual during melting to form the miocene nephelinites through tholeiites phlogopite ilmenite and sulfide were residual in the source of the pliocene quaternary nephelinites through alkali basalts highly incompatible element ratios e g nb u pb ce k u nb pb ba rb zr hf la nb ba th rb nb k nb zr nb th nb th la and ba la exhibit extreme variations in many cases larger than those reported for all other ocean island basalts but these ratios correlate well with degree of melting survival of residual phases at higher degrees of melting during the miocene cycle and differences between major and trace element concentrations and melt production rates between the miocene and pliocene tholeiites suggest that the miocene source was more fertile than the pliocene quaternary source s we propose a blob model to explain the multi cycle evolution of canary volcanoes and the temporal variations in chemistry and melt production within cycles each cycle of volcanism represents decompression melting of a discrete blob of plume material small degree nephelinitic and basanitic melts are derived from the cooler margins of the blobs whereas the larger degree tholeiitic and alkali basaltic melts are derived from the hotter centers of the blobs the symmetrical sequence of mafic volcanism for a cycle from highly undersaturated to saturated to highly undersaturated compositions reflects melting of the blob during its ascent beneath an island in the sequence upper margin corelower margin volcanic hiatuses between cycles and within cycles represent periods when residual blob or cooler entrained shallow mantle material fill the melting zone beneath an island

palynology dacryoconarids and the lower eifelian middle devonian basal chotec event case studies from the prague and appalachian basins

a multichannel seismic study of lithospheric flexure across the hawaiian emperor seamount chain existing models assume that the thickened crust beneath seamounts is the result of a surface volcanic load flexing an elastic plate new results suggest that flexed oceanic crust beneath the hawaiian emperor seamount chain is underlain by a 4 km thick deep crustal body we intepret the body as a deep crustal sill complex associated with the tholeiitic stage of volcano building along the chain

a seismic study of lithospheric flexure in the vicinity of tenerife canary islands seismic data have been used to determine the crustal and upper mantle structure of tenerife canary islands a volcanic island of tertiary age located on 140 ma oceanic crust reflection data show that oceanic basement dips gently towards the island forming a flexural moat which is infilled by 2 3 km of well stratified material the moat is characterised by a major angular unconformity which we attribute to volcanic loading of pre existing oceanic crust and overlying sediments and the subsequent infilling of the flexure by material that was derived at least in part from the islands refraction data show that the flexed oceanic crust has a mean thickness of 6 41 0 42 km and upper and lower crustal velocities of 4 8 5 4 km s 1 and 6 7 7 3 km s 1 respectively the flexure which has been verified by gravity modelling can be explained by a model in which tenerife and adjacent islands have loaded a lithosphere with a long term 106 yr elastic thickness of approximately 20 km seismic and gravity data suggest that up to 1 5 105 km3 of magmatic material has been added to the surface of the flexed oceanic crust which assuming an age of 6 16 ma for the shield building stage on tenerife implies a magma generation rate of about 0 006 to 0 02 km3 a 1 this rate is similar to estimates from other african oceanic islands e g reunion and cape verdes but is significantly less than that which has been calculated at hawaii there is no evidence in either the seismic or gravity data that any significant amount of magmatic material has underplated the flexed oceanic crust the crustal and upper mantle structure at tenerife therefore differs from other oceanic islands such as hawaii and marquesas where 4 km of underplated material have been reported

seismotectonics of the canary islands abstract a revision of the seismicity both historical and instrumental for the canary islands is presented the occurrence on may 9 1989 of an earthquake of magnitude 5 2 between the islands gran canaria and tenerife followed by a large number of aftershocks have been interpreted on seismotectonic grounds the main conclusion is that a horizontal compressional stress regime in nw se direction is present in the region which is compatible with the tectonics in the northwestern part of the african continent

k bentonites volcanic ash preservation and implications for early to middle devonian volcanism in the acadian orogen eastern north america lower to middle devonian marine strata in the appalachian foreland basin feature up to 80 or more thin k bentonites that represent ancient volcanic ashes the time vs space distribution of k bentonites through the lochkovian to eifelian stages representing 30 m y shows a distinct pattern of clustered multiple beds several scattered beds and thick intervals with no k bentonites four clusters of 7 to 15 individual closely spaced layers occur in the middle lochkovian bald hill k bentonites kalkberg new scotland formations late pragian or early emsian sprout brook k bentonites esopus formation and early eifelian two clusters the tioga middle coarse zone and tioga a g k bentonites onondaga formation detailed examination of these devonian k bentonites shows that in many cases they do not represent a single eruption multilayered beds fossil layers within beds authigenic minerals e g glauconite and phosphate nodules subjacent hardgrounds and an irregular distribution of beds through space and time raise questions about the depositional history and preservation potential of volcanic ash in marine environments and the degree to which the beds represent a primary record of volcanism these and other lines of evidence indicate that postdepositional physical biological and geochemical processes e g sedimentation rate event and background physical processes burrowing have modified the primary record of these water laid ash fall events these factors may lead to preservation of primary ash deposits or to their resedimentation and or partial to complete mixing with background sediments the preservation potential and resulting distribution of the devonian k bentonites can be analyzed across a spectrum of preservational magnafacies in this paper i present a model of ash preservation the model incorporates environmentally related physical biological and chemical processes active in epicontinental seas and marine foreland basins conclusions based on the model indicate that the middle lochkovian early emsian and early eifelian were times of peak volcanic activity in eastern north america related to times of increased tectonism in the acadian orogen

volcanic tephra bed formation and condensation processes a review and examination from devonian stratigraphic sequences abstractthe formation and preservation of airfall volcanogenic tephras is the result of various interacting factors explanations of the depositional history of individual tephra beds lie along a spectrum between two end member models of a primary single event and a complex depositional history nonrecognition of the history of a tephra bed may lead to errors in geochronology correlation and interpretation of the record of explosive volcanism in sedimentary successions increased understanding of sequence stratigraphic principles and condensation processes favors the model of tephras with a complex depositional history this is supported by studies that indicate many tephras in the rock record result from amalgamation and or reworking in the depositional environment a prediction of increased tephra bed formation preservation within transgressive systems tracts due to condensation processes is tested through 11 lochkovian to eifelian lower to lower middle devonian depositional sequences the character

calibrating the devonian time scale a synthesis of u pb id tims ages and conodont stratigraphy the recalibrated devonian time scale represents an important improvement of devonian chronology regarding two aspects firstly a data set of 13 biostratigraphically well bracketed u pb id tims zircon and monazite ages constitutes the framework of the scale secondly approximately time linear biostratigraphic scales have been used for the interpolation between the isotopic ages the new construction thus represents a biochronometric time scale which allows the assignment of numeric ages not only to stage boundaries but also to each biozone boundary the method of interpolation applied also enables the projection of the geochronological error onto the time scale according to the newly calibrated scale the devonian lasted 57 4 5 7 ma from 418 1 3 0 to 360 7 2 7 ma this is compared to previously published time scales the longest time span ever calculated for this period the age interpolations for the eight stage boundaries are famennian tournaisian devonian carboniferous 360 7 2 7 ma frasnian famennian 376 1 3 6 ma givetian frasnian 383 7 3 1 ma eifelian givetian 388 1 2 6 ma emsian eifelian 391 9 3 4 ma pragian emsian 409 1 3 8 ma lochkovian pragian 412 3 3 5 ma pridolian lochkovian silurian devonian 418 1 3 0 ma full size table table options view in workspace download as csv the duration of the middle devonian is calibrated here as quite short with 8 2 ma and the emsian and the famennian are the longest stages with interpolated durations of 17 2 and 15 4 ma respectively together all devonian stages contain 57 conodont zones including subzones according to the standard conodont zonation giving a mean duration of about 1 ma in the highly resolved part of the time scale mid eifelian to the devonian carboniferous boundary zonal resolution averages 0 6 ma in contrast the lowest resolution is shown in the early emsian to mid eifelian interval with zonal durations of up to 5 5 ma serotinus zone

brachiopod faunas facies and biostratigraphy of the pridolian to lower eifelian succession in the rhenish massif rheinisches schiefergebirge germany

pn velocities beneath continental collision zones the turkish iranian plateau summary tomographic imaging of the uppermost mantle velocity in the middle east shows normal pn velocities 8 0 8 2 kms beneath the black sea and the southern caspian sea in contrast low pn velocities 7 9 km s i are found beneath the aegean sea and much of the turkish iranian plateau a region of exceptionally low pn velocities c7 6 km s beneath the lesser caucasus mountains and along the turkish iranian border coincides with a region of high sn attenuation and extensive neogene volcanism all these features suggest that near solidus conditions exist within the uppermost mantle beneath the turkish iranian plateau such conditions may result either from the decompression melting associated with upwelling convection cells or by the infiltration of water released from subducted lithosphere into the mantle above the presence of a partially melted uppermost mantle weakens the lithosphere beneath the turkish iranian plateau thus allowing it to become the locus of deformation in the arabian eurasian collision zone

new u pb zircon ages and the duration and division of devonian time newly determined u pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the devonian time scale they are 1 417 6 1 0 ma for an ash within the conodont zone of icriodus woschmidti i w hesperius early lochkovian 2 408 3 1 9 ma for an ash of early emsian age correlated with the conodont zones of po dehiscens lower po inversus 3 391 4 1 8 ma for an ash within the po c costatus zone and probably within the upper half of the zone eifelian and 4 381 1 1 3 ma for an ash within the range of the frasnian conodont palmatolepis punctata pa punctata zone to upper pa hassi zone u pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites lepidophyta spore zone are dated at 363 8 2 2 ma and 363 4 1 8 ma respectively suggesting an age of363 ma for a level within the late famennian pa g expansa zone these data together with other published zircon ages suggest that the base and top of the devonian lie close to 418 ma and 362 ma respectively thus lengthening the period by20 over current estimates we suggest that the duration of the middle devonian eifelian and givetian is rather brief perhaps no longer than 11 5 myr 394 ma 382 5 ma and that the emsian and famennian are the longest stages in the period with estimated durations of15 5 myr and 14 5 myr respectively 1998 elsevier science b v all rights reserved

hotspot volcanism close to a passive continental margin the canary islands the canarian archipelago is a group of volcanic islands on a slow moving oceanic plate close to a continental margin the origins of the archipelago are controversial a hotspot or mantle plume a zone of lithospheric deformation a region of compressional block faulting or a rupture propagating westwards from the active atlas mountains fold belt have been proposed by different authors however comparison of the canarian archipelago with the prototypical hotspot related island group the hawaiian archipelago reveals that the differences between the two are not as great as had previously been supposed on the basis of older data quaternary igneous activity in the canaries is concentrated at the western end of the archipelago close to the present day location of the inferred hotspot this is the same relationship as seen in the hawaiian and cape verde islands the latter archipelago associated with a well defined but slow moving mantle plume shows anomalies in a plot of island age against distance which are comparable to those seen in the canary islands these anomalies cannot therefore be used to argue against a hotspot origin for the canaries individual islands in both archipelagoes are characterized by initial rapid growth the shield building stages of activity followed by a period of quiescence and deep erosion erosion gap which in turn is followed by a post erosional stage of activity the absence of post shield stage subsidence in the canaries is in marked contrast with the major subsidence experienced by the hawaiian islands but is comparable with the lack of subsidence evident in other island groups at slow moving hotspots such as the cape verdes comparison of the structure and structural evolution of the canary islands with other oceanic islands such as hawaii and reunion reveals many similarities these include the development of triple mercedes star rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones the apparent absence of these features in the post erosional islands may in part be a result of their greater age and deeper erosion which has removed much of the evidence for their early volcanic architecture we conclude that the many similarities between the canary islands and island groups whose hotspot origins are undisputed show that the canaries have been produced in the same way

paleo redox context of the mid devonian appalachian basin and its relevance to biocrises abstract the devonian period witnessed the expansion of vascular land plants and an atmospheric oxygenation event associated with enhanced organic mass burial the deposition of organic rich shales e g black shales of the marcellus subgroup and several biotic crises in the marine realm have been linked to devonian ocean anoxia however it is not clear how redox conditions evolved in different parts of the water column in such a context of dynamic changes in the atmosphere ocean system to address this problem we use the bulk carbonate i ca proxy on core samples from yates county ny in order to reconstruct the water column redox history through the onondaga limestone into the lower marcellus shale on the secular scale the range of i ca values support the notion of a devonian rise in atmospheric oxygen relative to time intervals earlier in the paleozoic in terms of eifelian stage stratigraphic trends i ca ratios are generally stable and high in the onondaga formation but show large fluctuations in lower marcellus strata low i ca ratios are found near the onset of organic rich shale deposition indicating relatively reducing subsurface waters the pattern of redox changes resembles that of contemporaneous sea level changes finally the reconstructed oxygenation changes are correlated to three biotic transitions in devonian marine systems

the channel between gran canaria and tenerife constructive processes and destructive events during the evolution of volcanic islands seismic sidescan sonar bathymetric multibeam and odp ocean drilling program data obtained in the submarine channel between the volcanic islands of gran canaria and tenerife allow to identify constructive features and destructive events during the evolution of both islands the most prominent constructive features are the submarine island flanks being the acoustic basement of the seismic images the build up of tenerife started following the submarine stage of gran canaria because the submarine island flank of tenerife onlaps the steeper flank of gran canaria the overlying sediments in the channel between gran canaria and tenerife are chaotic consisting of slumps debris flow deposits syn ignimbrite turbidites ash layers and other volcaniclastic rocks generated by eruptions erosion and flank collapse of the volcanoes volcanic cones on the submarine island flanks reflect ongoing submarine volcanic activity the construction of the islands is interrupted by large destructive events especially by flank collapses resulting in giant landslides several miocene flank collapses e g the formation of the horgazales basin were identified by combining seismic and drilling data whereas young giant landslides e g the guimar debris avalanche are documented by sidescan bathymetric and drilling data sediments are also transported through numerous submarine canyons from the islands into the volcaniclastic apron seismic profiles across the channel do not show a major offset of reflectors the existence of a repeatedly postulated major ne sw trending fault zone between gran canaria and tenerife is thus in doubt the sporadic earthquake activity in this area may be related to the regional stress field or the submarine volcanic activity in this area seismic reflectors cannot be correlated through the channel between the sedimentary basins north and south of gran canaria because the channel acts as sediment barrier the sedimentary basins to the north and south evolved differently following the submarine growth of gran canaria and tenerife in the miocene

factors controlling the morphology of monogenetic basaltic volcanoes the holocene volcanism of gran canaria canary islands spain abstract a detailed morphometric analysis was performed on the 24 holocene eruptions of gran canaria a nearly circular island located at the centre of the canary islands spain developed as result of the eastward movement of the african plate over a mantle hotspot rigorous field work was carried out to generate a palaeogeomorphological reconstruction of the holocene eruptions of gran canaria to obtain pre and post eruption digital terrain models dtms these eruptions were of strombolian monogenetic basaltic volcanism style with respect to the cones feeder fissures determine their location and some morphological features as crater openings which are usually perpendicular to the slope direction in addition the trade winds influence the final volcanic edifice shape and the extent of the pyroclastic sheet like fall deposits for the lava flows the most significant controls are the eruption rate affecting the maximum distance travelled and the gully slope and shape that condition their flow path concerning volcanic hazard and risk assessment the applied methodology has led to a better understanding of the recent eruptions and foresees the location and nature of future eruptions

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

palaeoenvironments of early devonian fish and other aquatic fauna of the campbellton formation new brunswick canada abstract the palaeoecology and palaeoenvironments of the classic fish bearing strata of the campbellton formation are here described a well documented fossil assemblage includes acanthodian placoderm chondrichthyan and cephalaspid fishes tracheophyte remains eurypterids ostracods and molluscs as part of the old red sandstone continent the emsian campbellton formation occupied a small basin within the mountainous terrain of the acadian orogen and may have connected through a narrow seaway to a closing foreland basin the highest diversity of vertebrate fossils was found above a basal unconformity with val d amour formation volcanics marked by fissure fills and unstratified breccia representing a craggy irregular palaeosurface that provided shelter for some fauna and sediment for rapid burial of skeletal remains overlying prodeltaic calcareous siltstones are also highly fossiliferous and represent a low energy habitat occurrences of pterygotid eurypterids cephalaspids and chondrichthyans in deltaic sandstones place these taxa in a habitat that may have been variably fresh or brackish the surrounding landscape was vegetated with primitive tracheophytes and abundant plant debris is preserved throughout the basin the diverse assemblage of fish arthropods gastropods plants and microbial growths suggests that a trophically complex ecosystem was in existence

seismic tomography model reveals mantle magma sources of recent volcanic activity at el hierro island canary islands spain summary we present a 3 d model of p and s velocities beneath el hierro island constructed using the traveltime data of more than 13 000 local earthquakes recorded by the instituto geogr afico nacional ign spain in the period from 2011 july to 2012 september the velocity models were performed using the lotos code for iterative passive source tomography the results of inversion were thoroughly verified using different resolution and robustness tests the results reveal that the majority of the onshore area of el hierro is associated with a high velocity anomaly observed down to 10 12 km depth this anomaly is interpreted as the accumulation of solid igneous rocks erupted during the last 1 myr and intrusive magmatic bodies below this high velocity pattern we observe a low velocity anomaly interpreted as a batch of magma coming from the mantle located beneath el hierro the boundary between the low and highvelocityanomaliesismarkedbyaprominentseismicitycluster thoughttorepresentanomalous stresses due to the interaction of the batch of magma with crust material the areas of recent eruptions orchilla and la restinga are associated with low velocity anomalies surrounding the main high velocity block these eruptions took place around the island where the crust is much weaker than the onshore area and where the melted material cannot penetrate these results put constraints on the geological model that could explain the origin of the volcanism in oceanic islands such as in the canaries which is not yet clearly understood

acadian dextral transpression and synorogenic sedimentary successions in the appalachians the successive seboomook littleton northern appalachians and catskill pocono central appalachians clastic wedges suggest oblique convergence and southwestward migration of acadian orogeny beginning in early devonian and continuing into early mississippian wrench fault movement in maritime canada coincided with deposition of all but the earliest components of the catskill pocono clastic wedge and continued into the pennsylvanian contrasts between a thin lower to middle devonian shallow shelf facies in the alabama appalachian fold thrust belt and a time equivalent thick shallowing upward sedimentary to volcanic succession in the adjacent talladega slate belt are interpreted to reflect a wrench fault basin a wrench fault setting for devonian rocks in alabama integrated with manifestations of oblique convergence during the acadian orogeny in the central and northern appalachians can be accommodated in dextral transpression along the entire length of the acadian appalachian orogen

the holocene volcanic history of gran canaria island implications for volcanic hazards previous published data combined with our results of 13 new radiocarbon ages and extensive geological fieldwork indicate that during the past 11 ka 24 monogenetic basaltic eruptions occurred in the north sector of gran canaria these eruptions can be grouped into three periods of eruptive activity 1900 3200 14c a bp 5700 6000 14c a bp and an older period represented by only one eruption el draguillo dated at 10 610 190 14c a bp archaeological studies have shown that the more recent eruptions affected prehistoric human settlements on the island field studies demonstrate that the eruptions typically built strombolian cones 30 250 m in height and associated relatively long lava flows 100 10 350 m in length a few eruptions also produced tephra fall deposits the total erupted volume of these eruptions is about 0 388 km3 46 1 as tephra fall 41 8 as cinder cone deposits and 12 1 as lava flows the relatively low eruption rate 0 04 km3 ka 1 during the past 11 ka is consistent with gran canaria s stage of evolution in the regional volcano tectonic setting of the canary archipelago the results of our study were used to construct a volcanic hazards map that clearly delimits two sectors in the ne sector of gran canaria where potential future eruptions would pose a substantial risk for densely populated areas copyright 2009 john wiley sons ltd

features of crustal structure under the canary islands abstract the data and interpretation of a seismic refraction project carried out in the canary islands in 1977 and 1979 are presented the moho is reached at about 15 km under fuerteventura gran canaria and tenerife whereas under lanzarote a value of 11 km has been found the velocity at the surface varies even within one island from 2 8 to 4 4 km s there are variations in the velocity of the main crustal layer under the volcanic deposits a continuous velocity depth function seems to be more appropriate for the island of tenerife contrary to fuerteventura lanzarote and gran canaria which seem to have a layered structure there is evidence for pronounced structural differences between lanzarote and fuerteventura the mantle velocity has a value of about 8 0 km s under the western islands whereas a very low value of 7 4 km s has been found under lanzarote and fuerteventura despite the clear structural differences between the islands our results leave little doubt about the oceanic character of all the islands the differences between the eastern and western group may be due to the islands being situated close to the african continental margin the seismic velocities under the volcanic deposits do not support the idea of a common basement for all the islands they rather suggest independent volcanic edifices finally a comparison of the structure of the crust under the canary islands with that under other volcanic islands reveals remarkable similarities

filamentous microfossils in the early proterozoic transvaal supergroup their morphology significance and paleoenvironmental setting abstract well preserved filamentous microfossils siphonophycus transvaalensis n sp are described here from the carbonate campbellrand subgroup to iron formation kuruman iron formation transition of the transvaal supergroup south africa estimated to be 2 5 2 3 ga years old the microfossils occur in petrographic thin sections of a core sample of carbonate chert they are preserved by permineralization in both chert and in sparry ferroan dolomite stratigraphically the fossiliferous core sample occurs as part of an upward transition from a stromatolitic dolomite and limestone sequence campbellrand to the overlying iron rich sediments of the kuruman griquatown iron formations the average 13 c value of the kerogen in the sample is about 36 9 the microfossils are filamentous unbranched tubular to somewhat flattened 15 25 m in diameter and a few to many hundred microns in length they exhibit a coriaceous finely granular external surface texture resulting from the presence of adhering randomly distributed fine mineralic carbonate needles in salient morphological characteristics they are comparable to the tubular originally polysaccharide encompassing sheaths of extant oscillatoriacean cyanobacteria in comparison with previously described precambrian microfossils these fossil filaments are unusual because of their preservation in sparry carbonate in addition to chert their relatively large diameter and their coating by adhering precipitated carbonate needles they appear to be among the oldest assured microfossils now known from proterozoic age sediments the microfossils are interwoven occurring in subparallel aggregates that form a stromatolitic mat like fabric they are considered to be of an endogenetic in situ benthic origin occurring at the proximal margin of a deep shelf environment at the front distal margin of the campbellrand carbonate platform the water depth for this environment at the break in slope between deep shelf and euxinic basin is estimated to have been of the order of 40 45 m paleomagnetic data support our interpretation that the micro organisms inhabited a warm water marine environment probably at low latitudes

stratigraphic and oxygen isotope evidence for my scale glaciation driving eustasy in the early middle devonian greenhouse world article i nfo million year scale 3rd order depositional sequences few 10s to 100 m thick are common in the devonian marine record and are correlated between sedimentary basins and across widely separated continents implying a eustatic origin tectonically driven changes in mid ocean ridge spreading rates lengths are too slow to account for the calculated 3rd order rise fall rates and typical orbital frequencies 20 400 ky are too fast we analyzed oxygen isotopes from conodont apatite to evaluate if early middle devonian 3rd order sea level changes were controlled by paleoclimatically driven ice volume glacio eustasy and seawater temperature change thermo eustasy two successive depositional sequences in the western u s nevada and czech republic prague basin were sampled the 18 o values range from 17 8

three dimensional p and s wave velocity structure of redoubt volcano alaska the three dimensional p and s wave structure of redoubt volcano alaska and the underlying crust to depths of 7 8 km is determined from 6219 p wave and 4008 s wave first arrival times recorded by a 30 station seismograph network deployed on and around the volcano first arrival times are calculated using a finite difference technique which allows for flexible parameterization of the slowness model and easy inclusion of topography and source receiver geometry the three dimensional p wave velocity structure and hypocenters are determined simultaneously while the three dimensional s wave velocity model is determined using the relocated seismicity and an initial s wave velocity model derived from the p wave velocity model assuming an average vp vs ratio of 1 78 convergence is steady with approximately 73 and 52 reduction in p and s wave arrival time rms respectively after 10 iterations the most prominent feature observed in the three dimensional velocity models derived for both p and s waves is a relative low velocity near vertical pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level this feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit the velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations high velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates no large low velocity body suggestive of a magma chamber is resolved in the upper 7 8 km of the crust

seismological studies at parkfield i simultaneous inversion for velocity structure and hypocenters using cubic b splines parameterization a model for the 3d p and s wave velocity structure at parkfield has been developed by the systematic inversion of arrival times for microearthquakes and surface vibroseis sources recorded by nearby calnet stations and by the local borehole installed 10 station high resolution seismic network there a modification of the linear b splines model parameterization method of thurber 1983 to a cubic b splines formulation through tests inverting synthetic data sets for the parkfield configuration is found to produce smooth velocity distributions that still retain some small scale features application of the method to 953 p wave and 288 s wave arrivals from 111 microearthquakes and 8 vibroseis locations throughout the study area yields a velocity structure having variable resolution a low velocity zone appears to coincide with the creeping segment of the san andreas fault zone northwest of the 1966 parkfield earthquake epicenter an increase of about 15 per cent in seismic velocities is seen from the northeast to southwest across this segment of the fault zone the higher velocities to the southwest apparently correspond to the granitic basement the contrast across the fault is subdued to the southeast along the 1966 rupture zone a high vp vs ratio of 1 9 is seen in a 2 km wide volume near the location of the 1966 main shock hypocenter presumably the nucleation zone for the expected m 6 parkfield earthquake

variations in oceanic layer 2 elastic velocities near hawaii and their correlation to lithospheric flexure analysis of the travel times and amplitude range distributions of both compressional and shear wave arrivals on 15 closely spaced refraction profiles reveals a significant systematic and symmetric dependence of average layer 2 velocities on their distance to the north and south of the hawaiian ridge beyond the flexural arch surrounding the ridge the velocity depth solutions indicate a normal layer 2 within the arch approximately 155 km from the ridge the average elastic velocities in layer 2 are lowered by 0 8 0 9 0 2 km s within 75 km of the ridge the average velocities are again normal elastic and elastic plastic flexural models for the regional compensation of the hawaiian islands predict tensional stress drops of 0 8 kbar in the upper lithosphere for the region having lowered velocities in layer 2 which are similar in magnitude with laboratory measurements of the confining pressure drop necessary to reduce velocities in porous basalts by 0 5 km s a significant inverse relationship correlation coefficient of 0 818 exists between the average elastic velocities in the upper 1 0 km of the igneous crust and the strain in the upper crust calculated from these flexural models the correlation between lowered average velocities in layer 2 and increased tensional stresses and strains suggest that crack opening in the upper crust accompanies the flexure these observations are the first reported for a midplate load and corroborate previous suggestions from seismic and flexural data at subduction zones

revisiting the hubbert rubey pore pressure model for overthrust faulting inferences from bedding parallel detachment surfaces within middle devonian gas shale the appalachian basin usa abstract both bedding parallel slickensides and cleavage duplexes are forms of mesoscopic scale detachment faulting populating black marcellus and geneseo burket and intervening gray mahantango shales of the middle devonian a section known for abnormal pore pressure below the appalachian plateau the abundance and the orientation of slickensides and cleavage duplexes in the more organic rich black shale relative to gray shale suggests that maturation related abnormal pore pressure facilitates detachment a mesoscopic manifestation of the hubbert rubey pore pressure model for overthrust faulting the former are discrete slip surfaces whereas the latter consists of nested anastomosing slip surfaces either cutting through bedding or on disrupted bedding surfaces stacked as mesoscopic versions of thrust duplexes cleavage duplexes are between a few cm and over 1 m thick with their hanging walls commonly transported toward the appalachian foreland regardless of local limb dip cleavage duplexes are most common near the stratigraphic maximum flooding surface the organic rich section most prone to develop maturation related pore pressure in the middle devonian gas shales bedding parallel slickensides are somewhat more evenly distributed in the black shale but also found in overlying gray shale in both black and gray shales slickensides are more abundant on the limbs of folds an indication of pore pressure related flexural slip folding on the macroscopic scale the pine mountain block of the southern appalachian mountains was enabled by a basal detachment cutting along the upper devonian chattanooga black shale which has a thermal maturity sufficient for the generation of abnormal pore pressure the pine mountain block is a large scale overthrust showing little evidence of collapse of the hinterland side a credible example of a pore pressure aided overthrust fault block of the type envisioned by the hubbert rubey model

microfossils from the neoarchean campbell group griqualand west sequence of the transvaal supergroup and their paleoenvironmental and evolutionary implications the oldest filament and colonial coccoid containing microbial fossil assemblage now known is described here from drill core samples of stromatolitic cherty limestones of the neoarchean approximately 2600 ma old campbell group ghaap plateau dolomite lime acres member obtained at lime acres northern cape province south africa the assemblage is biologically diverse including entophysalidacean eoentophysalis sp probable chroococcacean unnamed colonial coccoids and oscillatoriacean cyanobacteria eomycetopsis cf filiformis and siphonophycus transvaalensis as well as filamentous fossil bacteria archaeotrichion sp filamentous possible microfossils unnamed hematitic filaments also occur the campbell group microorganisms contributed to the formation of stratiform and domical to columnar stromatolitic reefs in shallow subtidal to intertidal environments of the transvaal intracratonic sea although only moderately to poorly preserved they provide new evidence regarding the paleoenvironmental setting of the campbell group sediments extend the known time range of entophysalidacean cyanobacteria by more than 400 million years substantiate the antiquity and role in stromatolite formation of archean oscillatoriacean cyanobacteria and document the exceedingly slow hypobradytelic evolutionary rate characteristic of this early evolving prokaryotic lineage

bulge migration and pinnacle reef development devonian appalachian foreland basin abstract detailed stratigraphic analyses of late emsian and early eifelian lower to middle devonian carbonate dominated strata in the northern appalachian basin indicate anomalous locally varying relative sea level changes and inversions of topography the distribution of a major basal bounding unconformity basinal pinnacle reefs local absence of parasequences and eastward migration of shallow marine carbonate lithofacies and related biofacies in the onondaga limestone and underlying strata mark the retrograde migration of an elongate northeast southwest trending area of positive relief bordered on its cratonward side by a similarly migrating basin of intermediate depth these features are thought to represent the forebulge and back bulge basin of the appalachian foreland basin system as it developed during a time of relative quiescence within the acadian orogeny however the relatively small size of the bulgelike feature ca 80 100 km wide 20 50 m positive relief its great distance from the

crustal structure of northern gran canaria canary islands deduced from active seismic tomography seismic p wave travel times collected during meteor cruise m24 are inverted to derive a three dimensional model of the p wave velocity structure of the northern part of gran canaria canary islands the data consist of 6689 p wave travel times from 1487 offshore air gun shots which were recorded by both land based seismometers and ocean bottom hydrophones the crustal structure is well imaged by the data set as demonstrated by analysis of the resolution and tests with synthetic data the volcanic island is characterized by generally high p wave velocities 5 5 km s and a heterogeneous structure with large lateral velocity variations high p wave velocities are found around the centers of the miocene shield volcanoes in the vicinity of aguimes san nicolas and agaete as well as the center of the pliocene roque nublo volcano the velocity structure suggests a high percentage of dense intrusive rocks some of the intrusive rocks were emplaced during the eruption of 1000 km3 of miocene felsic magmas following the basaltic shield phase the velocity structure beneath la isleta peninsula and its submarine continuation is interpreted as a volcanic rift zone with abundant dikes the velocities decrease to 5 km s north of the coastline a high velocity zone thinning away from the central edifice is interpreted as the massive island flank extending up to 50 km off the coast which is underlain by prevolcanic neogene jurassic sediments the igneous part of the oceanic crust exhibits an anomalous structure with a relatively small thickness 3 km layer 3 and a 2 4 km thick layer 2 probably reflecting a modification of the crust due to long lasting magmatic intrusive activity during the evolution of the canary islands the moho north of gran canaria is found at a depth of 15 km the structure of gran canaria and the adjacent ocean basin is thought to be the result of a diffuse mantle upwelling under a slowly moving plate

reflection seismic investigations in the volcaniclastic apron of gran canaria and implications for its volcanic evolution high resolution reflection seismic data obtained around gran canaria allow a detailed and consistent correlation of seismic reflectors of the northern and southern canary basins with the lithology drilled by dsdp leg 47a sse of gran canaria as well as with major phases of volcanic activity on gran canaria as mapped onshore two prominent reflectors were chosen as marker horizons and correlated with the drilled lithology the results indicate that reflector r7 above the miocene volcaniclastic debris flows v1 v3 reflects the shield building phase of gran canaria reflector r3 is interpreted as corresponding with the pliocene roque nublo formation the top of the massive island flank of gran canaria defined by seismically chaotic facies extends 44 to 72 km off the coast of gran canaria west of gran canaria the flank of tenerife onlaps the steeper and older flank of gran canaria which in turn is onlapping the older flank of fuerteventura to the east in a similar way erosional channels which can also be traced up to 50 km from the area between gran canaria and fuerteventura into the deeper northern basin have been identified in the bathymetry the data presented provide new detailed information for modelling the submarine and subaerial evolution of the central canary islands of gran canaria and tenerife i e the timing of their shield building phases and later stages of major volcanic activity as reflected by the position of prominent seismic reflectors in the seismic stratigraphy

seismic tomography of etna volcano abstract a 3 d velocity model beneath etna volcano has been obtained through inversion of p wave arrivals of local earthquakes about 300 seismic events distributed around this volcano from surface up to a depth of 20 km have been used to infer the p wave velocity structure high p wave velocity bodies have been found in the upper portion of the volcanic edifice in a region where positive values of bouguer anomalies have previously been found low velocity bodies are identified at depths lower than 10 km and may be related to magmatic reservoirs the spatial pattern of these deeper velocity anomalies appears to be correlated at surface with the distribution of spatter cones in the nw quadrant a high velocity anomaly is correlated to the presence of a deeper seismicity the distribution of relocated hypocenters is not homogeneous but shows some features apparently related to the presence of magmatic bodies

rates of magma ascent and depths of magma reservoirs beneath la palma canary islands peridotitic mantle xenoliths from historic and prehistoric eruptions on la palma show many similarities prolonged reactions of the xenoliths with their host magmas have been used to place constraints on the magma transport system beneath the island all xenoliths show crystalline selvages and 0 9 2 6 mm wide diffusion zones in olivine along most of their surface diffusion kinetics in olivine combined with fluid inclusion barometry document that selvages and diffusion zones formed at crustal levels within 8 to about 100 years some xenolith fractures lack selvages and were in contact with the host magma for less than 4 days a multistage magma ascent is proposed i peridotite wall rock was fragmented and became incorporated into the ascending magma years to decades prior to the eruption ii the xenoliths were rapidly transported to and deposited in crustal magma reservoirs forming selvages and diffusion zones at the xenolith rims iii renewed fragmentation of the xenoliths occurred days to hours prior to eruption possibly by decompressive strain fracturing during rapid ascent

basinwide stratigraphic synthesis and sequence stratigraphy upper pragian emsian and eifelian stages lower to middle devonian appalachian basin

imaging the crustal magma sources beneath mauna loa and kilauea volcanoes hawaii three dimensional seismic p wave traveltime tomography is used to image the magma sources beneath mauna loa and kilauea volcanoes hawaii high velocity bodies 6 4 km s in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro ultramafic cumulates from which the surface volcanism is derived the proximity of these high velocity features to the rift zones is consistent with a ridge spreading model of the volcanic flank southeast of the hilina fault zone along the south flank of kilauea low velocity material

fluvial dissection isostatic uplift and geomorphological evolution of volcanic islands gran canaria canary islands spain abstract digital analysis of torrential gullies barrancos deeply incised into the volcanic island of gran canaria canary islands allows us to extract the longitudinal profiles and pre incision surfaces for individual basins from which morphometric parameters length elevation area slope have been calculated other derived parameters such as ridgeline profiles maximum incision values volume removed by fluvial erosion geophysical relief and isostatic uplift have also been computed based on k ar ages for the island well constrained incision uplift rates have been calculated by means of the combination of different methodological approaches commonly used in orogens and large mountain ranges the geomorphological and morphometric analyses reveal that the island is clearly divided into four environmental quadrants determined by the combination of a couple of key factors the age of the volcanic surfaces and the climatic conditions these factors determine a young sector covered with plio quaternary platform forming lavas finished at 1 9 1 5 ma evolving under contrasting wet ne to dry se climates and an older sector conserving the residual surfaces of the miocene shield building 14 5 8 7 ma at the ridgelines also subjected to wet nw and dry sw climates incision is related to the age zonation of the island maximum incisions

effects of canary hotspot volcanism on structure of oceanic crust off morocco analysis of over 6400 km of multichannel seismics mcs and 50 sonobuoy reflection and refraction experiments reduced both in the domain of x t and tau p shows that a region within the jurassic quiet zone off morocco underwent dramatic changes as a result of the passage of the lithosphere over the canary hotspot commencing approximately 60 ma a seismic unit ucf interpreted as volcanic in origin is observed within the sediments in a region characterized by a broad bathymetric swell it shows diffractions from its upper surface and an internally chaotic seismic facies and pinches out between sedimentary units of continuous subparallel facies a velocity inversion is noted between the ucf 4 7km s and the underlying sediment 3 1 km s the ucf is time transgressive it lies near the cretaceous s tertiary boundary in the northern portion of the study area and is younger to the south kinematic studies of the movement of the canary hotspot relative to africa show that the hotspot first appeared off nw africa about 60 ma and was located beneath oceanic crust in the region where the ucf is observed depth to basement measurements in areas not effected by the hotspot show a consistent linear trend of increased depth with age in areas effected by the hotspot the thermal rejuvenation is evident as basement depths shoal with increased proximity to the present hotspot the reheating of the crust resets the thermal age of the lithosphere with many of the properties of crust of a younger age subsidence curves of the reheated crust off morocco show good correlation to subsidence curves of other reheated crust on a global basis a zone characterized by high crustal velocities 7 1 7 4 km s and greater crustal thicknesses by 1 2 km is observed in an area that corresponds to the bathymetric swell the region of the ucf and the reelevated basement the high velocities and increased crustal thickness are interpreted to be the result of underplating and assimilation of existing oceanic crust caused by the canary thermal anomaly the presence of high crustal velocities coupled with a thickened crustal section has been noted on various passive margins of the world they have generally been attributed to the thermal processes associated with continental rifting off morocco we believe that similar thermally induced phenomena have occurred but that here the heat anomaly was the midplate volcanism associated with the canary hotspot

continental subduction and three dimensional crustal structure the northern south island new zealand the three dimensional vp and vp vs structure of a region where subduction transitions to oblique transform faulting has been determined using arrival times from 579 local earthquakes recorded during a temporary deployment and 3146 earthquakes have been relocated between 40 km and 100 km depth the subducted plate is imaged as a relatively low velocity feature in the uppermost mantle reflecting the continental nature of the subducted crust in this region an increase in amplitude of this low velocity feature from northeast to southwest can be related to an increase in the thickness of the crust of the subducted plate in this direction velocity variations within the subducted and overlying plates show some spatial correlation this suggests an interaction between the plates which extends well beyond the plate interface and is consistent with other geophysical and geological evidence that the plate interface beneath marlborough is currently not accommodating much active subduction in the overlying plate the awatere fault is a major structural feature associated with a low velocity zone extending to 23 km depth there is a marked change in structure near this fault with seismic velocities being lower to the southeast a relatively high level of seismicity occurs in this region of lower seismic velocities suggesting a relationship between the two a possible explanation for this is elevated pore pressures caused by fluids derived from dehydration of the continental subducted crust the low velocity region in the overlying plate coincides with the region of most intense active deformation suggesting it is relatively weak

the absolute age of the eifelian tioga ash bed pennsylvania the tioga ash bed bed b of the zeigler pit union county pennsylvania lies in the polygnathus costatus costatus zone of the eifelian stage of the middle devonian series the 27 5 cm thick bed contains igneous zircon and monazite crystals that have been dated by precise u pb techniques zircons are characterized by inherited pb that occurs as barely perceptible interior regions enriched in inclusions the zircons are discordant and do not reveal the igneous age of the bed in contrast high quality monazite crystals lack any evidence of inheritance or loss of pb and multiple analyses have overlapping 207 pb 235 u ages of 390 0 pm 0 5 ma the monazite analyses are concordant or very slightly reversely discordant the consistency of the monazite data provides a new precise estimate of age for the lower eifelian

organic rich marcellus shale lithofacies modeling and distribution pattern analysis in the appalachian basin the marcellus shale is considered to be the largest unconventional shale gas resource in the united states two critical factors for unconventional shale reservoirs are the response of a unit to hydraulic fracture stimulation and gas content the fracture attributes reflect the geomechanical properties of the rocks which are partly related to rock mineralogy the natural gas content of a shale reservoir rock is strongly linked to organic matter content measured by total organic carbon toc a mudstone lithofacies is a vertically and laterally continuous zone with similar mineral composition rock geomechanical properties and toc content core log and seismic data were used to build a three dimensional 3 d mudrock lithofacies model from core to wells and finally to regional scale an artificial neural network was used for lithofacies prediction eight petrophysical parameters derived from conventional logs were determined as critical inputs advanced logs such as pulsed neutron spectroscopy with log determined mineral composition and toc data were used to improve and confirm the quantitative relationship between conventional logs and lithofacies sequential indicator simulation performed well for 3 d modeling of marcellus shale lithofacies the interplay of dilution by terrigenous detritus organic matter productivity and organic matter preservation and decomposition affected the distribution of marcellus shale lithofacies distribution which may be attributed to water depth and the distance to shoreline the trend of normalized average gas production rate from horizontal wells supported our approach to modeling marcellus shale lithofacies the proposed 3 d modeling approach may be helpful for optimizing the design of horizontal well trajectories and hydraulic fracture stimulation strategies

a two dimensional seismic investigation of crustal structure under the hawaiian islands near oahu and kauai two expanding spread profiles esps were analyzed in detail to investigate the deep structure of the volcanoes and the underlying oceanic crust near oahu one esp was located on the southeastern submarine flank of kauai esp 10 and the other was located directly over the ridge axis between oahu and molokai esp 5 two dimensional models of the entire crust were obtained by iterative comparison of both travel times and relative amplitudes of arrivals on the ray theoretical synthetic seismograms with those in the data a 2 4 km vertical offset in the preexisting crust inferred to be a large fault zone was found near the midpoint of esp 10 this fault may form the southern wall of a graben or half graben in which kauai sits the layering and seismic velocities of the preexisting oceanic crust near kauai have remained unmodified by the load of the volcanic pile esp 5 is located over a shallow 4 km thick basin filled with volcaniclastics and possibly volcanic flows bordered by the islands of oahu and molokai penguin bank and two buried rift zones under this basin the main volcanic edifice is 4 to 5 km thick the top of the preexisting oceanic crust is 8 to 9 km below sea level and is 3 to 4 km lower than the crust away from the islands the underlying oceanic crust is 6 to 7 km thick excluding the moho transition zone which is of normal thickness and at a depth from 15 to 16 km the existence of a large subcrustal plutonic body is refuted

metasedimentary xenoliths in the lavas of the timanfaya eruption 1730 1736 lanzarote canary islands metamorphism and contamination processes we report on the investigation of contact metamorphism provoked by the emplacement of a shallow magma chamber during the timanfaya eruption of lanzarote from 1730 to 1736 ad the study was carried out on metamorphic xenoliths from basaltic timanfaya lavas and shows how the primary basanitic magma was contaminated by sedimentary and metamorphic rocks mineralogical and chemical studies allowed the definition of several xenolith types silica xenoliths quartz tridymite cristobalite or a mixture of these constituting more than 50 of the xenolith and cale silicate xenoliths wollastonite sometimes the 2m type diopside forsterite or mixture of these constituting more than 50 of the xenolith are the most frequent other minerals recognized were calcite dolomite augite enstatite hypersthene spinel and scapolite the mineralogy and some textures of the metamorphic forsteritic xenoliths are identical to those found in ultrabasic xenoliths dunites and point to a possible metamorphic origin for some of them major and trace elements showed a diversity of composition controlled by the mineralogy the ree composition of the metamorphic xenoliths is high compared with the sedimentary xenoliths not affected by metamorphism the mineral assemblages define metamorphic facies of low medium and high grade depending on the distance of the sedimentary rocks from the magma chamber border the igpetwin mixing program was used to verify the contamination process taking the xenoliths as representative of the sedimentary metamorphic rocks that were melted the results indicated that sedimentary metamorphic rock contamination of a basanitic magma can produce tholeiitic compositions

three dimensional velocity structure in northern california coast ranges from inversion of local earthquake arrival times abstract the three dimensional p wave velocity structure in the upper crust in the northern california coast ranges from santa rosa to ukiah is obtained by simultaneous inversion of local earthquake and refraction travel time data for velocity and hypocentral parameters in this region where there are lateral heterogeneities the three dimensional inversion provides important results not found in two dimensional refraction studies the medium is parameterized with velocities at the intersections gridpoints of a nonuniform three dimensional grid travel times are calculated with approximate ray tracing along arcuate paths which are reasonable for lateral distances less than 45 km inversions with 5 to 10 and 2 to 3 km gridspacing achieved 80 per cent decreases in data variance the inversion with 2 to 3 km gridspacing reduced the rms residual level to approximately the level of timing error anomalously low velocities to at least 6 km depth are found along the maacama and healdsburg rodgers creek hrc fault zones the low velocity region is widest at the en echelon junction of the maacama and hrc fault zones low velocities are associated with the clear lake basin where there is a thick sequence of volcanics interbedded with sedimentary deposits there is a high velocity body located southeast of the geysers between the maacama and collayomi fault zones which may be associated with igneous intrusives or high grade metamorphism related to an underlying inferred partial melt body modeled in previous teleseismic travel time studies there is some indication in the vapor dominated geothermal reservoir of lower velocities relative to surrounding water saturated rock as has been shown in some laboratory experiments hypocenter locations obtained in the inversion show little variation from hypocenters obtained through inversion for one dimensional velocity model and station corrections for the inversion with 2 to 3 km gridspacing however some groups of events become more tightly clustered

the canary islands swell a coherence analysis of bathymetry and gravity summary the canary archipelago is an intraplate volcanic chain located near the west african continental margin emplaced on old oceanic lithosphere of jurassic age with an extended volcanic activity since middle miocene the adjacent seafloor does not show the broad oceanic swell usually observed in hotspot generated oceanic islands however the observation of a noticeable depth anomaly in the basement west of the canaries might indicate that the swell is masked by a thick sedimentary cover and the influence of the canarian volcanism we use a spectral approach based on coherence analysis to determine the swell and its compensation mechanism the coherence between gravity and topography indicates that the swell is caused by a subsurface load correlated with the surface volcanic load the residual gravity geoid anomaly indicates that the subsurface load extends 600 km ssw and 800 km n and nne of the islands we used computed depth anomalies from available deep seismic profiles to constrain the extent and amplitude of the basement uplift caused by a relatively low density anomaly within the lithospheric mantle and coherence analysis to constrain the elastic thickness of the lithosphere t e and the compensation depth of the swell depth anomalies and coherence are well simulated with t e 28 36 km compensation depth of 40 65 km and a negative density contrast within the lithosphere of 33 kg m 3 the density contrast corresponds to a temperature increment of 325 c which we interpret to be partially maintained by a low viscosity convective layer in the lowermost lithosphere and which probably involves the shallower parts of the asthenosphere this interpretation does not require a significant rejuvenation of the mechanical properties of the lithosphere

a detailed geophysical study in the canary basin eastern atlantic implications for the internal structure of 130 ma oceanic crust summary we report the results of a detailed geophysical survey sited on two previously imaged dipping reflectors one dipping towards and the other away from the present day mid atlantic ridge axis within mesozoic aged crust of the east atlantic the new data include gravity magnetic and seismic refraction and reflection profiles collected in a grid that constrain the crustal structure as well as the reflector geometry a second order axial discontinuity which is associated with anomalous crustal structure is located within the survey area the westward dipping reflector can be traced from the moho to the top of the igneous crust where it coincides with a step of 800 m in the basement this reflector is approximately planar with a dip of 28 2 w and occurs 8 km north of the axial discontinuity we interpret this reflector as being a whole crustal normal fault that was generated within the median valley the eastward dipping reflector cannot be traced across seismic layer 2 and does not correlate with any feature of the basement it penetrates 2 3 km into the upper mantle its reflection strength is about twice that of the moho reflection this reflector which is approximately planar strikes parallel to the isochrons has a length of 18 2 km and a dip of 28 2 e we speculate that this reflector is also a fault that was generated on the western wall of the median valley but was captured from the north american plate by a lateral shift in the axis of spreading possibly associated with a major change in plate motion

using biogenic structures to interpret sharp lithologic boundaries an example from the lower devonian of new york abstract trace fossils are abundant at the interface between the lower devonian esopus shale and carlisle center formation at cherry valley they give new evidence concerning the magnitude of the depositional break represented by the sharp contact which previously was interpreted as an unconformity traces include cruziana fustiglyphus horizontal and vertically oriented traces of various sizes and knobs and scratch markings many of which are well preserved sole markings on the lowermost carlisle center bed although the cruziana and scratch marks could have been produced in the underlying semi consolidated esopus muds and later preserved by infilling of carlisle center sands it is unlikely they would have survived an extended period of erosion or nondeposition cr ziana and scratch markings are cut by burrows which presumably were made by soft bodied animals and apparently extend through both esopus and carlisle center rocks implying that the esopus sediments were unconsolidated during deposition of the lowermost carlisle center sands clearly the sharp contact represents at most a short depositional hiatus recognition and interpretation of trace fossils at other sharp lithologic boundaries may clarify the stratigraphic relationships

multi stage magma ascent beneath the canary islands evidence from fluid inclusions gabbroic and ultramafic xenoliths and olivine and clinopyroxene phenocrysts in basaltic rocks from gran canaria la palma el hierro lanzarote and la gomera canary islands contain abundant co2 dominated fluid inclusions inclusion densities are strikingly similar on a regional scale histogram maxima correspond to one or more of the following pressures 1 minimum 0 55 to 1 0 gpa within the upper mantle 2 between 0 2 and 0 4 gpa the moho or the lower crust 3 at about 0 1 gpa upper crust fluid inclusions in several rocks show a bimodal density distribution the lower density maximum comprising both texturally early and late inclusions this is taken as evidence for an incomplete resetting of inclusion densities and simultaneous formation of young inclusions at well defined magma stagnation levels for gran canaria pressure estimates for early inclusions in harzburgite and dunite xenoliths and olivine phenocrysts in the host basanites overlap at 0 9 to 1 0 gpa indicating that such magma reservoir depths coincide with levels of xenolith entrainment into the magmas magma chamber pressures within the mantle inferred to represent levels of mantle xenolith entrainment are 0 65 0 95 gpa for el hierro 0 60 0 68 gpa for la palma and 0 55 0 75 gpa for lanzarote the highest density fluid inclusions in many canary island mantle xenoliths have probably survived in situ near isobaric heating at the depth of xenolith entrainment inclusion data from all islands indicate ponding of basaltic magmas at moho or lower crustal depths and possibly at an additional higher level strongly suggestive of two main crustal accumulation levels beneath each island we emphasize that repeated magmatic underplating of primitive magmas and therefore intrusive accretion are important growth mechanisms for the canary islands and by analogy for other ocean islands comparable fluid inclusion data from primitive rocks in other tectonic settings including iceland etna and continental rift systems hungary south norway indicate that magma accumulation close to moho depths shortly before eruption is not however restricted to oceanic intraplate volcanoes lower crustal ponding and crystallization prior to eruption may be the rule rather than the exception independent of the tectonic setting

sequence stratigraphy and a revised sea level curve for the middle devonian of eastern north america abstract the well exposed middle devonian rocks of the appalachian foreland basin onondaga formation hamilton group tully formation and the genesee group of new york state preserve one of the most detailed records of high order sea level oscillation cycles for this time period in the world detailed examination of coeval units in distal areas of the appalachian basin as well as portions of the michigan and illinois basins has revealed that the pattern of high order sea level oscillations documented in the new york pennsylvania section can be positively identified in all areas of eastern north america where coeval units are preserved the persistence of the pattern of high order sea level cycles across such a wide geographic area suggests that these cycles are allocyclic in nature with primary control on deposition being eustatic sea level oscillation as opposed to autocylic controls such as sediment supply which would be more local in their manifestation there is strong evidence from studies of cyclicity and spectral analysis that these cycles are also related to milankovitch orbital variations with the short and long term eccentricity cycles 100 kyr and 405 kyr being the dominant oscillations in many settings relative sea level oscillations of tens of meters are likely and raise considerable issues about the driving mechanism given that the middle devonian appears to record a greenhouse phase of phanerozoic history these new correlations lend strong support to a revised high resolution sea level oscillation curve for the middle devonian for the eastern portion of north america recognized third order sequences are eif 1 lower onondaga formation eif 2 upper onondaga and union springs formations eif giv oatka creek formation giv 1 skaneateles giv 2 ludlowville giv 3 lower moscow giv 4 upper moscow lower tully and giv 5 middle tully geneseo formations thus in contrast with the widely cited eustatic curve of johnson et al 1985 which recognizes just one major transgressive regressive t r cycle in the early mid givetian if prior to the major late givetian taghanic unconformity iia upper tully geneseo shale we recognize four t r cycles if restricted ig ih and ii we surmise that third order sequences record eustatic sea level fluctuations of tens of meters with periodicities of 0 8 2 myr while their medial scale fourth order subdivisions record lesser variations primarily of 405 kyr duration long term eccentricity this high resolution record of sea level change provides strong evidence for high order eustatic cycles with probable milankovitch periodicities despite the fact that no direct evidence for middle devonian glacial sediments has been found to date

spatial distribution of hotspot material added to the lithosphere under la reunion from wide angle seismic data wide angle seismic lines recorded by ocean bottom and land seismometers provide a pseudo three dimensional investigation of the crust and upper mantle structure around the volcanically active hotspot island of la reunion the submarine part of the edifice has fairly low seismic velocities without evidence for intrusives an upper unit with a velocity depth gradient is interpreted as made of material erupted subaerially then transported and compacted downslope between this unit and the top of the oceanic plate imaged by normal incidence seismic reflection a more homogeneous unit indicated by shadow zones on several wide angle sections may correspond to lavas of a different nature extruded underwater in the earlier phase of volcanism coincident wide angle and normal incidence reflections document that the oceanic plate is not generally downwarping toward the island but doming instead toward its southeastern part with limited evidence for some intracrustal intrusion deeper in the lithosphere the presence of a layer of intermediate velocity between the crust and mantle is firmly established it is interpreted as resulting from the advection of hotspot magmatic products possibly partially molten and of a composition for which the crust is a density barrier the extensive wide angle coverage constrains the extent of this body it does not show the elongated shape expected from plate drift above a steady hotspot supply alternative propositions can hence be considered for example that la reunion is caused by a solitary wave of hotspot material or by a young hotspot the size of the underplate 140 km wide and up to 3 km thick corresponds to less than half the volume of the edifice on top of the plate

three dimensional crustal structure of ascension island from active source seismic tomography we present a crustal velocity and moho depth model of the ascension volcanic edifice using one of the most densely sampled 3 d wide angle data sets for volcanic islands currently available we invert traveltimes of first and second arrivals by seeking a layer interface minimum structure model and then test the resulting velocity model by gravity modelling and a 3 d checkerboard resolution test within the shallow extrusive part of the crust two main high velocity regions coincide with the highest topography on land and the gravity maximum off the west coast of the island respectively these features are connected with a high velocity intrusive core that is created either within or on the top of oceanic layer 3 and is interpreted as a possible relic magma chamber the thickness of the surface low velocity region is similar to that observed at hawaii jasper seamount and great meteor seamount suggesting a similar process of edifice construction the mean density of the volcanic edifice is significantly less than that of normal oceanic crust and than load densities typically assumed in studies of flexure as a result of seamount loading there is no simple flexural model that explains the shape of the moho beneath the island perhaps because of the long lived volcanism and the proximity of the island to the mid atlantic ridge mar and the ascension fracture zone there is no evidence for magmatic underplating beneath ascension island

the marquesas archipelagic apron seismic stratigraphy and implications for volcano growth mass wasting and crustal underplating multichannel seismic lines sonobuoy and gravity data across the marquesas islands are used to study volcano growth island mass wasting and crustal underplating at island chains with overfilled moats the marquesas bathymetry reflects the changing thickness of the sedimentary infill rather than the basement topography the moat contains two major regions of differing seismic stratigraphy 1 the moat edges where a unit of continuous layered reflectors is present containing minor lenses of chaotic diffractors and 2 the central moat where the deep moat basins are overfilled by an acoustically opaque unit of discontinuous reflectors of up to 2 km thickness in places capped by a ponded unit plate flexure models require broad underplating of the crust by low density crustal material at the marquesas islands to explain the depth to volcanic basement and gravity observations the seismic velocities and seismic stratigraphy as well as the general structure of the islands and surrounding seafloor indicate the apron is mostly debris from island mass wasting reflectors of the outermost moat generally onlap the flexural arch in the lower section and offlap and overfill it in the upper section in the central moat reflectors change shape from concave up in the lower section to convex in the upper section three dimensional diffusion models of sedimentation which incorporate a time dependent seafloor deflection from progressive island loading and vary sediment influx as islands are formed and mass waste suggest that three main factors make the moat stratigraphy at the marquesas different from hawaii 1 the marquesas moat is overfilled while the hawaiian moat is underfilled 2 sediment diffusivities are lower at the marquesas and 3 the marquesas islands are separated by deep sedimentary basins in contrast to hawaii where islands are separated by a shallow ridge the lower sediment diffusivity at the marquesas may reflect a larger proportion of blocky massive material in the central marquesas moat or alternatively a change in the dominant process of sediment transport while there is similar sediment supply for a given along moat distance at both the marquesas and hawaii the underfilled moat at hawaii is apparently a consequence of greater moat volumes due to the larger size of the hawaiian volcanoes and possibly variations in underplating that load the plate the difference in sediment edifice ratios is likely related to the larger eruption rates at hawaii and different styles of volcano construction between hawaii and the marquesas

thickness trends and sequence stratigraphy of the middle devonian marcellus formation appalachian basin implications for acadian foreland basin evolution analysis of more than 900 wireline logs indicates that the middle devonian marcellus formation encompasses two third order transgressive regressive t r sequences mss1 and mss2 in ascending order compositional elements of the marcellus formation crucial to the successful development of this emerging shale gas play including quartz clay carbonate pyrite and organic carbon vary predictably within the proposed sequence stratigraphic framework thickness trends of marcellus t r sequences and lithostratigraphic units reflect the interplay of acadian thrust load induced subsidence short term base level fluctuations and recurrent basement structures rapid thickening of both t r sequences especially mss2 toward the northeastern region of the basin preserves a record of greater accommodation space and proximity to clastic sources early in the acadian orogeny however local variations in t r sequence thickness in the western more distal area of the basin may reflect the reactivation of inherited eocambrian basement structures including the rome trough and northwest striking cross structural discontinuities induced by acadian plate convergence episodes of block displacement locally warped the basin into northeast southwest trending regions of starved sedimentation and or erosion adjacent to depocenters in which regressive systems tract deposits were ponded block movement appears to have initiated in late early devonian time resulting first in thinning and local erosion of the oriskany sandstone in northwest pennsylvania this study in addition to providing the basis for a predictive sequence stratigraphic model that can be used to further marcellus exploration tells of a foreland basin more tectonically complex than accounted for by simple flexural models

the three dimensional structure of kilauea volcano hawaii from travel time tomography a linear travel time tomography study of the most active shield volcano of the world kilauea volcano hawaii was undertaken to determine the lateral heterogeneities produced by its intricate magmatic and tectonic environment kilauea provides an ideal setting to do tomography because of its dense seismograph array and many local earthquakes that allow excellent ray coverage of complex subsurface features local p wave data from 12 295 events were inverted using a one dimensional layered velocity model inversions were done for two cell sizes 5 5 5 km and 1 1 1 km to resolve structural regions on different length scales this study provided a view of the average velocity variations relative to a one dimensional velocity model analysis and interpretation of the tomographic images allowed us to infer the following model the main shallow magma reservoir is delineated by a slow velocity region southeast of the summit from 0 to 2 km depth there is a distinct high velocity region centered northwest of the summit from 0 to 2 km depth that represents a cap of dense intrusive dikes surrounding the magma chamber we suggest that the shallow reservoir is a narrow compartmentalized region of sills and dikes centered just south southeast of halemaumau caldera below the main reservoir the summit is imaged as a slightly fast region from 5 to 10 km in the coarse model indicating that the main conduit is structurally defined by an intrusive dike complex until about 10 km the rift zones of kilauea are imaged as major high velocity entities widening to the south with depth until 6 km these fast anomalies are related to the sheeted dike complexes along the rifts on a finer scale slow anomalies suggest the presence of magma pockets centered at 0 2 km depth beneath mauna ulu makaopuhi and puu oo along the east rift zone erz two significant high velocity regions along the lower erz near kalalua and kaliu are inferred to represent intrusive barriers to magma injection along the shallow 0 4 km erz conduit the southwest rift zone may have an intrusive barrier related to a high velocity region just southwest of mauna iki the hilina and kaoiki fault zones are imaged as slow features at shallow depths 5 km related to the open fractures and scarps along the normal faults the koae fault system is imaged as a slightly fast shallow structure 6 km possibly related to intrusive diking from the adjacent rift zones that fill and may even induce the extensional structures associated with this complex fault zone continued inversions with the immense amount of seismic data collected for hawaiian events will allow the detailed development of a three dimensional structural model for kilauea such a model will be extremely useful to seismologists and petrologists alike for understanding the tectonic growth and magmatic evolution of this dynamic shield volcano

cyclic caldera collapse piston or piecemeal subsidence field and experimental evidence many multicycle caldera volcanoes display a complex extracaldera fault system genetically linked to caldera evolution on gran canaria canary islands the miocene tejeda caldera was filled by ignimbrites and epiclastic sediments and intruded by syenites and a major cone sheet swarm obscuring intracaldera structural relations extracaldera radial and circumferential faults and dikes are well exposed we used field data and experiments scaled to the island of gran canaria to clarify the poorly understood structural temporal and genetic relationship of peripheral faults to the central caldera the experimental setup comprises a cone of medium grained sand in which a rubber balloon was repeatedly inflated and deflated balloon inflation resulted in updoming and a dominantly radial fault pattern whereas balloon deflation caused piecemeal caldera collapse and a concentric peripheral fault arrangement on the edifice flanks a complex interplay of repeated inflation and deflation cycles of the experimental magma chamber is found to explain the peripheral fault system of the tejeda caldera on gran canaria and offers insight into the structure of the caldera floor and the mechanisms acting in multicycle caldera volcanoes

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

two new emsian early devonian u pb zircon ages from volcanic rocks of the rhenish massif germany implications for the devonian time scale so far only few biostratigraphically well constrained isotopic ages constitute the geochronological framework of the devonian period to expand this sparse dataset two new u pb isotope dilution thermal ionization mass spectrometry id tims zircon ages were obtained from volcanic rocks of the rhenish massif germany these rocks are interbedded in emsian lower devonian marine sedimentary successions that are well documented by index fossils given that the u pb zircon data represent primary crystallization and eruption ages they provide an important contribution to the devonian time scale the older sample a stratiform volcaniclastic layer hans platte is collected from bundenbach hunsruck the type locality of the lower emsian hunsruck slate a cluster of five coherent single zircon analyses obtained from this layer yielded a weighted mean 206 pb 238 u age of 407 7 0 7 ma which is regarded as the time of eruption of the pyroclastic rock biostratigraphically the layer can be assigned to the upper part of the polygnathus excavatus conodont zone the younger u pb age was obtained from the global stratotype section and stratigraphic point section at wetteldorf eifel where the k bentonite hercules i is intercalated 13 m below the lower middle devonian boundary in the uppermost part of the polygnathus costatus patulus conodont zone some of the 19 single zircon analyses obtained from this bentonite appear to document significant influences of inheritance the 13 youngest points are however concordant and form an elongated cluster along concordia with 206 pb 238 u ages between 392 2 and 407 7 ma given the risky assumption that this age scattering is exclusively caused by varying amounts of inheritance the youngest point of this cluster represents the analysis with the least or no inheritance in this case its 206 pb 238 u age of 392 2 1 5 ma should approach the eruptional age of the bentonite the ages presented here in combination with u pb id tims zircon and monazite ages from other workers allow a recalibration of the early emsian to early eifelian interval of the devonian time scale the result is a duration of the emsian stage excluding the basal emsian p kitabicus conodont zone of more than 17 2 ma and an emsian eifelian early middle devonian boundary age of 391 8 0 4 ma

mudrock sequence stratigraphy a multi proxy sedimentological paleobiological and geochemical approach devonian appalachian basin abstract delineation of stratigraphic sequences and their component systems tracts in mudrock dominated facies is generally difficult due to the relatively homogenous fine grained nature of the strata in this study we apply a multi proxy analytical approach to a thick devonian mudrock dominated succession through detailed analysis of sedimentologic paleobiologic and geochemical data through 600 m of mudrock rich facies varied combinations of proxies prove to be most useful in delineating sequence development in anoxic dysoxic and oxic dominated mudrock settings and in mixed mudrock carbonate and mixed mudrock sandstone successions these interpretations are tested against an established sequence stratigraphic framework for 11 middle to upper devonian mid eifelian to lower famennian sequences in the appalachian basin the sequences presented here further detail and refine global devonian t r cycles id to iie of the well known johnson sandberg and klapper sea level curve the usefulness of proxies in delineating depositional sequences and systems tracts varies dependent on depositional paleoceanographic paleoecologic and early diagenetic conditions those proxies that show a range of variations in specific settings such as grain size degree of bioturbation and concentrations of toc and elements elemental ratios e g caco3 al ti mg sc si mo ni v si al and ti al may help delineate depositional dynamics related to redox conditions condensation dilution and clastic biologic and or authigenic sediment sources in fine grained anoxic dominated facies interpreted to represent basinal settings sequences and systems tracts are best delineated by anoxic related proxies toc and mo in intermediate dysoxic dominated settings toc mo bioturbation and al remain effective indicators of sequence development in relatively oxygenated mudrock rich and carbonate poor sequences bioturbation may function as the most effective proxy for recognizing systems tracts for mixed fine grained siliciclastic carbonate successions concentration and type of caco3 e g benthic macroskeletal pelagic styliolinid dacryoconarid and micritic calcisilt are useful in identifying position within cycles in more proximal carbonate poor successions fine and coarse grained fractions become increasingly differentiated these can be distinguished by relatively high si al ratios si al ca 5 elemental ratios indicative of coarser clastic input e g si al zr al and ti al are applicable to identifying position with a sequence but they may also be affected by input from eolian volcanogenic or biogenic sources in addition fluxes of siliciclastic carbonate and toc sediment types may dilute the concentration of the others multiple lines of evidence should be examined in interpreting relative depth and position within a sequence

three dimensional inverse modelling of magnetic anomaly sources based on a genetic algorithm we present a modelling method to estimate the 3 d geometry and location of homogeneously magnetized sources from magnetic anomaly data as input information the procedure needs the parameters defining the magnetization vector intensity inclination and declination and the earth s magnetic field direction when these two vectors are expected to be different in direction we propose to estimate the magnetization direction from the magnetic map then using this information we apply an inversion approach based on a genetic algorithm which finds the geometry of the sources by seeking the optimum solution from an initial population of models in successive iterations through an evolutionary process the evolution consists of three genetic operators selection crossover and mutation which act on each generation and a smoothing operator which looks for the best fit to the observed data and a solution consisting of plausible compact sources the method allows the use of non gridded non planar and inaccurate anomaly data and non regular subsurface partitions in addition neither constraints for the depth to the top of the sources nor an initial model are necessary although previous models can be incorporated into the process we show the results of a test using two complex synthetic anomalies to demonstrate the efficiency of our inversion method the application to real data is illustrated with aeromagnetic data of the volcanic island of gran canaria canary islands