strain partitioning in the transition area between oblique subduction and continental collision hikurangi margin new zealand spatial differences in late quaternary structural style and deformation rates indicate a complex pattern of strain partitioning within the transition area from oblique subduction beneath southern north island to oblique continental collision in northern south island new zealand the late quaternary structure of the offshore southern hikurangi margin is determined here using seismic reflection profiles mr1 side scan sonar swath images em12dual multibeam swath bathymetry and backscatter images and sediment core and dredge samples where oblique 50 subduction of the oceanic hikurangi plateau is occurring beneath southern wairarapa region the steep dissected upper margin consists of a wedge of rocks that are being deformed by strike slip and reverse faults beneath the lower margin an accretionary wedge of quaternary age has developed rapidly by frontal accretion of a thick succession of turbidites on the pacific plate estimates of late quaternary geological strain rates have been made on two margin perpendicular transects across southern north island and the offshore margin to budget the predicted nuvel 1a plate motion more than 33 55 of the total plate motion is expressed in the offshore part of the upper plate above the subduction detachment in the central hikurangi margin between 40 s and 41 s this offshore deformation could potentially include margin parallel fault slip of up to 14 15 mm yr across the upper plate strain is partitioned into zones of folding and thrust faulting and possibly more than one zone of strike slip faulting but the partitioning may be incomplete with oblique slip thrusting an important component of the deformation the wide distribution of deformation within the upper plate partially reflects strong coupling between the subducting oceanic plateau and the leading edge of the overriding plate this coupling increases toward the southwest where the continental part of the subduction zone beneath marlborough may now be inactive or very strongly coupled toward the southwest the transpressive deformation style of the upper wairarapa margin continues into the upper marlborough margin and onshore into the strike slip marlborough fault system of northern south island in contrast the accretionary wedge narrows to the southwest and terminates in southeastern cook strait approximately above the transition from subducted oceanic crust to subducted continental crust of the pacific plate farther southwest beneath the lower marlborough margin low strain folding and thrust faulting is occurring but the style of deformation is not typical of the accretionary wedge this shortening results either from a small amount of subduction slip beneath marlborough and or from contractional strain partitioned to the southeast of the continental transpression zone whereas the initial onset of continental collision occurs in marlborough the surface expression of deformation of the pacific plate occurs south of 42 30 s normal faulting of the northwestern margin of the continental chatham rise possibly reflects flexural extension of the pacific plate crust at the southern end of the subduction zone whereas folding and thrust faulting of the north canterbury coastal region results from nw se contraction of the delaminated upper crust entering the southern alps collision zone

novel paleoecology of a postextinction reef famennian late devonian of the canning basin northwestern australia reefs are widely supposed to be particularly susceptible to mass extinction events and to survive only as low diversity remnant communities dominated by holdover or disaster taxa famennian late devonian reefs exposed in the windjana limestone of the canning basin northwestern australia demonstrate however that a novel reef ecology was established in the immediate aftermath of the frasnian famennian mass extinction here diverse calcimicrobes including rothpletzella spp shuguria spp ortonella and girvanella together with bryozoans brachiopods and stromatoporoid sphinctozoan and lithistid sponges grew as complex framework intergrowths in previously undocumented morphological forms forming spectacular elevated laminar to platy structures to 3 m in diameter and 0 35 m thick at least 15 morphospecies of lithistids are now identified where only two were previously documented these communities show no substantial reduction in biodiversity compared to frasnian counterparts nor any change in tiering or loss of complex ecological interactions these observations suggest that where stable carbonate platforms persisted after mass extinction events reef building could continue more important they demonstrate that no protracted interval of time was necessarily required either for recovery to ecological stability or for completely new reef ecologies to assemble such studies highlight the need to document ecosystem recovery after mass extinction events using detailed paleoecological analyses in addition to simple compilations of global biodiversity changes

donnees sur la structure de l arc insulaire des petites antilles entre ste lucie et anguilla abstract geological and geophysical data were collected during a marine geological cruise arcante 1 carried out in 1977 1978 between st lucia and anguilla corresponding to about two thirds of the length of the lesser antilles archipelago they allow of a reconsideration of the structural framework of this island arc considered as a whole the lesser antilles ridge is characterized by a pattern contrasting sharply between its northern and southern halves the major discontinuity axis runs to the south of the guadeloupe archipelago the basement of the northern half is supposed to be mainly mesozoic and is connected with the evolution of the greater antilles whilst the southern half was generated only since the eocene the ne flanks of the lesser antilles ridge are steep and dissected by large submarine valleys such as the desirade sea trough their recent sedimentary cover post lower miocene is lacking or very poor enabling the outcropping of older formations volcanic mesozoic basement around la desirade upper cretaceous eocene and oligocene sediments conversely the nw flanks are gently sloping and are draped by a rather thick overburden of plio pleistocene deposits to the south the steep sw flanks are covered with a moderate thickness of recent sediments and display characteristics contrasting with those of the se flanks facing the barbados accretionary prism from the south up to martinique there is only one volcanic ridge of eocene to present age to the north of martinique this ridge splits into two axes the submarine landmarks of these two arcs have been disclosed during the present survey the eastern one or outer arc shows a row of seamounts and islands often marked by strong magnetic dien bien phu bank marie galante agouti bank or heavy gravimetric marie galante grande terre anomalies this outer arc was superimposed on the pre eocene basement and is expressed in the eocene and oligocene volcanic terrains cropping out in the islands of antigua st bartholomew st martin and anguilla which rise from the wide northern insular shelves a major ca 70 km interruption in the continuity of this axis takes place between dien bien phu bank and marie galante la desirade and barbuda islands although pertaining to the limestone caribbees are not included in the outer arc the western or inner arc made up of upper miocene to present volcanics begins with dominica island and terminates at luymes bank but an interruption of about 50 km is to be noted between basse terre and montserrat the outer and inner arcs are separated by the narrow ca 50 km and elongated ca 250 km kallinago depression this intra arc trough is generally filled by less than 1 km of recent sediments and is subdivided into three smaller basins it was not initiated by extensional rifting related to back arc spreading as was previously assumed it is possible that from martinique to guadeloupe an intermediate arc was in activity during the miocene data from exploratory oil surveys provide some new insights into the geology and the structure of the wide saba bank located to the west of the inner arc and near the northern end of the archipelago its volcanic substratum is of upper cretaceous paleocene age and is part of the pre eocene basement of the northern lesser antilles the general characteristics of the ne flanks of the lesser antilles ridge may indicate some tilting toward the west of the northern part of the island arc this may be ascribed to the arrival of atlantic fracture zone ridges barracuda and tiburon in the subduction zone during the miocene this event could explain the jump of the volcanic line from the outer to the inner arc

deformation of the oceanic crust between the north american and south american plates fracture zone trends and magnetic anomalies in the atlantic ocean indicate that the north american plate must have moved with respect to the south american plate during the opening of the atlantic a comparison of plate tectonic flow lines with fracture zones identified from geosat and seasat altimeter data suggests that the north american south american plate boundary migrated northward from die guinea demarara shear margin to the vema fracture zone before chron 34 84 ma to north of the doldrums fracture zone before chron 22 51 9 ma and to north of the mercurius fracture zone between chron 32 72 5 ma and chron 13 35 5 ma the paleoridge offset through time identified from magnetic anomalies and the computed cumulative strike slip motion in the plate boundary area indicate that the triple junction may have been located between the mercurius and the fifteen twenty fracture zones after 67 ma chron 30 plate reconstructions indicate a late cretaceous phase of transtension followed by transpression in the tertiary for the tiburon barracuda ridge area south of the fifteen twenty fracture zone the ocean floor in this area is characterized by a series of ridges and troughs with large bouguer gravity anomalies up to 135 mgal we use smoothing spline estimation to invert bouguer anomalies for crustal layer structure our model results suggest that the moho is uplifted 2 4 km over short wavelengths 70 km at the barracuda and tiburon ridges and imply large anelastic strains the severely thinned crust at the two ridges implies that crustal extension must have taken place before they were uplifted we propose that the north south american plate boundary migrated to the latitude of the tiburon ridge bounded by the vema and marathon fracture zones before chron 34 84 ma post chron 34 crustal thinning during a transtensional tectonic regime may have been localized at preexisting structural weaknesses such as the vema marathon mercurius and fifteen twenty fracture zone troughs but reaching the fifteen twenty fracture zone and future barracuda ridge area only after chron 32 72 5 ma this interpretation concurs with our crustal structural model which shows stronger crustal thinning underneath the tiburon ridge than at the barracuda ridge subsequent transpression may have continued along the existing zones of weakness in the tertiary creating the presently observed crustal deformation and uplift of the moho accompanied by anelastic failure of the crust middle eocene upper oligocene turbidites on the slope of the tiburon ridge now located 800 m above the abyssal plain suggest that most of its uplift occurred at post oligocene times the unusually shallow moho underneath the tiburon and barracuda ridges represents an unstable density distribution which may indicate that compressive stresses are still present to maintain these anomalies and that the north american south american plate boundary may still be located in this area

deep structure of the central lesser antilles island arc relevance for the formation of continental crust oceanic island arcs are sites of high magma production and contribute to the formation of continental crust geophysical studies may provide information on the configuration and composition of island arc crust however to date only few seismic profiles exist across active island arcs limiting our knowledge on the deep structure and processes related to the production of arc crust we acquired active source wide angle seismic data crossing the central lesser antilles island arc north of dominica where the oceanic tiburon ridge subducts obliquely beneath the forearc a combined analysis of wide angle seismics and pre stack depth migrated reflection data images the complex structure of the backstop and its segmentation into two individual ridges suggesting an intricate relation between subducted basement relief and forearc deformation tomographic imaging reveals three distinct layers composing the island arc crust a three kilometer thick upper crust of volcanogenic sedimentary rocks and volcaniclastics is underlain by intermediate to felsic middle crust and plutonic lower crust the island arc crust may comprise inherited elements of oceanic plateau material contributing to the observed crustal thickness a high density ultramafic cumulates layer is not detected which is an important observation for models of continental crust formation the upper plate moho is found at a depth of 24 km below the sea floor upper mantle velocities are close to the global average our study provides important information on the composition of the island arc crust and its deep structure ranging from intermediate to felsic and mafic conditions in this study we model the deep structure of the lesser antilles island arc we use a hybrid analysis of refraction and reflection seismic data we image the complex structure of two ridges forming the backstop island arc crust composition ranges from intermediate to felsic to mafic conditions we discuss the formation of island arc and continental crust

reef development at the frasnian famennian mass extinction boundary a newly compiled global reef database indicates that the 5 6 myr long frasnian late devonian metazoan reef episode had relatively lowdiversity compared to middle devonian highs w ith over 200 genera of calcitic rugose and tabulate corals following an initial early rise after late givetian coral and stromatoporoid extinctions reefs expanded for the last time during mid frasnian sealevel highstands but declined markedly in the late frasnian rhenana linguiformis conodont zones belowthe frasnian famennian f f boundary globally metazoan reefs were wiped out by the end frasnian some famennian reefs while partly retaining the structure of the underlying carbonate platform were built by cyanobacterial consortia such as renalcis rothpletzella girvanella and epiphyton during the famennian foraminiferans with calcite walls became abundant for the first time in the phanerozoic adding a newdimension to carbonate platforms colonial rugose corals phaceloid cerioid and thamnasterioid modules were absent in the early post extinction phases up into the mid famennian and very rare and non reefbuilding later but solitary deep water lazarus corals survived locally coral sponge reefs are unknown from the 21 myr long famennian also a time of very lowplatform carbonate production rare small isolated stromatoporoid sponge and lithistid sponge patch reefs returned episodically during the famennian in north america western europe australia and china the aragonitic stromatoporoids became extinct at the end of the famennian during a late devonian tectonically very active collisional caledonian mountain building phase oceanic and atmospheric cooling accompanied by sealevel lowstand systems exposed most carbonate platforms accelerating coastal erosion and karsting this increased the amount of clastics in the shelf slope setting in the last 1 3 myr prior to the f f boundary often burying reefs immediately following there were protracted losses in nearly all major tropical shelf benthic marine invertebrates exceeded only by the end permian extinctions in severity there is no apparent link between black organic rich horizons and reef demise at or close to the f f boundary the f f boundary not also marks the largest change from widespread flooded early and mid paleozoic continental cratons to narrow distal shelves but also spikes the largest known global phanerozoic shift in atmospheric o2 enrichment and co2 drawdown this threshold matched the rise of the first tropical rainforests and expansion of terrestrial biomes on the tropical coastal lowlands formerly occupied by carbonate platforms 6 2002 elsevier science b v all rights reserved

active faulting induced by slip partitioning in montserrat and link with volcanic activity new insights from the 2009 gwadaseis marine cruise data 1 new high resolution marine data acquired aboard r v le suroit was used to map active normal faults offshore montserrat in greater detail the main faults of the montserrat havers fault zone have cumulative scarps up to 200 m high and offset sedimentary layers by hundreds of meters they are arranged in a right stepping en echelon trans tensional array which confirms that they accommodate the left lateral component of motion resulting from slip partitioning of oblique convergence along the volcanic arc they cut across montserrat s recent volcanic complex faulting and fissuring exerted control on the position of andesitic domes which are aligned along the n110 e average fault trend the 10 km long fault segments that cross the island could produce damaging m 6 events comparable to the shallow 16 march 1985 mw 6 3 earthquake that ruptured a submarine n140 e striking left lateral fault near redonda

formation of forearc basins by collision between seamounts and accretionary wedges an example from the new hebrides subduction zone seabeam data reveal two deep subcircular reentrants in the lower are slope of the new hebrides island arc that may illustrate two stages in the development of a novel type of forearc basin the malekula reentrant lies just south of the partly subducted bougainville seamount this proximity as well as the similarity in morphology between the reentrant and an indentation in the lower arc slope off japan suggests that the malekula reentrant formed by the collision of a seamount with the arc an arcuate fold thrust belt has formed across the mouth of the reentrant forming the toe of a new accretionary wedge the efate reentrant may show the next stage in basin development this reentrant lies landward of a lower slope ridge that may have begun to form as an arcuate fold thrust belt across the mouth of a reentrant this belt may have grown by continued accretion at the toe of the wedge by underplating beneath the reentrant and by trapping of sediment shed from the island arc these processes could result in a roughly circular forearc basin basins that may have formed by seamount collision lie within the accretionary wedge adjacent to the aleutian trenches

paleoecology of secondary tierers from western pangean tropical marine environments during the aftermath of the end permian mass extinction abstract skeletobionts that colonized organic hard parts during the early and late aftermath of the end permian mass extinction had been undescribed previously evaluation of more than 7400 skeletonized benthic invertebrates and taphonomic processes reveal a general pattern of increasing diversity and abundances of skeletozoans through the early triassic in tropical marine environments on the coast of western pangea present day western u s a griesbachian age skeletobiont assemblages are dominated by episkeletozoans while spathian ones are dominated by endoskeletozoans bivalves were the primary hard substrate for the skeletozoans in all examined strata most likely because they were the most abundant skeletonized benthic invertebrate microconchids are hypothesized to have behaved opportunistically during the immediate aftermath of the end permian mass extinction and they had a strongly preferred association with claraia this and future studies of early triassic skeletobionts will contribute to further understanding arguably one of the most evolutionary significant intervals in earth s history

structure of the lesser antilles subduction forearc and backstop from 3d seismic refraction tomography in 2007 the sismantilles ii experiment was conducted to constrain structure and seismicity in the central lesser antilles subduction zone the seismic refraction data recorded by a network of 27 obss over an area of 65 km 95 km provide new insights on the crustal structure of the forearc offshore martinique and dominica islands the tomographic inversion of first arrival travel times provides a 3d p wave velocity model down to 15 km basement velocity gradients depict that the forearc is made up of two distinct units a high velocity gradient domain named the inner forearc in comparison to a lower velocity gradient domain located further trenchward named the outer forearc whereas the inner forearc appears as a rigid block uplifted and possibly tilted as a whole to the south short wavelength deformations of the outer forearc basement are observed beneath a 3 to 6 km thick sedimentary pile in relation with the subduction of the tiburon ridge and associated seafloor reliefs north offshore dominica island the outer forearc is 70 km wide it extends as far as 180 km to the east of the volcanic front where it acts as a backstop on which the accretionary wedge developed its width decreases strongly to the south to terminate offshore martinique where the inner forearc acts as the backstop the inner forearc is likely the extension at depth of themesozoicmagmatic crust outcropping to the north in la desirade island and along the scarp of the karukera spur the outer forearc could be either the eastern prolongation of the inner forearc but the crust was thinned and fractured during the past tectonic history of the area or by recent subduction processes or an oceanic terrane more recently accreted to the island arc

pliocene to pleistocene vertical movements in the forearc of the lesser antilles subduction insights from chronostratigraphy of shallow water carbonate platforms guadeloupe archipelago an integrated stratigraphic study was conducted on the shallow water carbonate platforms of the guadeloupe archipelago to refine the tectonic evolution of the lesser antilles forearc the carbonate platforms are now dated to the zanclean calabrian interval and their demise occurred between 1 5 and 1 07 ma the precise chronostratigraphy allows dating of the main extensional tectonic events since the late miocene an initial episode occurred during the late miocene related to the reactivation of inherited n130 e trending shear zones and led to the emergence of most parts of the forearc subsequently zanclean to early piacenzian carbonate platforms developed in association with a general subsidence of the forearc during the late piacenzan a second extensional episode occurred at this time la desirade underwent major uplift and emergence whereas most of the forearc remained submerged prior to 1 07 ma a third north south extensional episode occurred and led to the final demise of the carbonate platforms thus the forearc was characterized by general subsidence since the early pliocene interrupted by three main extensional episodes and related differential uplifts this suggests that the lesser antilles subduction is probably erosive north of latitude 15 n since c 5 ma related to aseismic ridge subduction supplementary data planktonic foraminiferal assemblages calcareous nannofossil taxa associations 40 ar 39 ar geochronological data and palaeomagnetic data are available at www geolsoc org uk sup18724

discovery of lower cretaceous synmetamorphic thrust tectonics in french lesser antilles la desirade island guadeloupe implications for caribbean geodynamics located east of guadeloupe the island of la desirade exhibits the oldest rocks of the lesser antilles arc and the eastern caribbean plate an old magmatic basement is composed of 1 late jurassic ophiolitic complex with meta basaltic pillow lavas and interbedded radiolarites 2 acid igneous complex comprising meta quartz diorite and meta rhyolitic lavas flows and 3 meta diabasic microdioritic dyke swarm complex we present and discuss the discovery of synmetamorphic thrust tectonics in this island based on detailed structural analysis we evidenced two main compressive events the first event d1 is characterized by pervasive folding associated with thrust development in the northeastern part of the island a major thrust fault the grand abaque thrust has been discovered which displaces for several kilometers the acid igneous complex onto the ophiolitic unit the second deformation event d2 is featured by a main pervasive cleavage s2 observed at the regional scale associated with upright folding f2 and by the development of two sets of conjugated steeply dipping strike slip shear zones dextral 130 n and sinistral 20 n striking respectively microstructural observations indicate that greenschist facies metamorphism is clearly contemporaneous with the development of d1 and d2 superimposed tectonic structures ar ar geochronology was performed on two bulk of adularia minerals sampled in the northeast volcanic complex within a deformed zone related to a d2 event these analyses yield well defined and concordant plateau ages at 106 2 1 7 ma and 107 2 1 8 ma thus shortening and thickening tectonics occurred during lower cretaceous albian in the available framework of caribbean geodynamics the synmetamorphic thrust tectonics we discovered in the french lesser antilles is related to the collision between an aptian albian oceanic plateau and the andean cordilleran east dipping subduction zone our results support subduction polarity reversal during lower cretaceous

black shale deposition and faunal overturn in the devonian appalachian basin clastic starvation seasonal water column mixing and efficient biolimiting nutrient recycling integrated geochemical data suggest that black shale deposition in the devonian geneseo formation of western new york was initiated by the coincidence of siliciclastic starvation and the intensification of seasonal water column stratification and mixing once established however black shale deposition was maintained through efficient recycling of biolimiting nutrients which enhanced primary productivity recycling efficiency was achieved through a positive feedback loop of oscillating benthic redox conditions that enhanced n and p regeneration from sediments sustained high primary productivity by returning nutrients to the photic zone during mixing and ensured a downward flux of organic matter that drove or enhanced the episodic development of benthic anoxia during stratification this feedback was ultimately disrupted by rising siliciclastic influx which diluted organic matter and restored benthic redox stability the abrupt overturn of diverse long standing appalachian basin marine communities may have been the result of trophic resource destabilization during geneseo deposition

the phylogenetic and palaeogeographic evolution of the miogypsinid larger benthic foraminifera access to new material from south africa corsica cyprus syria and sumatra has allowed a systematic biostratigraphic comparison and correlation of the miogypsinids from the mediterranean west africa and the indo pacific provinces and for the first time from south africa twelve new species have been identified neorotalia tethyana miogypsinella bornea miogypsina subiensis m niasiensis m regularia m samuelia miolepidocyclina banneri miogypsinella cyprea miogypsina mcmillania m africana m ianmacmilliana and m southernia the palaeogeographical evolution of the miogypsinids started with a trans atlantic migration of neorotalia from the americas where miogypsinids had originated the eastward migration followed two paths one to the south towards south africa where a distinct phylogenetic lineage but similar to that found in america developed but went extinct in the burdigalian the other to the north through the mediterranean corridor during the chattian and aquitanian significant miogypsinid forms evolved in the mediterranean from the morphologically distinct mediterranean neorotalia and migrated within a few million years of their first appearance into the indo pacific where they diversified further the tectonically driven closure of the seaway between the mediterranean and the indo pacific in the burdigalian triggered the extinction of mediterranean miogypsinids in the langhian miogypsinids survived in the indo pacific into the serravallian

the holocene drowned reef of les saintes plateau as witness of a long term tectonic subsidence along the lesser antilles volcanic arc in guadeloupe abstract resulting from the interplay between tectonics and eustatism reef terraces are powerful markers of vertical movements at a scale of 1000 to 100 000 years in the lesser antilles they grow around every island of the archipelago and record both local and subduction related tectonics the recent acquisition and interpretation of very high resolution bathymetry of les saintes submarine plateau french west indies together with seismic reflection profiles are a unique opportunity to study one of these submarine structures at metric to kilometric scales addressing the questions of its nature age and growth environment but also of the control of active tectonics on its formation the 20 km wide les saintes reef plateau lies at about 45 mbsl it is crosscut by nw se striking north dipping normal faults that belong to les saintes fault system and graben which produced a mw 6 3 earthquake in 2004 the plateau is composed of four 20 m thick reef units piled up in layer cake morphology down to 110 mbsl the upper unit has a fresh morphology and presents typical reef features like barrier and lagoon spurs and grooves pinnacles etc from its morphology we propose that it grew during the holocene last transgression below the three other units likely formed during pleistocene sea level highstands and were eroded during the low stands as evidenced in seismic reflection profiles this scenario would imply that les saintes plateau formed in a context of subsidence with a rate we evaluate to be of the order of tenths of mm yr probably linked to local tectonics we believe that this deformation is also related to plate scale subduction processes similarly to deformations occurring on the other islands of the guadeloupe archipelago

anoxic events in the late frasnian causes of the frasnian famennian faunal crisis carbon isotope data collected from five frasnian famennian boundary sections in central europe show two positive 13 c excursions in the late frasnian 367 ma both anomalies coincided with the deposition of the bituminous lower and upper kellwasser horizons the carbon isotope patterns indicate two phases of enhanced burial and subsequent recycling of organic carbon a maximum formation of warm saline waters on the subtropical to tropical epicontinental shelves during late frasnian transgressive episodes may have induced oceanic oxygen deficits variations in the c org burial rates may have resulted in changes in the co 2 concentrations in the oceans and in the atmosphere culminating in global climatic changes we propose that the repeated co occurrences of sea level fluctuations anoxic conditions and global climatic changes during the late frasnian would affect especially the subtropical to tropical shallow water communities and reef ecosystems which were severely affected during the frasnian famennian faunal crisis

the late frasnian kellwasser horizons of the harz mountains germany two oxygen deficient periods resulting from different mechanisms in the harz mountains germany three late devonian sections aeketal huhnertal and kellwassertal were analyzed for major and trace element concentration the inorganic geochemical data were used to determine the environmental conditions associated with the deposition of the two late frasnian black kellwasser horizons in a submarine rise environment low ti al and zr al values and slight enrichment in nutrient and organic matter related trace elements e g ba cu and ni suggest that the kellwasser horizons were deposited during two periods of minimum detrital input but relatively elevated primary production enrichments in u v and mo in both black kellwasser horizons and values of redox indices including u th v cr and ni co indicate oxygen restricted conditions prevailed during the late frasnian times under oxygen depleted conditions reductive diagenesis caused precipitation of iron sulphides such as pyrite that are observed with sem however variations in major and trace element concentrations are not similar in the two kellwasser horizons particularly regarding redox markers the lower kellwasser horizon seems to be more o2 depleted than the upper kellwasser horizon in some german sections on the basis of these results we propose that the two kellwasser horizons are not caused by identical conditions the lower kellwasser horizon results from increased primary productivity enhanced by land derived nutrient loading and which triggered the anoxic conditions recorded in drowned platform setting in contrast the upper kellwasser horizon results from the onset of oxygen impoverished bottom water in the deepest part of the ocean due to episodic water stratification during maximum frasnian flooding oxygen depleted water may have impinged shallower environment during the linguiformis transgressive pulse nutrients would have been released from organic matter decay under reducing conditions and brought up to the photic zone during episodic water mixing

platforms of the nicaraguan rise examples of the sensitivity of carbonate sedimentation to excess trophic resources the nicaraguan rise is an active tectonic structure in the western caribbean carbonate accumulation on its platforms has not kept pace with relative holocene sea level rise despite a tropical location remote from terrigenous sedimentation trophic resources apparently exceed levels favoring coral reef development because sponge algal communities dominate the drowning western platforms in contrast to mixed coral algal benthos on pedro bank and well developed coral reefs along the north coast of jamaica concentrations of biotic pigments in sea surface waters show a corresponding west east gradient oceanic waters flowing over the western banks carry nearly twice as much biotic pigment as oceanic waters north of jamaica sources enriching the western caribbean are terrestrial runoff upwelling off northern south america and topographic upwelling over the nicaraguan rise that relatively modest levels of trophic resources can suppress coral reef development holds important implications for understanding carbonate platform drownings in the geologic record

water column anoxia enhanced productivity and concomitant changes in δ13c and δ34s across the frasnian famennian boundary kowala holy cross mountains poland the investigation of the trace element and organic geochemistry of the frasnian famennian boundary section at kowala holy cross mountains poland shows that the lower water column was oxygen deficient during late frasnian and early famennian times the abundance and carbon isotopic composition of diaryl isoprenoids biomarkers indicative for green sulfur bacteria prove that euxinic waters reached into the photic zone at least episodically total organic carbon toc contents show two maxima that are time equivalent to the kellwasser horizons deposited in shallower water settings enhanced toc concentrations are explained by a higher primary productivity presumably as a consequence of an enhanced nutrient supply from the continent the increase in the abundance of hopanes and bituminite suggests that the bacterial contribution to toc increased at the frasnian famennian transition the sulfur isotopic composition of pyritic and organically bound sulfur shows a 27 excursion across the boundary the observation that the 34s values of organic bound sulfur closely resemble that of pyrite sulfur indicates a common sulfur source likely early diagenetic sulfide a change in the 13c of total dissolved inorganic carbon as a consequence of an enhanced burial of 12c enriched organic carbon is indicated by a 3 excursion measured for toc as well as for individual n alkanes and isoprenoids the burial of large amounts of organic carbon is expected to result in a decrease in pco2 and should affect the photosynthetic carbon isotope fractionation ep the fact that we observe no change in ep can be explained by the circumstance that ep was most probably at maximum values as a consequence of high atmospheric and oceanic dissolved co2 concentrations during the devonian

fluctuations in the trophic resource continuum a factor in global diversity cycles the trophic resource continuum trc in euphotic zones of the world s oceans is the spectrum of conditions from the richest runoff and upwelling areas to the most nutrient deficient subtropical seas that spectral range has likely varied through geologic history as more efficient phytoplankton taxa evolved as oceanic circulation rates changed and in response to oceanic mixing events reduced rates of oceanic turnover should produce regionally intensified eutrophy and oligotrophy that is trc expansion because oceanic waters as a whole are relatively nutrient rich increased rates of oceanic turnover should prevent extremely eutrophic and extremely oligotrophic conditions from developing causing trc contraction global biotic diversities in the oceans are strongly influenced by communities in oligotrophic environments nutrient deficient waters are more stable and more transparent than richer waters permitting higher degrees of specialization sparse nutrient supplies necessitate smaller phytoplankton and longer more complex food chains preservation potential of oligotrophic biotas is also greater because calcareous taxa are more prevalent and because calcium carbonate is less apt to be bioeroded or dissolved fluctuations in the trc should profoundly affect diversity of habitats within the euphotic zone of the oceans the evolutionary response to a trc expansion diversification would occur in a geologic time frame of millions of years while evolutionary responses to a trc contraction including extinction could occur in a biological time frame of generations a simple model indicates that a reduction in the trophic resource continuum from expansion during a major marine transgression down to modern levels could result in loss of 40 of the euphotic habitats how fluctuations in the trc control diversity of euphotic habitats in the oceans provides an hypothesis by which to interpret global taxonomic diversity cycles as well as taxonomically selective extinctions changes in species dominance and some morphologic trends

mercury evidence for anorthosite and basalt from mid infrared 7 3 13 5 μm spectroscopy abstract spectroscopic observations 7 3 13 5 m of three locations on the surface of mercury are reported the observed spectral radiance emanated from equatorial and low latitude regions between 12 and 32 mercurian longitude on 8 december 1990 from the longitudinal region 22 44 on 10 december 1990 and from the longitudinal region 110 130 on 12 july 1992 all locations are primarily intercrater plains spectra indicate compositional differences among these three locations the emissivity maximum or christiansen emission peak occurs at 8 1 m in the 8 december 1990 spectra but at shorter wavelengths in the data of 10 december 1990 and 12 july 1992 emission peaks near 8 m indicate rocks of intermediate or mafic composition spectra from 22 to 44 longitude resemble spectra of terrestrial basalt and diorite with sio2 content between 49 and 55 the christiansen feature in spectra from near 110 130 longitude strongly suggests the presence of plagioclase in particular labradorite while the overall spectrum resembles anorthosite the spectra from all three locations on mercury show distinct and recognizable features the principal christiansen emission peak being the most prominent but they also contain features that we have not yet identified the general indication from the spectra is that mercury s surface consists of minerals more depleted in oxidized iron than those on the moon we also explore the theoretical and observational complexities of ground based mid infrared spectroscopy of airless bodies in general and mercury in particular a spectroscopic study of quartzite in both reflectance and emittance illustrates the practical spectral validity of kirchhoff s law

the frasnian famennian boundary interval in the south polish moravian shelf basins integrated event stratigraphical approach abstract the late devonian mass extinction event near the frasnian famennian f f boundary has been analysed using conodont biostratigraphy and biofacies sedimentology magnetic susceptibility and geochemistry in reference sections of the south polish moravian shelf holy cross mountains cracow and brno areas high resolution biostratigraphic study revealed difficulties in the precise recognition of this natural stage boundary but confirmed the occurrence of a major third order sequence boundary in the f f transition in an active synsedimentary tectonic setting marked by erosional discontinuities hardgrounds and brecciation or omission surfaces conclusive evidence of an extraterrestrial impact has not been found among earth bound factors the main devastating role in the shelf habitats is ascribed to fluctuating anoxia and or nutrient dynamics in a disturbed greenhouse climatic setting the long term facies changes were determined by a conspicuous break in carbonate production accompanied by replacement of mature stromatoporoid coral reefs by pioneer shelly crinoid banks microbial mounds and localised oolitic bars the key f f passage interval was marked by intermittent but generally accelerated periplatform ooze debris input and severe storm events as well as by probably highly fluctuating oxygenation and biological overproduction best manifested in radiolarian silicisponge and cephalopod acmes eutrophication phenomena at least partly stimulated by various hydrothermal and volcanic processes were one of the major biogeochemical processes during this climax of the late devonian biotic crisis however significant oceanographic perturbations were also linked with the onset of the transgressive hypoxic upper kellwasser event still within the latest frasnian linguiformis zone i e well before the f f conodont collapse implied variations in the redox state of seawater through the kellwasser timespan probably in regionally highly variable temporal scales are in agreement with recent palaeoecological and biogeochemical inferences in particular suggesting recovering oxygenation just prior to the f f boundary in the other laurussian intrashelf basins all the data support a long time multicausal earth bound crisis instead a worldwide cosmic catastrophe

palaeoenvironmental changes at the frasnian famennian boundary in key european sections chemostratigraphic constraints abstract the study aims to put constraints on global environmental changes which took place during the frasnian famennian f f transition by using a geochemical multiproxy approach for this several key european f f boundary sections deposited in different palaeogeographic settings were selected including in addition to the stratotype and parastratotype sections of coumiac montagne noire france and steinbruch schmidt branau germany respectively also some other sections thoroughly characterized by other authors the drilling budesheimer bach prumer mulde germany kowala section holy cross mountains poland la serre france changes in the detrital flux along the sections were evaluated on the basis of both variations in mineral composition and in some diagnostic element ratios like ti al the biogenic flux was assessed as a function of the corg content the input of nutrients or the palaeoproductivity was determined by the p2o5 and ba in excess the degree of anoxia during deposition was constrained by determining the concentration of redox sensitive metals e g fe mn in the bulk sediment of specific element ratios e g v cr as well as the size of pyrite grains together with the degree of pyritization dop in the budesheimer bach core the hydrothermal and volcanic influence in the sedimentary record was detected using e g the al al fe mn and zr al2o3 ratios the kellwasser horizons are characterized by a general decrease in the detrital input together with the increase of al normalized concentration of some of the transition metals these changes are interpreted as reflecting a relative sea level rise and a higher hydrothermal influence in contrast to these the establishment of dysoxic anoxic conditions in the depositional environment as well as the increase of organic matter burial are not always restricted to the kellwasser horizons kwh moreover the hydrothermal influence can lead to misinterpretation with respect to redox conditions and productivity due to the additional input of some specific elements our results indicate the coincidence of sea level rise with hydrothermalism and volcanism during the deposition of the kwh in the area of south laurussia and north gondwana the resulting enrichment in metals and nutrients is coupled in several f f boundary sections with a higher microbial activity as already observed by some authors these effects coupled with a general lowering of the degree of oxygenation of the water bodies could have played a significant role in the demise of the biota

earthquake evidence for along arc extension in the mariana islands 1 analysis of data from a deployment of ocean bottom and land seismographs in 2003 2004 detected four swarms of earthquakes in the overriding plate of the mariana subduction system between the fore arc and the back arc spreading center two additional shallow swarms were identified by analyzing the teleseismic earthquake catalogs from 1967 to 2003 focal mechanism solutions for these swarms determined from regional waveform inversion for the 2003 2004 events or retrieved from the centroid moment tensor catalog for previous years suggest a complex system of deformation throughout the arc we observe arc parallel extension near volcanic cross chains arc perpendicular extension along the frontal arc and arc parallel compression farther into the back arc near the mariana trough a swarm beneath the middle and eastern summits of the diamante cross chain may have recorded magmatic activity volcanic cross chains showing evidence of adiabatic decompression melting from extensional upwelling are localized at regions of enhanced along strike extension the earthquake data are consistent with recent gps results indicating 12 mm a of extension between guam and agrihan the along arc extension may result from either increasing curvature of the mariana system with time or from deformation induced by oblique subduction in the northernmost and southernmost regions of the arc

a review of calcareous nannofossil astrobiochronology encompassing the past 25 million years this paper presents a review of astrobiochronological calibration of recent to late oligocene calcareous nannofossil datum events biohorizons included in the paper are those of the widely used standard nannofossil zonations of martini e 1971 standard tertiary and quaternary calcareous nannoplankton zonation in farinacci a ed proceedings of the second international conference on planktonic microfossils roma rome ed tecnosci vol 2 pp 739 785 and okada h and bukry d 1980 supplementary modification and introduction of code numbers to the low latitude coccolith biostratigraphy zonation bukry 1973 1975 marine micropaleontology 51 321 325 as well as supplementary biohorizons proposed in the literature the biohorizons have been selected on the basis of the unambiguous taxonomy of the index taxa and their biostratigraphic usefulness we emphasise the application of rigorous methodology in nannofossil studies which permits an evaluation of biohorizons in terms of reliability and calibrates their potential correlatability astrochronological age estimates rely on the geologic timescale developed by the ics in 2004 with some new calibrations included we provide an overview of the relative position of biohorizons versus the astronomically calibrated ages of magnetic reversals and reference isotope stratigraphies surprisingly there are still few high resolution quantitative biostratigraphic studies of astrochronologically tuned sections in spite of the central role of such studies in addressing fundamental problems such as the tempo and mode of plankton evolution

microconchid dominated cobbles from the upper devonian of russia opportunism and dominance in a restricted environment following the frasnian famennian biotic crisis abstract carbonate cobbles from the lower famennian crepida conodont zone brachiopod shell beds of the russkiy brod quarry central devonian field russia have been investigated with respect to paleoecology and paleoenvironment the cobbles composed of similar shell bioclasts as the host deposits were eroded from lithified shell beds during intervals of non deposition the smooth surfaces and the presence of borings and encrustations on all sides suggest that the cobbles were periodically transported and overturned the fact that all the bioerosion traces are encrusted and none of the encrusters were bioeroded indicates that the first colonizers of the cobbles were worm like suspension feeders leaving long cylindrical borings trypanites the encrusting organisms are dominated by spirally coiled microconchid tubeworms followed by cornulitids productid brachiopods hederelloids foraminifera enigmatic ascodictyon and trepostome bryozoans the high abundance but low diversity brachiopod fauna and general rarity of such stenohaline taxa as echinoderms in the shell beds or bryozoans on the cobbles suggest that the salinity fluctuated the presence of dolomite crystals in both the host deposit and cobbles suggests that salinity increased from normal marine to a higher salinity level during colonization of the cobbles in fact as shown by the facies and palynofacies data the cobble bearing deposits represent near shore restricted environments created during the first phases of transgression of the early famennian that followed the regional regression at the frasnian famennian transition in such shallow restricted settings a higher salinity could have appeared seasonally during a hot and dry climate as with the microconchids from the aftermath of the end permian mass extinction those from the post crisis early famennian interval of russia were also dominant due to unstable environmental conditions here at least in the case of the russkiy brod the periodic higher salinity episodes may have discouraged other encrusters and thus promoted the settlement of the opportunistic microconchids

colonization of rugose corals by diverse epibionts dominance and syn vivo encrustation in a middle devonian givetian soft bottom habitat of the holy cross mountains poland abstract middle devonian givetian rugose corals from the holy cross mountains miloszow poland have been analysed with respect to epibiont colonization patterns solitary microconchid tubeworms and colonial bryozoans hederelloids and ascodictyids numerically dominate on the coral hosts moreover the same taxonomic groups of epibionts dominate both the larger heliophyllum acanthophyllum stringophyllum ceratophyllum cystiphylloides and smaller thamnophyllum corallites indicating the true pattern of epibiosis was achieved the presence of common bioclaustrated epibionts constricted and rejuvenated coral calyces as well as epibionts growing concordantly with the host s growth direction indicate that at least some corals were colonized during life the observed low number of overgrowth cases of various epibionts on coral hosts suggests that competition for hard substrate was negligible most probably due to abundant coral substrates on muddy sea bottom of the givetian sea at miloszow this epibiont community is similar to other known devonian encrusting communities which likely developed in a more nutrient rich palaeoenvironments and differs markedly from taxonomically poor assemblages developing in a more oligotrophic conditions the presence of rothpletzella encruster which is considered to be related to green algae indicates that the miloszow coral community dwelled within the limits of the photic zone

frasnian famennian mass extinction and cold water oceans suturing of laurussia and africa elimination of easterly tropical currents and consequent equatorial diversion of cold and possibly dysaerobic waters are suggested as prime causes of the frasnian famennian late devonian extinction these are explained by using a new paleogeographic model evidence for stepdown extinctions that took place from givetian through frasnian time is taken particularly from atrypoid brachiopods one of the most abundant representatives of the global tropical shelly marine benthos during the middle and late devonian only 5 of 17 frasnian genera or subgenera of atrypoids are known to be present in late frasnian sediments and possibly only a single genus spinatrypa was present at the frasnian famennian boundary evidence for stepdown extinction from other invertebrate and vertebrate groups in general corroborates that provided by brachiopods

deciphering the upper famennian hangenberg black shale depositional environments based on multi proxy record abstract presented for the first time in this paper are the results of a detailed multi proxy investigation conducted on the hangenberg black shale hbs from the polish part of the laurussian shelf which provide details about the environmental conditions in existence during deposition of the shale and the role played by anoxic conditions in the mass extinction events that occurred at the end of the devonian times inorganic and organic redox indicators indicate that bottom water redox conditions changed periodically from being mainly anoxic euxinic to oxic or being partially depleted in oxygen u th values above 1 25 ni co values above 7 and v v ni values above 0 8 recorded from the lower part of the hbs all point to anoxic euxinic conditions being present as do high total organic carbon contents toc above 10 and degree of pyritisation dop values around 0 75 however the presence of benthic fauna over the lower part of the hbs attests to opportunistic colonisation of the seafloor during oxic episodes evidence for similar episodes has also been recognised over the middle part of the hbs e g u th values below 1 25 ni co values below 4 v v ni values below 0 8 toc values of 3 to 5 5 and dop values of 0 4 to 0 75 plus the common occurrence of benthic fauna anoxic conditions returned during the deposition of the upper part of the hsb though they were not as well developed as when the lower part of the shale was laid down of interest is the presence of small pyrite framboids and isorenieratene biomarkers in all the analysed samples which suggest that euxinic conditions persisted in the photic zone of the water column a twenty centimetre thick layer of volcanogenic deposits tuffites is present in the middle part of the hbs the geochemical characteristics of which are typical of ocean floor basalts the occurrence of volcanogenic material below and within the hbs together with an absence of calcium carbonate over its upper part the presence of abundant tetrads just above the black shale and a drastic decrease in faunal frequency in the upper part of the hbs imply that volcanism may have caused oceanic acidification or hypercapnia that in turn potentially may have influenced the hangenberg mass extinction event

relative motion between the caribbean and north american plates and related boundary zone deformation from a decade of gps observations global positioning system gps measurements in 1986 1994 and 1995 at sites in dominican republic puerto rico cuba and grand turk define the velocity of the caribbean plate relative to north america the data show eastward motion of the caribbean plate at a rate of 21 1 mm yr 1 standard error in the vicinity of southern dominican republic a factor of 2 higher than the nuvel 1a plate motion model prediction of 11 3 mm yr independent measurements on san andres island and an euler vector derived from these data also suggest a rate that is much higher than the nuvel 1a model available data combined with simple elastic strain models give the following slip rate estimates for major left lateral faults in hispaniola 1 the north hispaniola fault offshore the north coast of hispaniola 4 3 mm yr 2 the septentrional fault in northern dominican republic 8 3 mm yr and 3 the enriquillo fault in southern dominican republic and haiti 8 4 mm yr the relatively high plate motion rate and fault slip rates suggested by our study combined with evidence for strain accumulation and historical seismicity imply that seismic risk in the region may be higher than previous estimates based on low plate rate low fault slip rate models and the relatively low rate of seismicity over the last century

tectonic and sedimentary architecture of the karukera spur a record of the lesser antilles fore arc deformations since the neogene the karukera spur is an easternmost submerged rise of the lesser antilles fore arc in the guadeloupe archipelago culminating about 4000 m above the fore arc basin 150 km west of the deformation front the analysis of 3500 km 2d high resolution multichannel seismic reflection and multibeam bathymetric data and the study of 14 core samples allow for the first time to reconstruct its sedimentary anatomy and tectonic evolution seven seismic units us1 to us7 are evidenced organised into four major depositional sequences separated by erosional surfaces units us1 to us4 thicken to the south southeast on the spur the sedimentary deposits rest upon a deeply eroded metamorphic basement of the caribbean plate as in la desirade island sequence 1 units us1 and us2 remains unknown in its lower part because it does not outcrop its upper part comprises early miocene shallow water carbonates sequence s2 unit us3 only comprises an upper miocene transgressive systems tract deposited into basinal environment it is bounded by major erosional surfaces sb2 and sb3 sequence 3 us4 to us6 is zanclean to pleistocene it is dominantly composed of shallow water reefal deposits sequence 4 corresponds to recent deposits the karukera spur experienced three main extensional episodes with alternations between uplift and subsidence periods uplifts are responsible for emersions and erosions subsidence severely drowned shallow water deposits the first extensional episode led to the formation of horsts and grabens in the basement prior to early miocene deposits the second extensional episode occurred during upper miocene in accordance with data in surrounding islands the third tectonic episode developed since calabrian noticeable is the constant reactivation of n130 n150 n150 n180 and n40 trending faults since early miocene and the neoformation of e w trending faults since calabrian our results suggest that at the latitude of guadeloupean archipelago the lesser antilles subduction zone is an erosional margin because of the successive sweepings of the santa lucia then tiburon ridges

tectonics basin subsidence mechanisms and paleogeography of the caribbean south american plate boundary zone abstract using a mega regional dataset that includes over 20 000 km of on and offshore 2d seismic lines and 12 wells we illustrate three different stages of fault formation and basin evolution in the caribbean arc south american continent collisional zone transpressional deformation associated with oblique collision of the caribbean arc migrates diachronously over a distance of 1500 km from western venezuela in paleogene time 57 ma to a zone of active deformation in the eastern offshore trinidad area each diachronous stage of pre syn and post collisional basin formation is accompanied by distinct patterns of fault families we use subsidence histories from wells to link patterns of long term basinal subsidence to periods of activity of the fault families stage one of arc continent collision initial collision is characterized by overthrusting of the south and southeastward facing caribbean arc and forearc terranes onto the northward subducting mesozoic passive margin of northern south america northward flexure of the south american craton produces a foreland basin between the thrust front and the downward flexed continental crust that is initially filled by clastic sediments shed both from the colliding arc and cratonic areas to the south as the collision extends eastward towards trinidad this same process continues with progressively younger foreland basins formed to the east on the overthrusting caribbean arc and forearc terranes north south rifting adjacent to the collision zone initiates and is controlled by forward momentum of southward thrusting arc terranes combined with slab pull of the underlying and subducting north dipping south american slab uplift of fold thrust belts arc continent suture induces rerouting of large continental drainages parallel to the collisional zone and to the axis of the foreland basins stage two this late stage of arc continent collision is characterized by termination of deformation in one segment of the fold thrust belt as convergent deformation shifts eastward rebound of the collisional belt is produced as the north dipping subducted oceanic crust breaks off from the passive margin inducing inversion of preexisting normal faults as arc continent convergence reaches a maximum strain partitioning also begins to play an important role as oblique convergence continues accommodating deformation by the formation of parallel strike slip fault zones and backthrusting southward subduction of the caribbean plate beneath the south caribbean deformed belt as subsidence slows in the foreland basins sedimentation transitions from a marine underfilled basin to an overfilled continental basin offshore sedimentation is mostly marine sourced by the collided caribbean terranes localized islands and carbonate deposition stage three this final stage of arc continent collision is characterized by 1 complete slab breakoff of the northward dipping south american slab 2 east west extension of the caribbean arc as it elongates parallel to its strike forming oblique normal faults that produce deep rift and half grabens 3 continued strain partitioning strike slip faulting and folding the subsidence pattern in the caribbean basins is more complex than interpreted before showing a succession of extensional and inversion events the three tectonic stages closely control the structural styles and traps source rock distribution and stratigraphic traps for the abundant hydrocarbon resources of the on and offshore areas of venezuela and trinidad

the cenozoic tectonostratigraphic evolution of the barracuda ridge and tiburon rise at the western end of the north america south america plate boundary zone the barracuda ridge and the tiburon rise two major oceanic basement ridges lie at the western end of the diffuse north america south america plate boundary zone where they enter the subduction zone beneath the lesser antilles island arc there is a large degree of uncertainty in the motion between the north american and south american plates predicted by kinematic models of plate motion for the region of these two ridges during the cenozoic and quaternary from the analysis of new multibeam and seismic reflection profiles acquired in 2007 together with older geophysical and geological data we provide new information on the geological history of this area including the timing of the formation of the barracuda ridge and tiburon rise in their present day configurations the timing of the deformation in this region is now much better constrained through the correlation of several key seismic horizons with existing dsdp and odp holes the seafloor topography inherited from the process of formation of the crust at the mid oceanic ridge was buried by distal turbidites by the end of the paleogene beginning in the middle late miocene and then the pleistocene the tiburon rise and barracuda ridge respectively were uplifted and acquired their present day forms and elevation which is much more recent than previously believed in the quaternary the uplift was accompanied by the deposition of very large mass transport deposits the causes of uplift and deformation of the ridges have been convergence between the north american and south american plates and the flexure of these plates as they enter the lesser antilles subduction zone the zone of uplift and deformation migrated northward during the neogene and quaternary

palaeokarst and its implication for the extinction event at the frasnian famennian boundary guilin south china a prominent palaeokarst within cyclic peritidal strata reported here at the frasnian famennian boundary in guilin southern china displays karren scalloped surfaces dissolution pits and pipes the last contain residual soil terra rossa and are then filled with marine sediment of the overlying strata the features of the palaeokarst depth of pipes and amount of missing strata indicate a significant and long lasting c 50 ka fall of sea level at the end of the frasnian the coincidence of the significant sea level fall with the first stage of the frasnian famennian mass extinction which mostly affected shallow marine and reef dwelling fauna and of the subsequent rapid sea level rise with the second stage of the extinction which mostly affected deeper water organisms reinforces the importance of sea level change in this mass extinction

tectonic erosion at the front of the japan trench convergent margin abstract the imaging of a multichannel seismic record was improved by reprocessing using pre stack techniques the reprocessed record shows structures that indicate tectonic erosion and gravity collapse at the front of the japan trench margin much of the lower slope appears to be underlain by a detached coherent block of continental crust the lower slope has failed by mass wasting and the resulting apron of slump debris at the base of the slope has become involved in thrust faulting at the front of the subduction zone slumping continues as long as debris is removed from the front of the margin by subduction and the apron cannot build up sufficiently to stabilize the failing lower slope truncated beds at the base of the upper plate indicate subcrustal erosion as well this probably being the main cause of massive subsidence of the margin subsidence was the cause of oversteepening destabilization and subsequent gravity collapse of the leading edge of the upper plate

the devonian and carboniferous of the moscow syneclise russian platform stratigraphy and sea level changes abstract the moscow syneclise is a vast sedimentary basin located in the centre of the east european platform the palaeozoic sequence of this syneclise and especially its devonian carboniferous part is most suitable for sea level fluctuation analysis the devonian and carboniferous sediments consist mainly of shallow marine carbonates containing several minor terrigenous intervals they attain total thicknesses of up to 1 5 km the modern stratigraphic scale includes 33 regional stages for the devonian and 32 for the carboniferous correlation of this scale with global scales is supported by conodont miospore and foraminifera zonations the new calibrated devonian and carboniferous relative sea level curves for the moscow syneclise reflect late eifelian mid frasnian early tournaisian late visean early serpukhovian and moscovian gzhelian transgressions several of these sea level changes which are particularly evident on the margins of the moscow syneclise originated in response to differential tectonic movements of the voronezh anteclise and the tokmovo uplift as well as to vertical oscillations of the entire east european craton

paleoecology and sedimentary environment of the late devonian coral biostrome from the central devonian field russia the upper frasnian coral biostrome well exposed in the russkiy brod quarry central devonian field russia has been studied in detail with respect to paleoecology and sedimentary environment the biostrome formed by auloporid tabulates and solitary and colonial rugose corals originated in an offshore environment characterized by calmer periods with slow or halted sedimentation and more energetic periods when sedimentation rate increased the episodic higher sediment influx and stronger hydrodynamic regime are not only well expressed in the microfacies but also in the variability of colony integration of the rugose corals observed even within single coralla distinct development of constrictions rejuvenescences and deflection of growth directions in rugose corallites may also indicate unstable sedimentary conditions the latter features however may have in part also resulted from syn vivo biotic interaction with the associated auloporids both the facies and paleontological observations suggest that the biostrome originated by the colonization of deposited bioclasts by pioneering auloporids creating the framework for settlement of later generations of auloporids and rugose corals apart from abundant auloporids representing a single species and associated rugose corals the other encrusters are not numerous and poorly diversified represented by dominating foraminifers followed by single species of productid brachiopods stromatoporoids microconchids and cornulitids the coral associated macrobenthos has similarly a low diversity being represented by single species of spiriferid and rhynchonellid brachiopods and gastropods being developed in an offshore carbonate sedimentary system devoid of any organic rich deposits and characterized by extremely low abundance and diversity of suspension feeding organisms the biostrome is considered to have originated in a low productivity oligotrophic environment strictly dominated by heterozoan coral communities its development in a well oxygenated oligotrophic environment during the time when organic rich black kellwasser facies developed elsewhere additionally attests for multi causal scenarios for the frasnian famennian event during which other factors were responsible in different paleogeographic and facies settings

crustal deformation in the central and southern ryukyu arc estimated from gps data abstract deformation of the ryukyu arc in the period 1999 2001 was investigated on the basis of gps data for horizontal velocity the results show that deformation of the ryukyu arc is divided into three tectonic blocks with all counter clockwise rotation rates of between 18 and 195 nrad yr extensional strain along the ryukyu arc is observed in all three blocks being largest in the southwestern ryukyu arc this suggests that southward bending of the arc occurs in the southwest associated with the arc continent collision in taiwan resulting in clockwise block rotation of the taiwan ryukyu junction thus bending of the ryukyu arc appears to be caused by collision of the luzon arc with the eurasian plate and is likely to contribute to rifting of the okinawa trough

review and revision of cenozoic tropical planktonic foraminiferal biostratigraphy and calibration to the geomagnetic polarity and astronomical time scale planktonic foraminifera are widely utilized for the biostratigraphy of cretaceous and cenozoic marine sediments and are a fundamental component of cenozoic chronostratigraphy the recent enhancements in deep sea drilling recovery multiple coring and high resolution sampling both offshore and onshore has improved the planktonic foraminiferal calibrations to magnetostratigraphy and or modified species ranges this accumulated new information has allowed many of the planktonic foraminiferal bioevents of the cenozoic to be revised and the planktonic foraminiferal calibrations to be reassessed we incorporate these developments and amendments into the existing biostratigraphic zonal scheme in this paper we present an amended low latitude tropical and subtropical cenozoic planktonic foraminiferal zonation we compile 187 revised calibrations of planktonic foraminiferal bioevents from multiple sources for the cenozoic and have incorporated these recalibrations into a revised cenozoic planktonic foraminiferal biochronology we review and synthesize these calibrations to both the geomagnetic polarity time scale gpts of the cenozoic and astronomical time scale ats of the neogene and late paleogene on the whole these recalibrations are consistent with the previous work however in some cases they have led to major adjustments to the duration of biochrons recalibrations of the early middle eocene first appearance datums of globigerinatheka kugleri hantkenina singanoae guembelitrioides nuttalli and turborotalia frontosa have resulted in large changes in the durations of biochrons e7 e8 and e9 we have introduced upper oligocene zone o7 utilizing the biostratigraphic utility of paragloborotalia pseudokugleri for the neogene period major revisions are applied to the fohsellid lineage of the middle miocene and we have modified the criteria for recognition of zones m7 m8 and m9 with additional adjustments regarding the globigerinatella lineage to zones m2 and m3 the revised and recalibrated datums provide a major advance in biochronologic resolution and a template for future progress of the cenozoic time scale

cryptic encrusting communities in a middle devonian mesophotic paleoenvironment of the holy cross mountains poland abstract the middle devonian givetian chaetetid sponges and alveolitid tabulate corals that inhabited mesophotic paleoenvironments of the southern shelf of laurussia holy cross mountains poland have been studied with respect to encrustation patterns these epibiotic communities are characterized by modest diversity and high dominance and show distinct polarization with respect to the exposed and cryptic sides of the host s skeletons the most abundant davidsoniid brachiopods and microconchids show strong preferences toward the lower cryptic sides while auloporid tabulate corals dominate on the exposed sides of the hosts the remaining and much rarer epibionts cornulitids and rugose corals show no clear preferences in some shallow water silurian paleoenvironments auloporids are known to dominate the cryptic sides of the hosts thus considering the auloporid tabulates as photosymbiotic corals their absence or rarity in the middle devonian cryptic habitats might have resulted from insufficient irradiance levels in otherwise depleted light conditions as a result the available space and lack or lower competition for the area with faster growing colonial auloporids enabled solitary encrusters to colonize the cryptic niches the scarce bioerosion traces and rather low diversity of epibionts in our case may indicate that these mesophotic reefs developed in a nutrient poor oligotrophic habitats the davidsoniid dominated cryptic encrusting communities were widespread in some paleoenvironments during the middle devonian being known from both laurussia and south china craton however such mesophotic cryptic communities characterized by distinct polarization in comparison to open surface environments contrast with other givetian deep water aphotic cryptic communities reported so far where such polarization is hardly visible

deep structure of an island arc backstop lesser antilles subduction zone 1 we present the results from a coincident seismic reflection refraction grid conducted at the lesser antilles subduction zone near 16 n this paper focuses on the seismic refraction data and constraints these data place on the three dimensional structure of the island arc backstop we find that the backstop in this region contains considerable topography in both the strike and dip directions two ridges each 25 35 km in length and 10 km in width rise 1 6 km above the adjacent basement the eastern edge of one of the ridges deepens by 4 6 km over a horizontal distance of 10 km and forms the eastern edge of the backstop in contrast to the complex nature of the backstop the adjacent accretionary wedge displays little lateral variability at large scales this may be a consequence of the spatial scales involved the backstop topography is 10 35 km in width while the accretionary wedge extends 125 km from the deformation front to the backstop the top of the subducting oceanic crust as identified by an increase in velocities to 6 6 5 km s intersects the backstop at a depth of 14 15 km the updip limit of plate boundary seismicity is located 75 100 km west and downdip of the backstop however two earthquake clusters are observed at the intersection of the subducted barracuda ridge and tiburon ridge with the backstop suggesting active deformation associated with the backstop edge at these locations

the role of sea level change and marine anoxia in the frasnian famennian late devonian mass extinction johnson et al johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 proposed one of the first explicit links between marine anoxia transgression and mass extinction for the frasnian famennian f f late devonian mass extinction this cause and effect nexus has been accepted by many but others prefer sea level fall and cooling as an extinction mechanism new facies analysis of sections in the usa and europe france germany poland and comparison with sections known from the literature in canada australia and china reveal several high frequency relative sea level changes in the late frasnian to earliest famennian extinction interval a clear signal of major transgression is seen within the early rhenana zone e g drowning of the carbonate platform in the western united states this is the base of transgressive regressive cycle iid of the johnson et al johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 eustatic curve this was curtailed by regression and sequence boundary generation within the early linguiformis zone recorded by hardground and karstification surfaces in sections from canada to australia this major eustatic fall probably terminated platform carbonate deposition over wide areas especially in western north america the subsequent transgression in the later linguiformis zone recorded by the widespread development of organic rich shale facies is also significant because it is associated with the expansion of anoxic deposition known as the upper kellwasser event johnson et al s johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 original transgression anoxia extinction link is thus supported although some extinction losses of platform carbonate biota during the preceeding regression cannot be ruled out conodont faunas suffered major losses during the upper kellwasser event with deep water taxa notably affected this renders unreliable any eustatic analyses utilising changes in conodont biofacies claims for a latest frasnian regression are not supported and probably reflect poor biostratigraphic dating of the early linguiformis zone sequence boundary

tectonic segmentation of the north andean margin impact of the carnegie ridge collision the north andean convergent margin is a region of intense crustal deformation with six great subduction earthquakes mw 7 8 this century the regional pattern of seismicity and volcanism shows a high degree of segmentation along strike of the andes segments of steep slab subduction alternate with aseismic regions and segments of flat slab subduction this segmentation is related to heterogeneity on the subducting nazca plate in particular the influence of the carnegie ridge collision is investigated four distinct seismotectonic regions can be distinguished region 1 from 6on to 2 5on with steep ese dipping subduction and a narrow volcanic arc region 2 from 2 5on to 1os showing an intermediate depth seismic gap and a broad volcanic arc region 3 from 1os to 2os with steep ne dipping subduction and a narrow volcanic arc region 4 south of 2os with flat subduction and no modern volcanic arc the carnegie ridge has been colliding with the margin since at least 2 ma based on examination of the basement uplift signal along trench parallel transects the subducted prolongation of carnegie ridge may extend up to 500 km from the trench as suggested by the seismic gap and the perturbed broad volcanic arc these findings conflict with previous tectonic models suggesting that the carnegie ridge entered the trench at 1 ma furthermore the anomalous geochemical adakitic signature of the volcanoes in the broad ecuador volcanic arc and the seismicity pattern are proposed to be caused by lithospheric tears separating the buoyant shallowly subducting carnegie ridge from segments of steep subduction in regions 1 and 3 it is further suggested that carnegie ridge supports a local flat slab segment similar to that observed in peru the impact of the carnegie ridge collision on the upper plate causes transpressional deformation extending inboard to beyond the volcanic arc with a modern level of seismicity comparable to the san andreas fault system the pattern of instrumental and historical seismicity indicates 1 great earthquakes on the northern and southern flanks of the colliding ridge 2 a slight reduction in observed seismicity at the trench ridge intersection 3 increased stress far into the continent and 4 a nne displacement of the n andes block to be further effects of the collision 1999 elsevier science b v all rights reserved

differential uplift and tilt of pleistocene reef platforms and quaternary slip rate on the morne piton normal fault guadeloupe french west indies 1 the guadeloupe islands are cut by normal faults that accommodate oblique convergence between the north american and caribbean plates such faults are responsible for part of the shallow seismicity and have produced m 5 damaging earthquakes to better assess the seismic hazard in guadeloupe we quantify the slip rate on one of the largest fault morne piton this roughly e w fault crosses the island of marie galante and uplifts a flight of reef terraces from geomorphic analysis we mapped three main terraces new u th datings show that they formed during the latest interglacials 120 and 240 kyr ago correlation with specmap isotopic records implies that the marie galante plateau emerged during the 330 ka highstand topographic profiles show that the terraces and the plateau are deformed by faulting elastic modeling of their shape constrains the geometry of the fault 70 80 dip 5 km depth and its slip rate 0 5 0 2 mm yr given its length 50 km depth and slip rate this fault might produce maximum m 6 5 earthquakes with a recurrence time of 1400 to 3300 years or more likely smaller events such as the m 5 5 16 may 1851 and 3 august 1992 shocks that might recur every 400 to 1000 years we also show that all the islands and terraces are tilted westward perpendicularly to the trench la desirade closest to the trench is uplifted by 276 m whereas subsidence 70 m is observed 10 km east of the volcanic arc this tilt probably resulted from a transient deformation episode at the subduction interface that predated the late pleistocene

climate controlled mass extinctions facies and sea level changes around the devonian carboniferous boundary in the eastern anti atlas se morocco abstract detailed sedimentological and biostratigraphical studies of successions in the eastern anti atlas se morocco focused on changing depositional environments and reconstructions of sea level changes during the late famennian to middle tournaisian the investigations cover a transect from the central maider to the easternmost and southern tafilalt regions near the moroccan algerian border the moroccan data are compared with the standard succession of the german rhenish massif and with the regional and global stratigraphic record the results testify to high frequency sea level changes including two global transgressive and anoxic events the main hangenberg event hangenberg black shale level at the top of the wocklumeria zone upper devonian vi e and the lower alum shale event at the lower middle tournaisian lower carboniferous i ii boundary regionally both anoxic intervals coincided with mass extinctions followed by rapid radiation especially of pelagic biota a significant shallowing and regression occurred just below the devonian carboniferous boundary at the northern margin of gondwana and caused the sudden n nw progradation of a large deltaic complex over 300 500 km thick siliciclastic successions filled fast subsiding synsedimentary troughs of the maider and amessoui syncline southern tafilalt correlation with the glacial phases of southern gondwana south america south africa indicates a glacial eustatic origin of sea level changes and a major sea level fall in the scale of 100 m or more coinciding with the main regressive phase of the extended hangenberg crisis interval the new results are in accord with the hypothesis of an episode of cool humid climate at the end of the devonian that allowed contemporaneous glacial buildup in high latitudes and extensive clastic discharge in the middle latitudes of nw africa

convergent morphology in small spiral worm tubes spirorbis and its palaeoenvironmental implications calcareous tube worms generally identified as spirorbis range from ordovician to recent often profusely encrusting shells and other substrates whereas recent spirorbis is a polychaete annelid details of tube structure in pre cretaceous spirorbis suggest affinities with the microconchida an extinct order of possible lophophorates although characteristically palaeozoic microconchid tube worms survived the permian mass extinction before being replaced in late mesozoic ecosystems by true spirorbis recent spirorbis is stenohaline but spirorbiform microconchids also colonized freshwater brackish and hypersaline environments during the devonian triassic anomalies in the palaeoenvironmental distributions of fossil spirorbis are explained with the recognition of this striking convergence between microconchids and true spirorbis

microbial carbonates as indicators of environmental change and biotic crises in carbonate systems examples from the late devonian alberta basin canada microbial precipitation of calcium carbonate has played a vital role in the development of carbonate platforms since their initiation in the proterozoic we report here the varied roles that microbial carbonates played in late devonian carbonate platforms in the alberta basin canada we recognize microbial carbonates as important contributors within the carbonate system during times of major environmental change including transgressive events in platform environments and the recovery interval following the frasnian famennian mass extinction detailed sequence stratigraphic analysis of two isolated platforms in the canadian rockies was used to document their evolution from a regional ramp to isolated platforms with phases of progradation aggradation and backstepping and renewed progradation related to rates of second order and third order sea level change and basin infill the carbonate system was reorganized following annihilation of many carbonate producing biota during the frasnian famennian mass extinction microbial carbonates figure prominently in both frasnian platform development and the famennian recovery of the carbonate system following the frasnian famennian mass extinction during transgressive platform phases deeper water facies with a crinoid rugose coral and microbe dominated biota abruptly overlie prograding stromatoporoid framestones microbial carbonates consist of abundant girvinellid oncoids that nucleated around other fossil clasts the temporary replacement of stromatoporoid communities during transgression implies a shift from oligotrophic to mesotrophic conditions and the microbes likely capitalized on the change in nutrient supply microbes played a significant role in highstand reef margin facies where renalcis was a binder and cementer in stromatoporoid framestones and downslope rugose coral stromatoporoid mounds microbially laminated carbonates also form stromatolitic mats in peritidal shallowing upward cycles and repetitive stromatolitic intervals commonly indicate sea level lowstands associated with the development of sequence boundaries stromatoporoid reefs and their associated reef interior facies indicate an oligotrophic ecosystem where microbial carbonates were relegated mainly to cryptic or stressed marine habitats an end frasnian sea level lowstand exposed the isolated carbonate platforms transgression and mass extinction characterize the frasnian famennian boundary event and microbial carbonates occur at this horizon in western canada stromatolites oncoids and large scale microbial thrombolites appear to be

cryptic coral crinoid hanging gardens from the middle devonian of southern morocco an unusual and exceptionally well preserved cryptic community of cnidarians crinoids sponges and microbes developed in a submarine cavity of middle devonian age in the hamar laghdad area morocco the biota encrusted the cavity roof and grew predominantly in an upside down position forming spectacular hanging gardens the investigated assemblage differs strikingly from both its paleozoic and modern analogues it constitutes one of a very few known examples of fossil cryptic assemblages developed in relatively deep water settings and is the first report of a cryptic paleoecosystem dominated by rugose corals the results support the view that during the middle paleozoic there was no distinct polarization between open surface and cryptic faunas in deep water environments but keen competition for space already existed in devonian cryptic assemblages the regional species pool seems to have been the main determinant of the ecological succession and structure of this cryptic community

famennian and tournaisian recoveries of shallow water rugosa following late frasnian and late strunian major crises southern belgium and surrounding areas hunan south china and the omolon region ne siberia abstract the rugosa remained almost totally absent from the platform environments of southern belgium and surrounding areas hunan and omolon during the long time interval between the end frasnian crisis and the early part of the late famennian marginifera zone probably owing to cool climatic conditions they first reappear in the upper marginifera zone but are uncommon and poorly diversified few of them belong to pre famennian genera it is only near the beginning of strunian time that rugose corals radiated and became common their morphological and allometric variabilities were very large indicating their high potential for adaptation to free niches this first radiation was abruptly terminated by an extinction event and a second radiation quickly began mainly from new taxa and only from a few previously known ones in western europe and in hunan this second radiation was also stopped abruptly while species were evolving by the hangenberg event at the end of the strunian in omolon where the position of the devonian carboniferous boundary is doubtfull the second radiation may have been completed before the end of the strunian and probably the corals affected by the end famennian event were new ones resulting from a third radiation in the three regions and at each recovery the rugose corals are endemic indicating that marine connections were poor after the hangenberg event surviving rugosa reappeared almost immediately except in south china and were widespread indicating good marine connections however they remained poorly diversified sometimes until the late tournaisian the two major extinctions end frasnian and end famennian and the strunian ones were responsible for the major taxonomic differences between pre famennian and post famennian rugosa

subduction of aseismic ridges beneath the caribbean plate implications for the tectonics and seismic potential of the northeastern caribbean normal seafloor entering the puerto rico and northern lesser antillean trenches in the northeastern caribbean is interrupted by a series of aseismic ridges on the north and south american plates these topographic features lie close to the expected trend of fracture zones created about 80 110 m y ago when this seafloor was formed at the mid atlantic ridge the northernmost of the ridges that interact with the lesser antillean subduction zone the barracuda ridge intersects the arc in a region of high seismic activity some of this seismicity including a large shock in 1974 occurs within the overthrust plate and may be related to the deformation of the caribbean plate as it overrides the ridge a large bathymetric high the main ridge is oriented obliquely to the puerto rico trench and intersects the subduction zone north of the virgin islands in another cluster of seismic activity along the inner wall of the trench data from a seismic network in the northeastern caribbean indicate that this intersection is also characterized by both interpolate and intraplate seismic activity magnetic anomalies bathymetric trends and the pattern of deformed sediments on the inner wall of the trench strongly suggest that the main and barracuda ridges are parts of a formerly continuous aseismic ridge a segment of which has recently been overridden by the caribbean plate reconstruction of mid miocene to recent plate motions also suggest that at least two aseismic ridges and possibly fragments of the bahama platform have interacted with the subduction zone in the northeastern caribbean the introduction of these narrow segments of anomalous seafloor into the subduction zone has segmented the arc into elements about 200 km long these ridges may act as tectonic barriers or asperities during the rupture processes involved in large earthquakes they also leave a geologic imprint on segments of the arc with which they have interacted a 50 km landward jump of the locus of island arc volcanism occurred in late miocene time along the northern half of the lesser antilles we postulate that the subduction of a segment of seafloor of anomolously thick crust being more buoyant than adjacent seafloor resulted in a marked shoaling in the dip of the descending slab and therefore a shift of the locus of volcanism in the region near western puerto rico and eastern hispanolia plio pleistocene interaction with a similar feature in this case a part of the bahama platform about 3 4 m y ago led to a jump in the locus of subduction as evidenced by a gap in the downgoing seismic zone that segment of the bahama platform interferred with the subduction process and was subsequently sutured onto the caribbean plate when the boundary jumped about 60 km to the northeast the maximum size of historic shallow earthquakes along the lesser antillean arc varies from about 7 0 7 5 in the center of the arc where the dip of the shallow part of the plate boundary is steep to 8 0 8 5 along the northern part of the arc where the dip is shallow the interaction of anomalous seafloor as along the northern lesser antilles can lead to the development of a wider than normal zone of interplate contact and hence to earthquakes that are larger than those associated with more typical seafloor entering subduction zones major seismic gaps and regions of high seismic potential currently exist along the northern lesser antilles and to the north of puerto rico both gaps are bounded by anomalous features on the downgoing plate the intersection of these features with the plate boundary created large asperities that may be good places to search for precursors to future large earthquakes a great shock in 1787 may have ruptured an existing seismic gap north of puerto rico between 65 and 67 w thus that gap can be expected to eventually rupture again in a great shock and not to accommodate plate motion by totally aseismic processes

rapid pulses of uplift subsidence and subduction erosion offshore central america implications for building the rock record of convergent margins integrated ocean drilling program iodp expedition 334 to southern costa rica central america documented unprecedented subduction erosion in an area of active seismic slip widespread subduction erosion of the upper plate initiated when the cocos ridge an overthickened aseismic ridge arrived at the middle america trench subduction erosion was coeval with the rapid formation of deposition centers on the forearc of the upper plate the completely recovered shelf sequence constrains a short 2 m y interval of extreme subsidence 1200 m with a rapid pulse occurring during the first 0 3 m y this event removed an estimated 1 2 106 km3 of forearc material at a rate of 1690 km3 m y km of trench during a time of rapid 1035 m m y shelf sediment accumulation at this erosive margin a sediment starved trench persisted in spite of abundant sediment supply because subduction erosion led to the creation of forearc basins similar rapid pulses of subduction erosion may punctuate the evolution of many margins contributing disproportionately to crustal recycling at subduction zones with implications for the evolution of continental crust and mountain belts and recycling of continental material into the mantle

palynofacies around the frasnian famennian boundary in the holy cross mountains southern poland abstract palynofacies have been analysed in two representative frasnian famennian f f localities kowala quarry and agow plucki trench in the holy cross mountains poland with the aim of reconstructing sedimentary conditions and palynofloral history over the extinction boundary interval leiospheres are the most common palynomorphs taxonomically impoverished acritarch assemblages and a low proportion of land derived material indicate offshore sedimentation in a mid shelf environment with some evidence of an earliest famennian regression increased productivity of phytoplankton near the f f boundary was possibly related to eutrophication of the epeiric seas thus causing anoxic conditions close to and on the seafloor no significant changes in palynofacies have been observed through the f f boundary deposits in these laurussian shelf basins in agreement with data from other parts of the devonian world

platform margins reef facies and microbial carbonates a comparison of devonian reef complexes in the canning basin western australia and the guilin region south china devonian reef complexes were well developed in western australia and south china but no detailed direct comparison has been made between reef building in the two regions the regions differ in several respects including tectonic stratigraphic and palaeoceanographic palaeogeographic settings and the reef building styles reflect minor differences in reef builders and reef facies similarities and differences between the two reef complexes provide insights into the characteristics of platform margins reef facies and microbial carbonates of both regions here we present a comparison of platform margin types from different stratigraphic positions in the late devonian reef complex of the canning basin western australia and middle and late devonian margin to marginal slope successions in guilin south china comparisons are integrated into a review of the reefal stratigraphy of both regions reef facies reef complex architecture temporal reef builder associations 2nd order stratigraphy and platform cyclicity in the two regions were generally similar where the successions overlap temporally however carbonate deposition began earlier in south china carbonate complexes were also more widespread in south china and represent a thicker succession overall platforms in the canning basin grew directly on precambrian crystalline basement or early palaeozoic sedimentary rocks but in south china carbonate complexes developed conformably on older devonian siliciclastic strata pre frasnian reef facies in south china had more abundant skeletal frameworks than in canning basin reefs of equivalent age and famennian shoaling margins containing various microbial reefs may have been more common and probably more diverse in south china however late devonian platform margin types have been documented more completely in the canning basin deep intra platform troughs deep depressions containing non carbonate pelagic sediments nandan type successions that developed along syndepositional faults characterize devonian carbonate platforms in south china but have no equivalent on the lennard shelf canning basin where inter reef areas were more shallow the south china platform to depression pattern was generally continuous from the lower to upper devonian indicating that many pre devonian tectonic features continued to exercise considerable effect through deposition localized fault controlled subsidence was an important factor in both regions but similarities in 2nd order aggradation progradation cycles suggest that eustasy was also an important control on the larger scale stratigraphic development of both regions

the tsunamite problem the genetic term tsunamite is used for a potpourri of deposits formed from a wide range of processes overwash surges backwash flows oscillatory flows combined flows soft sediment deformation slides slumps debris flows and turbidity currents related to tsunamis in lacustrine coastal shallow marine and deep marine environments tsunamites exhibit enormous variability of features e g normally graded sand floating mudstone clasts hummocky cross stratification etc these sedimentary features may also be interpreted as deposits of turbidity currents turbidites debris flows debrites or storms tempestites however sedimentary features play a passive role when these same deposits are reinterpreted as tsunamites on the basis of historical evidence for tsunamis and their triggering mechanisms e g earthquakes volcanic explosions landslides and meteorite impacts this bipartite sedimentological vs historical approach which allows here classification of the same deposit as both turbidite and tsunamite has blurred the distinction between shallow marine and deep marine facies a solution to this problem is to classify deposits solely by a descriptive sedimentological approach the notion that tsunami waves can directly deposit sediment in the deep sea is unrealistic because tsunami waves represent transfer of energy and they are sediment starved during tsunamis and major storms submarine canyons serve as the physical link between shallow water and deep water environments for sediment transport tsunami related deposition involves four progressive steps 1 triggering stage offshore 2 tsunami stage incoming waves 3 transformation stage near the coast and 4 depositional stage outgoing sediment flows in this progression deep water deposition can commence only after the demise of incoming tsunami waves due to their transformation into outgoing sediment flows deposits of these sediment flows already have established names e g debrite and turbidite therefore the term tsunamite for these deposits is obsolete

the frasnian famennian mass extinction insights from high resolution sequence stratigraphy and cyclostratigraphy in south china two sequences sfr sfa each 1 1 2 myr in duration are recognised in the strata across the frasnian famennian f f transition both in carbonate platform and interplatform basinal successions in south china the sequence boundary between the two sequences is placed a little below the top of the frasnian the sequences are basically composed of coarsening upward bed thickness increasing upward cycles and shallowing upward cycles parasequences in basinal and platform deposits respectively which stack into cycle sets typically six to eight cycles 10 and 12 cycle sets are identified in sequences sfr and sfa respectively these cycle sets can be further grouped into larger scale composite cycle sets herein termed mesocycle and megacycle sets with two and four cycle sets respectively this vertical cycle stacking pattern and the hierarchy of cyclicity suggest a milankovitch style of forcing such that the cycles and cycle sets were formed in response to the orbital perturbations of precession 16 18 kyr and eccentricity v100 kyr in duration respectively in the basinal cycles smaller scale rhythmic stratification beds typically six to eight beds in a cycle are extensive and were likely caused by millennial scale climatic forcing in the lower sequence sfr the latest highstand deposits consist of calciturbidites and debrites in deep water strata and fenestral limestones in shallow water strata representing a major third order sea level fall within these deposits four cycle sets are further identified in both coeval deep water and platform successions succeeding deeper water organic rich facies within which three cycles occur are the transgressive deposits of the overlying famennian sequence sfa these cycles represent three higher frequency 16 18 kyr sea level fluctuations and accompanying anoxia superimposed on a major third order sea level rise the f f boundary is placed at the top of the first cycle based on conodont data thus a major sea level fall and then a rise occurred in the f f transitional period faunal and sedimentological data reveal a massive biotic decline in concert with the major sea level fall and a further biotic demise coinciding with the major sea level rise and its three superimposed higher frequency sea level fluctuations and accompanying anoxia the f f biotic crisis was therefore characterised by two episodes of step down extinction on the basis of milankovitch orbital rhythms the first major biotic extinction took place over v400 kyr and the subsequent event was v50 kyr in duration i e v450 kyr for the entire event at the same time as the massive decline of normal marine fossils during the latest frasnian sea level fall there was widespread cyanobacterial growth and a thriving of planktonic calcispheres suggesting eutrophic conditions this situation could have caused a severe biotic loss as a result of the deterioration of surface water clarity and formation of anoxic bottom waters due to over

reconnaissance de structures tectoniques et volcaniques sous marines de l arc recent des petites antilles kick em jenny qualibou montagne pelee nordouest de la guadeloupe abstract a multibeam bathymetric survey seacarib 1 was carried out in april 1985 on board the r v conrad lamont doherty geological observatory off the western coasts of several islands of the lesser antilles complementing a previous survey of the same type arcante 2 thermosite 1980 devoted to adjoining areas in guadeloupe martinique and st lucia it allowed us to precisely map submarine volcanoes in a marginal setting behind the recent arc the main volcanic axis of the archipelago emplaced during the neogene the kick em jenny volcano south of the grenadines is the only active submarine volcano of the lesser antilles it is a small and very young cone probably only tens or hundreds of years old which was hydrothermally active during the survey the directeur volcano guadeloupe is the largest submerged volcanic centre thus far detected in the lesser antilles having been formed between 3 3 and 2 9 ma during the 1980 survey two other large volcanoes were discovered off southern basse terre guadeloupe vieux fort volcano 2 5 2 0 ma and in front of fort de france bay martinique schoelcher volcano older than 4 2 ma several other much smaller volcanoes have been mapped off the same coasts particularly the bouillante seapeaks guadeloupe moreover large tectonic structures cut the recent arc transversally and obliquely the well known qualibou depression on the island of st lucia was interpreted in various ways neither the hypothesis of a large caldera the western side of which collapsed offshore nor the suggestion of a huge rotational gravity slide are confirmed the depression seems more likely to have been controlled by tectonic factors shaping a complex graben structure the seaward extension appears to be restricted to a northern channel the soufriere channel the st pierre fault in martinique is a large transverse feature extending seaward down to some 2000 m depth to the south it bounds the mount pelee active volcanic system and the escarpment of the fault forms a dam against subaqueous pyroclastic flows running down from the volcano these flows are responsible for the unusually smooth morphology of the submarine flanks the zombi fault of northwest guadeloupe is part of a first order feature extending along at least 130 km from montserrat in the north to marie galante in the east this curved fracture cuts across the northern central part of the lesser antilles passing progressively from a subparallel to a transverse orientation with respect to the axis of the island arc these types of surveys are important because they provide better understanding of the structure and recent geological evolution of the recent volcanic arc they are also a useful complementary tool for geothermal and seismological studies

structure of the lesser antilles subduction zone backstop and its role in a large accretionary system 1 the role of a backstop in subduction zones has been the subject of numerous laboratory and numerical modeling studies however few field observations exist revealing how backstops control deformation in subduction zones and accretionary wedge construction a seismic reflection and refraction survey acquired in 1998 with the r v maurice ewing reveals the geometry of the forearc igneous crust accretionary wedge and forearc basin structure of the northern guadeloupe area of the lesser antilles forearc an accreted block of buoyant crust accreted in the late miocene forms the toe of the overriding arc crust and forms the backstop we imaged the top of this surface beneath the forearc basin to its seaward edge where it meets the subducting oceanic crust the toe of the backstop was thrust upward and forms a steep buttress in contact with the lower half of the accretionary wedge the steep buttress produces a narrow inner deformation zone with minimal backthrusting of the accretionary complex landward over the backstop and a narrow 10 km transition between accreted and forearc basin sediment seismic reflections from the subducting crust and the decollement appear beneath the entire accretionary wedge and below the backstop toe separating the decollement and the subducting crust is an interval usually between 500 and 750 m of underthrust sediment carried underneath the accretionary wedge and subducted 15 km landward and beneath the toe of the backstop we speculate that the upturned geometry of the toe of the backstop and a weak fluid rich decollement may facilitate sediment subduction beneath the backstop and potentially into the mantle

arc parallel extension and localization of volcanic complexes in guadeloupe lesser antilles 1 subduction of atlantic seafloor under the caribbean plate causes shallow earthquakes within the lesser antilles volcanic arc such earthquakes above the subduction interface show strike slip or normal fault plane solutions the latter with e w striking nodal planes to better assess seismic hazard and the coupling between volcanism and tectonics we investigated faulting related to overriding plate deformation in the guadeloupe archipelago using aerial photographs satellite spot images and topographic maps 1 25000 scale we mapped active and middle to late pleistocene fissures and normal fault systems that cut the uplifted coral platforms grande terre and marie galante and the volcanic rocks of basse terre the available marine geophysical data show that the faults extend offshore to bound submarine rifts the e w striking 1500 m deep v shaped marie galante rift separates the two islands of marie galante and grande terre normal faults in the north of grande terre appear to mark the similarly v shaped western termination of the 5000 m deep n 50e to n130 e striking desirade graben three shallow m 5 5 earthquakes 6 may 1851 29 april 1897 3 august 1992 appear to have ruptured segments of the marie galante rift boundary faults the young la grande decouverte volcanic complex of basse terre including the 1440 a d soufriere dome lies within the western termination of the marie galante rift the ancient volcanic shoulders of the rift buttress the active dome to the north and south which may explain why major prehistoric sector collapses and pyroclastic avalanches have been directed southwestward into the caribbean sea or southeastward into the atlantic ocean the marie galante rift is typical of other troughs transverse to the northeastern edge of the caribbean plate we interpret such troughs which are roughly orthogonal to the arc to result from slip partitioning and extension perpendicular to plate convergence that they disappear southward implies that they result from interaction between the caribbean and north american plates