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

effect of the frasnian famennian extinction event on the stromatoporoids although paleozoic stromatoporoids were drastically reduced in abundance and diversity by the frasnian famennian f f mass extinction event at least 20 genera mostly labechiids and clathrodictyids are known from latest devonian rocks some typical frasnian genera survived the f f crisis to die out in early famennian time and others took part in the strunian resurgence of the stromatoporoids small stromatoporoid reefs are known from famennian and strunian rocks the history of the group suggests a large rapid but progressive environmental change at the f f boundary and the survival of genera better adapted to cool water

environmental record of devonian mississippian carbonate and low oxygen facies transitions southernmost canadian rocky mountains and northwesternmost montana uppermost devonian and lower mississippian strata in the southernmost canadian rocky mountains and adjacent montana record part of a widespread low oxygen episode in middle paleozoic epicontinental and shelf seas and provide critical information concerning the oceanographic setting of the western continental margin of euramerica at this time during early middle famennian time the region was the site of a westward deepening carbonate ramp palliser formation that was bordered to the west by a shale basin lussier region sedimentation patterns changed in middle late famennian time with the termination of carbonate ramp sedimentation and ultimate deposition of organicrich sediments in an oxygen stressed deep water setting exshaw formation a model for the widespread deposition of these sediments entails the initial flooding of epicontinental shelf seas with water derived from an expanded and intensified oxygen minimum zone during a late famennian transgression sedimentation of anaerobic to marginally aerobic deep water lower banff facies occurred into middle tournaisian and locally late tournaisian time prior to the westward progradation of carbonate ramp sediments of the middle and upper banff quartzofeld spathic clastic rocks in the exshaw and banff reflect the periodic influx of detritus from a likely western antler age orogenic source from late famennian into late tournaisian time degree of bottom water oxygenation during deposition of the exshaw and banff low oxygen facies was recognized using ichno fabric organic c and s relationships and degree of pyritization dop anaerobic laminated black shales with high dop values lack a macrobenthos with the notable exception of rare concentrations of inarticulate brachiopods on bedding planes dysaerobic to marginally aerobic facies have intermediate dop values and a gradient of increasing degree of bioturbation

late devonian glaciation in south america abstract an ice age in famennian late devonian time is documented by the presence of diamictites with striated faceted and polished pebbles rhythmites with dropstones erratic boulders and striated pavements and deformed sandstones the glacigenic beds occur in three huge intracratonic basins solimoes amazonas and parnaiba and in one pericratonic basin acre in northern brazil other possible late devonian diamictites may occur elsewhere in brazil and africa which if confirmed would extend considerably the area affected by this glacial age the onset of the late devonian glaciation caused a global narrowing of the warm climatic belts sharp regression increased clastic sedimentation massive biotic extinction reduced biochemical deposition and unconformities this resulted in important facies changes in the world geological record ice centers moved from northern africa to southwestern south america from late ordovician to early silurian time from mid silurian to early late devonian time no record of glaciation is known in late late devonian time intermittent glaciation began again in central south america and from late late devonian to early late permian time ice centers migrated towards antarctica across south america and south africa the devonian and ordovician silurian glaciations together with the better known permo carboniferous glaciations may all have primarily resulted from the shifting position of the gondwana continent with respect to the south pole

permian triassic sedimentology of jameson land east greenland incised submarine channels in an anoxic basin the presence of deeply erosive conglomeratic sandstone filled channels around the permian triassic p tr boundary in east greenland has been widely cited as evidence for a major late permian eustatic lowstand facies analysis of such channels and their associated strata in fact suggests that they record part of an intrinsic style of basinal deposition that persisted into early triassic time their origin can be explained without the need to invoke eustatic sea level fall active faulting and hinterland elevation is envisaged to have generated powerful sediment gravity flows that were capable of submarine erosion of fine grained unconsolidated strata stacked turbidite sandstone filled lenses also occur beneath fan delta sandbodies and probably record infill of channels or chutes cut into the subaqueous slopes of such deltas shale successions developed between the incised channel locations record complete p tr transitions in which a rapid onset of anoxic deposition is seen in latest permian time this is the local manifestation of a global anoxic event unusual aspects of the lower triassic sequence in greenland include the presence of well oxygenated intervals stromatolite bioherms and red algae

late mississippian bryozoan microbial build ups on a drowned karst terrain port au port peninsula western newfoundland bryozoan and microbial carbonate build ups occur within the late mississippian mid visean codroy group on the port au port peninsula western newfoundland build ups formed only adjacent to a rocky cliffed shoreline filling narrow submerged palaeovalleys of a well developed late devonian early mississippian karst terrain the nearshore setting was a stressed environment as indicated by 1 the absence of normal marine biota such as corals echinoderms and calcareous algae 2 high numbers and low species diversity of dominant taxa bryozoans brachiopods and microbial communities and 3 abundant plant bearing siliciclastics deposited by the episodic influx of fresh water from adjacent uplands build up development was terminated by meramec time due to falling sea level and seaward progradation of terrestrial sediments preserved structural and constructional fabrics within the build ups include 1 thickets of bryozoans and microbial microthrombolites structurally enhanced by probable marine mg calcite and aragonite cements 2 multigeneration internal sediment and 3 small colonies of serpulid worms and terebratulid brachiopods submarine cementation within the build ups appears to have been abundant during arrested sedimentation whereas intermound sediments carbonates and siliciclastics were lithified only during burial diagenesis shallow burial fracturing stylolitization sulphide and sulphate mineralization and precipitation of phreatic iron poor calcite cement occurred during burial diagenesis codroy build ups are distinct from the more common mississippian mud mounds their internal characteristics and the geologic setting are more like other late palaeozoic and holocene bryozoan rich build ups

late devonian early carboniferous deep water coral assemblages and sedimentation on a devonian seamount iberg reef harz mts germany abstract growth of the middle late devonian iberg reef a small atoll in the variscan geosyncline of central europe ceased towards the end of the frasnian during the famennian and dinantian the reef continuously subsided relative to sea level in the latest dinantian the reef was covered by clastics five deep water organism assemblages colonized the famennian dinantian seamount successively they are well comparable to recent organism communities on deep water coral banks in the famennian abundant crinoids and ancillary rugose corals and brachiopods colonized the reef top during the late tournaisian a coral crinoid assemblage established on the reef it developed into a varied fauna of corals crinoids trilobites brachiopods bivalves gastropods and goniatites in the early and middle visean the late visean assemblage was dominated by goniatites and pseudoplanktonic bivalves in the latest visean a monospecific brachiopod fauna and small microbial buildups thrived in extreme environmental conditions on the reef top the skeletal debris of the organisms was eroded post mortem and only accumulated in current protected depressions of the reef surface along with carbonate mud local depressions include hollows on the reef top neptunian dikes and pore space of a breccia that formed due to intensive shattering of the reef top during nearby volcanic activity during most of the famennian and tournaisian there is a hiatus caused by non deposition only reworked famennian and tournaisian conodonts recovered from upper tournaisian middle visean limestones give evidence of marine conditions on top of the reef the sedimentary environment on the drowned atoll compares well to that on recent guyots including hiatuses slow and patchy sedimentation erosion and redeposition both the aftermath of the frasnian famennian extinction that drastically reduced metazoan reef builders and a trend towards lower temperatures in the famennian and dinantian are believed to have prevented the reestablishment of a shallow water reef on the drowning devonian atoll

sponge constructed stromatactis mud mounds silurian of gaspe quebec abstract stromatactis calcilutite mounds from upper silurian rocks of gaspe peninsula quebec canada are important constituents of a reef complex in the southern part of the peninsula they reach thicknesses up to 115 m and had paleoslopes of about 40 stromatactis constitutes up to 30 percent of the rock volume the microfacies of the calcilutite consists of agglomerates of pelletlike bodies forming a pelletoidal network surrounded by uniform mudstone sponge spicules are ubiquitous by analogy with textural features of a well documented sponge malumispongium hartnageli clark 1924 which occurs slightly above the mounds it is suggested that the pelletoidal network of the mound calcilutite represents a former sponge network that underwent very early dingenetic change and cemen ation stromatactis would have originated as early marine cementation of growth cavities in the sponge network and of cavities created by decay of local uncemented sponge tissues

relations between submarine fissures internal breccias and mass flows during triassic and earlier rifting periods deep fissures in shallow water limestones filled with deep water sediments are described from many places especially in the triassic and jurassic of the tethys and in the middle to upper devonian of the variscian mountains mass flows occur in the same formations and areas on the island of hydra greece it was possible to show that both phenomena are linked by internal breccias of well fitted limestone fragments they are indicative of slope or near slope positions and are very probably caused by flexure like deformations of shallow burial limestones seismic shocks producing overpressure may be instrumental in the disintegration of the semi lithified limestones thus providing the material for mass flows these events are associated with a tectonical subsidence as shown by deep water matrix in the brecciated shallow water limestones they occur in areas and periods of submarine rifting especially in late devonian and triassic time at least four triassic brecciation events can be traced from greece to the alps and correspond presumably to major transgressions in the cratonic basin of middle europe

rare earth elements in seep carbonates as tracers of variable redox conditions at ancient hydrocarbon seeps marine hydrocarbon seeps are dynamic systems which are typically reflected in complex lithologies of limestones forming at these sites in order to test if seep limestones with their multiple generations of carbonate phases reflect variable redox conditions the rare earth element ree patterns of limestones from five ancient hydrocarbon seep localities hollard mound middle devonian iberg mississippian beauvoisin oxfordian canyon and satsop river oligocene and marmorito miocene have been investigated the total ree contents vary widely 0 3 43 7 p p m early microcrystalline phases tend to show higher contents than spatially associated later phases microspar sparite and blocky cement the shale normalized ree patterns of the carbonates show both negative and positive ce anomalies even for individual deposits suggesting that the redox conditions varied significantly it is apparent that in addition to anoxic conditions oxic conditions were common in some ancient seep environments intermittent oxygenation is presumed to have resulted from abrupt changes in fluid flow

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

depositional controls on lower carboniferous microbial buildups eastern midland valley of scotland in the eastern midland valley of scotland non skeletal carbonate buildup complexes are present in the charlestown main limestone brigantian a thin marine carbonate unit within a lower carboniferous basin fill otherwise dominated by fluvio deltaic sediments and volcanics the buildups are restricted geographically to west lothian and central fife and correspond to an area of reduced subsidence the burntisland high buildup geometry and local facies mosaics reflect the relative water depth and position on the burntisland high that because of its slight topographical relief and more distal position with respect to the location of fluvio deltaic systems became an area of increased carbonate productivity and hence a locus for buildup development away from the burntisland high in the fife midlothian low more monotonous argillaceous limestone facies of low energy and somewhat deeper water aspect accumulated buildup facies contain a diverse marine fauna and are characterized by peloidal clotted and homogeneous micrites interpreted as predominantly microbial in origin two types of buildup complex occur at charlestown vertically stacked tabular banks up to 2 m thick and 100 m wide form the western margin of an asymmetric buildup accumulation east of this margin a complex mosaic of isolated low relief buildups and inter buildup sediments was deposited skeletal sand shoals present within these inter buildup sediments indicate that high energy conditions prevailed during buildup growth in contrast at roscobie inter buildup sediments are of low energy aspect and buildup geometry is domical rather than tabular initiated in slightly deeper and calmer water on the flank of the burntisland high the roscobie buildups up to 15 m thick and 46 m wide accreted vertically rather than laterally as at charlestown and coalesced to form an elongate ridge shaped buildup complex

corals on seamount peaks provide evidence of current acceleration over deep sea topography geological and physical studies of seamounts have suggested the existence of distinct deep sea habitats characterized by exposed rocky bottom and a unique current regime1 9 however few biological data have been collected for deep seamounts10 12 here we present some of the first quantitative observations of hard bottom non hydrothermal fauna in the deep sea these observations show that black corals antipatharians and horny corals gorgonians present on the slopes of a multi peaked seamount are more abundant near peaks compared with mid slope sites at corresponding depths on narrow peaks corals are most abundant on the crest whereas on wide peaks coral densities are highest at the edge of the crest the abundance of corals also increases on knobs and pinnacles physical models and observations2 4 9 13 15 together with our direct measurements suggest that the seamount topography affects the local current regime corals appear to benefit from flow acceleration and some of their patterns of distribution can be explained by current conditions these results suggest that suspension feeders have some potential as indicators of prevailing currents at deep hard bottom sites

an interpretation of the variscan structures in sw england the variscan structures in sw england apart from the high level structures in the culm synclinorium of n devon are recumbent with an overall gentle southward dip of cleavages thrusts and recumbent folds translation was towards the nnw the structures are interpreted on a thin skinned model with a basal decollement dipping gently s related to a s dipping subduction zone s of the lizard the granites are thought to have been generated to the s of their present position and injected northwards above the decollement zone

d rex a program for calculation of seismic anisotropy due to crystal lattice preferred orientation in the convective upper mantle summary models of development of lattice preferred orientation lpo of crystals aggregates in convec tive flow are necessary to interpret the anisotropic seismic signature of the earth s upper mantle for that purpose we previously developed a model of lpo evolution in olivine aggregates by plastic deformation and dynamic recrystallization by subgrain rotation and grain boundary migration this paper presents a refined version of that model called d rex for dynamic recrystallization induced lpo a public version of which is made available on our web site the code displays two new features 1 enstatite is incorporated in the aggregates and 2 grain boundary sliding gbs of small grains is taken into account enstatite is incorporated on the assumption of no direct interaction with olivine the fast a axis of enstatite grains tend to be parallel to the slow c axis of olivine which dilutes the total anisotropy grain boundary sliding is included using a threshold dimensionless volume fraction defined as the ratio of the initial size of the grains over the size for which gbs is the dominant mechanism of deformation grains with a dimensionless volume smaller than do not rotate by plastic deformation and their strain energy is set to zero comparison with torsion experiments at very large strain constrains the threshold dimensionless volume to 0 3 0 1 the incorporation of grain boundary sliding prevents the lpo from becoming singular at large strains and yields more realistic predictions our kinematic formalism and the model s semi analytical character insures that it is fast robust and stable it can be applied efficiently to arbitrary 3 d convective flows

late mississippian thrombolite bioherms from the pitkin formation of northern arkansas two types of bioherms occur in the pitkin formation chesterian of northern arkansas they are composed of a complex series of ovoid thrombolite heads intergrown with various other algal and bryozoan biolithites and are distinguished from each other on the basis of geometry and faunal and floral content type i mounds have sharp lateral margins and interfinger with horizontally bedded contemporaneous flanking strata owing to having expanded and contracted in size during upward accretion they are interpreted as having had synoptic relief of 3 m or less during growth type ii mounds occur slightly higher stratigraphically to the east of type i mounds and formed in deeper water farther out on the ozark shelf they are interpreted as having had synoptic relief of 6 m or more during growth their margins are similar to those in type i mounds but owing to higher synoptic relief they interfinger with sediments derived from erosion higher on the mound

timescales for the evolution of seismic anisotropy in mantle flow 1 we study systematically the relationship between olivine lattice preferred orientation and the mantle flow field that produces it using the plastic flow recrystallization model of kaminski and ribe 2001 in this model a polycrystal responds to an imposed deformation rate tensor by simultaneous intracrystalline slip and dynamic recrystallization by nucleation and grain boundary migration numerical solutions for the mean orientation of the a axes of an initially isotropic aggregate deformed uniformly with a characteristic strain rate show that the lattice preferred orientation evolves in three stages 1 for small times recrystallization is not yet active and the average a axis follows the long axis of the finite strain ellipsoid 2 for intermediate times the fabric is controlled by grain boundary migration and the average a axis rotates toward the orientation corresponding to the maximum resolved shear stress on the softest slip system 3 for the fabric is controlled by plastic deformation and average a axis rotates toward the orientation of the long axis of the finite strain ellipsoid corresponding to an infinite deformation the infinite strain axis in more realistic nonuniform flows lattice preferred orientation evolution depends on a dimensionless grain orientation lag parameter x defined locally as the ratio of the intrinsic lattice preferred orientation adjustment timescale to the timescale for changes of the infinite strain axis along path lines in the flow explicit numerical calculation of the lattice preferred orientation evolution in simple fluid dynamical models for ridges and for plume ridge interaction shows that the average a axis aligns with the flow direction only in those parts of the flow field where 1 calculation of provides a simple way to evaluate the likely distribution of lattice preferred orientation in a candidate flow field at low numerical cost

modern deep water coral mounds north of little bahama bank criteria for recognition of deep water coral bioherms in the rock record abstract deep water ahermatypic coral mounds are present at water depths of 1 000 1 300 m on the lower slope north of little bahama bank the mounds are patchily distributed over a minimum area of 2 500 km2 and typically display 5 40 m of relief above the surrounding sea bottom a diverse benthic community exists on these apparently unlithified mounds including l 1 genera and 16 species of ahermatypic coral bathypsammia caryophyllia deltocyathus desmophyllum enallopsammia javania madrepora polymyces solenosmilia stephanocyathus and a previously undescribed genus alcyonaceans gorgonians antipatharians hydroids ophiuroids crinoids barnacles galatheid crabs polychaetes gastropods bivalves and sponges conspicuously absent from the coral fauna are lop elia and dendrophyllia common deep water corals in other parts of the atlantic radiocarbon dates on fresh coral and gorgonian fragments of 940 40 and 860 50 years indicate the mounds are at least in part recent and are probably actively forming today bored and stained corals date at around 22 10314c years b p which establishes a minimum age for these mounds we speculate that the mounds develop on sea floor perturbations in areas where strong bottom currents provide needed oxygen and nutrients to the fauna the mounds may have undergone multi stage evolution from colony to thicket to coppice to bank this evolution may be accomplished through the in situ contribution of skeletal material along with the baffling and trapping of fine grained carbonate sediment winnowed from adjacent areas by bottom currents if found in the rock record the coral mounds north of little bahama bank would probably be considered bioherms geologists should thus be aware that scleractinian bioherms are not uniquely shallow water in origin the distinction between ancient deep and shallow water coral buildups involves using multiple recognition criteria including 1 presence or absence of algae 2 diversity of corals 3 coral morphology and microstructure 4 abundance of planktonic benthonic components 5 microborings 6 surrounding litho and biofacies 7 stable isotopes of carbon and oxygen and 8 trace element geochemistry particularly sr and u concentrations the distinction between deep and shallow water bioherms is crucial to regional paleoenvironmental and stratigraphic interpretations

phenyldibenzofurans and phenyldibenzothiophenes in marine sedimentary rocks and hydrothermal petroleum abstract the phenyl derivatives of dibenzo b d furan and dibenzo b d thiophene so far not reported in geological samples have now been identified in some sedimentary rocks bitumen and hydrothermal petroleum through a comparison of their retention times and mass spectra with those of authentic standards all four possible positional isomers were detected for each phenyldibenzo b d furan phdbf and phenydibenzo b d thiophene phdbt their elution sequence is 1 4 2 and 3 phenyldibenzo b d furan and 1 4 2 and 3 phenyldibenzo b d thiophene on apolar stationary phases in contrast to phenyldibenzofurans the distributions of the thiophene series is controlled mainly by the organic matter maturity in the most mature samples 4 2 and 3 phdbts prevail over 1 phdbt while less mature samples contain mainly 4 phdbt or 1 phdbt and 2 3 phdbts occur at comparable concentrations however in samples of low maturity in addition to the phenyldibenzo b d thiophene c 18 h 12 s series other structural isomers of c 18 h 12 s possessing very similar mass spectra were detected these are likely to be either naphthylbenzo b thiophenes and or phenylnaphtho b thiophenes phdbfs and phdbts are likely to be intermediate products in the formation of more condensed heterocyclic polycyclic aromatic compounds like triphenyleno 1 12 bcd thiophene and triphenyleno 1 12 bcd furan and benzobisbenzofurans and benzobisbenzothiophenes which are commonly detected in geological samples

the global frasnian famennian kellwasser event during the uppermostp gigas conodont zone p linguiformis zone the stepwise frasnian extinction culminates in the global transgressive regressive frasnian famennian kellwasser event most pelagic organisms of the tropical marine environment are more or less affected by this mass extinction during the early upper devonian extinction rates are clearly related to the deposition of black shales and the storage of a great amount of organic carbon in the shelf sediments contemporaneous positive excursions of the 13c recorded from pelagic limestones of europe and australia prove a worldwide change in the co2 content of the oceans surface water which is in balance with the atmosphere if the climate is controlled by the co2 content of the atmosphere a cyclic operation process might have developed with the succession transgression high organic production deposition of organic carbon lowering of co2 in the atmosphere icehouse effect polar glaciation regression erosion of organic carbon and re supply of co2 to the ocean and atmosphere greenhouse effect deglaciation transgression during the change from a greenhouse to an icehouse effect an overturn of the anoxic oceans probably was one of the causes for the mass killing of low latitude marine organisms

facies patterns and depositional environments of palaeozoic cephalopod limestones abstract in the eastern anti atlas morocco a platform and basin topography was established during the late devonian probably as a result of early variscan tensional tectonics cephalopod limestones were deposited on shallow pelagic platforms platform slopes and shallow slowly subsiding basins on the platform a transition from land areas into nearshore quartzose brachiopod coquinas crinoidal limestones condensed cephalopod limestones and finally into nodular limestones is observed the latter often become disintegrated into incipient debris flows which pass into nodular limestone marl alternations of a shallow basin deeper basins with shale sedimentation lack cephalopod limestones similar facies types also occur in the late devonian of the montagne noire france rheinisches schiefergebirge west germany moravian karst czechoslovakia holy cross mountains poland and in the early carboniferous of the cantabrian mountains spain due to strong late variscan compressional tectonics and limited outcrops detailed facies patterns could not be mapped in these regions but the same facies types as in the eastern anti atlas suggest similar coast platform slope and shallow basin topographies during cephalopod limestone deposition water depth on the platforms was in the order of several tens to about one hundred metres as is inferred from repeated subaerial exposures and distinctive depositional and faunal floral features water depth in the adjacent shallow basins might have reached several hundreds of metres cephalopod limestones represent a typical stage in the evolution of geosynclines characterized by extremely low sedimentation rates 1 5 m m y 1 this stage is preceded by deposition of thick neritic clastics and or carbonates and is succeeded by deposition of deep water clastics or flysch

jurassic guyots on the southern iberian continental margin a model of isolated carbonate platforms on volcanic submarine edifices during the middle jurassic on the southern iberian continental margin at the westernmost end of the northern tethys isolated carbonate platforms developed over volcanic edifices forming guyots the volcanic edifices were composed of k rich pillow lavas and pyroclastic rocks with a radiometric age 170 myr such phenomena have not been described until now in this continental margin nor in other passive continental margins of alpine domains the presence of a shallowing upward megasequence bajocian bathonian with hummocky cross stratification strata below oolitic shoals shows that very shallow isolated carbonate platforms developed above the volcanic edifices with similar facies to those recognized in other guyots but with a different age and geodynamic context

lateral variations in sediment composition and bedding in middle triassic interplatform basins buchenstein formation southern alps italy hemipelagic deposits are widespread in triassic sequences of the alpine belt and provide important data for stratigraphy and the study of bedding rhythms the area of the western and central dolomites of northern italy escaped strong alpidic deformation and preserves such deposits in their original palaeogeographic setting the buchenstein formation the object of this study was deposited in up to 1000 m deep middle triassic interplatform basins which extend over an area of 500 km 2 within the dolomites excellent outcrops and volcaniclastic markers allow a detailed correlation of the formation in both laminated anoxic and bioturbated facies down to a bed scale and show its relationship to coeval carbonate platforms correlation of lithostratigraphically well constrained intervals in the bioturbated facies reveal that lateral thickening and thinning of the deposits depends on the amount of shallow water debris in the succession and is a function of the distance to coeval carbonate platform sources in the laminated background deposit thickness variations in limestones and marls parallel the thickness variations in ash layers and were caused by local redeposition of sediment on the basin floor lateral persistence of laminae indicates that bottom currents were weak in the buchenstein basin but were able to redeposit mud in a significant way in the area around seceda and geisler western dolomites a lateral transition from dark grey laminated to grey bioturbated to red bioturbated facies is observed which is probably linked to local relief with different oxygenation conditions on the sea floor a comparison shows that decimetre scale bedding is preserved in all facies types and that the bedding rhythm is partly the result of different cementation of the sediment during early diagenesis correlation of individual layers in the bioturbated facies reveals that beds are thicker and enriched in lime mud in the western part of the basin and decrease in thickness and contain less micrite towards the east further away from the main shallow water areas nearslope calciturbidites change gradually from distinct layers into lateral arrays of micrite nodules and bands further out in the basin these observations point to a platform source of lime mud in the buchenstein basin

book review the variscan fold belt in the british isles hancock p l editor 1983 adam hilger 217 pp price hardcover 34 00

the evolution of the hercynides of central sw england towards the end of lower carboniferous times sedimentation accompanied by widespread igneous activity proceeded in a tectonically active unstable and constricted basinal zone visean flysch and olistostromic sequences were generated in front of an advancing deformation front which caused erosion of submarine rises and heralded the beginning of the hercynian orogeny in this region between dartmoor and bodmin moor upper devonian basin and rise facies sediments were thrust northwards over both upper devonian and lower carboniferous northern equivalents which were themselves incorporated onto the allochthon the tectonic deformation history began in the late visean and early namurian with the gravity sliding dl of the bulk of the lower carboniferous northwards to form the greystone nappe subsequently the main thrusting event d2 from late lower namurian times onwards led to the successive overthrusting and emplacement of the heathfield petherwin and tredorn nappes towards the end of the namurian and in the westphalian the intrusion of the granite batholith caused the fold belt to tighten which resulted in the formation of numerous low angle normal faults d3 offsetting earlier thrusts to the n overall the regime is one of very thin skinned thrust and nappe tectonics with the allochthon probably not exceeding 1 km in thickness