transient regional uplift in the early tertiary of the northern north sea and the development of the iceland plume abstract forward and reverse 2d flexural modelling of syn rift and post rift stratigraphy has been used to investigate departures from mckenzie post rift subsidence for the cretaceous tertiary following late jurassic rifting in the northern north sea basin the analysis shows uplift in the palaeocene of 375 525 m relative to calibrated mckenzie subsidence curves followed by a rapid decrease in uplift in the early eocene of 160 310 m both palaeocene uplift and eocene subsidence increase northwards the timing distribution and magnitude of regional palaeocene uplift is consistent with an origin relating to the development of a mantle plume between 65 and 55 ma transient regional palaeocene uplift in the northern north sea basin was produced by long wavelength dynamic uplift generated by the flow field of a mantle plume heating of the asthenosphere or lithosphere beneath the north sea by hot plume material or magmatic underplating are not believed to have contributed to palaeocene uplift in the northern north sea basin rapid early eocene subsidence was generated by a decrease in dynamic uplift caused by a reduction in plume activity the plume responsible for north sea palaeocene uplift may have been the early iceland plume or a distinct british tertiary igneous province plume related to the same mantle convection event

geochronology and nd isotopic data of grenville age rocks in the colombian andes new constraints for late proterozoic early paleozoic paleocontinental reconstructions of the americas abstract new u pb zircon crystallization ages and 40ar 39ar cooling ages from the colombian andes confirm the existence of rocks metamorphosed during the orinoquian orogenic event ca 1 0 ga of northern south america end t 1 1 ga for these rocks range from 3 9 to 0 91 which is interpreted as a mixture of late archean early proterozoic crust with juvenile material produced during the 1 1 ga orogenic event the colombian grenville age rocks are part of a much longer metamorphic pericratonal belt sporadically exposed along the andes in western central peru southern bolivia and northern argentina in addition nd model tdm ages for the colombian rocks range from 1 9 to 1 45 ga similar to those obtained in the grenville province of the eastern u s and in the mexican basement placing constraints on late proterozoic early paleozoic paleocontinental reconstructions

archaeological sedimentology of overbank silt deposits on the floodplain of the ohio river near louisville kentucky abstract the surface of the floodplain of the ohio river about 20km southwest of louisville kentucky is a series of linear ridges and swales that are subparallel to the channel of the river which here is relatively straight and flows southward numerous prehistoric occupational sites are located on these ridges the sediments that underlie the ridges which were examined in four archaeological excavations as deep as 8 m are predominantly sandy silt and silty fine to very fine sand and appear to be mainly the product of overbank deposition from suspended load abundant cultural material and occupational sites dating as early as 10 000 years bp are found in the sediments at depths as great as 6 5 m the fine sediments of the floodplain are underlain by sand and gravel the context of the cultural materials and the stratigraphy and morphology of the deposits indicate that the ridged deposits began as linear riverside sand and gravel bars these were succeeded upward by fine grained overbank deposits in which the ridged morphology was maintained because the overbank silt and fine sand were deposited as prograding elongate bars at high water as the floodplain ridge built upward the sedimentation rate decreased and the sand content of the sediments diminished and as the river channel occasionally shifted the ridged deposits were built in successive subparallel sequences two archaeological consequences are implicit in this depositional model of orderly growth of the floodplain first available archaeological data from floodplain segments along other parts of the river should confirm the model and second the model should make it possible to search the floodplains of the ohio river for stratified sites of any desired age

formation of segmented normal faults a 3 d perspective the interpretation of fault kinematics from geometric data is an essential step in developing an understanding of the growth of fault systems constraints on fault geometry are however often restricted to 2 d maps or cross sections in this article we consider the extent to which kinematic interpretations of faulting benefit from a 3 d rather than 2 d geometrical perspective concentrating on relay zones and segmented normal fault arrays we suggest that very different interpretations of their evolution arise from the recognition that the propagation directions of faults and fault segments will rarely be contained within the inspection plane of 2 d data a 3 d perspective favours an interpretation in which the segments of a fault array are kinematically interrelated from their initiation individual segments in such systems may link into a single fault surface out of the plane of inspection or may be unconnected in 3 d we argue that this interpretation which conflicts with the often suggested model of incidental overlap of originally isolated faults should be the preferred model for the generation and growth of segmented normal fault arrays

early silurian glaciation along the western margin of gondwana peru bolivia and northern argentina palaeogeographic and geodynamic setting the record of the ordovician silurian transition within the southern peru bolivia palaeozoic basin extending across peru bolivia and northern argentina is characterized by a diamictite bearing unit which overlies several different ordovician units and underlies mid silurian shales we review the lithostratigraphy sedimentology and biostratigraphy of this unit revising stratigraphic relationships and several ideas and interpretations previously proposed analysis of facies and lithofacies associations allow for a reinterpretation of sedimentary processes and environments involved during its deposition turbidite and shale interbeds within the diamictites indicate a deep marine environment with interbedded mud flows debris flows slumps and large displaced slabs providing evidence for sediment instability and resedimentation chitinozoan biostratigraphy indicates a llandovery age in contrast with previous proposals of a hirnantian age and suggests the need for more detailed sedimentologic and biostratigraphic studies and a reassessment of this diamictite unit in relation to adjacent regions in south america the resedimented character of the deposit explains some of the ordovician fauna previously described which must be considered as recycled from underlying units in situ fauna needs to be reassessed as it may be endemic diachronic and or indicative of migrations within gondwana glacially faceted and striated clasts as well as large granitoid boulders within the resedimented materials provide evidence for glaciation of the source area and are interpreted as recycled from former glacigenic deposits the evidence found in the central andes indicates a glaciomarine origin for the diamictites and corroborates glaciation of a western source area prior to the late llandovery telychian the precise age of glaciation in this part of gondwana cannot be confirmed do to a lack of true tillites tectonic deformation and the resulting relief are respectively identified as the origin for sediment instability and for local glaciation along the active margin of western gondwana during the late ordovician and early silurian the new data imply that the ordovician silurian boundary was not preserved in some areas of the basin and that an erosional hiatus disconformity with variable regional significance is present between different ordovician units and the diamictite unit late ordovician late caradoc early ashgill euxinic black shales locally present in the central altiplano and eastern cordillera of bolivia may represent the youngest ordovician unit in the region and more research should be focused on them paleogeographic reconstruction of the early silurian peru bolivia basin depicts the extension of the diamictite unit southwards into northern argentina and western paraguay connecting with the parana basin through the asuncion arch to the north it continued into northern peru and ecuador connecting with the silurian record in colombia and venezuela and to the northeast into brazil solimoes and amazonas basins the sedimentary record of glaciation in the peru bolivia basin was due to the development of local ice fields to the west of the basin related with tectonism and resulting reliefs along the active margin of gondwana and probably did not coincide with the development of the north african late ashgillian ice cap

dynamic development of fault rocks in a crustal scale detachment an example from western norway 1 the nordfjord sogn detachment nsd zone of western norway juxtaposes eclogites and gneisses of lower crustal affinity with sedimentary deposits suggesting that the zone experienced substantial displacement during devonian extensional denudation of the caledonides renewed activation occurred in permian and jurassic cretaceous times the detachment zone consists of a succession of fault related rocks reflecting various crustal positions and deformation mechanisms during activation and unroofing in more detail the lower 1 2 km thick section of the nsd zone consists of mylonites with various protoliths showing a general upward decrease in metamorphic grade the mylonitic section is truncated by the nsd fault defining the boundary toward hanging wall nappe rocks that are topped by sedimentary basins in an attempt to provide precise descriptions of the observed fault rocks we classify these rocks into 1 noncohesive breccias 2 cemented and indurated breccias of secondary cohesion and 3 cataclasites phyllonites and mylonites formed with primary cohesion along and across strike sections of the fault reveal the spatial and temporal relationships of the nsd fault the fault zone consists of a lower section of phyllonites and cataclasites reaching a total thickness of 50 70 m significant volumes of pseudotachylyte were injected into these fault rocks and were later reworked reactivation of the fault is suggested by overprinting carbonate cemented breccias that are cut by a discrete fault itself associated with breccias and gouge by comparing the various fault rocks and their formation mechanisms some constraints can be applied to the unroofing history the nsd fault developed in the ductile brittle transition zone of the crust where it experienced an initial shift from mainly frictional to plastic flow caused by reaction softening before hardening caused a return to frictional flow at the same time repeated pulses of pseudotachylyte were generated possibly lubricating the fault zone and contributing to strain localization these pseudotachylyte pulses also show that the fault was affected by seismic slip events before returning to a creep regime within a wider section than that ruptured by earthquakes younger cemented breccias and noncohesive breccias and gouge reflect earthquake rupturing and frictional flow within the seismogenic crust

late ordovician global warming the boda event there is substantial evidence for mid ashgillian global warming before the latest ordovician hirnantian glaciation as shown by the movement of previously lower latitude benthic faunas such as trilobites and brachiopods to progressively higher latitudes and by an increase in endemic faunas at low latitudes this is shown by faunal dynamics on several paleocontinents and endorsed by published evidence of warmer water sediments from gondwana and elsewhere we term this global warming the boda event

early palaeozoic palaeobiogeography and palaeoecology of stylophoran echinoderms abstract stylophorans cornutes mitrates represent one of the most diverse classes of cambro ordovician echinoderms they were free living benthic non radiate forms closely related to asterozoans and crinoids taphonomic sedimentological and palaeosynecological data provide useful information on key aspects of stylophoran palaeoecology such a combined approach suggests that the rarity of stylophorans in proximal environments above storm wave base was probably original and does not exclusively result from the possession of a loosely articulated polyplated calcitic test conversely stylophorans were relatively abundant in deeper settings below storm wave base where they frequently occur in low diversity dense beds several tens to hundreds of individuals per square metre such assemblages were either largely dominated by stylophorans only middle cambrian darriwilian or by the association of both stylophorans and ophiuroids latest darriwilian silurian comparison with ecological requirements of similar modern and fossil dense populations of ophiuroids suggests that stylophoran beds occurred in well oxygenated oligotrophic waters with low predatory pressure and that sea temperature played a key role in the palaeobiogeographic distribution of stylophorans seven main stylophoran biofacies are identified and described the associated environments and tropical distribution of primitive heavily plated forms suggest that the initial radiation of the class probably took place in warm to temperate shallow settings earliest middle cambrian late cambrian however from this primitive stock stylophorans radiated several times towards deeper and or colder environments possibly because of the lower predation pressure in such settings cothurnocystid cornutes in the middle cambrian mitrates in the late cambrian hanusiids in the tremadocian as a consequence the fact that most cambro ordovician cornutes and mitrates were psychrospheric i e cold water adapted probably explains their relatively wide palaeobiogeographic distribution in high palaeolatitudes cambro ordovician stylophorans were abundant and diverse in shallow to deep environments but they were generally restricted to deep settings in low palaeolatitudes the great caradocian transgression favoured the extension of stylophorans from circum polar regions e g western margin of gondwana towards external settings at lower palaeolatitudes avalonia baltica and eastern margin of laurentia where one group of mitrates underwent a major radiation anomalocystitids and extended towards shallower and warmer palaeoenvironments in contrast all silurian stylophoran assemblages known so far are rare poorly diversified and restricted to shallow warm to temperate environments in tropical regions this distribution partly results from 1 the probable eradication of psychrospheric forms e g cornutes because of the prolonged anoxia of deep environments in the late hirnantian early silurian of west gondwana 2 the radiation of some mitrates anomalocystitids in shallow tropical settings in the late ordovician and 3 of strong taphonomic and or sampling biases numerous ghost lineages

monitoring and volumetric estimation of injected co2 using 4d seismic petrophysical data core measurements and well logging a case study at ketzin germany more than 50 000 tons of co2 have been injected at ketzin into the stuttgart formation a saline aquifer at approximately 620 m depth as of summer 2011 we present here results from the 1 st repeat 3d seismic survey that was performed at the site in autumn 2009 after about 22 000 tons of co2 had been injected we show here that rather complex time lapse signatures of this co2 can be clearly observed within a radius of about 300 m from the injection well the highly irregular amplitude response within this radius is attributed to the heterogeneity of the injection reservoir time delays to a reflection below the injection level are also observed petrophysical measurements on core samples and geophysical logging of co2 saturation levels allow an estimate of the total amount of co2 visible in the seismic data to be made these estimates are somewhat lower than the actual amount of co2 injected at the time of the survey and they are dependent upon the choice of a number of parameters in spite of some uncertainty the close agreement between the amount injected and the amount observed is encouraging for quantitative monitoring of a co2 storage site using seismic methods

the middle late cambrian reef transition and related geological events a review and new view abstract the reefs of the middle late cambrian cambrian epoch 3 furongian have long been simply considered as microbialites that flourished in the aftermath of the archaeocyath extinction thorough review of the reefs in these periods shows however that the cambrian epoch 3 and the furongian actually yield different types of reefs the cambrian epoch 3 reefs are dominated by thrombolites and dendrolites largely constructed by the calcified microbes epiphyton and renalcis on the other hand the furongian reefs consist mainly of maze like maceriate reefs and columnar stromatolites the maceriate reefs most likely formed by siliceous sponges and calcified microbes including girvanella and tarthinia whereas the columnar stromatolites were mainly constructed by girvanella tarthinia and minor siliceous sponges other microbial reefs e g non columnar stromatolites persisted during the cambrian epoch 3 and the furongian mainly as small patch reefs or reefal crusts lithistid sponge microbial reefs initially formed in the cambrian epoch 3 and occurred throughout the furongian but occupied only a minor portion during these periods several geological events occurred across the boundary between the cambrian epoch 3 and the furongian including positive carbon and sulfur isotope excursions a eustatic sea level drop major faunal turnover of trilobites and diversification of new organisms the coincidence of these events and the transition in reefal fabrics suggest that reef ecosystems were significantly influenced by at least some of these events among the events it is likely that sea level change would have affected reefs although further studies are required in order to test whether and how the other events influenced the reef transition epiphyton and renalcis and thrombolites and dendrolites formed by them declined greatly most likely due to sea level fall and thus decreased in shallow marine habitat at the end of cambrian epoch 3 the cambrian epoch 3 thrombolites and dendrolites were gradually replaced by a sponge microbial association of the maze like maceriate reefs and the columnar stromatolites in the furongian coincident with a sea level rise

structural anisotropy of normal fault surfaces abstract precise description of natural fault surfaces is indispensable to understanding the geometry mechanics and fluid transport properties of faults profiles of fault surfaces in the wasatch fault zone and oquirrh mountains utah are measured at 30 increments within the fault plane to determine the directional anisotropy of surface roughness at wavelengths between 10 3 m and 30 m and then compared with profiles of larger scale fault surfaces surface anisotropy and an increasing ratio of surface amplitude to wavelength are consistent with self affine fault topography at wavelengths between 1 mm and approximately 5 km fractal dimension of surface profiles generally decreases systematically as the angle to the slip direction increases directional anisotropy is described by an azimuthal scaling function k sin 0 or af af max 1 sin 1 where and af are the amplitude to wavelength ratio and anisotropy factor respectively at azimuth measured clockwise relative to slip direction within the fault surface and 0 is the amplitude to wavelength ratio parallel to slip direction k 90 0 is an anisotropy coefficient and increases systematically with spatial wavelength on the fault surface characterization of natural fault surfaces provides parameters such as fractal dimension d intercept log c of power spectra profile variance and variation in anisotropy factor af which are needed to generate fractal models of natural fault surfaces using spectral synthesis we generate sample models which illustrate the differences between fault surfaces characterized by constant versus azimuthally varying fractal dimension the latter model surfaces contain low amplitude corrugations superimposed on elongate ridges which parallel slip direction this surface texture resembles that of natural fault surfaces that refract across lithologic layering or are cut by secondary faults such as r and r shears

scandinavia s north atlantic passive margin 1 the tectonics of the eastern passive margin of the north atlantic are reexamined the scandinavian north atlantic passive margin includes not only the offshore exploration and basin domain but also large portions of the onshore domains of the scandinavian caledonides combined information from structural geology potential field data regional geology basin development and geomorphology made it possible to propose a new definition of the passive margin the rift shoulder is formed by linked faults defining the present rift flank these faults are the extensional structures located furthest to the east onshore norway sweden that can be linked to the rifting that led to the formation of the north atlantic this innermost boundary fault system ibf is formed by a set of normal west dipping crustal faults it extends over a distance exceeding 2000 km from the north sea across the caledonian mountain belt to the barents sea the passive margin width between the continent ocean boundary and the ibf ranges from 550 km in the south to over 700 km in mid norway to 165 km north of lofoten rifting and faulting on the ibf started in permo carboniferous and a succession of rift phases eventually culminated in continental breakup and the formation of the north atlantic basin development between permian and cretaceous was toward the future breakaway fault but faulting was also active on land from mesozoic to present onshore offshore crustal scale cross sections show the geometry of the passive margin the dip orientation of the major faults and the changes in crustal thickness

deformation and metamorphism of devonian rocks in the outer solund area western norway implications for models of devonian deformation many modern accounts of the devonian rocks of western norway which emphasise the extensional processes by which the basins were formed tend to ignore or gloss over the deformation and metamorphism which these rocks have suffered during contractional deformation the present account describes extensive ductile folding penetrative cleavage formation and low grade regional metamorphism developed in the devonian strata of the outer solund region although the deformation in this area is more intense than in other devonian basins it belongs to the same movement plan it will also be shown that the devonian rocks of the scandinavian caledonides apparently share a common tectonothermal development this regional contractional event conceptually may relate either to a mid late devonian arc continent collision or to a transpressional strain regime

evolutionary palaeoecology of early epifaunal echinoderms response to increasing bioturbation levels during the cambrian radiation abstract increasing bioturbation depth and intensity during the cambrian radiation created a transition in dominant subtidal soft substrates from firm proterozoic style soft substrates without a well developed mixed layer to soupier phanerozoic style soft substrates with a well developed mixed layer microbial mats were also relegated to settings with inhibited metazoan activity but made resurgences during later ecological crises previous work suggests that this substrate change strongly influenced the evolution of cambrian benthic suspension feeding echinoderms in order to test this previous work and reveal longer term evolutionary patterns the substrate adaptations of 93 genera in the three classes of benthic suspension feeding echinoderms with definitive cambrian origins edrioasteroids eocrinoids and helicoplacoids were examined throughout their fossil records this examination reveals that genera adapted to typical proterozoic style soft substrates were taxonomically dominant during and were almost entirely restricted to the early and middle cambrian thereafter from the late cambrian through the carboniferous genera adapted to typical phanerozoic style soft substrates were taxonomically dominant this trend supports previous studies and defines a fundamental evolutionary shift in echinoderm substrate interactions in response to increased mixed layer development during the cambrian radiation a notable exception to this trend is the late devonian edrioasteroid cooperidiscus which is morphologically convergent with the early and middle cambrian sediment attaching edrioasteroid stromatocystites this convergence is likely the result of cooperidiscus adapting as a sediment attacher to typical proterozoic style soft substrates that developed during or shortly after the late devonian mass extinction this study indicates for the first time that adaptation to non actualistic substrates during ecological crises can result in morphological convergence with forms adapted to similar substrates common during the cambrian radiation

fluvial activity in major river basins of the eastern united states during the holocene in the eastern united states existing paleo reconstructions in fluvial environments consist primarily of site specific investigations of climate and human impacts on riverine processes this paper

ordovician and silurian chitinozoan biozones of western gondwana a formal ordovician silurian chitinozoan biozonation for western gondwana is proposed this palaeogeographic province includes south america and was located in medium to high latitudes during ordovician and silurian times ordovician chitinozoans are known from northern argentina southern bolivia and brazil silurian chitinozoans occur in brazil northern argentina southern bolivia and southern peru no published information is available about ordovician silurian chitinozoans from ecuador colombia or venezuela altogether more than 150 localities including wells and outcrops are included in this study and 154 species have been encountered a biozonation based on the first occurrence of critical chitinozoan species is introduced five biozones are defined in the ordovician zones of desmochitina sp gr minor conochitina decipiens eremochitina brevis lagenochitina obeligis and tanuchitina anticostiensis and nine in the silurian zones of belonechitina postrobusta spinachitina harringtoni pogonochitina djalmai margachitina margaritana salopochitina monterrosae angochitina echinata eisenackitina granulata fungochitina kosovensis and the subzones of sphaerochitina solutidina and desmochitina cf d densa these biozones are compared with known graptolite conodont acritarch and spore zones from the same area and chitinozoan zones on a global basis

the middle devonian basins of western norway sedimentary response to large scale transtensional tectonics abstract the devonian basins of western norway were formed during late to post orogenic extension of overthickened caledonian crust the basins are situated in the hanging wall of the extensional nordfjord sogn detachment zone nsdz and display extensional half graben geometries in sections parallel to the local direction of principal extension based on overall facies configurations paleocurrent patterns and intrabasinal structures we infer an anticlockwise rotation of the syndepositional extension direction from nw se in the south solund basin to wsw ene in the north hornelen basin the axes of folds that are roughly parallel to the local extension direction are rotated correspondingly the kvamshesten basin is located between the solund and hornelen basins sedimentological and structural data show evidence of an early southeastwards tilt direction followed by a more eastwards tilt and associated e w flowing paleodrainage correspondingly nw se trending folds and reverse faults are superposed by e w trending ones at low to intermediate stratigraphic levels the variations in apparent tilt direction for the basins together with variations in intrabasinal structure is interpreted to reflect an anticlockwise rotation of the regional syndepositional strain field the above observations and inferences indicate that the devonian basins in western norway formed in a strain field dominated by regional transtension accommodated by extension along the nsdz and sinistral strike slip along orogen parallel shear zones and faults to the north of the basins alternatively nw directed extension preceded the introduction of a sinistral strike slip component the models are in accordance with recent work carried out in the footwall of the nsdz and illustrates the tectono sedimentary response to a complex interplay between extension and strike slip that appears to have been fundamental in the late stage disintegration of the caledonian orogen

palaeogeographical and palaeoecological aspects of the cambro ordovician radiation of echinoderms in gondwanan africa and peri gondwanan europe abstract ecology and tempo of the lower palaeozoic radiation of echinoderms are discussed in this paper based on comparison of the diversity patterns observed in cambro ordovician faunas from laurentia and the northern gondwana margin the cambrian agronomic revolution triggered a global radiation of echinoderms with the progressive disappearance of biomat related lifestyles and the colonisation of new environments both in laurentia and on the northern gondwana margin soft substrate echinoderm assemblages related to cold and or deep environments were dominated by blastozoans and stylophorans these assemblages show a pattern of continuous diversification from the middle cambrian to the middle ordovician the major radiation of crinoids in the lower to middle ordovician of laurentia is only a local diversification correlated with the development of hardgrounds in warm shallow environments no comparable major ordovician radiation event occurred in the cooler environments of the northern gondwana margin

the margins of avalonia during cambrian and earliest ordovician times avalonia was an area forming an integral part of the huge gondwanan continent probably along the northern margin of amazonia until in early ordovician late arenig or llanvirn time it split off from gondwana leaving a widening rheic ocean to its south today its southern margin with gondwana extends northeast from east of cape cod massachusetts through nova scotia north of the meguma terrane and thence below sea level to the south of newfoundland on the eastern side of the present atlantic the southern margin may separate southwest portugal from the rest of the iberian peninsula it can be traced eastwards with more certainty from the south cornwall nappes to a line separating the northern phyllite belt on the southern margin of the rhenohercynian terrane and the mid german crystalline high there is no certain evidence of avalonian crust to the northeast of the elbe line the northern margin of avalonia extends westwards from south of denmark to the british isles where it merges with the iapetus ocean suture between scotland and england traced westwards it crosses ireland and reappears in northern newfoundland to the east of new world island where it may follow the trace of the dog bay line and the cape ray fault recent work suggests that the northern margin of avalonia may clip the northern tip of cape breton island in nova scotia and then enter the north american mainland at the bay of chaleur it may then be traced from north and west of the popelogan and bronson hill arcs to long island sound near newhaven connecticut the cambrian to devonian faunas reflect the history of avalonia initially they were purely gondwanan but as ordovician time proceeded more genera crossed firstly the tornquist ocean as it narrowed between avalonia and baltica to close in latest ordovician and early silurian times and secondly the iapetus ocean so that by the early silurian most of the benthic shelly faunas apart from the ostracods were the same round the adjacent margins of all three palaeocontinents

vestiges of an ordovician west vergent thin skinned ocloyic thrust belt in the argentine precordillera southern central andes collision of the down going laurentia derived argentine precordillera terrane with the gondwanan margin drove the ordovician ocloyic orogeny including subduction volcanism metamorphism and top to west shearing east of the precordillera in the precordillera above passive margin carbonates lower ordovician san juan limestone and older carbonates a middle to upper ordovician westward prograding synorogenic clastic wedge of black shale gualcamayo shale and coarser clastic sediment las vacas conglomerate and trapiche formation fills a peripheral foreland basin new research has identified vestiges of a west directed thin skinned ocloyic foreland thrust belt that has been fragmented by east directed andean thrusting the el corral thrust sheet with hanging wall detachment in the san juan limestone extends over a west directed footwall frontal ramp and extensive flat to low angle footwall cutoff in the gualcamayo and las vacas formations las vacas conglomerates in the footwall include olistoliths 10 m scale exclusively of san juan limestone and gualcamayo shale the beds in some olistoliths are folded the advancing el corral thrust sheet successively supplied and overrode the stratigraphically restricted olistoliths in the el corral footwall tight west vergent folds and faults within an anticlinorium in the san juan limestone and gualcamayo shale suggest a deeper unexposed thrust fault the los celestitos fault west of the anticlinorium easterly dip restored to remove andean deformation beneath an angular unconformity between las vacas and trapiche beds is consistent geometrically with the trailing limb of a west vergent fault propagation anticline in the hanging wall of the subsurface los celestitos fault the same angular unconformity truncates the el corral fault and hanging wall strata in the trapiche formation contrasting sedimentary facies from sandy turbidites westward to limestone clast megabeds and olistoliths suggest another frontal ramp from a stratigraphically deeper detachment in a break forward sequence none of these observations separately defines an ocloyic thrust belt taken together however these vestiges of thrust belt style indicate the consistent geometry of an ordovician west vergent thin skinned ocloyic thrust belt

late middle ordovician environmental change and extinction harbinger of the late ordovician or continuation of cambrian patterns positive excursions in carbon isotope compositions of carbonate 3 and organic carbon 4 6 from the late middle ordovician middle caradocian of the midcontinent and the eastern united states indicate widespread increases in productivity and rates of organic carbon burial that may have drawn down atmospheric p co 2 precipitating global cooling although not necessarily ice sheet formation these climatic changes were associated with regional orogenic uplift a relative rise in sea level changes in epeiric sea circulation patterns and carbonate platform destruction that led to regional extinction of marine benthos the combination of sea level rise changing ocean circulation and extinction in the middle caradocian is similar to the suite of environmental changes described for cambrian biomere boundaries suggesting shared causes for these events in contrast middle caradocian environmental changes are markedly different from the environmental patterns associated with the late ordovician mass extinction despite the evidence for long term cooling from the middle to the late ordovician

seismicity and seismotectonics of norway and nearby continental shelf areas the earthquake activity of norway and nearby offshore areas is low to intermediate with few events above magnitude 5 recent significant improvements in instrumental coverage in parallel with a better utilization of older including historical data have shown that the seismicity in the south is predominantly confined to the coastal areas and to the viking graben while from the northern north sea to svalbard the earthquakes in a broad sense follow the continental margin fifty one focal mechanism solutions from these areas about half of them new reveal stress directions that clearly indicate a connection to the plate tectonic ridge push force at least for the areas at a minimum distance from the continental margin along the margin stress directions also indicate a possible connection to postglacial uplift as well as to lithospheric loading effects a dominance of normal faulting on the landward side and reverse faulting on the oceanic side agrees with this interpretation on a regional level the seismicity in these areas correlate quite well with geologic features such as grabens fault zones fault complexes fracture zones and the margin itself indicating that these structures act in a general sense as weakness zones in the presence of a regionally more stable stress field in the northern north sea however an area with quite anomalous stress orientations with strike slip faulting is found in a region transitional between normal and reverse faulting most of the earthquake foci are confined to the presumably brittle parts of the crust but many events are also located quite close to and on both sides of the moho discontinuity

a pre hirnantian late ordovician interval of global cooling the boda event re assessed facies analysis suggests that the early mid ashgill late ordovician boda event of fortey and cocks fortey r a cocks l r m 2005 late ordovician global warming the boda event geology 33 5 405 408 was an episode of global cooling not of warming as they proposed limestones are widely developed at this level from mid latitude to high latitude commonly interrupting thick ordovician successions of fine clastic sediments bryozoan carbonate mud mounds in a laterally extensive cool water carbonate belt along the high palaeolatitude margin of w gondwana are associated with glacial diamictites and grew during glacial lowstand with sea ice prior to the hirnantian glaciation from high to mid palaeolatitudes contemporaneous cool water carbonates with mud mounds including stromatactis both in gondwana and in baltica developed in mid outer ramp settings during regression in the dominantly clastic welsh basin of avalonia phosphatic facies on an iapetus facing carbonate ramp indicate upwelling cold waters down ramp yet up ramp coralliferous algal limestones suggest warm surface waters we propose that the late ordovician cool water carbonates developed in response to global cooling and expansion of gondwanan terrestrial and sea ice that lowered eustatic sea level and on the w gondwanan shelf reduced or shut down fluvial clastic input previously poorly circulated salinity stratified oceans that had restricted benthic dispersal in mid low latitudes were replaced by thermohaline ocean circulation that oxygenated bottom waters and dispersed benthic faunas an earlier caradoc carbonate interval in low mid palaeolatitudes that shares many facies characteristics with the ashgill cool water limestones and correlates with a widely recognised isotope excursion is interpreted as indicating an earlier global cooling episode

the great ordovician biodiversification event gobe the palaeoecological dimension abstract the great ordovician biodiversification event gobe saw a spectacular increase in marine biodiversity at all taxonomic levels largely within the phyla established much earlier during the so called cambrian explosion the diversification was probably the result of a combination of several geological and biological processes and the positive feedbacks resulting from them the present paper reviews the palaeoecological dimension of the gobe it involved major increases in s and biodiversity largely associated with the rise of the paleozoic evolutionary fauna dominated by suspension feeders and involving a greater occupation of ecospace and more complex ecological structures in the ecological evolutionary units p1 and p2 in the benthos these include more complex food webs than those of the cambrian greater tiering especially above the sediment water interface and the development of guild structures indicating increased competition between taxa for particular resources the ordovician is characterized by a profound change in reef composition with a switch from microbial dominated reefs in the early and middle ordovician to metazoan dominated reefs in the late ordovician increases in complexity of deep water trace fossil assemblages began in the early ordovician and mark the increasing exploitation in that environment and the development of hardgrounds permitted bioerosion and encrusting strategies together with the appearance of cryptic communities within the water column the gobe involved a significant increase in the diversity of the phytoplankton and the development of a diverse zooplankton including planktotrophic larvae from a range of invertebrate clades this revolution in the plankton enabled the establishment of a diverse fauna of pelagic vertebrates molluscs and arthropods and promoted the rise of suspension feeders in the benthos an escalation amongst predators and thus community evolution may also have been a major driver of biodiversification

origin of rollover rollover is the folding of hanging wall fault blocks by bending or collapse in response to slip on nonplanar commonly listric normal faults the shapes of rollover folds are controlled by a number of variables including 1 the shape of the fault 2 the total fault slip after a bed is deposited 3 the direction of relative particle motion in hanging wall collapse 4 the history of sedimentation rate relative to fault slip rate and 5 compaction the importance and role of each of these variables is illustrated by a two dimensional balanced structural modeling technique that treats continuously curved faults as though composed of a large number of straight fault segments in this modeling an active axial surface oriented parallel to the direction of relative p rticle motion in hanging wall collapse emanates from each fault bend and is the instantaneous locus of folding the quantitative correctness of this theory of rollover is tested by modeling natural structures from the gulf of mexico for which both fault shape and fold shape are known from high quality seismic and well sections the direction of hanging wall collapse commonly is in the antithetic or synthetic normal fault or coulomb shear orientations although sliding along weak bedding planes also is an important collapse mechanism in some regions collapse is in the antithetic shear direction for concave fault bends and in the synthetic shear direction for convex bends these collapse directions can be observed directly in some high quality seismic images as axial surfaces emanating from fault bends the shapes of rollovers within growth strata depend strongly on the sedimentation rate relative to fault slip rate as well as the total slip after a bed is deposited the crests of classic gulf coast rollovers are growth axial surfaces along which are abrupt changes in sedimentation rate within the growth st atigraphic interval these changes are produced by deformation of the sediment water interface along active axial surfaces compaction can substantially modify the relationship between fault shape and rollover shape however under certain common conditions the history of compaction can be neglected if the folding is modeled in the compacted state

unravelling extrinsic and intrinsic factors of the early palaeozoic diversification of blastozoan echinoderms abstract the subphylum blastozoa represents more than one third of the early palaeozoic echinoderm fauna a comprehensive database including all records of blastozoans was built to provide quantitative analyses of palaeogeography and diversity patterns and processes for the 10 classes currently included in this subphylum during the early palaeozoic the global pattern of taxonomic diversity shows two peaks during the cambrian series 3 and the late ordovician intervals in cambrian times the high taxonomic diversity seems to be related with a high turnover rate and a high endemicity of blastozoan genera whereas in ordovician times the rise in diversity is associated with a low endemicity and a low turnover rate the gradual increase of ordovician diversity can be explained by the progressive geographic extension of blastozoan genera onto most palaeocontinental margins associated to the long term gradual sea level rise this global pattern is subdivided into local trends to compare the relative influence of regional distributional patterns blastozoans occurred mainly on gondwanan and laurentian margins during the cambrian in both ordovician and silurian times blastozoans colonised different provinces characterised by varied latitudinal position and environmental conditions the laurentian province was mainly located in the equatorial latitudes temperate to warm waters mainly carbonate platforms and both the northwestern peri gondwanan and asian provinces in the intermediate to high latitudes temperate to cold water mainly siliciclastic environments after the hirnantian mass extinction blastozoans finally recovered chiefly on laurentian margins where climate and environmental conditions were probably more favourable the two diversification events recorded for blastozoans in the early palaeozoic concerned two distinct evolutionary faunas cambrian evolutionary fauna vs palaeozoic evolutionary fauna they were driven by distinct processes even if the ordovician diversification had indeed started during the middle furongian with a medium origination event difference in processes might be related to the evolution of global environmental climatic conditions coupled with the position of continental masses

the growth of non colinear normal fault systems what can we learn from 3d seismic reflection data abstract many rift zones exhibit a range of fault orientations rather than simple colinear faults that strike orthogonal to the inferred least principal stress the formation of non colinear fault sets has implications for assessing rift zone kinematics as well as determining palaeo stress state in extensional basins using 3d seismic reflection data we deduce the likely mechanisms responsible for the formation of a population of non colinear faults in the maloy slope area of the northern north sea three basement displacing fault populations exist on the maloy slope i large 1 km throw n s striking faults ii smaller

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

a review of lower and middle palaeozoic biostratigraphy in west peninsular malaysia and southern thailand in its context within the sibumasu terrane abstract fossils from the cambrian to devonian rocks of southern thailand the langkawi islands mainland kedah perlis north perak and central west peninsular malaysia are listed and reviewed and their stratigraphy and correlation reassessed the hitherto anomalous record of the trilobite dalmanitina from malaysia is reviewed and found to be of latest ordovician hirnantian age rather than lower silurian age as previously reported and is considered a probable synonym of the widespread mucronaspis mucronata a new stratigraphical nomenclature is erected for part of the langkawi mainland kedah and perlis area successions in which the term setul limestone which stretched from the ordovician to the devonian is abandoned and replaced by the middle ordovician kaki bukit limestone the late ordovician and early silurian tanjong dendang formation the silurian mempelam limestone and the early devonian timah tasoh formation all underlying the paraconformity with the late devonian langgun red beds there was a single depositional basin in the generally shallow water and cratonic areas of southern thailand langkawi and mainland kedah and perlis in contrast to the deeper water basin of north perak only silurian rocks are dated with certainty within another basin in central west malaysia near kuala lumpur which were also cratonic and shallow water although to the east in west pahang there are basal devonian deeper water sediments with graptolites the area is reviewed in its position within the sibumasu terrane which in the palaeozoic also included central and northern thailand burma myanmar and southwest china part of yunnan province

development of rift basins illustrated by the structural evolution of the oseberg feature block 30 6 offshore norway the mesozoic tilted fault block in norwegian north sea block 30 6 containing the giant oseberg oil and gas field is used to illustrate basin development during the jurassic and cretaceous there is seismic evidence for an early rifting phase in the northern viking graben on which the jurassic cretaceous rifting phase early bathonian to berriasian is overprinted the oseberg structure is representative of other fault blocks bordering the northern viking graben axis planar normal faults and listric faults which were restricted to the rifting phase dominate both fault types exhibit syn fault sedimentation listric faulting is recognized on seismic sections by the differential tilting reverse drag antithetic faulting and a wedge shaped syn rift reflector package the initiation of rifting is dated by baselap onto pre rift reflectors and cessation is dated by an unconformity beneath the generally onlapping post rift sediments steeply dipping planar normal faults often active along previously established fault zones played a significant part in the post rift development of the basin the last movement on planar normal faults in the oseberg fault scarp becomes younger away from the rift axis and this produced the complex fault scarp visible on many seismic lines the topography defined by the post rift unconformity is a composite surface which formed in response to subsidence processes it is not the result of orogenic events such as the kimmerian 9orogeny9 footwall uplift associated with planar normal faults caused local unconformities in complex fault scarps and on fault block crests

late ordovician hirnantian diploporitan fauna of anticosti island quebec canada implications for evolutionary and biogeographic patterns hirnantian latest ordovician localities containing echinoderm fossils are rare the few that have been discovered primarily contain disarticulated crinoid ossicles therefore relatively little is known about echinoderm evolutionary dynamics across the late ordovician early silurian boundary especially noncrinoid echinoderms new diploporitan echinoderms holocystites salmoensis and an unidentified holocystitid from reefal facies of the upper ordovician ellis bay formation of anticosti island provide a critical data point concerning diploporitan biogeography and evolutionary pathways undertaken during the ordovician and silurian these fossils also provide a crucial link in understanding the ancestry of the silurian holocystites fauna an unusual diploporitan fauna from the middle silurian of north america whose origination dates back at least 15 million years earlier than previously thought with the discovery of taxa described here new fossil data such as these stress the importance of uncovering

experimental models of hangingwall deformation in ramp flat listric extensional fault systems abstract the results of three experimental models of ramp flat extensional fault systems are presented the experiments were constructed from sand and mica layers to form an anisotropic sequence that would respond to the imposed deformation by both faulting and folding the geometry of the underlying detachment controls the deformation in the hangingwall sequence ramp flat detachment geometries produce an upper roll over with a crestal collapse graben system a ramp syncline and fold reverse fault zone and a lower roll over with a crestal collapse graben system short ramp geometries produce only minor perturbations in a larger roll over structure as extension progresses the crestal collapse systems migrate and superimpose earlier systems the models of ramp flat extensional structures produce templates for the interpretation of natural ramp flat listric fault systems

late mesozoic to early cenozoic components of vertical separation across the more trondelag fault complex norway abstract low temperature apatite fission track aft data from two horizontal transects across the more trondelag fault complex mtfc and along the coast of the fosen peninsula have defined a complicated series of structural blocks whose exhumation to temperatures cooler than the uppermost apatite partial annealing zone paz occurred during a broad mesozoic to cenozoic time span the 100 million year cooling difference between the innermost and outermost blocks indicates they were subjected to very different exhumation pathways track length histograms and inverse model results also suggest that significant differences in thermal histories are present over very short horizontal distances in conjunction with the offshore geological evidence the aft data and models strongly suggest that the innermost zones of the mtfc underwent between 2 and 4 km of structurally controlled net vertical rock column uplift subsidence following latest cretaceous time and potentially much of the tertiary as well the up to the east down to the west relative offset at the norwegian margin is interpreted in terms of a flexed nearly broken lithospheric plate architectural model for late mesozoic and tertiary scandes mountain building whose driving force was likely dominanted by erosionally induced loading unloading at the margin

tectonic and paleogeographic interpretation of the paleomagnetism of variscan and pre variscan formations of the bohemian massif with special reference to the barrandian terrane abstract paleomagnetic data from variscan and pre variscan formations of the bohemian massif bm have been interpreted tectonically and paleogeographically evaluated with respect to the european paleomagnetic results the interpretation of data from the bm was preceded by the evaluation of the effect of the trans european suture zone tesz on the dispersion of the european paleomagnetic pole positions during the variscan orogeny stability of the european lithospheric plate is well documented by paleomagnetic results for the early permian to the quaternary rocks of the regions between the ural mountains and great britain north of the alpine tectonic belt for the late carboniferous and earlier times the stable plate is defined in the regions ne of the tesz in the east european craton only late carboniferous and older rocks from the regions sw of the tesz largely occupied by the west european variscides show tectonic deformations controlled by prominent horizontal rotations these rotations can be studied on a theoretical model simulating the distribution of pole positions controlled by rotation of rock formations about a vertical axis in the bm horizontal paleotectonic rotations are well documented for variscan and pre variscan rocks they reach several tens of degrees up to 180 in extreme cases of mostly clockwise sense the study of the tectonics and paleogeography of cambrian to devonian formations of the barrandian area which is considered a peri gondwana terrane with affinities to armorica may serve as a case history of the study of a terrane incorporated into a stable lithospheric plate here the barrandian terrane became a part of the european plate as a component of the emerging pangea supercontinent in the final phase of the variscan orogeny high almost peri polar paleolatitudes for the cambrian rocks of the barrandian area are within the limits of data scatter in agreement with the presumed position of gondwana and armorica rocks of ordovician age did not produce consistent results they will require further paleomagnetic and paleoclimatologic studies in relation to the data for the late cambrian and early silurian rocks of the barrandian area the analysis of data presented here shows that paleomagnetic declinations of variscan and pre variscan formations reflect paleotectonic rotations following the formation of the respective rocks including rotations induced by the variscan orogeny and rotation of the european plate to which the rocks became incorporated therefore paleomagnetic declination of none of the pre variscan formations can be identified with paleotectonic rotation either of the barrandian terrane or even of the whole bm magnitudes of horizontal paleotectonic rotations in the bm affected by variscan tectonism are notably similar to those in the western carpathians affected by alpine deformation senses of rotation are however different with clockwise rotation prevailing in the bm and counterclockwise rotations prevailing in the western carpathians recognition of the effect of horizontal rotations of rock formations if located in tectonically mobile belts and incorporated into a stable plate during their later history should be respected while deriving the apparent polar wandering path apwp

paleoceanography and paleoclimatology an earth system perspective abstract the purpose of this paper is to provide an overview of paleoceanography and paleoclimatology as a framework for other papers dealing with the earth system geochemical perspectives an introduction to both paleoceanography and paleoclimatology is followed by examples of the temporal changes through the phanerozoic the important and interactive role of the biosphere is emphasized many important changes in the earth system have affected the coupled ocean atmosphere system and many in turn have been reflected in biotic events many such changes can be tracked through time using geochemical signatures as proxy indicators whereas the scale of past paleoceanographic and paleoclimatic changes have been generally appreciated for some time the recognition of periodic rapid change in the ocean climate state and the ability to study and measure these precisely is only a recent accomplishment the potential for such rapid change in the ocean climate biosphere of the earth system raises concerns for events in the near future that may be forced by anthropogenic activities that enhance natural variability

the early paleozoic carbon cycle a review of o c sr and s isotope trends for the entire phanerozoic shows that the present day values of isotope signals are similar to those at the proterozoic termination the sharp rise in 87sr 86sr since 65 ma has been attributed to an uplift and subsequent metamorphism and erosion associated with the himalayas and tibet this orogenic evolution has been postulated to have influenced the global organic and inorganic carbon cycles and climate as well a similar large scale orogeny the pan african event also dominated the neoproterozoic vendian times and the similarity of modern and neoproterozoic isotope values for seawater may therefore have had a comparable tectonic cause in this contribution we present the results of a numerical model of the coupled c alkalinity s sr cycles suggesting that the early paleozoic from early cambrian to late devonian evolution of sr o c and s seawater isotope signals could have been the consequence of progressive oxidation of a large reduced carbon reservoir exhumed during the pan african orogeny the 18o measured in brachiopod shells is used as a forcing of the model postulating that any change in the oxygen isotopic composition of seawater is the result of a disequilibrium in the organic carbon subcycle through the coupling of the oxygen isotopic and carbon cycles the calculated 13c 87sr 86sr and 34s are in good agreement with the data as is the reasonable calculated history for atmospheric pco2 and its relation to global climate

the hardangerfjord shear zone in sw norway and the north sea a large scale low angle shear zone in the caledonian crust the hardangerfjord shear zone is a more than 600 km long low angle extensional structure that affects the south norway and north sea caledonides the ductile shear zone which shows total maximum onshore displacement of the order of 10 15 km is primarily a basement structure with an associated passive monoclinal fold structure of the overlying caledonian nappes deep seismic data indicate that the shear zone continues down to the lower crust 20 25 km at a dip of 22 23 where it appears to flatten and merge with the general lower crustal deformation fabric onshore the hardangerfjord shear zone consists of a system of hard linked ductile shear zone segments brittle faults the l rdal gjende fault system occur in the folded caledonian allochthons in the ne part of the hardangerfjord shear zone and reappear in the north sea these may represent a high level brittle response to the devonian development of the hardangerfjord shear zone but were reactivated during permo triassic and late jurassic extensional events a c 5 km thick package of seismic reflectors along the hardangerfjord shear zone is presumed to represent a mylonite zone which is too thick to be formed entirely by 10 15 km of devonian displacement hence the hardangerfjord shear zone is likely to be a proterozoic shear zone reactivated during devonian extension

the geometry of listric normal faults and deformation in their hangingwalls abstract in cross sections containing listric extensional faults area balancing techniques for depth to decollement are usually based on either bed length conservation or displacement conservation listric fault geometry may be constructed from a hangingwall roll over profile using the chevron construction this construction based on conservation of heave necessitates a reduction in fault displacement with decreasing fault dip a modification of this construction utilizing conservation of fault displacement predicts a listric fault that detaches at a shallower depth a new construction based on slip lines uses fault perpendicular displacement segments to generate listric fault shape fault propagation strain may be responsible for anomalous hangingwall geometries and these can be predicted by forward modelling using either a modified chevron construction or a slip line construction

short term occupation surfaces in the lower ohio river valley exposing more of the late holocene hidden record as in other larger river valleys holocene alluvial deposition in the lower ohio river valley created a sampling bias towards certain prehistoric archaeological sites by burying them too deep to be accessed by conventional archaeological methods alternatively archaeological site types that do not leave a large signature i e a large sample of artifacts may also be obscured since they are not associated with recognizable geomorphic or soil development features such as a buried a horizon this obscuration has led to an incomplete record of the region s prehistory to better understand the age and type of prehistoric sites that may be buried within this alluvial landscape it is necessary to understand the structure and history of the alluvium in the valley this can be done by reconstructing the chronological development of alluvial deposits and the soils that formed in them regional models for the age and development of ohio river valley alluvium and the cultural deposits they may contain have been previously developed but must be continuously reviewed and revised as to their applicability to all and any alluvial packages found within the lower ohio river valley this study tests and expands some of these models through the investigation of an alluvial landscape near the confluence of the ohio and great miami rivers in indiana an age based landscape reconstruction which focuses on late holocene alluvium is presented cultural deposits can be linked to brief stability periods within alluvial packages stability periods that were too brief to have formed an a horizon this study shows that short term or ephemeral prehistoric occupations may co occur with periods where the surface of an alluvial landscape or landform was geomorphically stable for a brief period identifying these short term stable surfaces could likely lead to the better identification of underrepresented prehistoric cultural components or archaeological site types and help to reduce sampling bias in the regional prehistoric record

development of the north viking graben inferences from laboratory modelling abstract the north viking graben is a classic sedimentary basin in the north sea that has been thoroughly studied over the last decade despite the amount and quality of seismic and well data now available the processes of extension remain unclear and the relationship between sedimentation and deformation is still a matter of debate we present the results of small scale laboratory modelling the models are made with sand and silicone putty to simulate brittle and ductile behaviour on a crustal scale the experiments were designed to study the effects of a the degree of coupling between brittle and ductile layers b the obliquity of extension and c the reactivation of inherited crustal scale structures the results are used to discuss the symmetry of extensional processes on crustal and lithospheric scales as well as the relationship between sedimentation and deformation it is proposed that the asymmetry of faulting in the upper crust and the nearly symmetric thinning of the whole crust are not mutually exclusive a model involving nearly pure shear on the lithospheric scale is used to explain the development of an asymmetrical basin at shallow level in addition this model accounts for the nearly horizontal stratification of lower cretaceous sediments the basal cretaceous unconformity which caps many of the normal faults and the localization of deformation to the west of the graben during the lower cretaceous

modeling soil geomorphic associations and archaic stratigraphic sequences in the lower ohio river valley abstract adequate sampling of buried occupations in large river valleys requires an understanding of both the structure of valley fills at different scales and the properties of the archaeological record broad tracts of holocene alluvium representing compound bank side and point bars are present in the lower ohio river valley a substantial record of archaic sites also exists although certain hunter gatherer sites from the late wisconsin early holocene and middle holocene are poorly represented primarily because of their low archaeological visibility especially in buried contexts this study uses an extensive geological and archaeological base line data set from the caesars archaeological project to model soil geomorphic relationships and archaic stratigraphic sequences in alluvial units to better define the sampling parameters of these poorly known periods soil weathering properties as reflected in soil order are a proposed indicator of alluvium age radiocarbon ages from other sites in the lower ohio river valley which provide a test of this proposition are found to be correlated with the order of soil series alfisol mollisol entisol inceptisol mapped on landforms of different age early and late holocene alluvium are differentially distributed in the region a factor that may account for a better documented early archaic record below the falls of the ohio

probabilistic geomechanical analysis of compartmentalization at the snohvit co2 sequestration project pressure buildup caused by large scale co2 injection is a key concern during a carbon sequestration project large overpressures can compromise seal integrity reactivate faults and induce seismicity furthermore pressure buildup is directly related with storage capacity in this work we study the geomechanical response to co2 injection at snohvit to understand the potential for fault reactivation leakage and contamination of the producing interval through bounding faults furthermore we evaluate the potential contribution of a structural component to reservoir compartmentalization we combine simplified analytical models based on critically stressed fracture theory and a mohr coulomb failure criterion with a rigorous sensitivity analysis large stress uncertainties are present and reflected in the modeling results it was found that under the most likely stress state the faults are fairly stable and caprock hydrofracturing would be expected before fault reactivation in most of the analyzed cases the critical pressure perturbation needed for reactivation is above 13 mpa which was the limiting pressure increase before reaching the fracture pressure faults were found to be 20 less stable when considering variations in shmax orientation in those cases fault reactivation could be expected before caprock failure if injection continued however if the pressure increase did reach the critical values for seal failure estimated under the worst case and least likely stress state no indication of such failure can be observed in the measured pressure response finally the potential role of a structural component in the compartmentalization and fluid migration is difficult to assess due to the stress state uncertainty

the palaeogeography of early ordovician iapetus terranes an integration of faunal and palaeomagnetic constraints abstract new and existing fossil data from ireland britain newfoundland and scandinavia emphasize a significant degree of latitudinal variation in biogeographic patterns across the ordovician iapetus ocean platform provinces together with marginal belts and island complexes can be recognised with increasing clarity on the basis of palaeontological information statistical analysis of the distribution patterns of about 70 early ordovician brachiopod genera across some 25 sites using both cladistic and phenetic methods together with a critical analysis of their geological settings combined with current palaeogeographic and palaeomagnetic data reaffirm the existence of the celtic brachiopod province during the early ordovician the majority of sites assigned to the celtic province define a high latitude peri gondwanan belt shadowing the distribution of the low latitude circum laurentian toquima table head faunas rapidly changing ordovician faunal signals across the baltic province and exploits zone of central newfoundland track the cross latitude movement of these terranes from high temperate to near tropical belts during the period new fossil information together with continuing statistical appraisal of an expanding database are providing more accurate and sophisticated models for the dynamics of the iapetus ocean system

volcanic rocks in the devonian solund basin western norway large landslides of silurian 439 ma rhyolites abstract the devonian solund basin in sw norway is the only old red sandstone basin in the scandinavian caledonides from which volcanic rocks have been described these rhyolitic lavas yield a concordant id tims u pb zircon age of 439 1 ma early silurian interpreted as dating the crystallization of the rhyolite and are thus too old to be syndepositional with the devonian sedimentary rocks this new age constraint combined with field observations suggests that the volcanic rocks form part of a 30 km 2 landslide of rhyolite granite gabbro and metasedimentary rocks rather than extension related volcanism as previously suggested the landslides show an inverted stratigraphy with respect to the nearby solund stavfjord ophiolite complex and its overlying volcanic arc which was formed immediately prior to obduction of caledonian exotic terranes onto baltica the dated rocks thus appear to record the youngest pre collisional volcanism in the scandinavian caledonides tectonic models involving devonian old red volcanic rocks in the scandinavian caledonides must thus be revised

quaternary chronostratigraphy and stable isotope paleoecology of big bone lick kentucky usa abstract big bone lick bbl in northern kentucky usa has been a critical geologic site in the historical development of north american quaternary vertebrate paleontology since the 1700s sedimentology geoarcheology paleontology accelerator mass spectrometry radiocarbon and optically stimulated luminescence dating and stable carbon and nitrogen isotope analyses were undertaken to develop a chronostratigraphy and history of erosion and deposition for the site to provide a foundation for understanding taphonomy and species extinction and adaptation to periods of climatic and environmental change three geomorphic surfaces are recognized at bbl representing significant periods of floodplain aggradation since the last glacial maximum 26 5 19 ka dating to the oldest dryas tazewell 25 19 ka the older dryas cary 14 12 ka and late holocene 5 ka to the present unconformities suggest significant periods of degradation during the transitions from cold and dry to warm and moist climates from the oldest dryas tazewell to bolling oscillation from the older dryas cary to the allerod and from the younger dryas valders to the holocene climatic optimum increased anthropogenic activities since 5 ka may have increased soil upland erosion and floodplain aggradation stable isotopes demonstrate that the landscape has been dominated by c3 vegetation since the last glacial maximum

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

a 9000 year record of vertical and lateral accretion on the floodplain of the lower thames river southwestern ontario canada and implications for archaeological research abstract results of ground penetrating radar and grain size analysis of sediments from three 5 7 m long cores generally support a classic fining up point bar model of floodplain development on a reach of the lower thames river a single thread meandering channel that flows southwest into lake st clair bankfull discharge 411 m3 s 1 four radiocarbon dates on organic material recovered from cores indicate that floodplain development in this reach occurred over at least the past 9000 years these results are not typical for southern ontario channels previous studies have shown that some other large rivers in southern ontario have low energy cohesive bank channels with floodplains strongly dominated by vertical accretion the distribution of culturally diagnostic archaeological artifacts on the floodplain surface dating back to the middle archaic period but mostly confined to the early woodland period or later suggests that human settlement of the floodplain was restricted to the later holocene the observation that a middle archaic site component is located in what should be a younger part of the floodplain challenges the notion that a simple lateral channel migration occurred with orderly channelward emplacement of sediment by the river there is a possibility that the channel was anabranching in this reach of the river

high resolution record of tectonic and sedimentary processes in growth strata growth strata are used to determine the kinematics of synsedimentary structures such as faults classical methods of analysis such as thickness versus throw plot consider that the available space created by fault slip in the hanging wall of faults is instantaneously filled up by sediments this has lead many previous works to identify a cyclic activity for growth faults here we perform a careful analysis of the variation of strata thicknesses on each side of a very well documented normal growth fault in the niger delta we show that these thickness variations are induced by the alternation of sedimentary processes during continuous fault slip suspended load processes induce either uniform or slightly variable thickness of a large majority of mudstone layers bedload processes result in a preferential thickening of sand layers in the hanging wall these high quality data thus provide strong grounds for doubting the polycyclic growth diagnosed for some faults at the scale of sedimentary cycles and supports the notion that fault displacement rates can be very well behaved our study emphasizes the important conclusion that stable fault growth and related displacement rates can appear to be punctuated when viewed at the scale of sedimentary cycles it follows that care should be taken when attempting to derive displacement rates on temporal scales equivalent to those of alternating sedimentological cycles

the last phylum occupation of bryozoa morpho ecospace colony growth habits during the early phase of the great ordovician biodiversification event abstract most major phyla and all skeletonized phyla have their first appearance in the cambrian the exception is the phylum bryozoa which first appear in the early ordovician tremadocian 1b bryozoans have an excellent fossil record due in part to their benthic marine habitat with skeletal colonies composed largely of stable low magnesium calcite these factors provide an unrivaled opportunity to observe patterns and rates of radiation of a new phylum into disparate morpho ecospace through the great ordovician biodiversification event gobe in this study the colonial growth habits of all known skeletonized bryozoa 181 species from the early and middle ordovician are characterized in a new classification scheme based on processes of growth rather than their end geometry as most traditional classifications of bryozoan growth habits these fundamental categories are orientation dimensions of primary growth width of colony unit layers of zooecia substrate relationships space utilization skeleton mineralization plus sub categories of orientation based on their geometry in the early and middle ordovician there are 85 unique growth habits defined by these eight growth habit characters by the end of middle ordovician about 4 8 of the morpho ecospace defined by two subsets of the characters had been occupied by five bryozoan orders represented by 34 families 77 genera when plotted by ordovician stage time slices ca 2 2 my each a sharp increase in taxonomic and growth habit occurrence is observed at the early middle ordovician transition earlier than in other groups individual growth habit character states also show significant changes at this transition in the early ordovician low bryozoan taxonomic and growth habit richness is due in part to sampling bias and modified search methods are need however the overall patterns early mid ordovician transition observed in this study are robust and not expected to change fundamentally with additional data

the cambrian substrate revolution and the early evolution of attachment in suspension feeding echinoderms abstract the cambrian characterized by the global appearance of diverse biomineralized metazoans in the fossil record for the first time represents a pivotal point in the history of life this period also documents a major change in the nature of the sea floor neoproterozoic type substrates stabilized by microbial mats were replaced by unconsolidated soft substrates with a well developed mixed layer the effect of this transition on the ecology and evolution of benthic metazoans is termed the cambrian substrate revolution csr and this is thought to have impacted greatly on early suspension feeding echinoderms in particular according to this paradigm most echinoderms rested directly on non bioturbated soft substrates as sediment attachers and stickers during the cambrian epoch 2 as the substrates became increasingly disturbed by burrowing forming a progressively thickening mixed layer echinoderms developed new strategies for attaching to firm and hard substrates to test this model we evaluated the mode of attachment of 83 cambrian suspension feeding echinoderm species attachment mode was inferred based on direct evidence in fossil specimens and interpretations of functional morphology these data were analyzed quantitatively to explore trends in attachment throughout the cambrian in contrast to previous studies the majority of cambrian clades eocrinoids helicoplacoids helicocystoids isorophid edrioasteroids and solutes are now interpreted as hard shelly substrate attachers only early edrioasteroids attached directly to firm substrates stabilized by microbially induced sedimentary structures contrary to the predictions of the csr paradigm our study demonstrates that cambrian echinoderms were morphologically pre adapted to the substrate changes that occurred during the cambrian allowing them to fully exploit the appearance of hardgrounds in the furongian we find no support for the claim that the csr explains the peak in echinoderm diversity during cambrian epochs 2 3 or that it caused the extinction of helicoplacoids

a review of the late cambrian furongian palaeogeography in the western mediterranean region nw gondwana abstract the cambrian ordovician transition of the western mediterranean region nw gondwana is characterized by the record of major erosive unconformities with gaps that range from a chronostratigraphic stage to a series the hiatii are diachronous and involved progressively younger strata along the gondwanan margin from sw morocco to ne montagne noire they can be related to development of a multi stage rifting further north currently connected to the opening of the rheic ocean and concomitant erosion on southern rift shoulders the platforms of this margin of gondwana occupied temperate water mid latitudes and were dominated by siliciclastic sedimentation while carbonate factories were only episodically active in the montagne noire platform the upper cambrian is devoid of significant gaps in the southern montagne noire and the iberian chains there the sedimentation took place in a transgressive dominated depositional system with common offshore deposits and clayey substrates and was bracketed by two major regressive trends the late cambrian is also associated with the record of volcanic activity e g in the cantabrian and ossa morena zones and the northern montagne noire and widespread development of a tectonic instability that led to the episodic establishment of palaeotopographies and record of slope related facies associations several immigration events are recognized throughout the latest middle cambrian late cambrian and tremadocian the trilobites show a stepwise replacement of acado baltic type families e g the conocoryphid paradoxidid solenopleurid assemblage characterized by i a late languedocian latest middle cambrian co occurrence of middle cambrian trilobite families with the first anomocarid dorypygid and proasaphiscid invaders ii a late cambrian immigration replacing previous faunas composed of trilobites aphelaspidids catillicephalids ceratopygids damesellids eulomids idahoiids linchakephalids lisariids onchonotinids and pagodiids linguliformean brachiopods acrotretids obolids scaphelasmatids siphonotretids and zhanatellids echinoderms mitrates glyptocystitid cystoids and stromatocystoids and conodonts belonging to the lower peltura zone and iii the subsequent input of new trilobites asaphids calymenids catillicephalids nileids and remopleurids which marks the base of the proteuloma geinitzi zone associated with pelmatozoan holdfasts oryctoconus and a distinct input of late tremadocian conodonts paltodus deltifer zone the biogeographic distribution of latest middle and late cambrian trilobites supports brachiopod data indicating strong affinities between the western mediterranean region east gondwana north china korea south china australia and antarctica and kazakhstania during the late languedocian which became significantly stronger during the late cambrian this major shift may suggest modification in oceanic circulation patterns throughout gondwana across the middle late cambrian transition

geoarchaeology of the falls of the ohio river quaternary landforms at the falls at the narrowest point in the lower part of its valley the ohio channel falls through a length of rapids between louisville ky and new albany in known as the falls of the ohio below and above the falls area a ridge and swale topography characterizes the late pleistocene to late holocene alluvial landforms recording the shifting pattern of the channel and dictating the location of age based cultural materials this geoarchaeological study looks at four distinct landforms at the falls of the ohio on both the northern and southern banks in order to ascertain the development of holocene alluvial landforms in this area investigations undertaken recently within the falls of the ohio region at the newcomb 12cl2 m kraft 12cl935 and shippingport 15jf702 sites as well as information gained from prior excavations at the old clarkesville site 12cl1 have provided the necessary insight into the development of the individual bars that these four sites where found lying upon texture elevation and temporal comparisons of these four alluvial bars have allowed for a generalized sequence of bar development to be formulated at the falls forming as a mid channel bar the old clarkesville is the oldest landform dating to the early holocene this was followed by the middle holocene m kraft bar forming a side channel bar to the north and the similarly aged shippingport bar on the southern bank of the channel the newcomb bar formed last in the late holocene filling in the swale or channel between the old clarksville and m kraft bars and allowing the formation of a single floodplain surface this study shows a general conformity to other geoarchaeological models and patterns in the region and as such it appears that the falls of the ohio has had little effect on the overall natural and cultural deposition in the region the exploration of these landscapes helps to expand on the regional synthesis of the understanding of the prehistoric cultural period deposits they hold

structural styles and depositional architecture in the triassic of the ninian and alwyn north fields implications for basin development and prospectivity in the northern north sea abstract interpretation of well calibrated three dimensional seismic volumes sedimentological analysis and electrical well log correlations from the ninian and alwyn north fields challenge the long held view that mid late jurassic extensional faults in the east shetland basin represent a simple reactivation of older triassic fault systems restoration for the effects of the younger predominantly eastward dipping mid late jurassic structures clearly demonstrates that triassic precursors had a steep westerly dip in contrast to the eastern flank of the viking graben e g troll and oseberg areas where the west dipping triassic structures are reutilised in the mid late jurassic those of the east shetland basin have largely been dissected and rotated during the later event those west dipping faults that did see later movement appear to have simply acted as minor antithetic structures to the throughgoing east dipping ones the triassic normal fault patterns actively controlled sediment thicknesses and facies distribution within the lunde and teist formations in the basin use of seismic stratigraphic surfaces calibrated by biostratigraphy and chemostratigraphic markers provides strong evidence that the triassic depocentres are spatially offset from their mid late jurassic counterparts the combination of structural stratigraphic and sedimentary effects reveal the existence of an emergent deeper triassic play opportunity in footwall locations to the mid late jurassic normal faults which has the potential to extend the life of what is otherwise mature acreage

first order seismic attributes for clastic seismic facies interpretation examples from the east china sea abstract seismic attributes for the interpreting explorationist are numerous some are useful some duplicative and some less useful however with respect to optimizing a systematic basin analysis approach which relies upon heavily upon integrating seismic facies there are eight particularly useful attributes which have clear geophysical meaning strong underlying geological rock fluid implications and which for clastic depositional environments greatly assist in determining seismic facies associated paleoenvironments and lessening the number of interpretive possibilities they are amplitude envelope chaos cosine of phase dip deviation instantaneous frequency q relative acoustic impedance and variance a systematic application of these first order attributes for the east china sea in particular and for other clastic environments in general allows a first pass assessment of a basin s exploration potential through seismic reconnaissance an interpretive reconnaissance whose accuracy is limited only by the seismic fidelity of the lines and logic of the assumed geology employed

growth of normal faults in multilayer sequences a 3d seismic case study from the egersund basin norwegian north sea abstract we investigate the structural style and evolution of a salt influenced extensional fault array in the egersund basin norwegian north sea through analysis of 3d reflection seismic and well data analysis of fault geometry morphology throw distribution and syn kinematic strata reveal an intricate but systematic style of displacement and growth suggesting an evolution of 1 initial syn sedimentary fault growth contemporaneous with salt mobilization initiated during the late triassic 2 cessation of fault activity and burial of the stagnant fault tips and 3 subsequent nucleation of new faults in the cover above contemporaneous salt re mobilization initiated during the late cretaceous with downward propagation and linkage with faults stage 3 was apparently largely controlled by salt mobilization in response to basin inversion as reactivated faults are located where the underlying salt is thick while the non reactivated faults are found where salt is depleted based on the 3d throw analyses we conclude that a combination of basement faulting and salt re mobilization is the driving mechanisms behind fault activation and reactivation even though the sub and supra salt faults are mainly geometrically decoupled through the salt a kinematic coupling must have existed as sub salt faults still affected nucleation and localization of the cover faults

fault growth and interactions in a multiphase rift fault network horda platform norwegian north sea abstract physical models predict that multiphase rifts that experience a change in extension direction between stretching phases will typically develop non colinear normal fault sets furthermore multiphase rifts will display a greater frequency and range of styles of fault interactions than single phase rifts although these physical models have yielded useful information on the evolution of fault networks in map view the true 3d geometry of the faults and associated interactions are poorly understood here we use an integrated 3d seismic reflection and borehole dataset to examine a range of fault interactions that occur in a natural multiphase fault network in the northern horda platform northern north sea in particular we aim to i determine the range of styles of fault interaction that occur between non colinear faults ii examine the typical geometries and throw patterns associated with each of these different styles and iii highlight the differences between single phase and multiphase rift fault networks our study focuses on a ca 350 km 2 region around the 60 km long n s striking tusse fault a normal fault system that was active in the permian triassic and again in the late jurassic to early cretaceous the tusse fault is one of a series of large 1500 m throw n s striking faults forming part of the northern horda platform fault network which includes numerous smaller 2 10 km long lower throw nd stage nw se striking faults grew interacted and linked with the n s striking tusse fault documenting a range of interaction styles including mechanical and kinematic isolation abutment retardation and reactivated relays our results demonstrate that i isolated and abutting interactions are the most common fault interaction styles in the northern horda platform ii pre existing faults can act as sites of nucleation for 2 nd stage faults or may form mechanical barriers to propagation iii the throw distribution on reactivated 1 st stage faults will be modified in a predictable manner if they are intersected or influenced by 2 nd stage faults iv sites of fault linkage and relay breaching associated with the first phase of extension can act as preferential nucleation sites for 2 nd stage faults and v the development of fault intersections is a dynamic process involving the gradual transition from one style to another

extensional fault systems in sedimentary basins a review of analogue model studies abstract scaled analogue models have provided graphic new insights into the progressive development of extensional fault systems this paper reviews recent results of an on going analogue modelling programme and compares the structural styles in the models with examples of natural extensional fault systems four fundamental model styles scaled to simulate deformation in brittle sedimentary rocks in the upper 10 km of the crust are reviewed extension above a basal detachment which undergoes stretching over a limited are produces an asymmetric rift graben bounded by planar faults and in which the internal deformation is accommodated by rotational domino faults these experimental results are directly comparable to structures found in intracontinental rifts extension above a basal detechment which undergoes extension under the whole model and which has no constraints at the ends produces domino style fault arrays in the pre rift sequence and listric growth faults in the syn rift sequence these results compare with highly extended rift basins and terranes such as the basin and range province usa extension above a simple listric fault produces a characteristic hangingwall roll over and crestal collapse graben system at high values of extension superposed crestal collapse grabens occur and a fan of listric growth faults is developed these structures bear striking similarities to growth faults in progradational delta systems ramp flat listric extensional fault systems using sand mica models produce a characteristic family of structures with an upper roll over crestal collapse system a ramp syncline and reverse fault fold zone and a lower roll over crestal collapse system an example of a ramp flat fault system from the gulf coast usa is presented as a comparison with the analogue model results preliminary results of three dimensional extensional model experiments are presented to illustrate the complexities in such fault systems in all of the experimental models it is found that the geometry of the underlying detachment system exerts fundamental control on structures produced in the hangingwall the analogue models illustrated in this review provide valid geometric and kinematic templates for the progressive evolution of extensional fault systems in sedimentary basins

phanerozoic trends in skeletal mineralogy driven by mass extinctions changes in ocean chemistry that favoured the precipitation of aragonite or calcite are thought to have influenced the skeletal mineralogy of marine calcifyers an investigation of the original skeletal mineralogy of large numbers of marine taxa suggests that the selective recovery of marine organisms from mass extinctions has a much greater influence on the overall percentage of aragonitic organisms than the mg ca ratio of the oceans marine calcifying organisms that produce sediments and build reefs generally have skeletons and shells that are composed of either aragonite or calcite long term changes in the estimated mg ca ratios of sea water tend to correspond to changes in the prevailing mineralogy of these creatures1 2 high mg ca ratios are expected to favour the spread of aragonitic organisms whereas calcitic taxa are thought to benefit from low mg ca ratios3 4 5 6 here we test these patterns throughout the phanerozoic eon and assess the relative impacts of changing ocean chemistry and mass extinctions on the evolutionary success of calcifying organisms we find that mass extinctions are more important in regulating long term patterns of skeletal mineralogy than the mg ca ratios of the global oceans furthermore selective recovery from mass extinctions is usually more important than selective extinction in driving the phanerozoic pattern of skeletal mineralogy but even in the recovery phase there is no clear connection between changes in the dominance of aragonite or calcite and the mg ca ratio of the oceans thus providing further evidence for the complexity of biotic recoveries7

early cambrian eocrinoids from guizhou province south china abstract numerous specimens of guizhoueocrinus yui n gen et sp occur in the middle upper parts of the lower cambrian balang formation eastern guizhou and are the earliest well preserved gogiids mature specimens are larger than most comparable gogiids thecal plates are very numerous and sutural pores are smaller stalk is polyplated conical and long brachioles up to 10 are spirally coiled the species comprises a significant component of the balang fauna it is distinctly different than sinoeocrinus lui and sinoeocrinus globus from the middle cambrian kaili biota in the adjacent region in guizhou this new gogiid expands the geographic range of lower cambrian eocrinoids and provides significant new data on gogiid evolution

3d seismic analysis of the structure and evolution of a salt influenced normal fault zone a test of competing fault growth models abstract in this paper we determine the structure and evolution of a normal fault system by applying qualitative and quantitative fault analysis techniques to a 3d seismic reflection dataset from the suez rift egypt our analysis indicates that the october fault zone is composed of two fault systems that are locally decoupled across a salt bearing interval of late miocene messinian age the sub salt system offsets pre rift crystalline basement and was active during the late oligocene early middle miocene it is composed of four planar nw se striking segments that are hard linked by n s striking segments and up to 2 km of displacement occurs at top basement suggesting that this fault system nucleated at or more likely below this structural level the supra salt system was active during the pliocene holocene and is composed of four nw se striking listric fault segments which are soft linked by unbreached relay zones segments in the supra salt fault system nucleated within pliocene strata and have maximum throws of up to 482 m locally the segments of the supra salt fault system breach the messinian salt to hard link downwards with the underlying sub salt fault system thus forming the upper part of a fault zone composed of i a single amalgamated fault system below the salt and ii a fault system composed of multiple soft linked segments above the salt analysis of throw distance t x and throw depth t z plots for the supra salt fault system isopach maps of the associated growth strata and backstripping of intervening relay zones indicates that these faults rapidly established their lengths during the early stages of their slip history the fault tips were then effectively pinned and the faults accumulated displacement via predominantly downward propagation we interpret that the october fault zone had the following evolutionary trend i growth of the sub salt fault system during the oligocene to early middle miocene ii cessation of activity on the sub salt fault system during the middle miocene to early pliocene iii stretching of the sub and supra salt intervals during pliocene regional extension which resulted in mild reactivation of the sub salt fault system and nucleation of the segmented supra salt fault system which at this time was geometrically decoupled from the sub salt fault system and iv pliocene to holocene growth of the supra salt fault system by downwards vertical tip line propagation which resulted in downward breaching of the salt and dip linkage with the sub salt fault system the structure of the october fault zone and the rapid establishment of supra salt fault lengths are compatible with the predictions of the coherent fault model although we note that individual segments in the supra salt array grew in accordance with the isolated fault model our study thereby indicates that both coherent and isolated fault models may be applicable to the growth of kilometre scale basin bounding faults furthermore we highlight the role that fault reactivation and dip linkage in mechanically layered sequences can play in controlling the three dimensional geometry of normal faults

evolution of the oseberg fault block in context of the northern north sea structural framework abstract the central segment 60 20 61 n of the northern north sea 170 km in width demonstrates contrasting basin geometries related to permo triassic and jurassic rift episodes in the oseberg area representing a part of this segment major faults of two generations dip in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin ca 20 km in width is underlain by a wider ca 35 km w tilted permo triassic half graben the early jurassic thickness distribution was governed by a westerly palaeotilt mild extensional tectonics influenced early jurassic rhaetian aalenian deposition whereas the middle late jurassic main rift episode is expressed by an accelerated fault related subsidence from the late bajocian during the middle late jurassic the oseberg area evolved through a series of high frequency rift phases characterized by rotational tilt events separated by periods during which extension was less severe this allows the subdivision of the jurassic stretching episode into distinct rift phases 4 6 myrs which involved smaller scale units corresponding to rotational tilt events 1 2 myrs the large scale pattern of middle late jurassic syn rift infill is overall one of upwards fining reflecting a deepening trend as the rift evolved syn rotational sediment architecture related to a single rift phase shows systematic variations from a threefold shallow marine sandstone mudstone sandstone motif tarbert fm through a twofold shallow marine sandstone mudstone motif heather fm to a twofold deep marine conglomerate sandstone mudstone motif draupne fm the vertical stacking of these syn rotational packages reflects an inability of sediment supply to keep pace with the rift related subsidence and the temporal evolution from a sediment balanced through a sediment underfilled to a sediment starved rift basin

structural analysis of the smeaheia fault block a potential co2 storage site northern horda platform north sea abstract smeaheia a prominent fault block located on the horda platform northern north sea is identified as a potential subsurface co2 storage site we utilise the gn1101 3d seismic survey to generate a high resolution subsurface geomodel to inform the structural style and evolution of the fault block to investigate geological controls on proposed co2 storage and provide a geometric framework as a basis for future analyses two basement involved first order north south trending fault systems the vette fault zone vfz and the oygarden fault complex ofc bound the 15 km wide fault block the vfz bifurcates down section where it is hard linked with two separate basement structures a phenomenon we term as dual rooted apart from activity during the permo triassic rift phase 1 and the late jurassic early cretaceous rift phase 2 we present evidence that rifting in this part of the north sea continued into the late cretaceous with minor reactivation in the palaeocene eocene two segments of the vfz interacted and linked at a relay ramp during rift phase 2 second order thin skinned faults show basement affinity and developed during rift phase 2 in two distinct pulses a population of polygonal faults intersects the overburden and developed during the eocene to middle miocene we have revised the areal extent of two structural closures that define the smeaheia fault block alpha vfz footwall and beta ofc hanging wall which consist of upper jurassic viking group target formations simplified cross fault juxtaposition analysis of the vfz and second order intra block faults are presented and inform pressure communication pathways between the smeaheia and tusse fault block as well as reservoir integrity and compartmentalisation the geomodel further identifies important geological controls on co2 storage in the fault block including a thinning caprock above the alpha structure and identification of hard linkage between deep tectonic faults and shallow polygonal faults