early hydrothermal carbon uptake by the upper oceanic crust insight from in situ u pb dating it is widely thought that continental chemical weathering provides the key feedback that prevents large fluctuations in atmospheric co2 and hence surface temperature on geological time scales however low temperature alteration of the upper oceanic crust in off axis hydrothermal systems provides an alternative feedback mechanism testing the latter hypothesis requires understanding the timing of carbonate mineral formation within the oceanic crust here we report the first radiometric age determinations for calcite formed in the upper oceanic crust in eight locations globally via in situ u pb laser ablation inductively coupled plasma mass spectrometry analysis carbonate formation occurs soon after crustal accretion indicating that changes in global environmental conditions will be recorded in changing alteration characteristics of the upper oceanic crust this adds support to the interpretation that large differences between the hydrothermal carbonate content of late mesozoic and late cenozoic oceanic crust record changes in global environmental conditions in turn this supports a model in which alteration of the upper oceanic crust in off axis hydrothermal systems plays an important role in controlling ocean chemistry and the long term carbon cycle

u th dating of striated fault planes direct dating of brittle fault activity is of fundamental importance to tectonic reconstructions and paleoseismic studies one way to address this issue is by constraining the timing of fault striations but this requires a better understanding of the striation formation mechanism and associated mineralization we present results from a microstructural geochemical and geochronological study of calcite precipitates associated with striated fault planes from the dead sea fault zone in northern israel we recognize four types of coexisting calcite precipitates including calcite cement in dilation breccia calcite in striated groove morphology calcite gouge associated with hydraulic fracturing and pressure solution and calcite coating of the fault surface carbon oxygen isotopes 87sr 86sr ratios and rare earth element and yttrium rey patterns indicate various precipitation mechanisms associated with formation of syntectonic calcite cement and striations coseismic calcite gouge and interseismic calcite coating precipitates in the fault zone using u th dating of samples from three adjacent fault planes we delineate four welldefined deformation ages in the period from 220 to 60 ka we conclude that these ages constrain the timing of activity along the dead sea fault zone in northern israel and argue that a similar methodological approach could potentially shed light on the timing of deformation in other brittle fault zones

the faroe shetland basin a regional perspective from the paleocene to the present day and its relationship to the opening of the north atlantic ocean the faroe shetland basin is located offshore nw scotland on the se margin of the atlantic ocean and comprises numerous sub basins and intra basin highs that are host to a number of significant hydrocarbon discoveries the principal hydrocarbon discoveries are in palaeocene eocene strata though earlier ones are known and therefore their existence is intimately linked to the opening and evolution of the north atlantic from 54 ma the final rifting and separation of greenland from eurasia is commonly attributed to the arrival of a mantle plume which impacted beneath greenland in the early tertiary moreover the ensuing plate separation is commonly described in terms of instantaneous unzipping of the north atlantic whereas in reality proto plate boundaries were more diffuse during their inception and the linked rift system including connections with the arctic which we see today was not established until late palaeogene early neogene time from a regional analysis of ocean basin development including the stratigraphic record on the adjacent continental margins the significance of the greenland iceland faroe ridge and the age and role of iceland we propose a dual rift model whereby north atlantic breakup was only partial until the oligo miocene with true final breakup only being achieved when the reykjanes and kolbeinsey ridges became linked as final breakup coincides with the appearance of iceland this model negates the need for a plume to develop the north atlantic with rifting reliant on purely plate tectonic mechanisms lithospheric thinning and variable decompressive upper mantle melt along the rifts

wave mud interactions over the muddy atchafalaya subaqueous clinoform louisiana united states wave supported sediment transport 1 near bottom fluid mud layers were observed during two experiments conducted on the muddy atchafalaya inner shelf subaqueous clinoform louisiana united states on the face of the subaqueous delta 4 7 m water depth first experiment fluid mud layers are produced by seafloor liquefaction and resuspension forced by swells associated with cold front passages and supported by near bed wave induced turbulence the layers are episodic lifetime of 9 12 h form prior to significant postfrontal settling of sediment in the overlying water column and flow seaward downslope at about 5 cm s farther westward on the delta front finer grain size with negligible sand or coarse silt content second experiment similar wave supported fluid mud layers are observed to last longer 2 days show weaker alongshore westward flow of about 1 3 cm s the results suggest a sequence of near bed sediment transport processes triggered by frontal swell activity bed liquefaction resuspension and advection modulated by the bathymetric characteristics of the clinoform that contribute to the formation of clinoform stratigraphy of muddy subaqueous deltas

u pb geochronology of calcite mineralized faults absolute timing of rift related fault events on the northeast atlantic margin constraining the timing of brittle faulting is critical in understanding crustal deformation and fluid flow but many regional scale fault systems lack readily available techniques to provide absolute chronological information calcite mineralization occurs in crustal faults in many geological settings and can be suitable for u pb geochronology this application has remained underutilized because traditional bulk dissolution techniques require uncommonly high u concentration because u and pb are distributed heterogeneously throughout calcite crystals high spatial resolution sampling techniques can target domains with high u and variable u pb ratios here we present a novel application of in situ laser ablation inductively coupled plasma mass spectrometry la icp ms to basaltic fault rock geochronology in the faroe islands northeast atlantic margin faults that are kinematically linked to deformation associated with continental break up were targeted acquired ages for fault events range from mid eocene to mid miocene and are therefore consistently younger than the regional early eocene onset of ocean spreading highlighting protracted brittle deformation within the newly developed continental margin calcite geochronology from la icp ms u pb analysis represents an important and novel method to constrain the absolute timing of fault and fluid flow events

vein calcite dating reveals pyrenean orogen as cause of paleogene deformation in southern england an improved method of u pb dating of vein calcite formed during deformation is used to determine the age and cause of folding along the south coast of england fractures arising from folding of late cretaceous chalk of southern england occurred 34 7 1 7 myr ago underlying jurassic strata have veins within fractures with ages of 55 48 42 39 37 34 31 and 25 ma with 34 31 ma being the tectonic culmination folding was slightly younger than the age of the youngest strata in the overlying solent group suggesting that folding terminated basin sedimentation this age of north south shortening is inconsistent with attribution to intraplate forces from the mainly younger alps but is plausibly a result of the pyrenean orogen which evolved from 50 to 28 myr ago with a late eocene culmination a modified method for carbonate laser ablation inductively coupled plasma mass spectrometry u pb dating is presented that uses measured 232 th and 208 pb as a better monitor of common pb and it has distinct advantages over existing methods initial common lead determined on samples conforms closely to model compositions calculated by earlier workers with free regressions giving the most robust dates the modified method is applicable to structural geology carbonate diagenesis and to dating of carbonate relevant to palaeo environmental and archaeological studies supplementary material details of sample locations and characteristics photographs of sample localities microscopic images of veins details of the experimental procedure and u pb data for all samples and reference materials are available at https doi org 10 6084 m9 figshare c 3997086

lenticular shale fabrics resulting from intermittent erosion of water rich muds interpreting the rock record in the light of recent flume experiments lenticular lamination is a fabric that is known from shales of all ages but its origin and paleoenvironmental significance is poorly understood we have successfully reproduced this fabric in flume experiments beds of water rich mud were eroded in a flume and yielded sub millimeter to centimeter size fragments that can be transported in bedload for distances of ten kilometers or more upon redeposition and compaction these deposits have the same textural qualities as lenticular laminated shales from the rock record although accumulation of fecal pellets or abundant burrow tubes in a shale may produce comparable fabrics upon compaction these can be distinguished from erosion produced lenticular lamination via petrographic criteria lenticular lamination in shales that is due to deposition of water rich mud fragments most likely records intermittent erosion and transport of surficial muds by currents

the late holocene gargano subaqueous delta adriatic shelf sediment pathways and supply fluctuations the gargano subaqueous delta formed on the eastern and southeastern sides of the gargano promontory in the western adriatic this subaqueous deposit represents the southernmost portion of the late holocene highstand systems tract hst growing along the western side of the adriatic as an extensive wedge of deltaic and shallow marine mud the late holocene hst rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5 5 cal kyr bp at the end of the late pleistocene holocene sea level rise high resolution seismic stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5 5 and 3 7 cal kyr bp over much of the basin above this unit sediment accumulation rates increased to high values as much as 1 5 cm yr 1 reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics the late holocene mud wedge of which the gargano subaqueous delta is a significant component reaches up to 35 m in thickness and has a volume of ca 180 km3 the shore parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources with a combined modern delivery of 51 7 106 t yr 1 of mean suspended load in sections perpendicular to the coast the late holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets typically 0 5 the gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25 28 m and accounts for about 1 7th of the total volume of the late holocene mud wedge despite the absence of direct river supply to the gargano area in the area of maximum interaction between shore parallel currents and basin morphology progradation occurs onto a flat and barren bedrock outcrop in about 50 80 m water depth the rapid transition from a thickness of 30 m of late holocene mud to nil is a good indication of the role of southward flowing bottom hugging shelf currents in causing the redistribution of sediment along the adriatic inner shelf additional evidence of this regime comes from 1 the most recent sigmoid defined at seismic stratigraphic scale deposited since the onset of the little ice age showing a shore parallel thickness distribution and a main depocentre to the southeast of the gargano promontory 2 the maximum values of sediment accumulation rates over the last century documented by 210pb measurements defining a narrow shore parallel belt immediately seaward of the depocentre of the most recent sigmoid the gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones the gargano subaqueous delta differs from other documented late holocene subaqueous deltas because its growth reflects 1 sediment transport dominated by bottom currents sub parallel to the strike of the composing clinoforms 2 a complex supply regime including the po delta 350 km to the north and several coalescing apennine rivers acting as line source 3 several alternating intervals of enhanced outbuilding and condensed deposition and 4 an in phase growth of the most recent sigmoid with the major progradation of the po delta during the little ice age

la icp ms u pb geochronology and clumped isotope constraints on the formation and evolution of an ancient dolomite reservoir the middle permian of northwest sichuan basin sw china abstract recent advances in laser ablation inductively coupled plasma mass spectrometry la icp ms in situ u pb radiometric dating and clumped isotope thermometry 47 of carbonate minerals provide potential for refining the fluid flow and diagenetic history of carbonate successions in this study the middle permian dolomites proximal to the longmenshan fold and thrust belt in northwest sichuan basin southwest china were investigated using combined u pb geochronology clumped isotope thermometry and routine isotopic 13c 18o and 87sr 86sr and elemental geochemistry in an attempt to reveal the possible relevance of carbonate diagenesis and porosity evolution to the basin scale tectonic fluid flow events in the framework of absolute time overall formation and evolution of these dolomites temporally correlated well with major tectonic episodes of the longmenshan fold and thrust belt contrary to the previously assumed volcanic related model u pb dating and 47 analyses suggest a mid to late triassic replacive dolomitization event u pb ages of 240 12 ma to 233 8 6 4 ma by a hot 47 temperatures 88 104 c basinal brine which was likely driven by thrust related compression of the longmenshan fold and thrust belt during the triassic replacive dolomitization was immediately followed by cementation of euhedral dolomites u pb age of 228 10 ma and blocky calcites u pb ages of 224 8 1 8 ma to 213 4 3 3 ma precipitated from the basinal brine in the same tectonic regime afterwards there was long term cessation of diagenesis that was coincident with and thus may well be attributed to tectono thermal quiescence during most of the mesozoic era and paleogene finally saddle dolomite cements yield miocene ages u pb ages of 16 40 0 74 ma to 12 3 1 2 ma and precipitated in pre existing vugs representing a hydrothermal fluid flow event 47 temperatures up to 170 c during the reactivation of thrusting in addition similarities in u pb ages and geochemical signatures between host rocks replacive dolomites and the vug lining dolomite cements suggest that most porosity in these dolomite reservoirs was inherited from the precursor limestones which probably experienced meteoric leaching during late permian uplift this study highlights that there are geodynamic controls on fluid flow and consequent diagenetic evolution of carbonates in tectonically active sedimentary basins it illustrates that burial alone in this setting is not a sufficient driver for diagenetic alteration and porosity reduction the combination of u pb radiometric dating clumped isotope thermometry and routine geochemical analyses is a useful approach in refining the diagenetic and porosity evolution history of ancient carbonate successions

palaeoenvironments palaeogeography and physiography of a large shallow muddy ramp late cenomanian turonian kaskapau formation western canada foreland basin the kaskapau formation spans late cenomanian to middle turonian time and was deposited on a low gradient shallow storm dominated muddy ramp dense well log control coupled with exposure on both proximal and distal margins of the basin allows mapping of sedimentary facies over about 35 000 km2 the studied portion of the kaskapau formation is a mudstone dominated wedge that thins from 700 m in the proximal foredeep to 50 m near the forebulge about 300 km distant regional flooding surfaces permit mapping of 28 allomembers each of which represent an average of ca 125 kyr more than 200 km from shore calcareous silty claystone predominates whereas 100 to 200 km offshore mudstone and siltstone predominate from about 30 to 100 km offshore centimetre bedded very fine sandstone and mudstone record along shelf sse directed storm generated geostrophic flows five to thirty kilometres from shore decimetre bedded hummocky cross stratified fine sandstone and mudstone record strongly oscillatory wave dominated flows whereas some gutter casts indicate shore oblique apparently mostly unidirectional geostrophic flows nearshore facies are dominated by swaley cross stratified or intensely bioturbated clean fine sandstone interpreted as recording respectively areas strongly and weakly affected by discharge from distributary mouths shoreface sandstones grade locally into river mouth conglomerates and sandstones including conglomerate channel fills up to 15 m thick locally brackish lagoonal shelly mudstones are present on the extreme western margin of the basin there is no evidence for clinoform stratification which indicates that the kaskapau sea floor had extremely low relief lacked a shelf slope break and was probably nowhere more than a few tens of metres deep the absence of clinoforms probably indicates a long term balance between rates of accommodation and sediment supply mud is interpreted to have been transported 250 km offshore in a sea bed nepheloid layer repeatedly re suspended by storms fine grained sediment accumulated up to a mud accommodation envelope perhaps only 20 to 40 m deep continuous re working of the sea floor by storms ensured that excess sediment was redistributed away from areas that had filled to the accommodation envelope being deposited in areas of higher accommodation further down the transport path the facies distributions and stratal geometry of the kaskapau shelf strongly suggest that sedimentary facies especially grain size were related to distance from shore not to water depth as a result the 100 to 300 m depth interpreted from calcareous claystone facies for the more central parts of the interior seaway might be a significant overestimate

mud deposition and diagenesis within an early palaeozoic clinothem power steps formation newfoundland canada the early ordovician 385 ma power steps formation newfoundland canada exposes a well preserved mudstone dominated clinothem that serves as an excellent archive for understanding how mud has been produced transported and converted into mudstone prior to the evolution of globally widespread deep soil horizons sedimentological analysis of four sandstone and five mudstone facies along the ochre cove clinothem reveal that mud and sand were delivered by unidirectional currents and experienced episodic reworking by storm waves petrographic examination and x ray diffraction from described mudstone facies reveal significant variability in the distribution of illite versus chlorite between the lower and upper part of the ochre cove clinothem this research highlights that in the present day clay mineral fraction illite is often detrital whereas chlorite originated via the alteration of silt sized highly unstable mafic volcanoclastic grains throughout all sedimentologic facies albeit in different proportions these mafic lithic grains were diagenetically altered via in situ weathering before significant compaction occurred resulting in the precipitation of significant volumes of pore bridging silica and iron rich chlorite cement compositional diagenetic and textural attributes across the ochre cove mud clinothem vary as a function of starting composition hydrodynamic sorting and grain density given that a significant proportion of clay minerals has been generated via in situ transformation of a mafic non stable precursor assemblage we recommend future studies to incorporate detailed petrographic description along with x ray diffraction analyses when aiming to employ trends in whole rock clay mineral data as a proxy in provenance and palaeoclimate studies of very old pre devonian mudstones and sandstones

genesis and diagnostic value of soft sediment deformation structures a review abstract soft sediment deformation structures are recognized as important diagnostic features in the rock record for determination of depositional environments and slope processes the diagnostic value of these structures is reevaluated by analysis of the parameters controlling sediment deformation soft sediment deformation is contemporaneous with deposition and occurs dominantly in course silt to fine sand the high depositional rate low permeability and low shear strength of grains within this sediment range maximize the occurrence of deformation the dominant mechanisms responsible for sediment deformation include 1 liquefaction or fluidization 2 reverse density gradation 3 slumping or slope failure and 4 shear stress in most cases a combination of these mechanisms occurs the processes function in a continuum producing features that are microscopic to megascopic in scale it is shown that the processes and thus the structures are not environment specific the true diagnostic value of the structures may be in defining hydrodynamic conditions and in interpreting paleocurrents and paleoclimatic and paleoseismic events ultimately for the best diagnostic results soft sediment deformation structures should be studied in association with all other available lithologic structural and paleontological information

radiogenic isotopes record a drop in a bucket a fingerprint of multi kilometer scale fluid pathways inferred to drive fault valve behavior abstract minerals precipitated from fluids carry a chemical signature of fluid origin and transport history we use this concept to test the hypothesis that a subset of veins precipitated in the loma blanca fault zone rio grande rift nm usa record fault valve behavior previous studies of this site show syntectonic calcite veins formed in response to post seismic fluid discharge following repeated ground rupturing earthquakes u th ages on veins constrain the timing of fault slip over a period of 400 000 years the radiogenic isotope sr pb and u data we report here demonstrate that a cluster of earthquakes that occurred at 430 ka when fault slip frequency increased by nearly one order of magnitude corresponds with a brief period of particularly large and rapid variations in post seismic fluid chemistry isotopic variations are consistent with fluid input from the socorro magma body a large active mid crustal basalt intrusion 19 km below the surface the short duration of the earthquake cluster

clumped isotope palaeothermometry and la icp ms u pb dating of lava pile hydrothermal calcite veins calcite veins are a common product of hydrothermal fluid circulation clumped isotope palaeothermometry is a promising technique for fingerprinting the temperature of hydrothermal fluids but clumped isotope systematics can be reset at temperatures of ca 100 c to model whether the reconstructed temperatures represent calcite precipitation or closed system resetting the precipitation age must be known la icp ms u pb dating of calcite is a recently developed approach to direct dating of calcite and can provide precipitation ages for modelling clumped isotope systematics in calcite veins in this study clumped isotope and la icp ms u pb calcite analyses were combined in basalt hosted calcite veins from three settings in scotland samples from all three localities yielded precipitation temperatures of ca 75 115 c from clumped isotope analysis but veins from only two of the sites were dateable yielding precipitation ages of 224 8 ma and 291 33 ma 2 modelling from the dated samples enabled confident interpretation that no closed system resetting had occurred in these samples however the lack of a precipitation age from the third location meant that a range of possible thermal histories had to be modelled meaning that confidence that resetting had not occurred was lower this highlights the importance of coupling clumped isotope thermometry and la icp ms u pb calcite dating in determining the temperature of hydrothermal fluids recorded in calcite veins this paired approach is shown to be robust in constraining the timing and precipitation temperature of calcite formation and thus for tracking hydrothermal processes

the onset of the dead sea transform based on calcite age strain analyses the onset and evolution of the dead sea transform are re evaluated based on new in situ u pb dating and strain analyses of mechanically twinned calcites direct dating of 30 syn faulting calcites from 10 different inactive fault strands of the transform indicates that the oceanic to continental plate boundary initiated between 20 8 and 18 5 ma within an 10 km wide distributed deformation zone in southern israel ages from the northern dead sea transform 17 1 12 7 ma suggest northward propagation and the establishment of a well developed 500 km long plate bounding fault in 3 m y the dominant horizontal shortening direction recorded in the dated twinned calcites marks the onset of left lateral motion along the evolving plate boundary the observed changes in the strain field within individual fault strands cannot be simply explained by local weakening effects along strands of the dead sea transform or by gradual changes in the euler pole through time

temporal and spatial relations between large scale fault systems evidence from the sinai negev shear zone and the dead sea fault abstract in the major zones of crustal deformation within the arabia sinai nubia plates the interactions between the sinai negev shear zone snsz and the dead sea fault system dsf shed light on the interplay between neighboring large scale fault systems the snsz is composed of several e w to ene wsw trending mainly normal and dextral strike slip faults that are tens to hundreds of kilometers long these faults form a 120 km wide shear zone in the sinai sub plate on reaching the plate bounding dead sea fault system dsf individual lineaments of the snsz are observed in the arabian plate offset left laterally by 105 km which is the total estimated offset of the dsf in this contribution we review the geologic setting of the snsz and its complex relations with the dsf in light of newly obtained age strain analyses for this we use in situ u pb geochronology in conjunction with twin analysis of syn faulting calcite from both systems the results indicate that the deformation along the snsz initiated in the campanian maastrichtian or earlier as the oldest dates are 73 71 ma the main phase of fault activity began in the late oligocene early miocene 27 22 ma as documented by numerous dates that were obtained along several lineaments of the snsz the activity continued until 10 ma after which no direct ages have been obtained the dominant phase of activity along the snsz at 27 22 ma preceded the timing of initiation of lateral faulting along the dsf at 20 18 ma by a few myr for the overlapping period of activity between 20 and 10 ma episodes of fault activity along the snsz followed by episodes of fault activity along the dsf moreover dominant episodes of activity along one fault system were associated with a decrease in activity along the other system the temporal relations between the snsz and dsf highlight the possibility that these fault systems are mechanically interrelated but the exact mechanism for this fault interaction needs further study we consider the paleo strain or paleo stress that control the evolution and style of the snsz and assess them at the central sinai negev region during the cenozoic we show that the formation of new plate boundaries at the region i e the red sea suez rift and the dsf affected the strain field within the snsz the proximity of the two systems indicates that the dsf related stress originated within the snsz and possibly caused structural and style changes in the latter system syn faulting calcite twins analyses within the snsz show pronounced spatial and temporal variations of the principal strain directions between and along individual faults this observation demonstrates that the imposed stress within the central sinai negev were not uniform over time the high angle 70o between the traces of the snsz and the direction of the dsf related maximum shortening likely suppressed the dextral motion along the snsz post 20 ma field evidence u pb dates and recent seismicity shows that the current snsz is a long lived structure that has been active during the miocene alongside the dominantly dsf and may still be sporadically active today

traces in the dark sedimentary processes and facies gradients in the upper shale member of the upper devonian lower mississippian bakken formation williston basin north dakota u s a abstract black organic rich rocks of the upper shale member of the upper devonian lower mississippian bakken formation a world class petroleum source rock in the williston basin of the united states and canada contain a diverse suite of mudstone lithofacies that were deposited in distinct facies belts the succession consists of three discrete facies associations fas these comprise 1 siliceous mudstones 2 quartz and carbonate bearing laminated mudstones and 3 macrofossil debris bearing massive mudstones these fas were deposited in three facies belts that reflect proximal to distal relationships in this mudstone system the macrofossil debris bearing massive mudstones fa 3 occur in the proximal facies belt and contain erosion surfaces some with overlying conodont and phosphate lithoclast lag deposits mudstones with abundant millimeter scale siltstone laminae showing irregular lateral thickness changes and shell debris in the medial facies belt quartz and carbonate bearing laminated mudstones dominate exhibiting sub millimeter thick siltstone layers with variable lateral thicknesses and localized mudstone ripples in the distal siliceous mudstone facies belt radiolarites radiolarian bearing mudstones and quartz and carbonate bearing laminated mudstones dominate overall total organic carbon toc contents range between about 3 and 10 wt with a general proximal to distal decrease in toc content abundant evidence of bioturbation exists in all fas and the lithological and toc variations are paralleled by changes in burrowing style and trace fossil abundance while two horizontal traces and two types of fecal strings are recognized in the proximal facies belt only a single horizontal trace fossil and one type of fecal string characterize mudstones in the distal facies belt radiolarites intercalated into the most distal mudstones are devoid of traces and fecal strings bedload transport processes likely caused by storm induced turbidity currents were active across all facies belts suspended sediment settling from near the ocean surface however most likely played a role in the deposition of some of the mudstones and was probably responsible for deposition of the radiolarites the distribution pattern of high toc sediments in proximal and lower toc deposits in some distal facies is interpreted as a function of higher accumulation rates during radiolarian depositional events leading to a decrease in suspension derived organic carbon in radiolarite laminae the presence of burrows in all fas and nearly all facies in the upper bakken shale member indicates that dysoxic conditions prevailed during its deposition this study shows that in intracratonic high toc mudstone successions such as the upper bakken shale member bed load processes most likely dominated sedimentation and conditions promoted a thriving infaunal benthic community as such deposition of the upper bakken shale member through dynamic processes in an overall dysoxic environment represents an alternative to conventional anoxic depositional models for world class source rocks

isotopic evidence for microbial production and consumption of methane in the upper continental crust throughout the phanerozoic eon microorganisms produce and consume methane in terrestrial surface environments sea sediments and as indicated by recent discoveries in fractured crystalline bedrock these processes in the crystalline bedrock remain however unexplored both in terms of mechanisms and spatiotemporal distribution here we have studied these processes via a multi method approach including microscale analysis of the stable isotope compositions of calcite and pyrite precipitated in bedrock fractures in the upper crust down to 1 7 km at three sites on the baltic shield microbial processes have caused an intriguing variability of the carbon isotopes in the calcites at all sites with 13c spanning as much as 93 1 related to anaerobic oxidation of methane to 36 5 related to methanogenesis spatiotemporal coupling between the stable isotope measurements and radiometric age determinations micro scale dating using new high spatial methods la icp ms u pb for calcite and rb sr for calcite and co genetic adularia enabled unprecedented direct timing constraints of the microbial processes to several periods throughout the phanerozoic eon dating back to devonian times these events have featured variable fluid salinities and temperatures as shown by fluid inclusions in the calcite dominantly 70 85 c brines in the paleozoic and lower temperatures 50 62 c and salinities in the mesozoic preserved organic compounds including plant signatures within the calcite crystals mark the influence of organic matter in descending surficial fluids on the microbial processes in the fracture system thus linking processes in the deep and surficial biosphere these findings substantially extend the recognized temporal and spatial range for production and consumption of methane within the upper continental crust

a calcite reference material for la icp ms u pb geochronology u pb dating of calcite is an emerging but rapidly growing field of application in geochronology with great potential to inform problems in landscape basin and mountain belt evolution through age determination of diagenetic cements vein mineralisation and geological formations difficult to date otherwise in this brief we present isotope dilution u pb isotope measurements on a sample of calcite wc 1 that has been and will continue to be used as a reference material for in situ u pb laser ablation inductively coupled plasma mass spectrometry la icp ms dating and which is suitable to be distributed to the geochronological community we present in situ measurements using la icp ms to demonstrate the suitability of wc 1 for use as a u pb dating reference material in spite of it not being isotopically homogeneous the wc 1 calcite sample is 254 4 6 4 ma old and comprised of 85 to 98 radiogenic lead it presents a suitable reference material that can facilitate dating of calcite ranging in age from precambrian to late neogene age

u pb dating of calcite in ancient carbonates for age estimates of syn to post depositional processes a case study from the upper ediacaran strata of finnmark arctic norway results of in situ u pb dating of calcite spherulites cone in cone cic calcite and calcite fibres from a calcareous concretion of the upper ediacaran of finnmark arctic norway are reported ca

u pb dating of calcite veins reveals complex stress evolution and thrust sequence in the bighorn basin wyoming usa reply we report u pb absolute ages of calcite cements from a diffuse vein network documented in the bighorn basin wyoming usa where distinct systematic vein sets developed at the front of the thin skinned sevier orogen during laramide layer parallel shortening and during thick skinned laramide thrusting and folding the u pb age distribution illustrates 1 an outward eastward transmission of sevier orogenic stress from 89 7 2 9 ma 2 in the west and from 75 3 2 8 ma in the east and 2 an inward westward development of laramide related fracturing and folding 72 3 0 ma and 45 4 1 8 ma respectively in the east 60 5 4 6 ma and 27 9 1 1 ma respectively in the west which is in accordance with the known sequence of exhumation of the major laramide basement arches our results also show that the stress related to laramide compression first overprinted the stress related to sevier compression in the sedimentary cover around major basement uplifts this study highlights the utility of u pb calcite geochronology as a powerful tool for constraining complex sequences of deformation in orogenic forelands

effects of ambient currents and waves on gravity driven sediment transport on continental shelves abstract observations from several shelf environments show that down slope gravity driven transport may constitute an important mode of suspended sediment dispersal across shelves and highlight the influence of ambient waves and currents on gravity induced sediment flux the phenomena discussed here involve high concentrations of suspended sediment mixed with seawater and thus differ in genesis from hyperpycnal plumes released directly from sediment laden rivers the field sites examined are the gulf of bohai off the mouth of the yellow river huanghe the northern california shelf off the mouth of the eel river and the louisiana shelf west of the mouths of the mississippi river off the yellow river rapid down slope transport over distances of a few km occurred when frictional resistance induced by strong along shelf currents was temporarily relaxed more prolonged down slope motion over longer distances occurred following floods of the eel river when wave and current agitation provided turbulence to sustain gravity driven transport of fluid mud on the louisiana inner shelf the down slope gravity force was much weaker but observations suggest that thin gravity flows may still have occurred in the presence of waves a simple analytical theory is developed that incorporates the influence of ambient shelf currents on gravity driven transport of suspended sediment this theory is quantitatively consistent with the observations from the three sites if the supply of easily suspended sediment is less than the capacity of ambient currents including waves to carry sediment then intense turbulence limits gravity induced sediment transport by increasing the drag at the base of the flow when ambient currents abruptly cease rapid down slope transport can then occur over short distances until the sediment settles such flows do not remain intensely turbulent because the slope of the continental shelf is too gentle to induce shear instability within the gravity flow the maximum sustained rate of gravity induced sediment transport occurs when ambient currents are strong but the supply of easily suspended sediment exceeds the resuspension capacity of the ambient currents feedback then leads to values of the gradient richardson number ri within the flow that are near the critical value of 1 4 this partially damps bottom drag but still allows the generation of sufficient turbulence to maintain sediment in suspension observations also indicate systematic relationships among ri the supply of easily suspended sediment and the bottom drag coefficient acting on the gravity flow

bedform development in mixed sand mud the contrasting role of cohesive forces in flow and bed abstract the majority of subaqueous sediment on earth consists of mixtures of cohesive clay and cohesionless sand and silt but the role of cohesion on the development and stability of sedimentary bedforms is poorly understood the results of new laboratory flume experiments on bedform development in cohesive mixed sand mud beds are compared with the results of previous experiments in which cohesive forces in high concentration clay flows dominated bedform development even though both series of mixed sand mud experiments were conducted at similar flow velocities the textural and structural properties of the bedforms were sufficiently different to permit the designation of key criteria for identifying bedform generation under cohesive flows against bedform generation on cohesive substrates these criteria are essential for improving bedform size predictions in sediment transport modelling in modern sedimentary environments and for the reconstruction of depositional processes in the geological record the current ripples developing on the cohesive mixed sand mud beds with bed mud fractions of up to 18 were significantly smaller than equivalent bedforms in noncohesive sand moreover the bedform height showed a stronger inversely proportional relationship with initial bed mud fraction than the bedform wavelength this is in contrast with the bedforms developing under the cohesive clay flows which tend to increase in size with increasing suspended clay concentration until the flow turbulence is fully suppressed selective removal of clay from the mixed beds i e clay winnowing was found to be an important process with 82 100 clay entrained into suspension after 2 h of bedform development this winnowing process led to the development of a sand rich armouring layer this armouring layer is inferred to have protected the underlying mixed sand mud from prolonged erosion and in conjunction with strong cohesive forces in the bed may have caused the smaller size of the bedforms winnowing was less efficient for the bedforms developing under the cohesive clay flows where bedforms consisting of muddy sand were more characteristic the winnowed sand was also found to heal irregularly scoured topography thus reestablishing classic quasitriangular bedform shapes in cohesive flows the bedforms had more variable shapes and the healing process was confined to lower transitional plug flows in which strong turbulence is only present close to the sediment bed furthermore the bedforms on the cohesive beds tended to form angle of repose cross lamination whereas low angle cross lamination was more common in bedforms under cohesive flows in general terms erosional bedforms prevail when cohesive forces in the bed dominate bedform dynamics whereas depositional bedforms prevail when cohesive forces in the flow dominate bedform dynamics empirical relationships between the proportion of cohesive mud in the mixed sand mud bed and the development rate and size of the bedforms are defined for future use in field and laboratory studies

sources of ca2 in the major carbonate cements in eocene sandstones and conglomerates evidence from sr isotopes sr ca ratios and rare earth elements abstract different sources of calcium have important effects on the formation and distribution of carbonate cements on the basis of identifying all possible sources of calcium comprehensive quantitative analyses of sr c and o isotopic values and trace elements including rare earth elements were conducted to determine the ca2 sources and their changes in the same type of carbonate cements at different vertical positions in the same reservoirs ferroan calcite and ankerite were the major types of carbonate cements ca2 in ferroan carbonate cements in the sandstones near the mudstone sandstone m s interfaces was derived primarily from diagenetic fluids mixed with ca2 originating from the transformation of smectite to illite and from original sedimentary water in the adjacent mudstones however ca2 in the ferroan carbonate cements in the sandstones away from the m s interfaces originated from the transformation of smectite to illite the dissolution of carbonate minerals and original sedimentary water in source rocks the gradual change of ca source of the same type of ferroan carbonate cements indicates the diversity of migration direction of diagenetic paleo fluid in the same period during the transformation of smectite to illite concentration gradients were created from mudstones to sandstones ca2 mg2 fe2 and other cations in the mudstones diffused to the adjacent sandstones and provided sources of ferroan carbonate cements at the edge of the sandstones pore water with ca2 mg2 fe2 co32 and other cations in the source rocks was collectively charged into sandstones during oil emplacement and promoted the precipitation of ferroan carbonate cements in residual pore water due to oil emplacement and material supplied by the adjacent mudstones the content of ferroan carbonate cements in the sandstones was lower and the reservoir porosity was higher at a greater distance from the m s interfaces however in thick bedded sandstones due to lack of material supply from the adjacent mudstones ca2 mg2 fe2 and co32 in the ferroan carbonate cements were mainly derived from source rocks as a result no significant changes were observed in the content of ferroan carbonate cements and reservoir porosity in the vertical direction

a tectonic model for the norwegian passive margin with implications for the ne atlantic early cretaceous to break up a sub regional tectonic study of the mid norwegian margin has been assimilated into a broader regional study of the ne atlantic margin the ne atlantic margin experienced several extensional events between devonian post orogenic collapse and break up in early tertiary this paper focuses on the extensional events between early cretaceous and early tertiary it is suggested that ne trending early cretaceous rifting followed the entire margin from the southern rockall trough to the bjornoya basin of the sw barents sea this rift had a markedly different trend than the preceding n trending late jurassic rift of e g the north sea seamounts may have been emplaced in the highly thinned basin axes during early cretaceous rifting subsequent rift events followed the early cretaceous rift trend an enigmatic 9mid9 cretaceous event probably extensional is observed in the northern part of the mid norwegian margin the event is expressed by faulting in the inner voring basin and by uplift of the outer voring and lofoten margins uplift is associated with a widespread unconformity uplift of the gjallar ridge in the voring basin culminated during the latest cretaceous to early tertiary rifting with structural geometries broadly similar to those seen in core complexes a new tectonic model for ne atlantic margin is proposed based on these observations and builds on analogues from the modern rift system in the red sea and woodlark basin of papua new guinea

a critical analysis of the structure and tectonic significance of rift oblique lineaments transfer zones in the mesozoic cenozoic succession of the faroe shetland basin ne atlantic margin abstract nw se trending rift oblique lineaments transfer zones9 occur along the length of the ne atlantic margin previous workers have suggested that these lineaments played an important role in providing conduits and or barriers to sedimentation during the cretaceous and palaeocene it has also been suggested that they were active as discrete basin wide strike slip faults this study uses a well calibrated 3d seismic survey of regional extent to critically assess the structural and stratigraphic evidence for three rift oblique lineaments in the uk sector of the faroe shetland basin victory clair and judd lineaments structures previously attributed to basin wide strike slip deformation can be more simply explained as igneous intrusions hydrothermal vent complexes gas chimneys and or faults that transfer extensional strain between en echelon rift segments there is little evidence to suggest that activity along discrete basin wide lineaments controlled palaeocene sedimentation within the faroe shetland basin rather sediment transport and deposition at this time are likely to have been controlled by along and across strike variations in the magnitude of thermal subsidence which in turn reflect the 3d nature of the underlying mesozoic rift architecture

a new phase diagram for combined flow bedforms abstract combined flows which involve a combination of unidirectional and wave induced oscillatory flow are omnipresent in coastal and lacustrine environments despite the extensive progress made in understanding the bedforms generated by such flows in past studies there still remains a wide range of unexplored flow conditions where the bedform geometry and hence consequent sedimentary structures have not been explored especially for strong unidirectional flows greater than 0 30 m s 1 and intermediate oscillation periods between 2 and 8 seconds to address this gap in our knowledge the stability of bedforms in a 0 25 mm diameter sand bed was studied under pure unidirectional pure oscillatory and combined flow conditions with oscillation periods of 4 5 and 6 s the maximum orbital velocity uo was varied from 0 00 to 1 00 m s 1 while the unidirectional component uu was varied from 0 to 0 50 m s 1 the experimental data collected under unidirectional flows stronger than 0 30 m s 1 allows expansion of current understanding of the bed configurations for current dominated combined flows where the phase boundary between combined flow bedforms and current ripples was uncertain under these flow conditions ten distinctive bedform states can be recognized no motion nm 2d symmetric ripples 2d sr 3d symmetric ripples 3d sr 3d symmetric dunes 3d sr 3d asymmetric ripples 3d ar 3d quasi asymmetric ripples 3d qar 3d asymmetric dunes 3d ad 3d current ripples 3d cr 3d current dunes 3d cd and upper stage plane bed uspb each of these bedform stages is described quantified and characterized in dimensional phase diagrams a complete re evaluation of the nomenclature for combined flow bedforms is proposed which includes their planform and cross sectional geometry in order to better represent the bed morphologies this new nomenclature also unifies past research on bedforms in both unidirectional and oscillatory flows and thus presents a new synopsis of bedforms developed under such flows one of the main changes proposed that allows integration with the nomenclature used in unidirectional flows is the reclassification of large ripples as dunes furthermore the introduction of the planform and cross sectional geometries as properties by which to classify bedforms leads to the definition of a stable phase space for two dimensional symmetrical ripples and three dimensional quasi asymmetrical ripples these new data and analysis allow proposition of a new unified phase diagram for combined flows

deposits of flows transitional between turbidity current and debris flow the relationship between submarine sediment gravity flows and the character of their deposits is poorly understood annular flume experiments were used to investigate the depositional dynamics and deposits of waning sediment laden flows decelerating fast 3 m s flows with fixed sand content 10 vol and variable mud content 0 17 vol resulted in only four deposit types clean sand with a mud cap that resembled a turbidity current deposit turbidite formed if the flow was turbulent when deposition began or if the muddy fluid had insufficient strength to suspend the sand the clean sand could contain structures if mud content was low 300 s ungraded muddy sand with a mud cap that resembled a debris flow deposit debrite formed if the flow became laminar before sand could deposit clean sand overlain by ungraded muddy sand and a mud cap formed either from a transitional flow or by late stage settling of sand from a muddy suspension these deposits resemble enigmatic submarine flow deposits called linked debrite turbidites the experiments provide a basis for inferring flow type from deposit character for submarine sediment laden flows

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

mud re distribution in epicontinental basins exploring likely processes abstract fine grained clastic sediments are very common in the interior deposits of ancient epicontinental seas not only do they make up the gross lithology in these basins but they can also be traced for more than 1000 km offshore from basin margins given that epicontinental seas were overall shallow and in many parts most likely less than 100 m deep basin floor slopes can safely be expected to be in the 0 01 to 0 001 range for much of depositional history known processes that bring muds to the basin margin and beyond are hypopycnal river plumes hyperpycnal fluvial discharge events storm setup relaxation flows and gravity driven fluidized muds with the exception of river plumes all of these processes require the presence of sufficient slope for sustained movement due to that constraint these processes combined might in the majority of situations have been able to move muddy sediments on the order of 100 km offshore whereas this is sufficient to distribute mud across marginal shelf seas it becomes problematic in the case of much larger epicontinental seas for example those of upper devonian or upper cretaceous times extended in places for thousands of kilometers and thus a process is needed that can move muddy sediments the rest of the way flume studies of the bedload transport of mud combined with observations from the rock record suggest that wind or tide induced bottom current circulation was most likely essential for moving muddy sediments from the periphery of epicontiental seas to their interiors remobilization of seafloor muds during frequently recurring lowering of sea level is likely to have aided in this process

genesis of the gaosong sn cu deposit gejiu district sw china constraints from in situ la icp ms cassiterite u pb dating and trace element fingerprinting abstract the gaosong sn cu deposit in the gejiu ore district sw china is a large cassiterite sulfide deposit hosting total ore reserves of 67 4 mt 1 3 sn and 19 0 mt 1 1 cu two types of mineralization developed in the deposit i e cassiterite sulfide ore within the proximal skarn in contact with the gaofengshan biotite granite and fault controlled stratiform like cassiterite iron oxide sulfide ore in the distal carbonate country rock cassiterite grains are disseminated in both ores in situ u pb dating of one cassiterite sample from the cassiterite sulfide ore and two from the cassiterite iron oxide sulfide ore yielded weighted mean 206pb 238u ages of 84 3 1 4 ma 85 1 1 0 ma and 83 5 2 1 ma respectively the three mineralization ages are consistent with the emplacement age of the gaofengshan granite 85 8 0 6 ma within error suggesting a close temporal link between tin mineralization and granitic magmatism cassiterite grains can be divided into two types based on cathodoluminescence cl illustrations namely euhedral cst i and veinlet like cst ii in the cassiterite sulfide ore cst i has clear oscillatory zonation and is dull luminescing in the cassiterite iron oxide sulfide ore cst i core is dull luminescing blue in om cl and surrounded by a bright luminescing cst i rim yellow in om cl cst i is replaced by cst ii veinlets with bright luminescing yellow in om cl the sem cl luminescing intensity of cassiterite is mainly controlled by ti content elevated w and fe but low nb ta zr and hf concentrations of cassiterites from the gaosong deposit are distinctly different from those of cassiterites in vms sedex tin deposits but similar to those from granite related tin deposits the late cretaceous crystallization ages and trace element characteristics demonstrate that cassiterites from both ores were formed in a magmatic hydrothermal system associated with the gaofengshan granite and preclude the sedex origin of the stratiform like cassiterite iron oxide sulfide ore

absolute ages of multiple generations of brittle structures by u pb dating of calcite direct dating of brittle structures is challenging especially absolute dating of diagenesis followed by a series of superimposed brittle deformation events we report 22 calcite u pb ages from tec

directly dating geologic events u pb dating of carbonates 1 carbonates are ubiquitous forming in a variety of settings including caves soils the oceans during burial from hydrothermal fluids and along faults u pb dating of carbonates is applicable to almost the entire geologic time scale with results from pleistocene speleothems showing great promise for dating records 1 ma old here we review studies of u pb dating of carbonates from a range of depositional and diagenetic environments and consider published results with regard to stratigraphic associations and the behavior of u and pb in various fluids we detail the steps required to select suitable samples summarize current laboratory techniques and provide directions for improvement of analytical protocols the u pb dating of carbonates has tremendous potential for dating events of geologic interest and is virtually untapped

seismic cycles recorded in late quaternary calcite veins geochronological geochemical and microstructural evidence southwest turkey is seismically active as a result of the hellenic subduction process in the eastern mediterranean we conducted high resolution micro sampling high precision u series dating and microchemical analysis on an extensional vein system in a tectonically active but non hydrothermal area u th age data and microscopic observations provide evidence of repeated fracturing of a previously sealed crack system followed by a new increment of veining repeated injection of veinlets suggests that the vein system was formed by the crack seal mechanism four major u th age groups for the emplacement of the vein system fall between 23 9 0 2 ka and 23 2 0 4 ka 21 7 0 4 ka and 19 2 0 2 ka 17 3 0 1 ka and 16 2 0 3 ka and at 11 8 0 2 ka stable and sr isotope geochemistry of the calcite vein samples indicates that surface water interacting with the soil cover was the major component of the groundwater system from which the extensional veins precipitated trace element and 0 isotope data of the vein system are interpreted to reflect carbonate precipitation associated with seismic cycles involving fluids with different trace element compositions and co2 contents initial carbonate precipitation during a single seismic cycle occurred from co2 dominated fluids that were degassed from the original co2 water mixture this was followed consecutively by carbonate precipitation from the remaining water which was relatively impure with higher trace element contents millimetre to submillimetre scale u series dating in conjunction with geochemistry of carbonate veins related to active tectonism offers an innovative means of constraining the absolute timing of late quaternary seismic and inter seismic events c 2010 elsevier b v all rights reserved

supercritical flow structures on a late carboniferous delta front sedimentologic and paleoclimatic significance comment ventra et al 2015 propose a model of hyperpycnal supercritical flow regime deposition related to a megamonsoonal climate for a series of interpreted cyclic steps on a carboniferous delta front the new model has major implications for paleoenvironmental reconstructions of this well studied area in terms of climate and geographical setting we contend that fundamental sedimentological observations do not support their proposed model ventra et al interpret that each cross bedded set is the deposit of a single mega monsoonal flood event we propose that each set represents multiple events e g their set 3 is at least 30 discrete events event bed sandstones are represented by variable to normal grading crude cross stratification and plane parallel lamination and a finer grained top which is generally ripple cross laminated fig 1 these are capped by a very thin silty to fine grained sand layer with abundant organic material representing interflood deposition hampson 1997 this repeated motif is only interrupted where bed tops are eroded abundant loading dewatering and flame structures between beds and rip up clast horizons support the interpretation of discrete depositional events fig 1 a mega monsoonal origin cannot be invoked for 20 cm thick beds ventra et al state that there is a lack of ripple cross lamination or stratification aside from some upflow dipping crude laminae most bed tops are laminated to crosslaminated fig 1 these are interpreted as current ripples rather than antidunes or climbing ripple backsets as they have clearly developed tangential foresets these ripples suggest paleoflow broadly toward the east in contrast to the overall southwesterly paleoflow eastward paleocurrents typically occur on the updip side of the undulatory beds of mccabe 1977 and hampson 1997 suggesting that the exposed section is oblique to depositional dip rather than parallel as proposed we infer that there is a significant lateral as well as downstream accretion component to these three dimensional bedforms the lack of bioturbation between beds cannot be used as evidence for the short duration of events as there is in general a lack of bioturbational structures in the sandy marine sediments of the british carboniferous basins however the depositional environment as proposed by ventra marine delta front is at odds with the existing fluvial models which are based on detailed mapping and correlations mccabe 1977 hampson 1997 the large scale architecture shows a progressive decrease in depositional dip that we interpret to reflect healing of scour related topography the depth of the scour minimum of 13 m corresponds to that observed in major fluvial confluences and is aligned with hampson s 1997 interpretation the overlying section which ventra et al do not discuss is represented by many smaller scale trough cross beds interpreted to represent local shallowing in a fluvial setting associated with filling of the scour in this stratigraphic unit features of a similar geometry but at a smaller scale are convincingly shown to represent supercritical flow conditions bijkerk 2014 in summary we concur with the observations and interpretations of hampson 1997 that these beds represent the fill of a major scour potentially associated with a fluvial confluence which filled in a stepwise manner by gravity flow in the deepest parts with periods of minor erosion of the downslope sides of the bedforms e g ullah et al 2015 figure 1 a short sedimentological log from the base of ventra s 2015 set 2 showing the general character of event beds b character of event beds and finer interbeds i and amalgamation surfaces a c small dune with tangential foresets f d ripple cross lamination r with tangential foresets e loading l between beds

s wave scattering by 3 d heterogeneities at the base of the mantle the hypothesis of s wave scattering by three dimensional heterogeneity in the lowermost mantle is shown to provide a plausible alternative to the spherically stratified models recently proposed by lay and helmberger to explain certain observed complexities in long period s wave data a result of central importance is that contrary to the conclusions of lay and helmberger and most recently young and lay sharp increases of s velocity with depth are not required to explain their data

the norway basin revisited from continental breakup to spreading ridge extinction abstract we re evaluate the structure and spreading evolution of the southeastern norway basin nb based on a new high resolution aeromagnetic survey nb 07 the survey covers a complete oceanic spreading segment from the continental oceanic transition of the more margin off norway to the aborted aegir ridge the new survey documents a transform margin an orthogonally rifted segment and an oblique sheared volcanic margin formed during the onset of breakup observed from the east jan mayen fracture zone to the faroe platform the detailed fabric of the nb revealed by the new data indicates that two distinct tectonic phases have reshaped the basin before the cessation of seafloor spreading and abortion of the aegir ridge in the late oligocene after continental breakup phase i from c24 to c21r 52 to 49 ma marks the earliest phase of spreading probably initiated in the central and outer part of the more basin during this period competing oceanic segments led to the formation of overlapping systems and pseudo fault development we observe a significant change in the nb s oceanic spreading system in the late early eocene and based on observations from surrounding areas we suggest that this is a record of a major tectonic event in the norwegian greenland sea around c21r 49 47 9 ma during phase ii from c21r to c10 48 to 28 ma of nb s development spreading rates decreased spreading direction changed and the number of faulting with large displacement increased leading to the formation of unexpected n s oriented oceanic fracture zones the fan shaped development of the spreading system initiated around c21r 49 47 9 ma instead of c18 c17 40 38 ma or c24 53 3 52 3 ma as previously proposed these new observations were used to re evaluate the tectonic evolution of the norwegian greenland sea and discuss some implications on the syn and post breakup development of the surrounding continental margins and the evolution of the jan mayen microcontinent

dating and characterizing primary gas accumulation in precambrian dolomite reservoirs central sichuan basin china insights from pyrobitumen re os and dolomite u pb geochronology abstract primary gas accumulation with trillions of cubic meters of gas volumes was discovered recently in the precambrian dengying formation of the gaoshiti moxi block central sichuan basin china in this study we investigated the pervasive saddle dolomite cements and solid bitumens within karst vugs in the dengying dolomite reservoirs using laser ablation inductively coupled plasma mass spectrometry la icp ms in situ u pb dating we obtained a high precision absolute age of 259 4 3 0 ma for the saddle dolomite cementation consistent in timing with the eruption of emeishan flood basalts 262 251 ma combined with high homogenization temperatures th and salinities of primary fluid inclusion as well as rare earth element ree compositions we consider that the saddle dolomite precipitation was likely related to hydrothermal activity driven by the emeishan mantle plume the identification of rare surviving oil inclusions and extensive solid bitumens within the dolomite vugs is indicative of the presence of paleo oil reservoirs these bitumens are characterized by high equivalent vitrinite reflectance requ no fluorescence and deformed fibrous textures typical of highly mature pyrobitumens gas geochemistry data indicates that only minor thermochemical sulfate reduction tsr has occurred thus the pyrobitumen was interpreted to result mainly from the thermal cracking of paleo oils and its associated re os isochron age of 154 21 ma representing the timing of dry gas formation petrographical evidence suggests that the paleo oil charge must have taken place after sparry dolomite cementation but prior to pyrobitumen generation this combined with coeval aqueous inclusion th data and published thermal burial models constrains the time of paleo oil emplacement to ca 222 205 ma suggesting an oil filling event related to the indosinian orogeny this study documented the first chronological data constraining the complex evolution history of a petroleum system in one of the oldest primary gas reservoirs in the world

bedload transport of mud across a wide storm influenced ramp cenomanian turonian kaskapau formation western canada foreland basin abstract mudstone dominated shallow marine rocks of the kaskapau formation were deposited on a low gradient ramp that spanned the foredeep of the western canada foreland basin during the late cenomanian to middle turonian organic clay rich and silt rich mudstone accumulated on the flank of the forebulge 200 km from the western shoreline within this mudstone a large proportion of the clay minerals are organized into silt and very fine sand size aggregate grains these aggregates were produced both in the water column as marine snow and phytodetritus and also through reworking of previously deposited cohesive mud to form intraclasts the latter along with siliceous silt grains form wave and combined flow ripples graded beds scour fills and ripple tail lamination where sand size sediment comprising detrital siliceous calcareous bioclastic or phosphatic grains is present it is molded into combined flow ripples hcs gutter casts and lags thus all sediment grades indicate storm wave and current reworking of the sea floor at a distance of 200 km offshore the common occurrence of clay minerals in the form of aggregate grains organized into combined flow ripples and parallel lamination implies advective transport of clay minerals as bedload driven by combined flows across a very low gradient ramp on the distal part of this ramp latest cenomanian rocks include thin tongues of sw prograding quartz rich sandstone that was derived from an emergent forebulge this source was drowned during the early turonian eustatic rise when the sediment abruptly changed to organic rich mudstone dominated by clay mineral aggregates this compositional change was mainly a response to a sudden increase in distance to detrital sources in the west rather than a dramatic increase in water depth throughout much of early to middle turonian time the sea floor in the forebulge region lay above effective storm wave base for silt estimated at 70 m at sea level lowstands wave winnowing and erosion of the sea floor concentrated bioclastic lags at the top of siltier upward sequences lags are interpreted to correspond to falling stage lowstand and early transgressive systems tract deposits on the western margin of the basin previous studies may have substantially overestimated water depth for organic and clay rich calcareous mudstones in the western interior seaway

fault zone permeability structure evolution in basalts a combination of field microstructural and experimental static permeability characterization is used to determine fault permeability structure evolution in upper crustal basalt hosted fault zones in the faroe islands the faults comprise lower strain fracture networks to higher strain breccias that form tabular volumes around a principal slip zone hosting gouge or cataclasite samples representative of these fault zone components are used for static experimental permeability measurement results indicate that within the appropriate effective pressure depth range 10 90 mpa 0 3 to 3 0 km basalt hosted faults evolve from low strain 10 17 m2 structures sample analyses reveal that static permeability is controlled by the development of a fault parallel clay alteration decreasing permeability and b porous zeolite vein connectivity due to hydrofracture increasing permeability fault parallel permeability is increased relative to the host rock while fault normal permeability is low throughout fault rock evolution this configuration will tend to promote across fault compartmentalization and along fault fluid flow facilitating migration between relatively high permeability horizons e g vesicular flow unit tops and siliciclastic horizons bypassing the bulk of the stratigraphy

fractures in mudrocks advances in constraining timing and understanding mechanisms abstract recent advances in fracture timing techniques have led to new insights about sequences and mechanisms of fracture formation in mudrocks methods to constrain fracture timing in mudrocks include i field evidence including crosscutting relationships and evidence of compaction ii petrographic evidence including signs of soft sediment deformation and diagnostic mineral assemblages or textures iii stable isotopic evidence iv thermometric dating using burial history modelling and v radiometric age dating in this contribution we briefly review each method with salient examples from the literature many documented examples of mudrock hosted fractures formed during early burial a non intuitive finding that demands a re assessment of our assumptions about what types of materials can develop opening mode fractures in general the style and distribution of fractures varies dramatically based on fracture timing highlighting the importance of constraining timing for predicting fracture patterns and interpreting their mechanisms including the role of fluid flow

chronologic constraints on hominin dispersal outside africa since 2 48 ma from the zarqa valley jordan abstract recent discoveries constrain the presence of hominins in north africa since ca 2 4 ma and in china since ca 2 1 ma providing a new temporal framework for the earliest migration out of africa no paleolithic sites of such age exist in the levant the natural corridor between africa and asia the dawqara formation in the zarqa valley jordan has been known since the early 1980s because of the presence of artifacts at different stratigraphic levels within its fluvial sediments consisting of choppers cores and flakes although most of the artifacts display signs of transport they bear unambiguous evidence of manufacture and document hominin presence in the zarqa valley during the deposition of dawqara formation based on integrated chronology provided by paleomagnetic 40ar 39ar and u pb dating methods our study shows that the dawqara formation was deposited between 2 52 0 01 ma and the matuyama olduvai geomagnetic reversal 1 95 ma by linear interpolation the artifact bearing stratigraphic levels within the dawqara formation have ages of ca 2 48 ma 2 24 ma 2 16 ma 2 06 ma and 1 95 ma respectively possibly documenting continuous hominin presence in the zarqa valley these new ages for the dawqara assemblage constrain the earliest hominin dispersal out of africa to the beginning of the pleistocene and pre date by ca 300 kyr the hominin occupation of chinese loess plateau

palaeocene recent plate boundaries in the ne atlantic and the formation of the jan mayen microcontinent abstract breakup and sea floor spreading between greenland and eurasia established a series of new plate boundaries in the north atlantic region since the late palaeocene a conventional kinematic model from pre breakup to the present day assumes that eurasia and greenland moved apart as a two plate system however new regional geophysical datasets and quantitative kinematic parameters indicate that this system underwent several adjustments since its inception and suggest that additional short lived plate boundaries existed in the ne atlantic among the consequences of numerous plate boundary relocations is the formation of a highly extended or even fragmented jan mayen microcontinent and subsequent deformation of its margins and surrounding regions the major oligocene plate boundary reorganization and microcontinent formation might have been precluded by various ridge propagations and or short lived triple junctions ne and possibly sw of the jan mayen microcontinent from the inception of sea floor spreading 54 ma to c18 40 ma our model implies a series of failed ridges offshore the faeroe islands a northern propagation of the aegir ridge ne of the jan mayen microcontinent and a series of triple junctions and or propagators in the southern greenland basin

an image mapping approach to u pb la icp ms carbonate dating and applications to direct dating of carbonate sedimentation we present a new approach to laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating of carbonates based on selection and pooling of pixels from 2 d elemental and isotopic ratio maps this image mapping technique is particularly useful for targeting subdomains in samples with complex geological histories key major and trace elements that are sensitive to detrital components postformational fluid ingress mineralogical changes or diagenetic overprinting are measured along with the pb and u isotopic data laser sampling is undertaken along successive linear rasters that are compiled into maps using the monocle add on for iolite with one pixel in the map corresponding to one time slice of the time resolved signal these element element ratio and isotope ratio maps can be overlain over photomicrographs or scanning electron microscopy images to spatially link compositional data to textural and structural features the pixels corresponding to likely homogeneous age domains can be isolated by applying appropriate selection criteria e g th 0 3 ppm mg ca 0 004 and pooled into pseudo analyses using a proxy for the parent daughter ratio e g 207pb 235u 238u 208pb to retrieve the largest possible spread of the data points on isochron diagrams the approach is best suited for analytical setups capable of rapidly or simultaneously scanning over a large mass range and can yield a precision of 1 or better on quadrupole instruments depending on u concentration 238u 204pb and age of the sample the sample specific filtering criteria for selection and rejection of data and their rationale can be reported resulting in more transparency with regard to data processing

provenance and tectonic evolution of ganderia constraints on the evolution of the iapetus and rheic oceans we provide estimates for the width timing and rates of opening and closing of the iapetus and rheic oceans the evolution of which profoundly infl uenced paleozoic global paleogeography these estimates are primarily derived from the transfer of ganderia and avalonia from gondwana to laurentia which led to closure of the iapetus ocean and opening of the rheic ocean ganderia a long lived arc terrane separated from the paleo caribbean margin of amazonia at 505 ma with a latitudinal speed of 9 cm a northward initiating the rheic ocean as a backarc basin ganderia s trailing edge was reduced to 5 cm a following opening of a 600 800 km wide backarc basin within ganderia at 475 ma opening and closing of the iapetus ocean was largely driven by far fi eld stresses slab pull in some places and slab rollback in others

u pb dating of geodic calcite new insights on western europe major tectonic events and associated diagenetic fluids this study presents the first application of the u pb dating method to highly pb depleted diagenetic geodic calcites of the jurassic formations of the paris basin that leads to a reappraisal of the palaeohydrological history of this region composite u pb ages from multiple geodes combined with 18 o analyses reveal two main phases of diagenetic fluid circulations linked with major regional tectonic events dogger formations recorded a first diagenetic fluid episode at 147 8 3 8 ma i e at the very beginning of the emersion of the basin during the tithonian period and 30 ma earlier than previously assumed 18 o results confirmed that most of the calcitic cement phases that closed the porosity of these formations precipitated at the beginning of the cretaceous period oxfordian formations recorded another major meteoric fluid circulation at 33 5 2 8 ma related to the initial stage of the european cenozoic rift system ecris consequently the porosity of the mesozoic formations of the studied area may have been closed sooner than previously thought before the main ecris rifting phase of oligocene age this study shows that u pb dating of secondary geodic calcite offers a new powerful way for reconstructing the coupled palaeohydrological and diagenetic history of sedimentary basins supplementary material pb pb diagrams 238 u and 235 u series isochron diagrams and effect of blank correction on u and pb isotopic compositions and on ages calculation are available at https doi org 10 6084 m9 figshare c 3886885

onshore evidence for progressive changes in rifting directions during continental break up in the ne atlantic abstract current models for the palaeogene aged continental break up in the north atlantic invoke a nw se extension vector throughout the rift to drift process accommodated by margin parallel normal faults and margin oblique strike slip transfer zones however palaeogene and younger faults in the faroe islands provide evidence for a progressive anticlockwise rotation in extension vectors immediately prior to and following north atlantic break up six deformation stages are recognized 1 east west to ne sw extension accommodated by dip slip north south and nw se trending faults 2 continued ne sw extension accommodated by nw se and nne ssw oriented dykes 3 north south extension accommodated by ene wsw and ese wnw conjugate dykes 4 crustal extrusion involving both east west shortening and further north south extension along ene wsw dextral and ese wnw sinistral conjugate strike slip faults 5 during the final stages of rifting the regional extension vector became nw se and was accommodated predominantly by slip along ne sw dextral oblique slip faults 6 pre existing structures were locally reactivated as tensional and extensional shear features characterized by the entrainment of clastic material along fault planes the present study reveals a distinct period of margin parallel extension immediately prior to break up that is not accounted for by existing models illustrating the importance of conducting field based studies to validate otherwise widely accepted margin scale models worldwide

the development of cavities and clastic infills along fault related fractures in tertiary basalts on the ne atlantic margin field based geological observations have revealed the hitherto unrecognised development of post magmatic brittle deformation structures cutting tertiary volcanic rocks in the faroe islands these faults and fractures are characteristically associated with different styles of clastic sedimentary infill including 1 0 3 1 0 m thick clastic units infilling open fractures formed along pre existing steeply dipping to sub vertical faults 2 0 1 0 6 m thick sub horizontal clastic units displaying internal features consistent with deposition from flowing water passing through complex open subterranean cavity systems within fractured basalts 3 anastomosing mm scale and planar dm scale clastic intrusion features mobilised and emplaced during transient fault related overpressuring events along pre existing fractures cutting the surrounding volcanic units the infill features provide evidence for the existence of sustained open cavities in the sub surface the clastic materials are commonly internally affected by later fault related deformation and lack mineralisation unlike all preceding faulting episodes in the faroes region perhaps reflecting their near surface development we believe structures equivalent to these features may occur widely in other parts of the ne atlantic margin particularly along the outer arcs of gentle regional scale fold hinges the uncemented fracture hosted clastic infills potentially represent important fluid migration pathways within the otherwise low permeability cenozoic volcanic sequences of the ne atlantic region

dating of anatase forming diagenetic reactions in rotliegend sandstones of the north german basin diagenetic conditions controlling authigenic formation of anatase and in situ la icp ms u pb isotope dating of this phase are studied in upper rotliegend ii sandstones from two wells in nw germany anatase grew after breakdown of detrital ti phases e g ilmenite although local scale ti transport and mobilization from detrital clay hematite coats or condensed hydrocarbons cannot be ruled out the anatase forming reaction marks the change from a regime of reducing conditions imposed by first hydrocarbon generation to oxidizing conditions probably caused by influx of a fluid from evaporitic zechstein rocks this change in fluid influx is interpreted as response to enhanced normal faulting and halokinesis during accelerated burial in triassic times isotope data of u and pb indicate incorporation of crustal common pb from mesozoic pore fluids but precisely mark diagenetic growth of anatase at 224 3 5 1 5 6 ma in a tera wasserburg plot locally u pb isotope signatures are consistent with either additional incorporation of u and pb from detrital precursor phases or with uptake of uranogenic pb from hydrocarbons generated prior to 224 ma anatase is shown to be a valuable authigenic phase suitable for u pb chronometry of diagenetic events which appears to be unaffected by protracted burial and temperatures exceeding temperatures of crystallization

an emerging thermochronometer for carbonate bearing rocks 47 u pb assessing the thermal evolution of sedimentary basins is critical for understanding the origin of natural resources including ores geothermal fluids or hydrocarbons and for deciphering larger scale tectonic and geodynamic evolutions modern reconstructions of past subsurface temperatures mostly rely on thermochronometers that are not applicable to carbonate rocks e g fission track and u th he analyses here by coupling carbonate clumped isotope 47 thermometry and laser ablation u pb geochronology on a complete paragenetic sequence we demonstrate the applicability of an emerging thermochronometer for carbonate bearing rocks paired 47 and u pb data were obtained for calcite and dolomite phases precipitated in a middle jurassic carbonate hydrocarbon reservoir of the paris basin depocenter france the absolute thermochronological data allow the precise reconstruction of the thermal history of these rocks from shallow burial temperatures 40 c occurring in the late jurassic toward a progressive burial and heating stage up to 87 c during the cretaceous followed by a cooling stage down to 69 c during the tertiary uplift of the basin the inferred time temperature path based on 47 u pb data is mostly consistent with the thermal scenario independently deduced from organic maturity indicators from the underlying lower jurassic shales the 47 u pb thermochronological data also highlight a thermal anomaly during aptian albian time that requires revisiting the accepted timing for hydrocarbon migration in the middle jurassic reservoir carbonates

bioturbating animals control the mobility of redox sensitive trace elements in organic rich mudstone bioturbating animals modify the original mineralogy porosity organic content and fabric of mud thus affecting the burial diagenetic pathways of potential hydrocarbon source seal and reservoir rocks high sensitivity synchrotron rapid scanning x ray fluorescence elemental mapping reveals that producers of phycosiphoniform burrows systematically partition redox sensitive trace elements i e fe v cr mn co ni cu and as in fine grained siliciclastic rocks systematic differences in organic carbon content total organic carbon 1 5 wt and quality 13corg 0 6 are measured between the burrow core and host sediment the relative enrichment of redox sensitive elements in the burrow core does not correlate with significant neo formation of early diagenetic pyrite via trace metal pyritization but is best explained by physical concentration of clay and silt sized components a measured loss 15 of the large ionic radius elements sr and ba from both burrow halo and core is most likely associated with the release of sr and ba to pore waters during biological in vivo weathering of silt to clay sized lithic components and feldspar in conclusion this newly documented effect has significant potential to inform the interpretation of geochemical proxy and rock property data particularly from shales where elemental analyses are commonly employed to predict reservoir quality and support paleoenvironmental analysis

lithostratigraphy of the cambrian lower ordovician bell island and wabana groups of bell little bell and kellys islands conception bay eastern newfoundland the upper cambrian arenigian succession of bell little bell and kellys islands conception bay eastern newfoundland consists of at least 1500 m of interbedded micaceous sandstones siltstones shales and ironstones the succession has previously been formally subdivided into only two groups namely a lowermost bell island group and an overlying wabana group the existing lithostratigraphic nomenclature below group level has to date only been informally proposed and is therefore herein formally revised the lowermost bell island group comprises from base to top the kellys island little bell island beach redmans ochre cove and dominion formations of these the ochre cove and dominion formations are newly proposed and the beach formation is considerably revised from its historical usage the beach formation contains two newly proposed members the mcgraw and eastern head members both of which in previous nomenclature were informally referred to as beds the disconformably overlying wabana

gravity driven sediment transport on the continental shelf implications for equilibrium profiles near river mouths an analytical model is developed for equilibrium bathymetric profiles off river mouths associated with the shoreward convex upward portion of subaqueous deltas and clinoforms the model builds on recent field results demonstrating that gravity driven flux of suspended mud is important on shelves provided that wave induced suspension of sediment supports the requisite turbid hyperpycnal layer because the maximum sediment load is determined by the critical richardson number the results are independent of the properties of the suspended mud or the bed the model assumes the equilibrium state to represent a balance between the supply of sediment by a river at the coast and the downslope bypassing of sediment to deep water within wave supported turbid near bed layers progressive seaward increases in bed slope across the convex shelf profile allow the attenuation of wave agitation with depth to be compensated for by a downslope increase in the contribution of gravity the model is consistent with shelf profiles off the mouths of the eel california ganges brahmaputra bangladesh waiapu new zealand po italy and rhone france rivers the equilibrium profile is predicted to be a function of wave climate and riverine sediment supply only with deeper and broader profiles associated with decreasing sediment supply increasing wave height and or increasing wave period

u pb dating of cements in mesozoic ammonites dating sedimentary carbonates using the u pb method can help improve the phanerozoic timescale using a novel combination of laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms and thermal ionization multi collector mass spectrometry tims u pb numerical ages were obtained on early diagenetic calcite cements in jurassic ammonites in which concentrations of u range from 0 47 to 5 3 ppm the calcite cements of two ammonites is1 and is2 from the uppermost bifrons zone of the toarcian 179 180ma of the uk gave tims normalized la u pb dates of 164 9 5 3 ma and 166 7 4 8ma respectively normalizing la icp mc ms data to an in house calcite standard gave a more precise date of 165 5 3 3 ma for is1 cement an unzoned ammonite ss2 of bajocian age 168 170 ma yield a tims normalized la u pb age of 158 8 4 3 ma for its early diagenetic cement both the combined la mc icp ms and tims approach and the use of a calcite laser ablation standard can result in accurate ages of cements with uncertainties of 2 3 2 the later however is more efficient and precise these u pb dates of cements are 10 to 20 myr younger than the numerical ages of the biostratigraphic intervals from which the ammonites derive the u pb dates are taken to represent the time at which the aragonite shell of the ammonite inverted to calcite and released its u to precipitate in a late diagenetic alteration of early diagenetic fringing cements concentrations of u and pb in a range of other pristine biogenic carbonateswere found too low u b 0 01 ppm for meaningful dating using laser ablation method

combined zircon and cassiterite u pb dating of the piaotang granite related tungsten tin deposit southern jiangxi tungsten district china abstract the large low grade piaotang w sn deposit in the southern jiangxi tungsten district of the eastern nanling range south china is related to a hidden granite pluton of jurassic age the magmatic hydrothermal system displays a zonation from an inner greisen zone to quartz veins and to peripheral veinlets stringers five floor zonation model most mineralization is in quartz veins with wolframite cassiterite the hidden granite pluton in underground exposures comprises three intrusive units i e biotite granite two mica granite and muscovite granite the latter unit is spatially associated with the w sn deposit combined la mc icp ms u pb dating of igneous zircon and la icp ms u pb dating of hydrothermal cassiterite are used to constrain the timing of granitic magmatism and hydrothermal mineralization zircon from the three granite units has a weighted average 206pb 238u age of 159 8 0 3 ma 2 mswd 0 3 the cathodoluminescence cl textures indicate that some of the cassiterite crystals from the wolframite cassiterite quartz vein system have growth zonations i e zone i in the core and zone ii in the rim dating on cassiterite zone ii yields a weighted average 206pb 238u age of 159 5 1 5 ma 2 mswd 0 4 i e the magmatic and hydrothermal systems are synchronous this confirms the classical model of granite related tin tungsten mineralization and is against the view of a broader time gap of 6 myr between granite magmatism and w sn mineralization which has been previously proposed for the southern jiangxi tungsten district the elevated trace element concentrations of zr u nb ta w and ti suggest that cassiterite zone ii formed in a high temperature quartz vein system related to the piaotang granite pluton

improving paleohydrological and diagenetic reconstructions in calcite veins and breccia of a sedimentary basin by combining δ47 temperature δ18owater and u pb age abstract in sedimentary basins the precise temperature and timing at which relatively shallow

ten million years of activity within the eastern california shear zone from u pb dating of fault zone opal abstract reconstructions of long term fault activity are essential for understanding both the mechanisms controlling fault behavior and accurate earthquake hazard assessments increasing evidence for temporal variations in strain accumulation suggests non uniform strain rates over a range of historic to geologic timescales the paucity of long term records of fault activity has limited our ability to resolve these variations we present a method for constraining long term fault activity based on u pb dating of fault related opal from secondary fault segments within the eastern california shear zone ecsz the presence of sheared and breccia cemented opaline silica within well exposed faults at near surface conditions suggest that opal formation is associated with high magnitude earthquakes capable of surface rupture 6 m temporal constraints from massive and sheared syntectonic opal n 74 on related secondary faults from this study provide new insights on the timing of fault initiation reactivation and longevity the oldest dates obtained indicate that ecsz activity commenced at or before 10 ma multiple deformation events dated within a single structure on episodically deposited and sheared opal up to six generations demonstrate that fault reactivation occurred over 105 yr timescales 0 7 0 1 myr relative probabilities of dated deformation events can be used to evaluate changes in fault activity in the past 2 5 ma n 60 this analysis indicates enhanced fault activity starting at 2 ma and peaking around 1 ma possibly due to fault interactions and distribution of deformation between the ecsz and the san andreas fault

the role of wave reworking on the architecture of storm sandstone facies bell island group lower ordovician eastern newfoundland stacked shallow marine cycles in the lower ordovician bell island group of bell island newfoundland show upward thickening and upward coarsening sequences which were deposited on a storm affected shelf in the beach formation each cycle has a facies sequence comprised from base to top of dark grey mudstones light grey mudstones tabular sandstones and mudstones lenticular sandstones and mudstones and thick bedded lenticular sandstones reflecting a progressive increase of wave orbital velocities at the sediment surface the mudstones and tabular sandstones reflect an environment in which the sea floor lay in the lower part of the wave orbital velocity field and in which tempestites were deposited as widespread sheets from weak combined flow currents the lenticular sandstones in the succeeding facies are wave reworked sands commonly lying in erosional hollows and having erosional tops and internal hummocky cross stratification planar lamination is relatively uncommon and sole marks are mainly absent in this facies oscillatory currents were dominant and accumulated sand in patches generally 10 30 m in diameter the facies formed on the inner shelf where the oscillatory currents generated by storm waves had powerful erosional effects and also determined the depositional bedforms mud partings and second order set boundaries within sandstone beds are believed to separate the products of individual storms so that many lenticular sandstone beds represent the amalgamation of several event beds this interpretation has important implications for attempts to estimate event frequency by counting sandstone beds within a sequence and for estimates of sand budgets during storm events the thick bedded lenticular facies appears to have been formed by erosion of the mud beds between the lenticular sands leading to nearly complete amalgamation of several lenticular sand bodies except for residual mud partings in the overlying redmans formation the process of amalgamation progressed even further so that nearly all the mud partings were removed resulting in the formation of thick bedded tabular sandstones sequence stratigraphic analysis of the cyclical sequence suggests that the cycles were eustatically controlled the rising limb of the sea level curve produced only the dark grey mudstone part of the cycle while the remainder of the cycle was deposited on the falling limb there is a gradational but rapid facies transition from the tabular to the lenticular sandstone facies which is interpreted as occurring at the inflexion point on the falling limb the thick bedded facies of the beach formation and the thick bedded tabular facies of the redmans formation represent periods of maximum sea level fall the stacked cycles in the beach formation are interpreted as an aggradational high frequency sequence or parasequence set bounded at the top by a sequence boundary and succeeded by the three aggradational parasequences of the redmans formation the recognition of storm facies with sandstone beds of very different bed length has important implications for the reservoir modelling of such facies

controls on floc size in a continental shelf bottom boundary layer simultaneous in situ observations of floc size waves and currents in a continental shelf bottom boundary layer do not support generally accepted functional relationships between turbulence and floc size in the sea in september and october 1996 and january 1997 two tripods were deployed in 70 m of water on the continental shelf south of woods hole massachusetts on one a camera photographed particles in suspension 1 2 m above the bottom that had equivalent circular diameters larger than 250 m and on the other three horizontally displaced acoustic current meters measured flow velocity 0 35 m above the bottom the tripods were separated by 150 m typically maximal floc diameter stayed relatively constant around 1 mm and it showed a dependence on turbulence parameters that was significantly weaker than that predicted by any model that assumes that turbulence induced stresses limit floc size occasionally when waves and currents generated intense near bed turbulence flocs were destroyed these precipitous decreases in maximal floc size also were not predicted by conventional models the correlation in time between episodes of floc destruction and elevated combined wave current stresses provides the first quantitative support for the hypothesis that floc size throughout bottom boundary layers can be controlled by breakup in the intensely sheared near bed region these observations demand a reassessment of the forces limiting floc size in the sea and they indicate the potential for significant simplifying assumptions in models of floc dynamics

u pb dating of calcite cement and diagenetic history in microporous carbonate reservoirs case of the urgonian limestone france microporous carbonates can constitute excellent hydrocarbon reservoirs if their micro pore and or nanopore structure is sufficiently developed and continuous in such deposits assessing the exact timing of reservoir property stabilization is critical to better understand the postdepositional processes favorable to the creation or preservation of porosity however placing reliable and accurate chronological constraints on the formation of microporosity in these reservoirs is a major challenge in this study we performed absolute u pb dating of calcite cements occurring in the urgonian microporous limestone northern tethys margin of southeastern france u pb ages ranging between 96 7 4 9 ma and 90 5 1 6 ma were obtained on the major calcitic phase responsible for the cementation and therefore the stabilization of microporosity indicating that this diagenetic process occurred synchronously at the regional scale following an extended subaerial exposure our results show that 1 the mineralogical stabilization process responsible for the formation of an excellent pervasive microporous network took place relatively early and 2 the so acquired reservoir quality was preserved for more than 90 m y these observations emphasize the importance of long exposure periods and associated meteoric influx for the formation and preservation of good microporous reservoirs

pore geometry as a control on rock strength the strength of rocks in the subsurface is critically important across the geosciences with implications for fluid flow mineralisation seismicity and the deep biosphere most studies of porous rock strength consider the scalar quantity of porosity in which strength shows a broadly inverse relationship with total porosity but pore shape is not explicitly defined here we use a combination of uniaxial compressive strength measurements of isotropic and anisotropic porous lava samples and numerical modelling to consider the influence of pore shape on rock strength micro computed tomography ct shows that pores range from sub spherical to elongate and flat ellipsoids samples that contain flat pores are weaker if compression is applied parallel to the short axis i e across the minimum curvature compared to compression applied parallel to the long axis i e across the maximum curvature numerical models for elliptical pores show that compression applied across the minimum curvature results in relatively broad amplification of stress compared to compression applied across the maximum curvature certain pore shapes may be relatively stable and remain open in the upper crust under a given remote stress field while others are inherently weak quantifying the shape orientations and statistical distributions of pores is therefore a critical step in strength testing of rocks

evidence of across shelf transport of fine grained sediments turbidite filled shelf channels in the campanian aberdeen member book cliffs utah usa the shore normal transport of fine grained sediments by shelf turbidity currents has been the focus of intense debate over the last 20 years many have argued that turbidity currents are unlikely to be a major depositional agent on the shelf however sedimentological architectural stratigraphic and palaeogeographic data from the campanian aberdeen member book cliffs eastern utah suggests otherwise and clearly demonstrates that storm generated and river flood generated underflows can transport a significant volume of fine grained sediments across the shelf these across shelf flowing turbidity currents cut large subaqueous channel complexes up to 7 m deep tens of kilometres basinward of their time equivalent shoreface the shelf channels were filled with organic rich siltstones mudstones and very fine to fine grained bouma like sandstone beds including wave modified turbidites hyperpycnites and classical turbidites deposition was above storm wave base palaeocurrent data reveal an overwhelmingly dominant across shelf east south east offshore directed transport trend tectonic activity and or concomitant palaeogeographic reorganization of the basin may favour the generation of these turbidite rich shelf deposits by altering the relative balance of wave versus fluvial energy increased erosion and sediment supply rates because of tectonic uplift of the hinterland may have increased the probability of fluvial dominance along the coastline and hence the possibility of submarine channelization in front of the river mouths additionally the coastline may have become more sheltered from direct wave energy thus allowing the fluvial processes to dominate seasonal increases in rainfall and storm activity may also favour the generation of across shelf underflows on wave dominated shorelines isolated shelf channels and lobes are most likely to be found down dip of fluvial feeder systems in relatively high sediment supply settings these features are also most likely to occur in systems tracts that straddle a sequence boundary especially those which are tectonically generated as these would enhance the potential for altering basin morphology and hence the balance of fluvial and wave energy isolated shelf channels are recognized in older and younger strata in the book cliffs region implying that wave supported gravity flows were a recurrent phenomena in the campanian of utah it is probable that isolated shelf bodies are preserved in other stratigraphic intervals in the cretaceous western interior of north america and other basins worldwide and are currently being overlooked or misidentified shoreface to shelf facies models should be revised to incorporate turbidite rich shelf deposits in some shelf settings

calcite twinning strains from syn faulting calcite gouge small offset strike slip normal and thrust faults we have evaluated the stress strain behavior of calcite precipitated and mechanically twinned in small offset strike slip normal and thrust faults of a variety of ages and from a variety of tectonic settings n 3001 twin measurements 63 strain analyses from 18 field sites five strike slip faults with syn faulting horizontally striated calcite rake 0 were studied and we report the orientations of the contemporaneous stress strain field associated with each fault intrusion of the marathon large igneous province mafic dikes 2 1 ga in archean crust minnesota usa post keweenaw rift 1 1 ga faulting island lake fault central ontario canada subduction associated with metamorphic core complex formation cretaceous china subduction cretaceous to miocene italy and continental extension recently active furnace creek fault death valley california usa seven normal faults with synfaulting dip slip striated calcite were studied and are from the following tectonic settings a normal fault slip surface in an ordovician piedmont fold appalachian s paleo subduction associated with cretaceous metamorphic core complex formation china 3 sites the paleo extensional atlantic margin 55 ma ireland 1 site with a u pb calcite age continental extension 1 active site mojave desert a transcurrent margin jamaica 1 active fault site and subduction 2 active faults along the eur african margin in italy with calcite u th disequilibria ages and crete respectively six thrust fault examples are all from convergent orogenic settings the basal thrust of the penokean 1850 ma fold and thrust belt the penokean orogen foreland in mesabi range banded iron formation folds an offset breccia body in the permian gondwanide belt ellsworth mountains antarctica the frontal thrust of the gondwanide cape belt south africa the paleocene frontal prospect thrust sevier belt wyoming and an alpine foreland back thrust lulworth cove u k for each strike slip fault system the twinning shortening strain is horizontal and at an angle of 0 60 to the respective fault plane dextral or sinistral although in the majority of cases the shortening axis is parallel to fault strike 13 of 23 results in each normal fault example dip slip kinematic striations dominate the faulted surface yet the orientation of the maximum principal compressive stress 1 and shortening strain axis e1 are not 45 to the fault plane as predicted but are sub horizontal and either strike parallel 25 of 35 results or strike normal 10 of 35 results thrust faults preserve shortening strain axes parallel to the dip slip kinematic direction within the fault plane plane strain and not at 45 to the principal plane 5 of 5 results none of the fault stress strain field results reported here support the andersonian or mohr coulomb criteria for stress strain relations predicted along faults

a geophysical interpretation of the geology of conception bay newfoundland geophysical data from conception bay and the adjacent peninsulas of the avalon peninsula newfoundland are presented and quantitatively interpreted using two dimensional models to interpret the geology beneath the bay the portion of the bay underlain by mafic volcanic rocks is determined and the maximum extent of the cambro ordovician rocks containing the wabana hematite deposit is delineated all gravity and magnetic anomalies in the area are explained in terms of density and magnetic susceptibility variations confined to the upper 12 km of the crust the geophysical models indicate that mafic volcanics underlie a significant portion of the study area and are more extensive than indicated by the surface outcrop on land the models also indicate significant vertical movement on the topsail fault and on the extension of a fault passing out into the bay near holyrood the cambro ordovician sediments are confined to the southern portion of the block bounded by these faults the geophysical data are unable t

wave enhanced sediment gravity flows and mud dispersal across continental shelves reappraising sediment transport processes operating in ancient mudstone successions recent studies of marine shelf sediment dispersal show that wave enhanced sediment gravity flows are widespread phenomena and can transport large volumes of fluid mud rapidly across low gradient shelves flow evolution is controlled by sediment supply seabed gradient and spatial distribution of wave energy at the seabed using existing flow models we predict that such flows in mud dominated sediments will develop a three part microstratigraphy produced by changing flow conditions beginning with wave induced turbulent resuspension then development of a wave enhanced sediment gravity flow prior to lutocline collapse and suspension settling petrographic examination of modern flow deposits collected from the eel shelf reveals that resultant beds possess a microstratigraphy consistent with our hypothesis a silt rich basal subunit with curved ripple laminae abruptly overlain by a subunit composed of continuous intercalated silt clay laminae and an upper clay rich drape analyses of beds from ancient mud rich outer shelf and basinal successions cleveland ironstone jurassic uk and mowry shale cretaceous united states show that they too contain beds with this three part organization suggesting that such flows were active in these ancient settings too recognition of these microstructures in these ancient mud dominated successions demonstrates that sediment in these settings was commonly reworked and transported advectively downslope by high energy events contrasting with previous interpretations of these units that deposition was dominated by quiescent suspension settling identification of these recognition criteria now allows the products of this newly recognized sediment dispersal mechanism to be identified in other shale dominated successions

hematite fault rock thermochronometry and textures inform fault zone processes abstract minerals on fault surfaces record fluid rock interaction strain and or heat during fault slip fault hosted hematite is amenable to u th he he thermochronometry hematite he dates reflect fault related processes or exhumation depending on hematite growth above or below the grain size controlled closure temperature and processes that promote open system behavior deconvolving these phenomena requires multi scale hematite textural characterization and constraints on the ambient thermal history from conventional thermochronometry two examples of this approach include investigations of hematite coated fault surfaces from exhumed damage zones in the seismically active wasatch fault zone wfz ut and painted canyon fault pcf paralleling the southern san andreas fault mecca hills ca wfz fault mirrors preserve sub m scale polygonal grain textures and hematite he data patterns that together with host rock apatite he data are consistent with localized friction generated heat hematite he loss and hematite recrystallization during damage zone seismicity