encrusting corals on a latest ordovician to earliest silurian rocky shore southwest hudson bay manitoba canada paleozoic tabulate corals are generally thought to have been free standing a flattened disc shaped to dome shaped morphology providing a degree of stability in shallow water high energy environments the ability to encrust has previously been suggested by patterns of competitive overgrowth in certain species definite proof of encrustation by favositid corals is exhibited in an extraordinary example of an ancient rocky shore exposed for 350 m on hudson bay near churchill manitoba carbonate strata attributed to the upper ordovician port nelson or lower silurian severn river formations locally transgress a massive precambrian quartzite an ancient shoreface is clearly marked by large smoothly eroded boulders of the dark quartzite commonly 2 10 m in diameter the boulders are buried in coarse carbonate debris but corals up to 20 cm in diameter are found cemented directly onto the surface of some boulders deep pitting of many boulders to a depth of 2 3 cm was contemporaneous and may have been promoted by unpreserved encrusters such as sponges or anemones

lower silurian aeronian megafaunal and conodont biofacies of the northwestern michigan basin lower silurian llandovery aeronian carbonates of the burnt bluff group northwestern michigan basin represent a transect along a southward dipping ramp that extends from tidal flat to basin environments benthic megafaunas include an ostracod biofacies tidal flat stromatoporoid coral biofacies very shallow subtidal pentamerid crinozoan and crinozoan stromatoporoid biofacies deeper subtidal and a crinozoan sponge biofacies distal ramp and basin the crinozoan sponge biofacies which includes diverse small crinozoan ossicles 19 types of siliceous sponge spicules and at least 65 other taxa has a biota that is similar to those of silurian continental margins megafaunal biofacies indicate an early silurian gradient going from a shoreline in the north to water depths of perhaps 60 m in the south the burnt bluff group contains conodonts of the icriodella discreta icriodella deflecta zone as an onshore biofacies with panderodus kockelella ozarkodina icriodella and oulodus and an offshore biofacies with panderodus walliserodus and aspelundia rcsumc les carbonates du silurien infkrieur llandovery aeronien du groupe de burnt bluff dans la rcgion nord ouest du bassin de michigan rephentent un transect le long d une rampe inclince vers le sud s ktalant d un environnement d estran tidal a celui d un bassin les mkgafaunes benthiques incluent un biofaciks a ostracodes estran tidal un biofaciks a stromatoporoi des coraux infratidal trks peu profond des biofaciks a pentamkrides crinozoaires et crinozoaires stromatoporoi des infratidal profond et un biofaciks a crinozoaires cponges rampe distale et bassin le biofaciks a crinozoaires cponges qui inclut diverses petites plaques de crinozoaires 19 types de spicules d cponges siliceux et au moins 65 autres taxons posskde un biote qui est similaire a ceux des marges continentales siluriennes les biofaciks mkgafauniques indiquent un gradient au silurien prccoce allant d une ligne de rivage dans le nord jusqu a des profondeurs d eau atteignant peut etre 60 m dans le sud le groupe de burnt bluff contient des conodontes de la zone a icriodella discreta icriodella deflecta comme biofaciks intracdtier accompagncs de panderodus kockelella ozarkodina icriodella et oulodus et un biofaciks extrac6tier avec panderodus walliserodus et aspelundia traduit par la rcdaction

carbon isotopes and event stratigraphy near the ordovician silurian boundary yichang south china abstract the organic carbon isotope data through the unweathered ordovician silurian boundary strata at the wangjiawan riverside section which is c 180 m southeast of the wangjiawan north section the gssp for the base of the hirnantian stage upper ordovician show that a positive 13 c org excursion begins just below the base of the hirnantian stage and peaks in the lower part of the n extraordinarius biozone this is followed by an interval of slightly reduced 13 c values and a second peak of 2 above pre hirnantian values which occurs in the lower part of the n persculptus biozone upper hirnantian the peaks in 13 c org values can be correlated well with episodes of glacial expansion described from africa and peri gondwanan europe evidence from sedimentological faunal and geochemical data from south china as well as the evidence of glacial sediments in north africa all suggests a short lived glaciation of 1 ma in the ordovician south pole region consisting of at least two major pulses the first phase of gradual glacial expansion began just before the hirnantian epoch and the second phase ended with rapid melting in the late hirnantian early n persculptus biozone

a pliocene cliff line around the giza pyramids plateau egypt abstract escarpments bordering the giza pyramids plateau represent the cliff line of a pliocene transgression up the pre nile eonile valley geomorphologically a limestone cliff can be distinguished from a slip block shore associated with a distinct fining up sequence differences in bedrock lithology and in structure joint pattern faults are morphogenetic controls the pre pliocene morphology with escarpments that allowed the development of later cliff lines is related to deep incision of the eonile drainage system caused by the desiccation of the mediterranean sea during the messinian

variations in permafrost thickness in response to changes in paleoclimate solutions to the stefan problem for the motion of the base of ice bearing permafrost in response to changes in paleoclimate were obtained using perturbation finite difference and finite element methods paleotemperature models were used to investigate the thickness response to compare solution methods to determine the current state of the permafrost and to determine constraints on the models the perturbation and finite difference methods used the approximation of linear temperature profiles while the finite element method did not there was a transient thickness response of about 41 kyr implying that paleotemperature records of greater length are needed for models and that the permafrost loses its memory of past conditions for much longer times faster thawing rates slower freezing rates and greater variations in thickness were found for the perturbation and finite difference solutions compared to the finite element solution these results appear to be caused by the simplifying assumptions in the former solutions a lag about 20 kyr exists between changes in surface temperature and thickness response and a small thermal offset is apparent in the finite element solution small asymmetries exist in the freezing and thawing rates and the thickness response paleotemperature models based on ice cores predict current permafrost thicknesses that are too large models with the long term mean surface temperature of permafrost within a few degrees of the current value of 11 c and with the last glacial period temperatures no more than 6 8 c lower are compatible with current prudhoe bay conditions these include models developed for east siberia from isotopic profiles in deep sea sediments and for barrow alaska modified for prudhoe bay these models predict that the permafrost thickness at prudhoe bay varied by about 10 or less 60 m over the last glacial cycle freezing and thawing rates were less than 6 mm yr 1 at present this permafrost should be near its long term equilibrium thickness and thawing at 1 mm yr 1

early cretaceous rifts of western and central africa an overview abstract the structure and evolution of early cretaceous rift basins in western and central africa are described two stages of rift development and fracturing have been identified 1 from neocomian to early aptian roughly e w and nw trending troughs upper benue n cameroon s chad sudan etc opened in response to a submeridian extensional regime in central africa while in western africa the n s trending transsaharian fault zone acted as a sinistral wrench 2 from middle aptian to late albian large northwest trending troughs e niger sudan sirte etc opened in response to a northeast extensional regime while the central african fault zone from benue to sudan exhibited strike slip movements generating pull apart basins these rift and fracture systems delimit three large blocks within the african plate a western block an arabian nubian block and an austral block the arabian nubian block tends to separate from the two other blocks migrating towards the north during the first stage of basin development and then towards the ne during the second stage the opening of the atlantic ocean was the dominant driving force for the western and austral blocks while the arabian nubian block probably moved in response to the opening of the indian ocean and to the evolution of the tethyan margin

gas hydrate dissociation in sediments pressure temperature evolution 1 hydrate bearing sediments may destabilize spontaneously as part of geological processes unavoidably during petroleum drilling production operations or intentionally as part of gas extraction from the hydrate itself in all cases high pore fluid pressure generation is anticipated during hydrate dissociation a comprehensive formulation is derived for the prediction of fluid pressure evolution in hydrate bearing sediments subjected to thermal stimulation without mass transfer the formulation considers pressure and temperature dependent volume changes in all phases effective stress controlled sediment compressibility capillarity and the relative solubilities of fluids salient implications are explored through parametric studies the model properly reproduces experimental data including the pt evolution along the phase boundary during dissociation and the effect of capillarity pore fluid pressure generation is proportional to the initial hydrate fraction and the sediment bulk stiffness is inversely proportional to the initial gas fraction and gas solubility and is limited by changes in effective stress that cause the failure of the sediment when the sediment stiffness is high the generated pore pressure reflects thermal and pressure changes in water hydrate and mineral densities comparative analyses for co2 and ch4 highlight the role of gas solubility in excess pore fluid pressure generation dissociation in small pores experiences melting point depression due to changes in water activity and lower pore fluid pressure generation due to the higher gas pressure in small gas bubbles capillarity effects may be disregarded in silts and sands when hydrates are present in nodules and lenses and when the sediment experiences hydraulic fracture

mount elbert gas hydrate stratigraphic test well alaska north slope coring operations core sedimentology and lithostratigraphy abstract in february 2007 bp exploration alaska the u s department of energy and the u s geological survey completed the bpxa doe usgs mount elbert gas hydrate stratigraphic test well mount elbert well in the milne point unit on the alaska north slope the program achieved its primary goals of validating the pre drill estimates of gas hydrate occurrence and thickness based on 3 d seismic interpretations and wireline log correlations and collecting a comprehensive suite of logging coring and pressure testing data the upper section of the mount elbert well was drilled through the base of ice bearing permafrost to a casing point of 594 m 1950 ft approximately 15 m 50 ft above the top of the targeted reservoir interval the lower portion of the well was continuously cored from 606 m 1987 ft to 760 m 2494 ft and drilled to a total depth of 914 m ice bearing permafrost extends to a depth of roughly 536 m and the base of gas hydrate stability is interpreted to extend to a depth of 870 m coring through the targeted gas hydrate bearing reservoirs was completed using a wireline retrievable system the coring program achieved 85 recovery of 7 6 cm 3 in diameter core through 154 m 504 ft of the hole an onsite team processed the cores collecting and preserving approximately 250 sub samples for analyses of pore water geochemistry microbiology gas chemistry petrophysical analysis and thermal and physical properties eleven samples were immediately transferred to either methane charged pressure vessels or liquid nitrogen for future study of the preserved gas hydrate additional offsite sampling analyses and detailed description of the cores were also conducted based on this work one lithostratigraphic unit with eight subunits was identified across the cored interval subunits ii and va comprise the majority of the reservoir facies and are dominantly very fine to fine moderately sorted quartz feldspar and lithic fragment bearing to rich sands lithostratigraphic and palynologic data indicate that this section is most likely early eocene to late paleocene in age the examined units contain evidence for both marine and non marine lithofacies and indications that the depositional environment for the reservoir facies may have been shallower marine than originally interpreted based on pre drill wireline log interpretations there is also evidence of reduced salinity marine conditions during deposition that may be related to the paleo climate and depositional conditions during the early eocene

observations related to tetrahydrofuran and methane hydrates for laboratory studies of hydrate bearing sediments the interaction among water molecules guest gas molecules salts and mineral particles determines the nucleation and growth behavior of gas hydrates in natural sediments hydrate of tetrahydrofuran thf has long been used for laboratory studies of gas hydrate bearing sediments to provide close control on hydrate concentrations and to overcome the long formation history of methane hydrate from aqueous phase methane in sediments yet differences in the polarizability of thf polar molecule compared to methane nonpolar molecule raise questions about the suitability of thf as a proxy for methane in the study of hydrate bearing sediments from existing data and simple macroscale experiments we show that despite its polar nature thf s large molecular size results in low permittivity prevents it from dissolving precipitated salts and hinders the solvation of ions on dry mineral surfaces in addition the interfacial tension between water and thf hydrate is similar to that between water and methane hydrate the processes that researchers choose for forming hydrate in sediments in laboratory settings e g from gas liquid or ice and the pore scale distribution of the hydrate that is produced by each of these processes likely have a more pronounced effect on the measured macroscale properties of hydrate bearing sediments than do differences between thf and methane hydrates themselves

volume change associated with formation and dissociation of hydrate in sediment 1 gas hydrate formation and dissociation in sediments are accompanied by changes in the bulk volume of the sediment and can lead to changes in sediment properties loss of integrity for boreholes and possibly regional subsidence of the ground surface over areas where methane might be produced from gas hydrate in the future experiments on sand silts and clay subject to different effective stress and containing different saturations of hydrate formed from dissolved phase tetrahydrofuran are used to systematically investigate the impact of gas hydrate formation and dissociation on bulk sediment volume volume changes in low specific surface sediments i e having a rigid sediment skeleton like sand are much lower than those measured in high specific surface sediments e g clay early hydrate formation is accompanied by contraction for all soils and most stress states in part because growing gas hydrate crystals buckle skeletal force chains dilation can occur at high hydrate saturations hydrate dissociation under drained zero lateral strain conditions is always associated with some contraction regardless of soil type effective stress level or hydrate saturation changes in void ratio during formation dissociation decrease at high effective stress levels the volumetric strain during dissociation under zero lateral strain scales with hydrate saturation and sediment compressibility the volumetric strain during dissociation under high shear is a function of the initial volume average void ratio and the stress dependent critical state void ratio of the sediment other contributions to volume reduction upon hydrate dissociation are related to segregated hydrate in lenses and nodules for natural gas hydrates some conditions e g gas production driven by depressurization might contribute to additional volume reduction by increasing the effective stress

searching for travertines calcretes and speleothems in deep time processes appearances predictions and the impact of plants common models for modern calcite precipitation in and around caves soils springs and streams involve co 2 supplied by thick high p co 2 biogenic soils which were probably thin or non existent before vascular plants indeed plant influenced chemical weathering might have caused accelerated terrestrial carbonate production from the devonian onwards however terrestrial carbonates have also been documented from the archaean proterozoic cambrian ordovician and silurian mechanisms which could have caused non marine carbonates to precipitate without organic rich soils are described and some geological events likely to have influenced non marine carbonate precipitation up to the origin of vascular plants are highlighted as organisms have evolved so have the petrographic characteristics of non marine carbonates some examples of this are also given here

palaeokarst tidal erosion surfaces and stromatolites in the silurian eke formation of gotland sweden irregular scalloped erosion surfaces in the shelf carbonate sequences of the lower eke formation ludlow series upper silurian in the east of gotland sweden comprise series of shallow hollows separated by sharp crested ridges and cavities with sculptured undercut walls cut into lithified sediment these represent analogues of the solution basins formed in modern coastal and subaerial karst terrains discrete erosional cavities merge on enlargement by breaching of the intervening walls to leave remnant tapering ridges sets of the ridges and basins seen in surface view show an average width of basins of 1 2 m with relief of 40 50 cm and pronounced n s axes for the ridges this alignment may reflect the local drainage direction the lowermost erosion surface passes laterally into a planar mineralized horizon at the top of the underlying hemse group that was resistant to and forms the base level of erosion because of restricted exposure of higher eke formation sediments the upper limit of erosion remains unknown there is no evidence of caliche or subaerial diagenetic textures but solution vugs are common in the eroded limestones marine hard bottom biota attached to some surfaces and transition from scalloped to planar surfaces indicate erosion in tidal zones but subaerial karstic erosion is also inferred the resubmerged karst eroded topography is overlain by shallow marine carbonates including small organic buildups finely layered stromatolitic mats developed over the initial infill in subtidal environments and grew to form domed mounds within the erosional cavities they abut sharply against bounding side walls and overhangs some emergence is evident from desiccation features in the upper parts of mounds biostratigraphical evidence dating the events from initial uplift and karstic erosion to covering of the drowned relief topography places the whole sequence within upper ludlow times

a stepped karst unconformity as an early silurian rocky shoreline in guizhou province south china abstract where succeeded by marine strata karst unconformities signify a former rocky coastline such relationships may help sort out relative sea level changes and aspects of local geography controlling facies distribution an exceptional example of an early silurian karst shore is well exposed near the village of wudang in central guizhou province near the capital city of guiyang in south china here the lower silurian kaochaitien formation oversteps 63 m of paleotopographic relief in limestones belonging to the llanvirn guniutan formation and caradoc to early ashgill huanghuachong formation ordovician the corresponding rise in sea level took place coeval with tectonic uplift as confirmed by a regionally diachronous relationship in the ordovician silurian boundary across a 250 km track from central to northern guizhou province the change in sea level also fits with a global rise of sea level in late aeronian later llandovery early silurian time borings of the ichnofossil trypanites are reported from the karst surface of the huanghuachong formation and silurian strata fill sink holes in this unit over 5 m deep the silurian karst shoreline near wudang is integrated with other regional data to construct a paleogeographic map covering the northern half of guizhou province

a possible relation between pulses of platform activation and plate kinematics abstract the idea of the cyclic evolution of platforms may have an explanation related to plate kinematics as a function of two main parameters the spreading rate and rotation pole switches these kinematic parameters as defined by other authors studying the south atlantic appear to bear a coherent relationship with pulses of platform activation in south america and africa in gondwana s history after its break up at least four major peaks of volcano tectonic activity on the continents seem to be related to important changes in position of the rotation poles and the spreading rates of the south american and african plates mantle convection patterns such as those suggested by mckenzie on the pacific floor can be seen as feasible mechanisms for explaining the origin and shape of large syneclises and archings

arctic north american seasonal temperatures from the latest miocene to the early pleistocene based on mutual climatic range analysis of fossil beetle assemblages late tertiary and early quaternary fossil beds in the arctic regions of north america have yielded abundant well preserved remains of plants and arthropods documenting the existence of coniferous forests in the high arctic latitudes nearly all of the beetle coleoptera specimens in these fossil assemblages represent extant species we have applied the mutual climatic range mcr method of paleotemperature analysis to fossil beetle assemblages from 11 sites to estimate mean summer t max and winter t min temperatures we found that arctic t min values during the latest miocene and pliocene were substantially warmer than they are today the mcr estimates therefore support the scenario derived from the paleobotanical data namely that arctic pliocene climates were far less continental several pliocene age assemblages from the high arctic yielded t max estimates 9 10 c warmer than modern values at the sites this is the same degree of warming required to allow coniferous forests to grow in the high arctic by 3 million years bp a cooling trend is marked in the paleobotanical and fossil beetle evidence from alaska all assemblages dating between 5 7 and 2 million years bp yielded calibrated t max values between 12 4 and 13 8 c regardless of location thus the insect fossil data support the theory that there was far less latitudinal gradation in temperatures during the late pliocene than there is today our reconstructions suggest regional climatic cooling especially winter temperatures began by at least 2 million years bp

alkaline rocks from continental brazil abstract the present literature review on brazilian alkaline rocks stresses mainly the petrographic and geologic aspects at least eight different rock associations are represented agewise four groups are found among southern brazilian outcrops an older one about 240 m y only that is still poorly known the massifs clustered around jacupiranga about 130 m y old a few occurrences 100 110 m y old tunas itapirapua and the youngest and most important one with an age spread from about 80 m y to about 53 m y recent research shows a clear tectonic control both on local and on regional scales of alkaline occurrences in southern brazil alkaline magmatism was set off by pre drift and drift activity and is at its onset geologically related to basaltic activity emplacement of many massifs is also locally controlled by old lineaments e g in the minas gerais goias belt as is emphasized by geophysical data on a petrographic and chronologic basis several alkaline provinces are distinguished in southern brazil preliminary data on the cambrian precambrian rocks from southern bahia state a province with undersaturated syenites and litchfieldites and from cratonic areas in northern brazil are also presented

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

uniformitarianism as a guide to rocky shore ecosystems in the geological record literature on pleistocene and neogene rocky shores is reviewed from a uniformitarian perspective to assess the fidelity of physical and biological information entrained in the geological record through present day processes coverage by latitude spans tropical to subarctic shores variations in paleotopography are illustrated by unconformities between sedimentary accumulations and rocks of igneous or non igneous origin former rocky shores occur across a range of geographic scales that include i spot localities ii embayments with continuous transition from exposed outer to protected inner shores and iii entire islands with windward and leeward shores differences in rate and mag nitude of sea level change affect rocky shore physiography terrace deposits characterize the pleistocene but ramp de posits typify older neogene shores on average species with hard parts account for about 50 of the modern rocky intertidal fauna on a regional basis regardless of latitude biodiversity is highest in mid latitudes fixed organisms with encrusting wedging or boring habits corals barnacles oysters other bivalves and vermetid gastropods show high potential for fossilization in growth position mobile organisms that cling to rocks gastropods crabs and echinoids suffer post mortem transport but may be immured within neptunian dikes or interstices among cobbles and boulders at best localized fossil deposits from the pleistocene reflect 30 of the biodiversity of skeletonized organisms tabulated from modern rocky shores on a regional basis uniformitarianism provides little insight into the diversity of soft bodied organisms excluding stromatolites that joined the ecosystem in precambrian times and the extent to which soft bodied organisms dominated shore life through later times

mount elbert gas hydrate stratigraphic test well alaska north slope overview of scientific and technical program abstract the mount elbert gas hydrate stratigraphic test well was drilled within the alaska north slope ans milne point unit mpu from february 3 to 19 2007 the well was conducted as part of a cooperative research agreement cra project co sponsored since 2001 by bp exploration alaska inc bpxa and the u s department of energy doe in collaboration with the u s geological survey usgs to help determine whether ans gas hydrate can become a technically and commercially viable gas resource early in the effort regional reservoir characterization and reservoir simulation modeling studies indicated that up to 0 34 trillion cubic meters tcm 12 trillion cubic feet tcf gas may be technically recoverable from 0 92 tcm 33 tcf gas in place within the eileen gas hydrate accumulation near industry infrastructure within ans mpu prudhoe bay unit pbu and kuparuk river unit kru areas to further constrain these estimates and to enable the selection of a test site for further data acquisition the usgs reprocessed and interpreted mpu 3d seismic data provided by bpxa to delineate 14 prospects containing significant highly saturated gas hydrate bearing sand reservoirs the mount elbert site was selected to drill a stratigraphic test well to acquire a full suite of wireline log core and formation pressure test data drilling results and data interpretation confirmed pre drill predictions and thus increased confidence in both the prospect interpretation methods and in the wider ans gas hydrate resource estimates the interpreted data from the mount elbert well provide insight into and reduce uncertainty of key gas hydrate bearing reservoir properties enable further refinement and validation of the numerical simulation of the production potential of both mpu and broader ans gas hydrate resources and help determine viability of potential field sites for future extended term production testing drilling and data acquisition operations demonstrated that gas hydrate scientific research programs can be safely effectively and efficiently conducted within ans infrastructure the program success resulted in a technical team recommendation to project management to drill and complete a long term production test within the area of existing ans infrastructure if approved by stakeholders this long term test would build on prior arctic research efforts to better constrain the potential gas rates and volumes that could be produced from gas hydrate bearing sand reservoirs

dividing the south american continent to fit a gondwana reconstruction a model based on continental geology abstract the south american continental plate has been affected by intraplate deformation since the start of west gondwana disruption in the lower cretaceous about 140 ma that the present shape of south america is not precisely the same as its shape in reassembled gondwana partly explains the imperfect fits of the conjugate margins of the south atlantic proposed since the first reconstruction models of the early 20th century several attempts at defining subplates within south america have been published but not all take account of existing knowledge of its continental geology here a subdivision into eight rigid subplates is proposed based primarily on geological and tectonic evidence our model is tested against three published models of a multi subplate africa as re shaped to the pre breakup outline of that continent by visual fitting and the use of piercing points the south america blocks were rotated and the euler poles calculated interactively in reconstruction software all three proposed fits had overlapping block margins within south america indicating post breakup rifting except for the transbrasiliano lineament this nne ssw crustal scale shear zone was used as a boundary for seven of the eight blocks it is clearly the main intraplate accommodation zone in south america and an important piercing point in relation to the kandi lineament in west africa the other block boundaries correspond to narrow zones with sedimentary basins and or dyke swarms that have developed since south atlantic opening each fit required a different configuration of the south america subplates since the pre rift disposition of the african subplates also differ from each other contributing to the uncertainty in any detailed reassembly

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

physical properties of sediment from the mount elbert gas hydrate stratigraphic test well alaska north slope this study characterizes cored and logged sedimentary strata from the february 2007 bp exploration alaska department of energy u s geological survey bpxa doe usgs mount elbert gas hydrate stratigraphic test well on the alaska north slope ans the physical properties program analyzed core samples recovered from the well and in conjunction with downhole geophysical logs produced an extensive dataset including grain size water content porosity grain density bulk density permeability x ray diffraction xrd mineralogy nuclear magnetic resonance nmr and petrography this study documents the physical property interrelationships in the well and demonstrates their correlation with the occurrence of gas hydrate gas hydrate gh occurs in three unconsolidated coarse silt to fine sand intervals within the paleocene and eocene beds of the sagavanirktok formation unit d gh 614 4 m 627 9 m unit c gh1 649 8 m 660 8 m and unit c gh2 663 2 m 666 3 m these intervals are overlain by fine to coarse silt intervals with greater clay content a deeper interval unit b is similar lithologically to the gas hydrate bearing strata however it is water saturated and contains no hydrate in this system it appears that high sediment permeability k is critical to the formation of concentrated hydrate deposits intervals d gh and c gh1 have average plug intrinsic permeability to nitrogen values of 1700 md and 675 md respectively these values are in strong contrast with those of the overlying gas hydrate free sediments which have k values of 5 7 md and 49 md respectively and thus would have provided effective seals to trap free gas the relation between permeability and porosity critically influences the occurrence of gh for example an average increase of 4 in porosity increases permeability by an order of magnitude but the presence of a second fluid e g methane from dissociating gas hydrate in the reservoir reduces permeability by more than an order of magnitude published by elsevier ltd

effect of cementation on the small strain parameters of sands natural cementation affects the properties of soils the interpretation of in situ and laboratory test results and the selection of criteria for geotechnical design in this paper published exper

formation history and physical properties of sediments from the mount elbert gas hydrate stratigraphic test well alaska north slope abstract the synthesis of available geological information and surface temperature evolution in the alaska north slope region suggests that biogenic and deeper thermogenic gases migrated through fault networks and preferentially invaded coarse grained layers that have relatively high hydraulic conductivity and low gas entry pressures hydrate started forming before the beginning of the permafrost eventually the permafrost deepened and any remaining free water froze so that ice and hydrate may coexist at some elevations the single tested specimen depth 620 47 620 62 m from the d unit consists of uncemented quartzitic fine sand with a high fraction of fines 56 by mass finer than sieve 200 the as received specimen shows no evidence of gas present the surface texture of sediment grains is compatible with a fluvial deltaic sedimentation environment and shows no signs of glacial entrainment tests conducted on sediments with and without thf hydrates show that effective stress porosity and hydrate saturation are the major controls on the mechanical and geophysical properties previously derived relationships between these variables and mechanical geophysical parameters properly fit the measurements gathered with mount elbert specimens at different hydrate saturations and effective stress levels we show that these measurements can be combined with index properties and empirical geomechanical relationships to estimate engineering design parameters volumetric strains measured during hydrate dissociation vanish at 2 4 mpa therefore minimal volumetric strains are anticipated during gas production at the mount elbert well however volume changes could increase if extensive grain crushing takes place during depressurization driven production strategies if the sediment has unexpectedly high in situ porosity associated to the formation history or if fines migration and clogging cause a situation of sustained sand production

extent and bathymetry of north american platform seas in the early silurian the north american craton is 25 covered by lower silurian llandovery rocks based strictly upon the geographic area of surviving marine strata preserved in outcrop and the subsurface this figure does not take into account extensive post silurian tectonics and erosion isolated structural basins in which these strata are found today were not necessarily defined as corresponding topographic basins in the silurian analysis of interbasin structural arches and outliers provides important clues as to the actual extent of early silurian seas information on the age of tectonic origin for 15 prominent arches is reviewed the placement and significance of 11 key outliers is also discussed evidence of this kind indicates early silurian platform seas were among the most extensive of the paleozoic probably more than 65 of the north american craton was then flooded nothing on so vast a scale serves as a recent guide to the past the pliocene holocene bahamian banks do provide however worthy models for the role of bathymetry and water circulation as related to the changeover from laterally monotonous blanket deposits to a more complex mosaic of facies the original bathymetry of early silurian environments may be determined correlated and mapped on the basis of widespread carbonate cycles linked to sea level fluctuations the range of fully integrated facies patterns includes 1 coral stromatoporoid stromatolite paleosol cycles williston basin 2 pentamerid brachiopod coral stromatoporoid stromatolite cycles michigan basin and 3 stricklandiid brachiopod pentamerid brachiopod coral stromatoporoid cycles east iowa basin with shallow bathymetries of 0 30 m the williston class tends to represent mosaic facies while with bathymetries of 0 60 m and 10 90 m the deeper water michigan and iowa classes typically involve blanket deposits bathymetry of other basin deposits generally fits one of these three classes maximum and minimum stands in sea level during late llandovery time are represented by bathymetric maps

rocky shoreline deposits in the lower silurian upper llandovery telychian chicotte formation anticosti island quebec the upper llandovery telychian chicotte formation is a regionally extensive crinoid rich unit exposed in the south central part of anticosti island in the gulf of st lawrence the chicotte encrinites represent an inner ramp crinoidal sand shoal complex about 80 m thick that prograded over deeper middle to outer ramp facies of the underlying jupiter formation in response to a long term sea level fall the typical depositional unit in the chicotte formation is a metre scale subtidal cycle indicating that higher frequency sea level changes were also present metre scale cycles are typically characterized by coarsening upward locally cross bedded encrinitic material capped by a sharp erosional surface these bounding surfaces change progressively upsection from simple planar to low relief scalloped erosional surfaces to complex polyphase surfaces formed by distinct but superimposed erosional events three dimensional paleomorphological features with local relief up to 50 m associated with erosional sur