marine oxygenation lithistid sponges and the early history of paleozoic skeletal reefs abstract microbial carbonates were major components of early paleozoic reefs until coral stromatoporoid bryozoan reefs appeared in the mid ordovician microbial reefs were augmented by archaeocyath sponges for 15 myr in the early cambrian by lithistid sponges for the remaining 25 myr of the cambrian and then by lithistid calathiid and pulchrilaminid sponges for the first 25 myr of the ordovician the factors responsible for mid late cambrian microbial lithistid sponge reef dominance remain unclear although oxygen increase appears to have significantly contributed to the early cambrian explosion of marine animal life it was followed by a prolonged period dominated by greenhouse conditions as sea level rose and co2 increased the mid late cambrian was unusually warm and these elevated temperatures can be expected to have lowered oxygen solubility and to have promoted widespread thermal stratification resulting in marine dysoxia and hypoxia greenhouse conditions would also have stimulated carbonate platform development locally further limiting shallow water circulation low marine oxygenation has been linked to episodic extinctions of phytoplankton trilobites and other metazoans during the mid late cambrian we propose that this tendency to dysoxia hypoxia in shallow marine environments also limited many metazoan reef builders in contrast during the mid late cambrian the ability of lithistid sponges to withstand low oxygen levels allowed them to create a benthic association with microbial carbonates that dominated global reefs these conditions ameliorated during the ordovician as temperature decline promoted ocean ventilation the prolonged time gap occupied by low diversity reefs between the cambrian explosion and the great ordovician biodiversification event reflects elevated temperatures and reduced marine oxygenation that limited metazoan diversification in shallow marine environments

the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

development and demise of a fringing coral reef during holocene environmental change eastern ningaloo reef western australia abstract reefs lining the western exmouth gulf located at the northern limit of the 300 km long ningaloo reef in western australia represent modern incipient coral reefs and veneers of non reef building coral algal communities on exposed pleistocene or give up holocene reef surfaces acquisition of sixteen cores alongside u series tims dates were used to confirm the nature of the pleistocene foundation and characterise holocene reef development three calcretised pleistocene units were identified as 1 the last interglacial mis 5e reef directly underlying holocene units 2 a mid pleistocene mis 7 bioclastic conglomerate unit and 3 a pleistocene alluvial fanglomerate eight holocene reef facies total thickness of 1 8 5 3 m included coral framework facies domal arborescent mixed tabulate and encrusting and detrital facies carbonate sand skeletal rubble and alluvial fan deposits holocene ages range from 7 93 to 5 8 ka bp with vertical accretion ranging from 1 46 to 9 88 mm year avg 4 11 mm year highest rates of accretion and thickest accumulation occurred in the most seaward and deepest cores composed of massive coral framestone and coralline algal crusts a six stage holocene chronology is proposed including 1 coastal inundation from 8 to 8 5 ka bp 2 initiation start up from 8 to 7 5 ka bp 3 rapid growth catch up and back step from 7 5 to 7 ka bp 4 rapid aggradational growth catch up from 7 to 6 5 ka bp 5 reef decline give up and detrital buildup from 6 5 to 5 8 ka bp and 6 detrital buildup and progradation from 5 8 ka bp to present changes in reef facies and the ultimate demise of the holocene reef probably involved a combination of increased sea level coastal flooding and erosion during the mid holocene highstand with associated increase in sedimentation turbidity and decline in water quality burial by sediment buildup during the mid holocene highstand and detrital progradation during the mid to late holocene regression and the introduction of alluvial sediment during cyclones and other severe storms to an already stressed community modern communities have thus shifted from coral dominated to bored macroalgal pavements this study shows that integration of reef development processes with response to environmental change can be used to assess future pressures on coral reef ecosystems globally

the glacial sequence at killiney se ireland terrestrial deglaciation and polyphase glacitectonic deformation depositional conditions of a complexly deformed glacigenic sequence at killiney bay on the west central margin of the irish sea are reconstructed deformation geometries provide conclusive evidence for polyphase glacitectonic deformation generated by terrestrial ice sheets they are dominated by pure shear simple shear and compressional deformation styles with abundant evidence for glacitectonic induced fracturing and hydrofracturing there is no evidence of subaqueous sediment flow induced deformation and impact deformation iceberg scouring rained out clasts glacigenic diamicton facies associations fa s are interpreted as glacitectonically stacked diachroneous units younging laterally away from palaeo ice margins simultaneous deposition of proximal overconsolidated subglacial tills and distal low viscosity flowtills occurred with the latter being deformed during re advances structural chronology of deformation styles demonstrates polyphase deformation of tills where glacial overriding produced overconsolidated and polyphase deformed subglacial tills from sediments initially deposited as low viscosity flowtills it is proposed that relatively late during deglaciation after retreat of a grounded irish sea ice sheet midland ice invaded the area and deformed and reworked recessional irish sea ice sequences deformation of these recessional sequences led to a heterogeneous stack of polyphase deformed glacigenic sediments with abundant hydrofracturing the killiney bay sequence and other sequences in the southern irish sea basin demonstrate that mis 2 deglaciation took place under terrestrial conditions with lower relative sea levels than present

production and off bank transport of carbonate sediment black rock southwest little bahama bank abstract surficial sediments between the intertidal zone and 600 m were studied with the objectives of characterizing their source dispersal pathways and sites of accumulation bioerosion is a major source of sediment in the intertidal and shallow subtidal environments in situ enclosure experiments showed that the urchin echinometra lucunter produced 667 mg sediment cm 2 yr 1 and an associated diverse rock infauna produced an additional 183 mg cm 2 yr 1 microborers caused erosion of 25 mg cm 2 yr 1 and feeding activity by the chiton acanthopleura granulata caused additional erosion of 10 mg cm 2 yr 1 sequential weighing of tethered limestone plates showed an abrasion rate of 5 5 mg cm 2 yr 1 due chiefly to impacts on the plate edges surficial sediments between the intertidal zone and the top of the bank margin wall at 30 m are gravel sand mixtures containing 0 2 mud molluscs and halimeda plates are the main constituents of gravel fractions sand fractions are composed of bioerosion produced carbonate rock fragments 1 70 skeletal material from halimeda 3 63 forams 1 33 molluscs 6 15 and coral 0 6 gravel and sand are transported as bedload in chutes across the narrow rocky shelf chutes end at 45 m and sediment traps indicate an average flux of 5 4 kg chute 1 yr 1 equivalent to 945 kg km 1 yr 1 moving to deep water a dense population of halimeda living on the wall between 30 70 m contributes gravel and sand to sediment on wall ledges at the base of the steep wall 65 a ramp slopes into the northwest providence channel between 120 300 m the ramp 30 slope is a zone by passed by coarse and fine sediment at 300 m the slope decreases to an average of 13 and an apron shaped body of mud is accumulating the apron extends parallel to the bank margin and wall and reaches depths 600 m traps showed that sediment flux to the ramp is 0 12 kg m 2 yr 1 which is 2 of the particle flux overtopping the bank margin surficial sediment of the ramp is mostly mud 70 which is primarily of shallow water origin some form of bottom current transporting gravel and sand mostly halimeda and abraded coral heads has cut gullies into the ramp this bottom flow is probably episodic and turbulent enough to suspend and supply halimeda sand to sediment traps on the ramp at 463 m

origin of minerals in joint and cleat systems of the pottsville formation black warrior basin alabama implications for coalbed methane generation and production coalbed methane is produced from naturally fractured strata in the lower pennsylvanian pottsville formation in the eastern part of the black warrior basin alabama major fracture systems include orthogonal fractures which consist of systematic joints in siliciclastic strata and face cleats in coal that strike northeast throughout the basin calcite and minor amounts of pyrite commonly fill joints in sandstone and shale and less commonly cleats in coal joint fill calcite postdates most pyrite and is a weakly ferroan coarse crystalline variety that formed during a period of uplift and erosion late in the burial history pyrite forms fine to coarse euhedral crystals that line joint walls or are complexly intergrown with calcite stable isotope data reveal large variations in the carbon isotope composition of joint and cleat fill calcite 10 3 to 24 3 peedee belemnite pdb but only a relatively narrow range in the oxygen isotope composition of this calcite 16 2 to 4 1 pdb negative carbon values can be attributed to 13c depleted co2 derived from the oxidation of organic matter and moderately to highly positive carbon values can be attributed to bacterial methanogenesis assuming crystallization temperatures of 2050c most joint and cleat fill calcite precipitated from fluids with 18o ratios ranging from about 11 to 2 standard mean ocean water smow uplift and unroofing since the mesozoic led to meteoric recharge of pottsville strata and development of freshwater plumes that were fed by meteoric recharge along the structurally upturned southeastern margin of the basin influxes of fresh water into the basin via faults and coalbeds facilitated late stage bacterial methanogenesis which accounts for the high gas content in coal and the carbonate cementation of joints and cleats diagenetic and epigenetic minerals can affect the transmissivity and storage capacity of joints and cleats and they appear to contribute significantly to interwell heterogeneity in the pottsville formation in highly productive coalbed methane fields joint and cleat fill calcite have strongly positive 13c values whereas calcite fill has lower 13c values in fields that are shut in or abandoned petrographic analysis and stable isotope geochemistry of joint and cleat fill cements provide insight into coalbed methane reservoir quality and the nature and extent of reservoir compartmentalization which are important factors governing methane production

changes in meridional temperature and salinity gradients in the north atlantic ocean 30 72 n during the last interglacial period eight deep sea sediment cores from the north atlantic ocean ranging from 31 to 72 n are studied to reconstruct the meridional gradients in surface hydrographic conditions during the interval of minimum ice volume within the last interglacial period using benthic foraminiferal 18o measurements and estimates of sea surface temperature sst and sea surface salinity sss we show that summer ssts and ssss decreased gradually during the interval of minimum ice volume at high latitude sites 52 72 n whereas they were stable or increased during the same time period at low latitude sites 31 41 n this increase in meridional gradients of ssts and ssss may have been due to changes in the latitudinal distribution of summer and annual average insolation and associated oceanic and atmospheric feedbacks these trends documented for the eemian ice volume minimum period are similar to corresponding changes observed during the holocene and may have had a similar origin

barnett shale gas production fort worth basin issues and discussion newark east barnett shale field fort worth basin texas is currently the most productive gas field in texas in terms of daily production and is growing at an annual rate of more than 10 however despite the fact that the barnett play has been studied intensely by very capable geologists and engineers from several companies over a period of many years there continues to be several misunderstandings concerning fundamental factors controlling the success of the barnett play of north texas barnett gas production is poorer in areas near faults and structural flexures anticlines and synclines fractures which are most abundant in these structural settings are detrimental to barnett production open natural fractures are rare in the barnett and have little or nothing to do with barnett productivity in areas where barnett shale is thermally mature with respect to gas generation it is slightly overpressured about 0 52 psi ft 11 76 kpa m limestone beds within the barnett formation are the product of debris flows that originated on a carbonate shelf to the north of the present basin center it appears that the barnett can be used as an exploration model for other basins especially analogous basins of the ouachita trend the history of the development of the barnett reservoir in north texas provides an excellent example of how persistence can lead to success in nonconventional gas plays

glaciomarine deposition around the irish sea basin some problems and solutions reconstructing the depositional processes and setting marine or terrestrial depositional environment of late devensian age glacigenic sediments around the irish sea basin isb is critical for developing an all embracing and consistent glacial model that can account for all observed field evidence identifying episodes of marine and terrestrial glacial deposition from field data is considered the first step in achieving this goal criteria for distinguishing marine and terrestrial glacial environments in the isb include the geomorphology sedimentology and faunal content biofacies of the associated deposits exposures of glacigenic sediments around the isb are very diverse in terms of their morphosedimentary characteristics and associated biofacies and thus inferred depositional processes and setting possible reasons for the diverse geological record include the differing geometry of eastern and western isb coasts time transgressive ice retreat and differential land rebound effects as a result of forebulge collapse and neotectonics poor geochronometric control on ice sheet events has not helped the correlation of isb events with glacial and climatic events elsewhere future investigations of glacial sites around the isb should use an integrated methodological approach involving a range of geomorphological sedimentary and biofacies data and dating control where possible this will help in developing a more precise and holistic late devensian glacial model that is constrained rigorously by field geological evidence copyright 2001 john wiley sons ltd

observations of wave transformation over a fringing coral reef and the importance of low frequency waves and offshore water levels to runup overwash and coastal flooding many low lying tropical islands are susceptible to sea level rise and often subjected to overwash and flooding during large wave events to quantify wave dynamics and wave driven water levels on fringing coral reefs a 5 month deployment of wave gauges and a current meter was conducted across two shore normal transects on roi namur island in the republic of the marshall islands these observations captured two large wave events that had waves with maximum heights greater than 6 m with peak periods of 16 s over the fore reef the larger event coincided with a peak spring tide leading to energetic highly skewed infragravity 0 04 0 004 hz and very low frequency 0 004 0 001 hz waves at the shoreline which reached heights of 1 0 and 0 7 m respectively water surface elevations combined with wave runup reached 3 7 m above the reef bed at the innermost reef flat adjacent to the toe of the beach resulting in flooding of inland areas this overwash occurred during a 3 h time window that coincided with high tide and maximum low frequency reef flat wave heights the relatively low relief characteristics of this narrow reef flat may further drive shoreline amplification of low frequency waves due to resonance modes these results 1 demonstrate how the coupling of high offshore water levels with low frequency reef flat wave energetics can lead to large impacts along fringing reef lined shorelines such as island overwash and 2 lend support to the hypothesis that predicted higher sea levels will lead to more frequent occurrences of these extreme events negatively impacting coastal resources and infrastructure

joint sets that enhance production from middle and upper devonian gas shales of the appalachian basin the marine middle and upper devonian section of the appalachian basin includes several black shale units that carry two regional joint sets j1 and j2 sets as observed in outcrop core and borehole images these joints formed close to or at peak burial depth as natural hydraulic fractures induced by abnormal fluid pressures generated during thermal maturation of organic matter when present together earlier j1 joints are crosscut by later j2 joints in outcrops of black shale on the foreland northwest side of the appalachian basin the east northeast trending j1 set is more closely spaced than the northwest striking j2 set however j2 joints are far more pervasive throughout the exposed devonian marine clastic section on both sides of the basin by geological coincidence the j1 set is nearly parallel the maximum compressive normal stress of the contemporary tectonic stress field shmax because the contemporary tectonic stress field favors the propagation of hydraulic fracture completions to the east northeast fracture stimulation from vertical wells intersects and drains j2 joints horizontal drilling and subsequent stimulation benefit from both joint sets by drilling in the north northwest south southeast directions horizontal wells cross and drain j1 joints whenever present then staged hydraulic fracture stimulations if necessary run east northeast i e parallel to the j1 set under the influence of the contemporary tectonic stress field thereby crosscutting and draining j2 joints

linking reef ecology to island building parrotfish identified as major producers of island building sediment in the maldives reef islands are unique landforms composed entirely of sediment produced on the surrounding coral reefs despite the fundamental importance of these ecological sedimentary links for island development and future maintenance reef island sediment production regimes remain poorly quantified using census and sedimentary data from vakkaru island maldives a sand dominated atoll interior island we quantify the major sediment generating habitats the abundance of sediment producers in these habitats and the rates and size fractions of sediment generated by different taxa the estimated annual sediment production is 685 000 kg or 370 m 3 75 of which is produced on the narrow outer reef flat despite composing only 21 of the total platform area approximately 65 of the platform acts solely as a sediment sink census data identify parrotfish as the major sediment producers generating 85 of the 5 7 kg m 2 of new sand grade sediment produced on the outer reef flat each year halimeda macroalgae produce a further 10 most as gravel grade material comparisons between production estimates and sedimentary data indicate that reef ecology and island sedimentology are tightly linked reef flat and lagoon sediments are dominated by coral and halimeda although fine to medium grained coral sand is the dominant 59 island constituent the generation of sediment suitable for maintaining this reef island is thus critically dependent on a narrow zone of high productivity reef but most especially on the maintenance of healthy parrotfish populations that can convert reef framework to sand grade sediment

upper cambrian intrashelf basin nolichucky formation southwest virginia appalachians an intrashelf basin located on the upper cambrian carbonate rimmed shelf miogeocline of the appalachian orogene appears to have controlled facies distribution during deposition of the nolichucky formation 0 to 985 ft 0 to 300 m thick the intrashelf basin was bordered along strike and toward the regional shelf edge by a rim of peritidal carbonates and by nearshore clastics toward the craton the peritidal carbonates passed into the intrashelf basin by way of a gently sloping carbonate ramp peritidal facies are cyclic upward shallowing stromatolitic carbonates elbrook and or honaker dolomite that grade basinward into cross bedded ooid and oncolitic intraclast grainstones these pass downslope into subwave base deeper ramp ribbon carbonates and thin limestone conglomerate maryville nolichucky lower limestone and maynardville limestone ribbon limestones are layers and lenses of trilobite packstone parallel and wave ripple laminated quartzose calcisiltite and lime mudstone arranged in storm generated fining upward sequences 0 39 to 2 in 1 to 5 cm thick that may be burrowed intrashelf basin facies nolichucky lower and upper shale are storm generated sequences of green calcareous shale with open marine biota parallel with hummocky laminated calcareous silt tone and intraformational flat pebble conglomerate and skeletal or ooid limestone with trace fossils glauconite zones and hardgrounds a 49 ft 15 m thick tongue of bioherm bearing cyclic carbonates within the shale package nolichucky middle limestone developed during a period of shoaling of the intrashelf basin development of the late cambrian carbonate rimmed shelf and its intrashelf ramp and basin may have been influenced by high carbonate production along the regional shelf edge by tectonic subsidence associated with a major shelf depocenter and by influx of terrigenous sediments which suppressed carbonate deposition in the basin understanding the nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar continental shelf facies which are widely distributed in the lower paleozoic and in the subsurface of the mesozoic recognition of basins located on pericratonic shelves is important because such basins influence the distribution of potential petroleum source beds and reservoir facies whose trends may be unrelated to regional shelf edge tr nds

the shale gas potential of tournaisian visean and namurian black shales in north germany baseline parameters in a geological context carboniferous black mudrocks with known petroleum potential occur throughout northern germany however despite numerous boreholes exploring for conventional hydrocarbons the potential for shale gas resources remains uncertain therefore an integrated investigation was conducted to elucidate the shale gas potential for three different carboniferous facies incorporating baseline parameters from sedimentological and organic geochemical analyses tournaisian namurian fine grained rocks of the culm facies with type ii iii kerogen were deposited in the basin center toc contents of up to 7 occur in the lower alum shale 3 6 vrr and up to 6 in the upper alum shale 4 4 vrr bands of organic rich black shales reflecting sea level variations controlled by global eustatic cycles occur within the tournaisian visean kohlenkalk facies north of the rhenish slate mountains and in the rugen island area in both areas the organic matter is characterized by a kerogen type ii iii with toc contents of up to 7 and maturities of up to 4 2 and 1 8 vrr respectively black hemipelagites intercalated with coarser grained silt and sandstones occur in the synorogenic flysch formation of the namurian a along the southern basin margin toc contents vary from 0 5 to 2 0 with type iii kerogen dominated organic matter and maturities of up to 2 5 vrr the baseline parameters presented in this paper indicate a shale gas potential for the sediments of the culm facies on the southern basin margin and of the kohlenkalk facies in the rugen area

understanding seismic heterogeneities in the lower mantle beneath the americas from seismic tomography and plate tectonic history we combine results from seismic tomography and plate motion history to investigate slabs of subducted lithosphere in the lower mantle beneath the americas using broadband waveform cross correlation we measured 37 000 differential p and s traveltimes 2000 pcp p and scs s times along a wide corridor from alaska to south america we invert the data simultaneously to obtain p and s wave velocity models we interpret slab structures and unravel subduction history by comparing our v s tomographic images with reconstructed plate motion from present day up to 120 myr convergence of the pacific with respect to the americas is computed using either 1 the pacific and indo atlantic hot spot reference frames or 2 the plate circuit passing through antarctica around 800 km depth four distinctive fast anomalies can be associated with subduction of the nazca cocos and juan de fuca plates beneath south central and north america respectively and of the pacific plate beneath the aleutian island arc the large fast anomalies in the lowermost mantle which are most pronounced in the s wave models can be associated with late cretaceous subduction of the farallon plate beneath the americas near 2000 km depth the images record the post 80 myr fragmentation of the proto farallon plate into the kula plate in the north and the farallon plate in the northeast near 1000 km depth we infer separate fast anomalies interpreted as the kula pacific juan de fuca and farallon slabs this interpretation is consistent with the volume and length of slabs estimated from the tomographic images and the plate history reconstruction

structural control of coalbed methane production in alabama abstract thin skinned structures are distributed throughout the alabama coalbed methane fields and these structures affect the production of gas and water from coal bearing strata extensional structures in deerlick creek and cedar cove fields include normal faults and hanging wall rollovers and area balancing indicates that these structures are detached in the pottsville formation compressional folds in gurnee and oak grove fields by comparison are interpreted to be detachment folds formed above decollements at different stratigraphic levels patterns of gas and water production reflect the structural style of each field and further indicate that folding and faulting have affected the distribution of permeability and the overall success of coalbed methane operations area balancing can be an effective way to characterize coalbed methane reservoirs in structurally complex regions because it constrains structural geometry and can be used to determine the distribution of layer parallel strain comparison of calculated requisite strain and borehole expansion data from calliper logs suggests that strain in coalbed methane reservoirs is predictable and can be expressed as fracturing and small scale faulting however refined methodology is needed to analyze heterogeneous strain distributions in discrete bed segments understanding temporal variation of production patterns in areas where gas and water production are influenced by map scale structure will further facilitate effective management of coalbed methane fields

a comparison of reef protected environments in western australia the central west and ningaloo coasts variability in the regional setting and morphology of cuspate forelands on the west coast of western australia is examined in this paper in accordance with this aim principal differences in the geologic and geomorphologic setting of three prominent sites on the west coast were established and their association with historical changes and contemporary oceanographic processes was examined the cuspate forelands investigated are jurien bay winderabandi point and turquoise bay the most significant differences in geologic setting are associated with the structure and location of an extensive offshore reef system morphologically the reef alters from south to north changing from a discontinuous ridge parallel to the shore along the central west coast to a nearly continuous fringing reef at ningaloo the reefs vary in distance from the shore being farthest in the south and closest in the north and they impound a series of inshore basins or lagoons the deeper southern basins are dominated by locally generated wind waves and wind generated currents the shallower northern basins are most markedly affected by tidal currents and wave pumping across the reef flats the large cuspate foreland at jurien on the central west coast has undergone shoreline configuration change in response to changing phases of storminess as well as in response to a change in focus for sediment deposition as a result of offshore reef erosion at winderabandi point on the ningaloo coast relict pleistocene limestone has provided the focus for sedimentation and morphology has been controlled by a balance in refracted wave energy and nearshore currents driven by tidal and wave set up variability at turquoise bay where the lagoonal basin is most shallow and narrow the morphology of the foreland suggests that it may at some stage have been migratory but its present asymmetrical shape is maintained by strong northerly longshore drift and strong currents exiting the lagoon through a nearby gap in the reef crest fundamental differences between the two coastal regions include the structure of the offshore reef processes driving flow of water within the lagoons and the role of storminess in evolution of coastal landforms although many questions regarding storm surge dynamics and landform change remain unanswered this research provides a significant contribution to the understanding of the evolution of morphological systems in low wave energy protected environments copyright 2000 john wiley sons ltd

the use of mineral magnetic analyses in the study of glacial diamicts a pilot study mineral magnetic methods of characterising glacial diamicts and their associated sediments are applied to deposits within the manx quaternary sequence the possible advantages of these techniques over more traditional methods of sediment characterisation are outlined and the results obtained in a pilot study are examined results show that both distinctions and similarities exist within the magnetic mineral assemblages of the four diamict units studied the possible implications of these results for interpreting the late quaternary history of the isle of man and the future potential of the techniques are briefly discussed

estimating the settling velocity of bioclastic sediment using common grain size analysis techniques most techniques for estimating settling velocities of natural particles have been developed primarily for siliciclastic sediments therefore to understand how these techniques apply to bioclastic environments measured settling velocities ws of bioclastic sedimentary deposits sampled from a nearshore fringing reef in western australia were compared with settling velocities calculated using results from several common grain size analysis techniques sieve laser diffraction and image analysis and established models the effects of sediment density and shape were also examined by using a range of density values and three different models of ws sediment density was found to have a significant effect on calculated ws causing a range in normalized root mean square error of up to 28 depending upon settling velocity model and grain size method accounting for particle shape improved errors in predicted ws by 3 to 6 and removed any velocity dependent bias which is particularly important for the fastest settling fractions when shape was accounted for and measured density was used normalized root mean square errors were 4 10 and 18 for laser diffraction sieve and image analysis respectively the results of this study show that established models of ws that account for particle shape can be used to estimate settling velocity of irregularly shaped sand sized bioclastic sediments from sieve laser diffraction or image analysis derived measures of grain size with a limited amount of error collectively these findings will allow for grain size data measured with different methods to be accurately converted to settling velocity for comparison this will facilitate greater understanding of the hydraulic properties of bioclastic sediment which can help to increase our general knowledge of sediment dynamics in these environments this article is protected by copyright all rights reserved

characteristics and origins of coal cleat a review abstract cleats are natural opening mode fractures in coal beds they account for most of the permeability and much of the porosity of coalbed gas reservoirs and can have a significant effect on the success of engineering procedures such as cavity stimulations because permeability and stimulation success are commonly limiting factors in gas well performance knowledge of cleat characteristics and origins is essential for successful exploration and production although the coal cleat literature spans at least 160 years mining issues have been the principal focus and quantitative data are almost exclusively limited to orientation and spacing information few data are available on apertures heights lengths connectivity and the relation of cleat formation to diagenesis characteristics that are critical to permeability moreover recent studies of cleat orientation patterns and fracture style suggest that new investigations of even these well studied parameters can yield insight into coal permeability more effective predictions of cleat patterns will come from advances in understanding cleat origins although cleat formation has been speculatively attributed to diagenetic and or tectonic processes a viable mechanical process for creating cleats has yet to be demonstrated progress in this area may come from recent developments in fracture mechanics and in coal geochemistry

early holocene deglaciation of the eastern coast of hudson bay abstract the final stage of deglaciation of hudson bay was a major holocene catastrophic event marked by the drainage of lake agassiz ojibway at 8 47 ka cal bp and the rapid collapse of the laurentide ice sheet previous work undertaken in the nastapoka river area eastern hudson bay demonstrated that during the relative sea level highstand that shortly followed the drainage of the lake the western margin of the quebec labrador ice sector rapidly retreated eastward to reach a stillstand position in a coastal hill range in this study an analysis of landsat 7tm images has allowed a mapping of large scale glacial landforms outwash deposits eskers flutings and de geer and rogen moraines between kuujjuaraapik se hudson bay and puvirnituq ne hudson bay the key results from this mapping are i ice contact outwash deposits mapped along the entire arc shaped coastline of the eastern hudson bay outline a major ice stillstand phase in the coastal hills that extended at least from kuujjuaraapik to inukjuak the presence of these hills allowed a stabilisation of the ice margin that led to the accumulation of thick and extensive ice contact submarine fans ii the position of these deposits on the down ice side west of large sets of flutings indicates an important phase of sediment delivery by a rapid ice flow phase toward a marine based ice margin iii a second system of outwash deposits observed farther inland indicates a subsequent phase of stabilisation of the ice margin during its retreat toward central quebec labrador

incremental accretion of a sandy reef island over the past 3000 years indicated by component specific radiocarbon dating 1 low lying reef islands appear particularly threatened by anticipated sea level rise and determining how they formed and whether they are continuing to accumulate sediment is essential for their sustainable management depositional chronology of warraber island a small sand cay in torres strait australia is re examined based on ams radiocarbon dating of specific skeletal components whereas radiometric dating of bulk sand samples indicated one or more discrete phases of mid late holocene deposition component specific ams radiocarbon dating of sand grains indicates sustained incremental growth over the past 3000 years ages on gastropods that lived on the reef flat around the island indicate continuing sediment production and island progradation in contrast to bulk ages and other components produced at greater distances growth of sand cays depends on the rate and pattern of sediment supply which are functions of the local ecology of the surrounding reef and reef flat and hydrodynamic constraints

the influence of coral reefs and climate change on wave driven flooding of tropical coastlines a numerical model xbeach calibrated and validated on field data collected at roi namur island on kwajalein atoll in the republic of marshall islands was used to examine the effects of different coral reef characteristics on potential coastal hazards caused by wave driven flooding and how these effects may be altered by projected climate change the results presented herein suggest that coasts fronted by relatively narrow reefs with steep fore reef slopes 1 10 and steeper and deeper smoother reef flats are expected to experience the highest wave runup wave runup increases for higher water levels sea level rise higher waves and lower bed roughness coral degradation which are all expected effects of climate change rising sea levels and climate change will therefore have a significant negative impact on the ability of coral reefs to mitigate the effects of coastal hazards in the future

glaciomarine sediments of the isle of man as a key to late pleistocene stratigraphic investigations in the irish sea basin the northern part of the isle of man in the central irish sea basin is identified as a raised marine foreland containing the largest subaerial exposure of last glaciation marine and glaciomarine sediments yet recognized on the british continental shelf a large push ridge that crosses the foreland identifies a major ice limit the ridge divides the foreland stratigraphy into a coarsening upward marine sequence of pelagic muds with dropstones sand and gravel to the south from offlapping stratified and massive sandy diamict assemblages overlying glaciotectonized marine sediments to the north coarse grained diamicts are argued to form part of a push ridge subaqueous outwash depositional system deposited when processes of suspension deposition density underflow ice rafting highly variable traction current activity and sediment gravity flow were operative adjacent to a grounded marine ice margin the identification of large offshore submarine banks aligned parallel to the bride moraine suggests that construction of the push ridge subaqueous outwash depositional system may have been repeated during ice recession this and published descriptions of other irish sea tills indicate that analogous structures and sediments are present offshore and around the irish sea basin

role of the birmingham basement fault in thin skinned thrusting of the birmingham anticlinorium appalachian thrust belt in alabama the birmingham anticlinorium is a northeast striking northwest verging thrust related fold associated with the jones valley and opossum valley frontal thrust ramps in the southern appalachian thin skinned sedimentary thrust belt in alabama the amplitude of the southeastern trailing limb of the anticlinorium cahaba synclinorium is greater than that of the forelimb coalburg syncline the depth to the top of basement rocks beneath the decollement is greater beneath the cahaba synclinorium than beneath the coalburg syncline commensurate with vertical separation of the top of basement along the down to southeast birmingham basement fault at the northwest boundary of the birmingham basement graben the frontal ramp that controls the geometry of the birmingham anticlinorium rises northwestward over the down to southeast birmingham basement fault the geometry kinematics and mechanics of structure of the birmingham anticlinorium reflect stratigraphic variations in mechanical properties within the cambrian to pennsylvanian stratigraphic succession the stratigraphic variations record episodic synsedimentary movement on the birmingham basement fault the regional decollement at the birmingham anticlinorium is in the middle to lower upper cambrian conasauga formation which is dominantly a massive carbonate and less than 800 m thick northwest of the birmingham basement graben but is a succession of shale and thin bedded limestone more than 2 000 m thick within the graben ductile deformation of the thick shale dominated succession localized the palmerdale and bessemer mushwads ductile duplexes along strike beneath the birmingham anticlinorium the massive carbonate regional stiff layer the cambrian ordovician knox group forms the mushwad roof the upper part of the knox group was eroded as a consequence of inversion of the graben during flexural subsidence associated with taconic tectonic loading of the southeastern margin of laurentia small scale synsedimentary structures indicate minor structural reactivation from late ordovician through early mississippian thickness and facies variations in upper mississippian lower pennsylvanian synorogenic clastic wedge deposits document large scale reactivation of the down to southeast birmingham basement fault the birmingham basement fault localizes both the leading edge of the mushwads of shale dominated conasauga formation and frontal ramps of the regional decollement

quaternary deposits and glacial stratigraphy in ireland quaternary stratigraphic studies in ireland have been based largely on lithostratigraphy the division of complex sedimentary sequences into the traditional framework of munsterian and midlandian events has created a series of stratigraphic scenarios which cannot be fully substantiated either by biostratigraphy or by facies basin analysis many of the current problems of glacial stratigraphy in ireland therefore arise directly from the field procedures used and the frameworks used to subdivide sedimentary sequences these problems are centred on the selection of type sites the subdivision of sedimentary sequences into unnatural divisions the concepts of direct and indirect stratigraphy classical models of climatically determined ice advance retreat cycles and the genetic inferences of the term till the conceptual basis of various stratigraphic schemes has changed little since the work of farrington 1934 1966 it is argued that a more realistic approach to description and assessment of glacigenic sediments should be based on basinal facies analysis and must include a documentation of the composition and geometry of three dimensional facies variations palaeoenvironmental interpretations of complex glacigenic sequences especially in coastal locations should take account of the influences of marine ice sheets on the sedimentary record in the past most sequences were interpreted in terms of glacioterrestrial models a large body of sedimentary evidence now indicates that shallow glaciomarine environments occurred along the margins of the last ice sheet during its maximum and subsequent retreat phases the locations and patterns of associated icemarginal systems indicate that the magnitude of and patterns of crustal deformation were greater and more complex than formerly realised thus the primary control on sea level variation at successive ice sheet margins was largely a function of glacioisostatic disequilibrium although complex glacial and glacially related sequences are known it is argued here that most of the multiple glacigenic sequences in ireland can be accommodated within the midlandian cold stage the basal units from certain sequences and erratic fans have been attributed to events earlier than the midlandian however it is difficult to compare these traces of earlier events from different sectors of the island due to poor dating correlation and the fact that direct and indirect stratigraphy is not adequately defined or separated the age of the gortian style interglacial sequences the implications of their floristic composition and their relationships to drift stratigraphy remains a major problem in stratigraphic constructions of the irish quaternary the stratigraphic significance of many till units must remain largely unknown until these matters are resolved at present it is not clear if the gortian sequences represent more than one interglacial a series of exposures in ulster provide evidence for major environmental changes during the midlandian cold stage these include an early stadial an early forest biozone 48 1 ka bp an early herb biozone 41 5 ka bp a middle interstadial phase of cold but non glacial aspect 30 5 ka bp a late stadial max 24 22 ka bp and a late glacial climatic oscillation the late midlandian stadial comprises a major glaciation that almost covered the island and a later more restricted phase when drumlins formed in the northern and western parts of the island max 17 ka bp

response of a fringing reef coastline to the direct impact of a tropical cyclone tropical cyclones generate extreme hazards along coastlines often leading to losses of life and property although coral reefs exist in cyclone prone regions globally few studies have measured the hydrodynamic conditions and morphological responses of reef fringed coastlines to tropical cyclones here we examine the impact of tropical cyclone olwyn on a section of australia s largest fringing reef ningaloo reef using in situ wave and water level observations topographic surveys and numerical modeling despite forereef significant wave heights reaching 6 m and local winds of 140 km h 1 average beach volume change was only 3 m3 m 1 the results indicate that this erosion was due to locally generated wind waves within the lagoon rather than the offshore waves that were dissipated on the reef crest a comparison of these volume changes to observations of tropical cyclone impacts along exposed sandy beaches quantitatively demonstrates the substantial coastal protection reefs can provide against extreme storms

natural fractures in the barnett shale and their importance for hydraulic fracture treatments gas production from the barnett shale relies on hydraulic fracture stimulation natural opening mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone knowledge of both the present day maximum horizontal stress which controls the direction of hydraulic fracture propagation and the geometry of the natural fracture system which we discuss here is therefore necessary for effective hydraulic fracture treatment design we characterized natural fractures in four barnett shale cores in terms of orientation size and sealing properties we measured a mechanical rock property the subcritical crack index which governs fracture pattern development natural fractures are common narrow 0 05 mm 0 002 in sealed with calcite and present in en echelon arrays individual fractures have high length width aspect ratios 1000 1 they are steep 75 and the dominant trend is west northwest other sets trend north south the narrow fractures are sealed and cannot contribute to reservoir storage or enhance permeability but the population may follow a power law size distribution where the largest fractures are open the subcritical crack index for the barnett shale is high indicating fracture clustering and we suggest that large open fractures exist in clusters spaced several hundred feet apart these fracture clusters may enhance permeability locally but they may be problematic for hydraulic fracture treatments the smaller sealed fractures act as planes of weakness and reactivate during hydraulic fracture treatments because the maximum horizontal stress trends northeast southwest and is nearly normal to the dominant natural fractures reactivation widens the treatment zone along multiple strands

mineralogy and geochemistry of palaeozoic black shales from peninsular malaysia implications for their origin and maturation abstract palaeozoic black shale bearing formations comprise 25 of the sedimentary cover in peninsular malaysia however nothing has been published regarding their geology composition and maturation representative samples from different ages and localities of the black shales were subjected to detailed mineralogical and geochemical investigations during this study to determine their origin these investigations also provide an opportunity to trace the changes in depositional environments and paleoclimate during the palaeozoic as well as the nature of unknown and hidden basement rocks in malaysia this paper reports nineteen palaeozoic formations in malaysia that contain black shales that are classified into seven categories based on their age these are the cambrian ordovician ordovician devonian silurian devonian devonian carboniferous carboniferous permian and permian black shales although illite was identified in all black shales other clay minerals including kaolinite and smectite illite mixed layers show significant variations among the studied samples the al 2 o 3 tio 2 ratios 13 33 sio 2 contents of probable magmatic source rocks 54 69 wt and zr tio 2 bivariate diagram suggest a mixture of felsic and intermediate source rocks for the studied black shales this indicates that the hidden basement rocks in malaysia are dominated by felsic igneous rocks variations in clay minerals sio 2 and al 2 o 3 tio 2 ratios and upper continental crust ucc normalized ree patterns suggest a local provenance for each locality rather than regional and common source rocks for all black shales al 2 o 3 sio 2 ratios vary from one age to the other ranging between 0 09 and 0 37 this indicates changes in the degree of weathering of the sediment source rocks of these shales and suggests climate changes in the peninsular malaysia during the palaeozoic from relatively wet conditions during the cambrian to relatively dry conditions during the ordovician followed by relatively wet conditions extends from the silurian to the carboniferous which followed by relatively dry conditions during the formation of carboniferous permian black shales and finally to relatively wet conditions during the permian the v ni v v ni and v v cr ratios as well as the positive ce anomalies indicate that these black shales were deposited under reducing conditions the high v ni ratios 3 also suggest a purely marine source input for the organic matter devonian black shales show relatively high concentrations of redox sensitive elements which may suggest the possible existence of devonian anoxia as well as the devonian carboniferous d c boundary in malaysia based on the abundance of illite 85 and illite crystallinity ic values 27 46 2 the majority of the palaeozoic black shales in peninsular malaysia are probably anchimetamorphic and over matured

pore throat sizes in sandstones tight sandstones and shales pore throat sizes in siliciclastic rocks form a continuum from the submillimeter to the nanometer scale that continuum is documented in this article using previously published data on the pore and pore throat sizes of conventional reservoir rocks tight gas sandstones and shales for measures of central tendency mean mode median pore throatsizes diameters are generally greater than2 mm in conventionalreservoir rocks range from about 2 to 0 03 mm in tight gas sandstones and rangefrom0 1to0 005 mminshales hydrocarbonmolecules asphaltenes ring structures paraffins and methane form another continuum ranging from 100 a 0 01 mm for asphaltenes to 3 8 a 0 00038 mm for methane the pore throat size continuum provides a useful perspective for considering 1 the emplacement of petroleum in consolidated siliciclastics and 2 fluid flow through fine grained source rocks now being exploited as reservoirs

parrotfish erosion underpins reef growth sand talus development and island building in the maldives abstract parrotfish play a key functional role on coral reefs as external bioerosion agents and produce large quantities of carbonate sediment as a by product of grazing on reef surfaces parrotfish are therefore an important potential source of sediment for island construction and maintenance within atoll reef environments particularly under future scenarios of sea level rise and island morphological change here we present the first field based estimates of excavating parrotfish erosion chlorurus sordidus and chlorurus strongylocephalus within the indian ocean and quantify the contribution of parrotfish to the carbonate and sediment budgets of an atoll interior reef platform in the maldives we note that parrotfish erosion rates are high 6 3 kg m 2 y 1 generating large amounts of new coral based sediment 2 6 kg m 2 y 1 that has a comparable grain size distribution to island deposits mean erosion rates by individual c strongylocephalus 405 kg individual y 1 were higher than c sordidus 55 kg individual y 1 but their contribution to erosion per unit area of reef was less due to a lower relative biomass c strongylocephalus 1 3 kg m 2 y 1 c sordidus 5 0 kg m 2 y 1 parrotfish also facilitate sediment export from reefs 0 7 kg m 2 y 1 which contributes extensively to the development of the sand talus on the fore reef slope and to the evolution of the wider atoll basin our results provide strong evidence that parrotfish erosion and sediment generation underpins island morphology on maldivian reefs and highlight the importance of larger parrotfish as producers of island grade sediment ecological processes must therefore be considered within future coastal management strategies for enhancing island stability

contemporary sedimentation in the cocos keeling islands indian ocean interpretation using settling velocity analysis abstract textural parameters of grain size distributions derived from sieve analysis and component analysis have been used to the exclusion of other methods to examine sedimentary processes in modern reef environments however because these methods do not reflect the hydraulic behaviour of bioclastic sediment this study uses settling velocity analysis accounting for grain size density and shape variability and component analysis of separated settling velocity fractions to describe and differentiate bioclastic deposits and infer transport pathways in the cocos keeling islands an indian ocean atoll principal component and cluster analysis of settling 251 samples and component 90 samples characteristics discriminated eight settling velocity and five component classes a derived settling velocity classification reflecting the hydraulic properties of the sediments describes a lagoonward gradient from those with fast settling characteristics on the outer reef flat to those with moderate settling character on sand aprons the active sediment transport system is constrained between these zones component analysis of bulk samples identifies two broad sediment types 1 those with reef derived components found throughout the active transport zone reef flat to sand aprons and 2 those characterised by greater proportions of gastropod and halimeda fragments which are produced and deposited in situ in the lagoon component analysis of settling fractions further resolves details of sediment movement in the active transport zone sediment is transported from the productive reef flat to passage entrances which form initial depositional environments slower settling material is selectively transported from the entrances through the passage conduits to passage exit environments these form the main depositional areas under mean energy conditions during moderate to high energy events sediment is flushed from the passage to sand apron zones with slower settling grains deposited in the deep lagoon sinks results show that settling velocity analysis and component analysis of settling fractions can resolve the nature of sediment transport patterns in reef environments at a much finer scale than studies in which analysis is based on grain size distributions

biofacies and sediments in an emergent late pleistocene glaciomarine sequence skerries east central ireland abstract late devensian sedimentation ca 18 ka b p on the coastal margins of the irish sea basin occurred in shallow water glaciomarine environments around retreating tidewater ice margins high relative sea levels were the result of glacioisostatic crustal depression around the periphery of the last british ice sheet at skerries in east central ireland ice proximal glaciomarine diamict mud sand and gravel facies are selectively preserved in a bedrock depression the coastal exposure about 500 m long can be divided into three lithofacies associations 1 a diamict gravel association resting on bedrock was emplaced by sediment gravity flows and records the downslope reworking of glacial debris released from a retreating ice margin 2 an overlying mud association was deposited from suspended sediment plumes with minor ice rafting and records ice retreat and increasing distality of the site muds contain a mixed foraminiferal microfaunal assemblage typical of open water shallow marine shelves species can be grouped into reworked temperate cosmopolitan and well preserved boreo arctic elements and indicate mixing of derived and retransported temperate species with an in situ glaciomarine fauna 3 at the top of the section a gravel association derived from a nearshore fan delta rests on planated muds and is attributed to wave reworking and slumping of the fan delta front in shallow water during rapid basin rebound this and other sequences elsewhere in the irish sea basin is a record of rapid evacuation of the basin by calving tidewater glaciers and the uplift and erosion of glaciomarine sedimentary sequences in response to rapid late glacial crustal rebound

characterizing the shale gas resource potential of devonian mississippian strata in the western canada sedimentary basin application of an integrated formation evaluation devonian mississippian strata in the northwestern region of the western canada sedimentary basin wcsb were investigated for shale gas potential in the subsurface thermally mature strata of the besa river horn river muskwa and fort simpson formations attain thicknesses of more than 1 km 0 6 mi encompassing an area of approximately 125 000 km2 48 300 mi2 and represent an enormous potential gas resource total gas capacity estimates range between 60 and 600 bcf section of particular exploration interest are shales and mudrocks of the horn river formation including the laterally equivalent lower besa river mudrocks muskwa formation and upper besa river formation which yield total organic carbon toc contents of up to 5 7 wt fort simpson shales seldom have toc contents above 1 wt horn river and muskwa formations have excellent shale gas potential in a region between longitudes 122w and 123w and latitudes 59n and 60n national topographic system nts 94o08 to 94o15 in this area which covers an areal extent of 6250 km2 2404 mi2 average toc contents are higher 3 wt as determined by wire line log calibrations and have a stratal thickness of more than 200 m 656 ft gas capacities are estimated to be between 100 and 240 bcf section and possibly greater than 400 tcf gas in place a substantial percentage of the gas capacity is free gas caused by high reservoir temperatures and pressures muskwa shales have adsorbed gas capacities ranging between 0 3 and 0 5 cm3 g 9 6 16 scf t at reservoir temperatures of 60 80c 140 176f whereas besa river mudrocks and shales have low adsorbed gas capacities of less than 0 01 cm3 g 0 32 scf t liard basin region because reservoir temperatures exceed 130c 266f potential free gas capacities range from 1 2 to 9 5 cm3 g 38 4 to 304 scf t when total pore volumes 0 4 6 9 are saturated with gas the mineralogy has a major influence on total gas capacity carbonate rich samples indicative of adjacent carbonate platform and embayment successions commonly have lower organic carbon content and porosity and corresponding lower gas capacity 1 toc and 1 porosity seaward of the carbonate slave point edge muskwa and lower besa river mudrocks can be both silica and toc rich up to 92 quartz and 5 wt toc and most favorable for shale gas reservoir exploration because of possible fracture enhancement of the brittle organic and siliceous rich facies however an inverse relation between silica and porosity in some regions implies that zones with the best propensity for fracture completion may not provide optimal gas capacity and a balance between favorable reservoir characteristics needs to be sought

wave driven circulation of a coastal reef lagoon system abstract the response of the circulation of a coral reef system in kaneohe bay hawaii to incident wave forcing was investigated using field data collected during a 10 month experiment results from the study revealed that wave forcing was the dominant mechanism driving the circulation over much of kaneohe bay as predicted theoretically wave setup generated near the reef crest resulting from wave breaking established a pressure gradient that drove flow over the reef and out of the two reef channels maximum reef setup was found to be roughly proportional to the offshore wave energy flux above a threshold root mean square wave height of 0 7 m at which height setup was negligible on the reef flat the wave driven currents increased approximately linearly with incident wave height however the magnitude of these currents was relatively weak typically 20 cm s 1 because of i the mild fore reef slope of kaneohe bay that reduced setup resulting from a combination of frictional wave damping and its re

a budget of carbonate framework and sediment production kailua bay oahu hawaii abstract sediments of the bay and coastal plain of kailua oahu hawaii are 90 biogenic carbonate produced by destruction of primary reef framework coral and encrusting coralline algae and by direct sedimentation through the biological activity of calcifying organisms the green alga halimeda the branching coralline alga porolithion gardineri molluscs and benthic foraminifera field measurements of benthic community structure gross carbonate production bioerosion and direct sedimentation in 17 physiographic zones in kailua bay are used to calculate modern calcareous sediment production rates in the 12 km2 fringing reef system total gross carbonate productivity by corals and encrusting coralline algae based on mapped percent cover and known growth rates occurs at an average rate of 1 22 0 36 kg m 2 y 1 over hard substrates of the reef platform corresponding to 0 8 0 2 mm y 1 using a bulk density of 1 48 g cm 3 the average of coral and coralline algae coralline algae contributes 42 of the total gross productivity bioerosion of coral and coralline algae facies at and near the reef surface estimated from slabbed reef samples occurs at average rates of 0 10 1 15 kg m 2 y 1 and releases 1 911 436 m3 of unconsolidated carbonate sediment annually mechanical erosion coral breakage likely contributes an additional 315 m3 y 1 carbonate sediment is also produced directly by the green alga halimeda branching coralline algae molluscs and benthic foraminifera at a combined rate of 1 822 200 m3 y 1 using densities specific to sediment origin the total rate of production of unconsolidated carbonate sediment in kailua bay is the sum of these sources amounting to 4 048 635 m3 y 1 normalizing gross sediment production in kg y 1 by reef habitat area in m2 generates average rates of productivity in kg m 2 y 1 that are directly comparable to each other and to the literature such rates can also be employed and tested in other reef settings in kailua bay the total production of calcareous sediment corresponds to an average normalized rate of 0 53 0 19 kg m 2 y 1 with 0 33 0 13 kg m 2 y 1 contributed through erosion of the coralgal framework and 0 20 0 06 kg m 2 y 1 contributed by direct sediment production on the reef surface applying these modern sediment production rates over the 5 000 years that kailua bay has been completely inundated by postglacial sea level rise an estimated 20 2 3 2 106 m3 of unconsolidated carbonate sediment has been produced in the system the volume of sediment stored in the various reef channels and holes in kailua bay is 3 7 0 3 106 m3 or 19 of that produced since 5 000 y bp the volume of sand in the modern beach is 1 0 0 1 106 m3 or 5 of holocene sediment production the volume of carbonate sediment stored in the coastal plain is estimated using core log data and associated radiocarbon ages to be 10 0 1 8 106 m3 or 51 of holocene sediment production the remaining 25 likely represents sediment loss due to the natural processes of dissolution attrition and transport offshore these export terms are not well understood and emphasize the need for sediment dynamics to be incorporated into reef and sediment budgets although sediment production in this reef system is prodigious the rate of new sediment supplied to the beachface is less than 2 of what moves on and off the beach seasonally

post glacial sea level changes around the australian margin a review abstract it has been known since rhodes fairbridge s first attempt to establish a global pattern of holocene sea level change by combining evidence from western australia and from sites in the northern hemisphere that the details of sea level history since the last glacial maximum vary considerably across the globe the australian region is relatively stable tectonically and is situated in the far field of former ice sheets it therefore preserves important records of post glacial sea levels that are less complicated by neotectonics or glacio isostatic adjustments accordingly the relative sea level record of this region is dominantly one of glacio eustatic ice equivalent sea level changes the broader australasian region has provided critical information on the nature of post glacial sea level including the termination of the last glacial maximum when sea level was approximately 125 m lower than present around 21 000 19 000 years bp and insights into meltwater pulse 1a between 14 600 and 14 300 cal yr bp although most parts of the australian continent reveals a high degree of tectonic stability research conducted since the 1970s has shown that the timing and elevation of a holocene highstand varies systematically around its margin this is attributed primarily to variations in the timing of the response of the ocean basins and shallow continental shelves to the increased ocean volumes following ice melt including a process known as ocean siphoning i e glacio hydro isostatic adjustment processes several seminal studies in the early 1980s produced important data sets from the australasian region that have provided a solid foundation for more recent palaeo sea level research this review revisits these key studies emphasising their continuing influence on quaternary research and incorporates relatively recent investigations to interpret the nature of post glacial sea level change around australia these include a synthesis of research from the northern territory queensland new south wales south australia and western australia a focus of these more recent studies has been the re examination of 1 the accuracy and reliability of different proxy sea level indicators 2 the rate and nature of post glacial sea level rise 3 the evidence for timing elevation and duration of mid holocene highstands and 4 the notion of mid to late holocene sea level oscillations and their basis based on this synthesis of previous research it is clear that estimates of past sea surface elevation are a function of eustatic factors as well as morphodynamics of individual sites the wide variety of proxy sea level indicators used their wide geographical range and their indicative meaning some progress has been made in understanding the variability of the accuracy of proxy indicators in relation to their contemporary sea level the inter comparison of the variety of dating techniques used and the nuances of calibration of radiocarbon ages to sidereal years these issues need to be thoroughly understood before proxy sea level indicators can be incorporated into credible reconstructions of relative sea level change at individual locations many of the issues which challenged sea level researchers in the latter part of the twentieth century remain contentious today divergent opinions remain about 1 exactly when sea level attained present levels following the most recent post glacial marine transgression pmt 2 the elevation that sea level reached during the holocene sea level highstand 3 whether sea level fell smoothly from a metre or more above its present level following the pmt 4 whether sea level remained at these highstand levels for a considerable period before falling to its present position or 5 whether it underwent a series of moderate oscillations during the holocene highstand

evolution of the concept and structure of a mushwad abstract a mushwad forms as a result of bulk ductile deformation and large scale tectonic thickening of depositionally thick weak decollement host strata a mushwad has floor and roof thrusts like a conventional brittle duplex but the internal structure of a mushwad which includes disharmonic small scale folds and faults differs from the large scale imbricate horses in a conventional duplex the concept of mushwad structure has evolved as more subsurface data from deep drill holes and seismic reflection profiles have become available the formation of a mushwad requires an anomalously thick shale dominated succession at the level of the decollement and a structural buttress generally a basement fault to deflect the decollement upward in a frontal ramp tectonic thickening of the mushwad elevates and distorts the roof producing a complex antiformal structure that differs from conventional frontal thrust ramps

sequence stratigraphy of an intrashelf basin carbonate ramp to rimmed platform transition maryville limestone middle cambrian southern appalachians middle and upper cambrian strata in the southern appalachians consist of a sequence of six alternating limestone and shale formations conasauga group the conasauga group constitutes part of a thick pericratonic cambro ordovician passive margin sequence along the eastern north american continent the cambrian carbonate platform was flanked by a high relief shelf margin toward the east facing the open ocean while to the west the carbonate platform sloped into an intrashelf basin it is this western shelf margin that is the topic of the present study detailed lithofacies analysis of the middle cambrian maryville limestone along a shelf to basin depositional transect reveals that the shelf evolved from a gently basinward sloping ramp to a rimmed platform fringed with steeper slopes cyanobacterial buildups renalcis girvanella dominated the platform margin environments progradation of the platform occurred toward the craton a process oriented approach has allowed us to define the sequences sequence boundaries and the stacking pattern of the maryville limestone the maryville limestone sequence consists of two depositional subsequences the boundary between the two subsequences is not a sequence boundary because it does not separate rocks deposited in different environmental regimes the two subsequences within the maryville sequence consist of a combination of aggradational retrogradational and progradational units with respect to the platform interior the stacking pattern recognized is the result of variations in sedimentation rate subsidence and eustatic sea level change each of the dominantly carbonate units within the conasauga represents this gradual transition from a ramp like platform to basin transition into a rimmed platform the transition between the maryville limestone middle cambrian and the overlying nolichucky shale late cambrian is a sequence boundary this sequence boundary is both an exposure surface and a drowning unconformity and it marks a distinct shift in the pattern of sedimentation shallow water carbonate deposition terminated at the boundary followed by the onlap of deeper water basinal siliciclastics over shallow carbonates the approach presented here can serve as a useful analogue to other lower paleozoic and possibly younger passive margin sequences

ice marginal depositional responses to readvance episodes in the late devensian deglaciation of the isle of man abstract remapping of the quaternary geology of the isle of man and consequent revision of the stratigraphic succession identifies three glacigenic formations each separated by a major unconformity the oldest formation the shellag represents an extensive ice advance beyond the island limits to the last glacial maximum lgm the overlying formation the orrisdale represents a major readvance episode during retreat from the lgm and is associated with the construction of the bride moraine and the deposition of extensive proglacial subaqeous sediment examination of the sedimentology and micropalaeontology of these sediments indicates that the water body was most likely lacustrine and not marine application of sequence stratigraphy to the overlying jurby formation identifies evidence for three further phases of readvance each off lapping one another into the margin of the lake basin via a complex system of ice contact subaqueous fans and outwash fan deltas the jurby formation is dated by organic sediments overlying it as older than 18 5 14 4 kyr bp and provides an ice marginal correlative for heinrich event 1 readvance limits identified 50 km to the west in eastern ireland

hydrodynamics and sediment flux of hoa in an indian ocean atoll detailed hydrodynamic and sediment ux measurements are reported from 11 hoa shallow cross reef channels in the cocos keeling islands indian ocean all hoa exhibit unidirectional oceanside reef to lagoon uxes these currents are driven by tides wave set up and incident waves and the presence of islands that generate alongshore gradients so that currents ow toward the topographic low points of hoa entrances in the reef rim two functional groups of hoa are identi ed that extend chevalier s typology of hoa and possess different process signatures sediment limited hoa slh are ef cient conduits of sediment transport they are located close to the reef rim where incident wave energy propagates across the reef crest into the hoa and is able to entrain sediment transport limited hoa tlh are characterized by low rates of sediment transport because incident wave energy is negligible as they are located much further from the reef edge than slh in the absence of an entrainment mechanism the oceanside reef at is laden with sediment storm energy increases transport ef ciency through hoa however the net sedimentation response differs between the two hoa types proximity to the reef edge means that frequent storms ush sediment from slh increasing hoa depth and enhancing the potential for erosion of the conglomerate boundary in contrast the greater reef width fronting tlh means that sediment transport from reef ats to the lagoon is only activated during infrequent storms the contrasting process signatures account for morphological differences between sediment limited hoa lagoonward decrease in depth and increase in width and transport limited hoa lagoonward increase in depth the number and type of functional hoa are found to have signi cant implications for the rate of lagoon sedimentation in enclosed atolls in general an increase in frequency of functional hoa and increased proportion of slh will promote more rapid rates of lagoon in ll copyright 2004 john wiley sons ltd

an integrated approach to the study of glaciolacustrine landforms and sediments a case study from hagavatn iceland abstract this paper describes the landform assemblage associated with the neoglacial fluctuation of hagafellsjokull eystri into proglacial hagavatn iceland this landform assemblage is dominated by three components firstly a series of moraines formed both by thrusting within the glacier margin and by proglacial subglacial deformation the internal sedimentary architecture of these moraines ranges from stacked sediment slabs separated by listric thrusts to complexly folded and faulted sequences all in glaciolacustrine sediments the second component is a morainal bank and associated ice contact delta the morainal bank consists of a series of low amplitude ridges composed of laminated silts and clays which have been deformed proglacially during the neoglacial ice advance 1890 this morainal bank helped stabilise the 1890 ice limit within the proglacial lake and was the focus for subaqueous outwash first in the form of a subaqueous out wash fan and subsequently as an ice contact delta the third component is a series of lake bed kame terraces formed by rapid sedimentation in a canal like lake formed as the ice retreated away from the push moraines a range of glaciolacustrine facies is present within the lake bed kame terraces and the sedimentary architecture records a complex pattern of ice marginal oscillations and changes in lake level this detailed case study provides an important analogue for the interpretation of both glaciolacustrine and glaciomarine landform sediment assemblages of pleistocene age and illustrates a range of styles of glaciolacustrine sedimentation and glaciotectonic deformation

subglacial conditions in a branching saalian esker in north central poland abstract the results of a sedimentological study of a branching esker system near uniszki north central poland provide a deeper insight into the depositional processes that took place within a subglacial tunnel formed during the wartanian late saalian glaciation the internal structure of the esker deposits is complex and coarse grained debris intercalates with silt and clay layers ten main lithofacies types are recognized including one formed in a tunnel mouth environment and three other lithofacies which must have been deposited in a truly subglacial environment a subglacial tunnel association is defined fluctuations in meltwater discharge through the tunnels resulted in cyclicity in the sedimentary succession deposition of fine grained facies took place during low discharge whereas boulder and gravel lithofacies formed in the tunnel mouth during high discharge changes in the hydrostatic conditions finally resulted in the collapse of the tunnel roof so that the succession became covered with supraglacial deposits the uniszki deposits record deposition under highly variable sedimentary hydrostatic conditions which is typical of environments in the polish lowlands the results of the present study provide some criteria for the interpretation of subglacial meltwater debris and thus may contribute to the current discussion on subglacial tunnel sedimentation

mississippian barnett shale fort worth basin north central texas gas shale play with multi trillion cubic foot potential the mississippian barnett shale serves as source seal and reservoir to a world class unconventional natural gas accumulation in the fort worth basin of north central texas the formation is a lithologically complex interval of low permeability that requires artificial stimulation to produce at present production is mainly confined to a limited portion of the northern basin where the barnett shale is relatively thick 300 ft 92 m organic rich presentday total organic carbon 3 0 thermally mature vitrinite reflectance 1 1 and enclosed by dense limestone units able to contain induced fractures the most actively drilled area is newark east field currently the largest gas field in texas newark east is 400 mi 2 1036 km 2 in extent with more than 2340 producing wells and about 2 7 tcf of booked gas reserves cumulative gas production from barnett shale wells through 2003 was about 0 8 tcf wells in newark east field typically produce from depths of 7500 ft 2285 m at rates ranging from 0 5 to more than 4 mmcf day estimated ultimate recoveries per well range from 0 75 to as high as 7 0 bcf efforts to extend the current barnett play beyond the field limits have encountered several challenges including westward and northward increases in oil saturation and the absence of lithologic barriers to induced fracture growth patterns of oil and gas occurrence in the barnett in conjunction with maturation and burial history data indicate a complex multiphased thermal evolution with episodic expulsion of hydrocarbons and secondary cracking of primary oils to gas

a detrital sediment budget of a maldivian reef platform abstract sediment dynamics are an important control on the morphology and development of reef systems by actively removing and redistributing excess detrital sediment this study presents quantitative data from direct point measurements of sediment transport on the platform surface and fore reef slope of vabbinfaru reef north male atoll maldives a suite of sediment traps were used to construct actual rates of platform sediment fluxes and off reef export over different spatial and temporal seasonal scales to establish key sediment transport pathways findings showed that high sediment fluxes occur on vabbinfaru platform in the absence of major storm activity up to 1905 g m 1 d 1 with 95 of annual transport occurring during the southwest monsoon as a result of increased wave energy climate driven changes in the platform process regime caused a reversal of net sediment transport pathways between each monsoon season off reef export rates were high reaching a maximum of 12 58 kg m 1 y 1 for gravel and 407 g m 1 d 1 for sand sized sediment an estimated 127 120 kg is exported from the platform annually equating to a significant loss from the reef sediment budget and contributing to the long term geomorphic development of the fore reef slope and atoll basin detrital sediment reservoirs on vabbinfaru are not purely depositional carbonate sinks but rather temporary stores that are important in the transfer of sediment between reef zones

carbonate ramp to deeper shale shelf transitions of an upper cambrian intrashelf basin nolichucky formation southwest virginia appalachians the nolichucky formation 0 300 m thick formed on the cambrian pericratonic shelf in a shallow intrashelf basin bordered along strike and toward the regional shelf edge by shallow water carbonates and by nearshore clastics toward the craton lateral facies changes from shallow basinal rocks to peritidal carbonates suggest that the intrashelf basin was bordered by a gently sloping carbonate ramp peritidal facies of the regional shelf are cyclic upward shallowing stromatolitic carbonates these grade toward the intrashelf basin into shallow ramp cross bedded ooid and oncolitic intraclast grain stones that pass downslope into deeper ramp subwave base ribbon carbonates and thin limestone conglomerate ribbon limestones are layers and lenses of trilobite packstone parallel and wave ripple laminated quartzose calcisiltite and lime mudstone arranged in storm generated fining upward sequences 1 5 cm thick that may be burrowed shallow basin facies are storm generated upward coarsening and upward fining sequences of green calcareous shale with open marine biota parallel to hummocky laminated calcareous siltstone and intraformational flat pebble conglomerate there are also rare debris flow paraconglomerate 10 60 cm thick and shaly packstone wackestone with trace fossils glauconite horizons and erosional surfaces hardgrounds a 15 m thick tongue of cyclic carbonates within the shale package contains subtidal digitate algal bioherms which developed during a period of shoaling in the basin understanding the nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar facies which are widely distributed in the lower palaeozoic elsewhere the study demonstrates the widespread effects of storm processes on pericratonic shelf sedimentation finally recognition of shallow basins located on pericratonic shelves is important because such basins influence the distribution of facies and reservoir rocks whose trends may be unrelated to regional shelf edge trends

evidence of spice related anoxia on the laurentian passive margin paired δ13c and trace element chemostratigraphy of the upper conasauga group central appalachian basin abstract this study reports data from the upper cambrian conasauga group and overlying copper ridge formation of the central appalachian region eastern u s a geochemical isotopic and petrographic analysis of core material was carried out to constrain the extent of marine anoxia and to characterize sediment fluxes on the carbonate platform and continental shelf of laurentia contemporaneous with the steptoean positive carbon isotope excursion spice a late cambrian global marine anoxic event carbonate rocks primarily dolostone record a positive 13ccarb excursion starting in the middle nolichucky formation reaching its peak 4 3 at the boundary between the maynardville and copper ridge formations strontium isotope ratios in the dolostone units are only slightly offset from the expected cambrian seawater values suggesting minimal post diagenetic disturbance of isotopic and trace element systematics selective leaching of carbonate units reveal upward decreasing trends in dissolved redox sensitive trace metals e g u ni v indicative of drawdown from regional and global marine anoxia during the peak of the late cambrian spice event

gigantic gaseous mushwads in cambrian shale conasauga formation southern appalachians usa giant duplexes called mushwads in the southern appalachian thrust belt are estimated to contain a natural gas resource base of about 17 7 tcm 625 tcf early development efforts in mushwads of the cambrian age conasauga formation encountered significant challenges and highlight the need for an integrated multidisciplinary approach to shale gas exploration to facilitate development of this gigantic resource an integrated geological analysis of stratigraphy sedimentation structural geology basin hydrodynamics petrology geochemistry gas storage and mobility and reservoir volumetrics was conducted the results of this analysis demonstrate the myriad geological factors that need to be considered when developing shale gas resources and suggest that the greatest reservoir potential lies deep in the mushwads where free gas is concentrated meeting the challenges posed by deformed shale masses in thrust belts is a major frontier for hydrocarbon exploration that could result in a major expansion of natural gas reserves

mushwad ductile duplex in the appalachian thrust belt in alabama structural style in thin skinned thrust belts is controlled substan tially by the stratigraphic succession and relative thicknesses of lith otectonic units stiff layers and weak layers in contrast to the rela tively predictable geometry of fault related folds fault bend folds fault propagation folds and detachment folds ductile deformation of a stratigraphically thick weak layer generates a ductile duplex that elevates and distorts the overlying stiff layer a ductile duplex is herein termed a mushwad malleable unctuous shale weak layer accretion in a ductile duplex in the appalachian thrust belt in alabama mushwads nucleated in a thick shale dominated suc cession of weak rocks in association with basement faults beneath the regional decollement the stiff layer roof is deformed by folds and faults and is elevated by tectonic accretion of weak rocks in a mushwad shortening within the mushwad may drive translation of the stiff layer from the roof over the foreland lateral termina tions range from plunge of the stiff layer roof over a laterally thin ning mushwad to a transverse fault the examples in the appala chian thrust belt suggest a style of structure that may be more common than presently recognized the structural geometry of a mushwad as well as the potential for concentration of fractures in the distorted stiff layer suggests important applications in petro leum exploration and reservoir development

variable gas saturation in coalbed methane reservoirs of the black warrior basin implications for exploration and production abstract gas saturation is highly variable in carboniferous coalbed methane reservoirs of the black warrior basin usa and diverse geologic data derived from more than three decades of exploration and development provides insight into the origin of this variability and the consequences for production performance coalbed methane is produced from numerous thin 0 3 to 95 importantly this range of variation is commonly developed among closely spaced seams within the same well exploration has to date been successful where coal seams are in the thermogenic gas window geochemical evidence indicates that thermogenic gases have been altered by subsurface water movement and may have been augmented with late stage biogenic gases particularly in areas affected by fresh water recharge adsorption isotherms of coal samples in the black warrior basin typically have langmuir volume between 15 and 30 cm3 g and langmuir pressure between 2 and 6 mpa both langmuir pressure and langmuir volume correlate significantly with coal rank in deep normally pressured coal beds where reservoir pressure is substantially above langmuir pressure even a small degree of undersaturation can necessitate prolonged dewatering before a large reservoir volume can reach the critical desorption pressure permeability moreover decreases exponentially with depth which can make dewatering coal seams deeper than 800 m difficult where reservoir pressure is relatively low however isotherm geometry indicates that significantly undersaturated reservoirs can be near the critical desorption pressure consequently areas of underpressure favor high gas production along with minimal water production

pore types in the barnett and woodford gas shales contribution to understanding gas storage and migration pathways in fine grained rocks the identification of organoporosity microscale and nanoscale pores within organic matter in shales its importance to storage and perhaps transfer of gas molecules through shales and methods for gathering three dimensional images of the pores such as by argon ion milling and or field emission scanning electron microscopy have all been well documented and discussed for unconventional gas shales however other types of pores exist within shales that can be important to storage and migration of gas and oil and other technologies are available for their identification and imaging the different pore types found in the barnett and woodford shales are described and classified in this article scanning electron microscopy revealed the presence of porous floccules in both the barnett and woodford shales which appear similar to laboratory produced floccules and to those in other ancient shales published experimental and observational studies indicate that floccules are hydraulically equivalent to coarser grains and are transported by traction processes current induced microsedimentary structures and textures within the barnett and woodford shales as well as the preserved floccules suggest such processes were active during transport and deposition pore spaces between the floccules are open and can provide storage space as well as permeability pathways for gas molecules through the shales pores are also found within organic matter that occurs both as discrete particles and as adsorbed coatings around clay grains in the shale they are referred to here as organopores porous fecal pellets are also common in the barnett shale preserved fossil fragments such as organic walled spores and inorganic sponge spicules have hollow central chambers which may remain partially or completely open even after burial intraparticle pores occur between grains of various minerals e g pyrite framboids microchannels within shale matrix which may be the bounding surfaces of scours or microsedimentary structures may also provide permeability pathways for hydrocarbon migration mircrofractures are also common and their initiation might be related to mineral crystal structure when present in sufficient quantity these pore types offer potential gas and oil molecule storage spaces and permeability pathways through the shales

geometry migration and evolution of wave orbital ripples at leo 15 observations of the temporal evolution of the geometric properties and migration of wave formed ripples are analyzed in terms of measured suspended sand profiles and water velocity measurements six weeks of bedform observations were taken at the sandy medium to coarse sized sand leo 15 site located on beach haven ridge during the late summer of 1995 with an autonomous rotary sidescan sonar during this period six tropical storms several of hurricane strength passed to the east of the study site ripples with wavelengths of up to 100 cm and with 15 cm amplitudes were observed the predominant ripples were found to be wave orbital scale ripples with ripple wavelengths equal to 3 4 of the wave orbital diameter although orbital diameters become larger than 130 cm during the maximum wave event it is unclear if a transition to non orbital scaling is occurring ripple migration is found to be directed primarily onshore at rates of up to 80 cm day suspended transport due to wave motions calculated by multiplying acoustic backscatter measurements of suspended sand concentrations by flow velocity measurements are unable to account for a sufficient amount of sand transport to force ripple migration and are in the opposite direction to ripple migration thus it is hypothesized that the onshore ripple migration is due to unobserved bedload transport or near bottom suspended transport bedload model calculations forced with measured wave velocities are able to predict the magnitude and direction of transport consistent with observed ripple migration rates sequences of ripple pattern temporal evolution are examined showing mechanisms for ripple directional change in response to changing wave direction as well as ripple wavelength adjustment and erosion due to changing wave orbital diameter and relative wave to current velocities

linking pattern to process in reef sediment dynamics at lady musgrave island southern great barrier reef linking surficial sediment patterns in reef environments to the processes that underlie their depositional dynamics enables predictions to be made of how environmental changes will influence reef associated sedimentary landforms such as islands and beaches geomorphic linkages between sediment deposition patterns and the biophysical processes that drive them are often poorly resolved particularly at broad landscape scales where tangible statements can be made about structural changes to landforms the present study applies geospatial techniques to link patterns in reef sediment dynamics at lady musgrave island to the underlying processes driving them in situ calcification is characterized by developing a high resolution map of the surficial calcium carbonate producing communities inhabiting the reef platform and associated sediments across the reef flat are analysed for grain size kurtosis sorting and threshold bed shear stress to explore transport pathways across the reef flat and lagoon wave energy is modelled across the entire reef platform as a potential driver of sediment dynamics and morphometric linkages are empirically defined between wave energy and grain size findings indicate that carbonate sediments are primarily sourced from calcifying communities colonizing the outer periphery of the reef platform and that sediment grain size can be reliably linked to wave energy by virtue of a linear model

predicting the hydrodynamic response of a coastal reef lagoon system to a tropical cyclone using phase averaged and surfbeat resolving wave models abstract tropical cyclone tc olwyn travelled along the coast of ningaloo reef in northwestern australia as a category 3 tc during 12 13 march 2015 with sustained wind speeds of over 130 km h 1 and significant wave heights on the forereef reaching 6 m observations from tc olwyn showed that contrary to typical wave transformation patterns across a coastal reef lagoon under the tc conditions there was a substantial shoreward increase of wave height this unusual pattern was primarily due to strong local wind wave generation under the extreme wind conditions despite the lagoon itself being relatively small order 1 km wide and shallow order 1 m depth two common types of coastal numerical wave models that include either wave growth i e the phase averaged model swan or infragravity waves i e the surfbeat resolving model xbeach but not both processes were used to assess the capabilities of numerical models to predict the cyclone induced hydrodynamics model results showed that wave conditions in the lagoon and at the shoreline were dominated by locally generated wind waves with the reef efficiently dissipating the large incident waves offshore the infragravity waves in the lagoon were only of secondary importance during the tc compared to the locally generated sea swell waves although both the phase averaged swan and surfbeat resolving xbeach models were able to predict some of the local hydrodynamic responses for this specific site and storm the use of a phase averaged model yielded the most accurate predictions of the hydrodynamics given that it included wind wave growth however because the influence of infragravity waves cannot be neglected in reef environments in general these results emphasize the need for a more general modeling approach that requires the addition of wind wave growth formulations into surfbeat or fully phase resolving classes of numerical wave models and or the addition of an infragravity wave formulation in spectral wave models

deformation styles as a key for interpreting glacial depositional environments lithostratigraphical and lithofacies approaches used to interpret glacial sediments often ignore deformation structures that can provide the key to environment of formation we propose a classification of deformation styles based on the geometry of structures rather than inferred environment of formation five styles are recognised pure shear p simple shear s compressional c vertical v and undeformed u these dictate the first letter of the codes the remaining letters conveying the evidence this information can be used to reconstruct palaeostress fields and to infer physical properties of sediments when they deformed individual structures are not diagnostic of particular environments but the suite of structures their relative scale stratigraphical relationships and orientation relative to palaeoslopes and to palaeoice flow directions can be used to infer the environment in which they formed this scheme is applied at five sites in west wales the typical succession is interpreted as subglacial sediments overlain by meltout tills flow tills and sediment flows paraglacial redistribution of glacial sediments is widespread large scale compressional deformation is restricted to sites where glaciers readvanced large scale vertical deformation occurs where water was locally ponded near the ice margin there is no evidence for glaciomarine conditions copyright 2003 john wiley sons ltd

sedimentation at the margins of a late pleistocene ice lobe terminating in shallow marine environments dundalk bay eastern ireland late pleistocene morainic sequences around dundalk bay eastern ireland were deposited in a variety of shallow glaciomarine environments at the margins of a grounded ice lobe the deposits are essentially ice proximal delta fan and apron sequences and are divided into two lithofacies associations lithofacies association 1 occurs as a series of morainal banks formed at the southern margin of the ice lobe in a body of water open to influences from the irish sea the morainal banks consist mainly of diamictic muds deposited from turbid plumes and by ice rafting with minor occurrences of turbidites cross bedded gravels subaqueous outwash and massive boulder gravels high density debris flows lithofacies association 2 was deposited in a narrow arm of the sea at the north eastern margin of the ice lobe the deposits consist mainly of a series of coalescing ice proximal gilbert type fan deltas which are interbedded distally with tabular and lens shaped subaqueous deposits the latter are mainly ice rafted diamictons debris flow deposits and subaqueous sands and gravels both lithofacies associations are draped by diamictons formed by a combination of rain out debris flow and traction current activity at a few localities the upper parts of the sequence have been sheared by minor oscillations of the ice sheet margin these sequences form part of an extensive belt of glaciomarine deposits which border the drumlin swarms of east central ireland lithostratigraphic variability is partially related to the arrival of large volumes of debris at the ice lobe margin when the main lowland ice sheet surged during drumlin formation complex depositional continua of this type lack any major erosional breaks and should not be used either as climatic proxies or for stratigraphic correlations

reef to island sediment connections on a maldivian carbonate platform using benthic ecology and biosedimentary depositional facies to examine island building potential reef islands are low lying accumulations of unconsolidated sediment formed from the skeletal remains of carbonate producing reef organisms and are therefore perceived as highly vulnerable to environmental change however basic elements of island composition are not well described and given their high inter and intra basinal variability a better understanding of reef and island sedimentary environments and the connections between them are needed to predict future morphological response here we use detailed ecological and sedimentological datasets to delineate key sediment production zones and biosedimentary depositional facies across the surface of vabbinfaru platform maldives field measurements of platform hydrodynamics are applied to sedimentary deposits to determine the potential mobility of grains and identify transport pathways carbonate production was dominated by coral framework mean 52 within a narrow zone on the outer reef rim 22 of platform area resulting in coral rich detrital sediments reef 51 island 64 that closely resemble living assemblages the net transfer of sediment occurred lagoonward by wave driven processes leading to a decrease in grain size towards the island r2 0 502 which acts as a major control on depositional facies development within the lagoon island sediments were distinct from reefal deposits comprising a restricted suite of durable sands mean 1 34 throughout long term development our findings suggest that the production breakdown and redistribution of coral derived sediment by platform currents is fundamental to future island stability at vabbinfaru and although alterations away from current ecological states may reduce sediment supply the timescales over which island morphological response will occur depends upon phase lags between initial coral mortality and the conversion of this material into island grade sand copyright 2016 john wiley sons ltd

holocene sea levels last glacial maximum glaciomarine environments and geophysical models in the northern irish sea basin uk newly acquired geological records from the isle of man reveal intercalated intertidal and terrestrial sediments that record a relative sea level rise from ca 3 86 m in the early holocene up to a mid holocene maximum between ca 6 6 and 4 5 cal kyr bp at ca 2 25 m when compared with similar marine records from elsewhere in the northern irish sea basin the sea level data confirm a strong north south trend in glacioisostatic loading but little east to west difference in loading this pattern results from the central northern sectors of the british ice sheet over scotland strongly influencing the glacioisostatic downwarping throughout the northern irish sea basin differential ice thicknesses over the irish sea the lake district and ireland did not cause perturbations of local glacioisostatic signatures the holocene marine data in the central irish sea record a slow termination of global eustatic sea level rise during the early holocene geophysical predictions of relative sea level partially constrained by the holocene rsl observations but extrapolated to the last glacial maximum show the potential for shallow marine conditions in the central irish sea basin and in northeast ireland between ca 21 0 16 0 cal kyr bp however glaciomarine deposits in northeast ireland suggest the model relative sea level predictions are too low and require increased ice loading or a thinner lithosphere to generate extra glacioisostatic depression at the time of deglaciation furthermore predicted deglacial relative sea level for northeast ireland does not match the geological record highlighting complex ice margin ocean interaction during deglaciation on the isle of man where glacioisostatic loading is of a similar magnitude to that across northeast ireland the presence of grounded ice inhibited marine incursion during early deglaciation but the occurrence of glaciolacustrine conditions along the ice margin as it moved northwards supports model predictions that relative sea level fell below present during the late glacial early holocene due to rapid glacioisostatic rebound

sedimentology of an ice contact glaciomarine delta carey valley northern ireland an extensive late pleistocene delta body related to a water plane at 100 m above sea level is exposed in the upper carey valley northern ireland exposures along the modern river show a lowermost facies association of massive diamict and poorly sorted gravel deposited as sediment gravity flows overlain by a gravelly foreset and topset facies association recording the progradation of a large glacier fed delta diamict facies were emplaced as subaqueous debris flows associated gravels are chaotically bedded and were deposited by the downslope slumping of poorly sorted boulder gravel their subtle grading characteristics can be linked with a variety of mass flow processes sediment gravity flow facies originated upvalley from rapidly deposited sediments which accumulated near the exit of a narrow subglacial channel below an ice margin fronting in water subsequent ice retreat allowed the growth of a gilbert type delta regional evidence shows that the delta top records high relative sea levels in response to isostatic downwarping around the periphery of the last british ice sheet the sedimentology and structure of the carey valley infill may be typical of high level glaciomarine deltas preserved in topographic lows around the coastline of north britain

unified view of sediment transport by currents and waves i initiation of motion bed roughness and bed load transport attention is given to the properties of sediment beds over the full range of conditions silts to gravel in particular the effect of fine silt on the bed composition and on initiation of motion critical conditions is discussed high quality bed load transport data sets are identified and analyzed showing that the bed load transport in the sand range is related to velocity to power 2 5 the bed load transport is not much affected by particle size the prediction of bed roughness is addressed and the prediction of bed load transport in steady river flow is extended to coastal flow applying an intrawave approach simplified bed load transport formulas are presented which can be used to obtain a quick estimate of bed load transport in river and coastal flows it is shown that the sediment transport of fine silts to coarse sand can be described in a unified model framework using fairly simple expressions the proposed model is fully predictive in the sense that only the basic hydrodynamic parameters dep

reflectance of vitrinite like macerals as a thermal maturity index for cambrian ordovician alum shale southern scandinavia the middle cambrian to lower ordovician alum shale in southern scandinavia contains kerogen macerals resembling vitrinite the age of this rock unit excludes terrestrially derived vitrinite as an origin for these macerals nevertheless the vitrinite like macerals respond to heating in a way similar to that of suppressed vitrinite in younger shales this similarity is demonstrated both for the natural system where alum shale maturity ranges from immature to low grade metamorphic conditions and for hydrous pyrolysis experiments where an immature sample of alum shale was isothermally heated at temperatures ranging from 280 to 360 degrees c for 72 hr reflectance values from the naturally matured alum shale show an increase in standard deviations i e anisotropy with i creasing maturity and a negative relationship with atomic h c ratios of the total kerogen these relationships are similar to those observed in post ordovician vitrinites comparisons with other vitrinites subjected to hydrous pyrolysis indicate the vitrinite like macerals in the alum shale follow the suppressed vitrinite pathway rather than the coal vitrinite pathway the occurrence of vitrinite like macerals in the alum shale indicates that traditional vitrinite reflectance measurements are useful in evaluating thermal maturity of pre silurian rocks

the influence of sea level rise and changes in fringing reef morphology on gradients in alongshore sediment transport 1 climate change induced alterations to coral reef ecosystems in combination with sea level rise have the potential to significantly alter wave dissipation across reefs leading to shifts in alongshore sediment transport gradients and alterations to tropical coastlines we used delft3d to model schematized profiles of two reef flat widths based on the south molokai hawaii coast simulated anthropogenic modifications include incremental degradation of the reef structure as well as sea level rise our findings indicate that sea level rise has a greater relative effect on wave energy flux and alongshore sediment transport over a wide flat whereas both reef degradation and sea level rise exert similar influence over a narrow flat these results suggest reefs that vary in width alongshore are more likely to experience changes in alongshore sediment transport gradients and therefore shifts in shoreline erosion and accretion patterns than more uniform reef systems

late quaternary structure and development of the northern ningaloo reef australia ningaloo reef situated on the central west coast is australia s largest fringing reef system extending southward from 22 s for over 200 km its narrow lagoon is backed by a coastal plain which is largely composed of an emergent last interglacial reef on the flank of folded tertiary limestones the west facing reef is exposed to strong oceanic swells across a narrow 8 km continental shelf climatic aridity cyclones tsunamis and the poleward flowing leeuwin current all influence the reef system seismic profiling and a coring and dating program along a transect through a reef pass indicate two periods of reef development in the northern part of the reef holocene and last interglacial seaward of the crest the holocene reef forms either a prominent 500 m wide bulge with 10 m of relief and an abrupt seaward slope or a series of discrete patch reefs holocene reef development is limited to depths of less than 30 m and reaches a maximum thickness of ca 10 15 m below the reef crest u th tims dates from distal parts of the last interglacial section between 18 and 36 m give ages toward the end of the high stand 120 115 ka last interglacial reef growth was more extensive of the two filling much of the available accommodation space perhaps as a result of a stronger leeuwin current this substrate subsequently provided an antecedent foundation for holocene reef development

megaripple migration in a natural surf zone migrating megaripples are bedforms that appear in the surf zone of sandy coasts1 with heights of 0 1 0 5 m and wavelengths of 1 5 m they are similar in size and shape to small dunes large ripples or sand waves such sedimentary bedforms have been studied in subaerial2 steady flow3 and intertidal4 environments as well as in laboratory flume experiments5 they affect overlying currents by introducing hydraulic roughness4 6 and may provide a mechanism for sediment transport7 8 as well as forming sedimentary structures in preserved facies9 10 the formation orientation and migration of such bedforms is not understood well11 12 dunes for example can be aligned with their crests perpendicular to steady unidirectional winds13 but in more complex wind fields their orientation becomes difficult to predict14 15 16 17 similarly it is not known how sea floor megaripples become aligned and migrate in the complex flows of the surf zone here we present observations in the surf zone of a natural beach which indicate that megaripples do not migrate in the direction of the vector sum of the currents but are aligned so that the sediment transport normal to the bedform crest is maximized17 this may need to be taken into account in modelling morphology change and interpreting existing and fossil morphologic patterns

a review of topographic controls on moraine distribution ice marginal moraines are often used to reconstruct the dimensions of former ice masses which are then used as proxies for palaeoclimate this approach relies on the assumption that the distribution of moraines in the modern landscape is an accurate reflection of former ice margin positions during climatically controlled periods of ice margin stability however the validity of this assumption is open to question as a number of additional nonclimatic factors are known to influence moraine distribution this review considers the role played by topography in this process with specific focus on moraine formation preservation and ease of identification topoclimatic controls are not considered published literature indicates that the importance of topography in regulating moraine distribution varies spatially temporally and as a function of the ice mass type responsible for moraine deposition in particular in the case of ice sheets and ice caps 1000 km2 one potentially important topographic control on where in a landscape moraines are deposited is erosional feedback whereby subglacial erosion causes ice masses to become less extensive over successive glacial cycles for the marine terminating outlets of such ice masses fjord geometry also exerts a strong control on where moraines are deposited promoting their deposition in proximity to valley narrowings bends bifurcations where basins are shallow and or in the vicinity of topographic bumps moraines formed at the margins of ice sheets and ice caps are likely to be large and readily identifiable in the modern landscape in the case of icefields and valley glaciers 10 1000 km2 erosional feedback may well play some role in regulating where moraines are deposited but other factors including variations in accumulation area topography and the propensity for moraines to form at topographic pinning points are also likely to be important this is particularly relevant where land terminating glaciers extend into piedmont zones unconfined plains adjacent to mountain ranges where large and readily identifiable moraines can be deposited in the case of cirque glaciers 10 km2 erosional feedback is less important but factors such as topographic controls on the accumulation of redistributed snow and ice and the availability of surface debris regulate glacier dimensions and thereby determine where moraines are deposited in such cases moraines are likely to be small and particularly susceptible to post depositional modification sometimes making them difficult to identify in the modern landscape based on this review we suggest that despite often being difficult to identify quantify and mitigate topographic controls on moraine distribution should be explicitly considered when reconstructing the dimensions of palaeoglaciers and that moraines should be judiciously chosen before being used as indirect proxies for palaeoclimate i e palaeoclimatic inferences should only be drawn from moraines when topographic controls on moraine distribution are considered insignificant

the late devensian glaciation of the eastern lleyn peninsula north wales evidence for terrestrial depositional environments the glacial deposits of the eastern lleyn peninsula record the advance coalescence and subsequent retreat and uncoupling of welsh and irish sea ice sheets during the late devensian cold stage during advance a thick sheet of basal diamict was deposited over much of the area and during retreat and uncoupling which occurred after 14 5 ka the eastern part of the area was dominated by the formation of a large sandur system draining from the retreating margin of the irish sea ice sheet subsequent stages of retreat are marked by a series of arcuate cross valley moraines formed either by ice contact deposition during stillstand or by structural deformation during minor snout oscillation in the western part of the area sedimentation was controlled by a series of dead ice ridges running parallel to the retreating ice margin and this led to the development of a complex assemblage of localised depositional environments including ice front alluvial fans marginal sandur troughs and pro glacial lake basins all formed under supraglacial ice marginal conditions no evidence of glaciomarine deposition is recorded 1998 john wiley sons ltd

glaciomarine facies within subglacial tunnel valleys the sedimentary record of glacioisostatic downwarping in the irish sea basin coastal exposures of late pleistocene sediments deposited after 19 000 yr bp near dublin ireland provide a window into the infill of a subglacially cut tunnel valley exposures close to the steeply dipping bedrock wall of the valley show boulder gravels within multi storey u shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head gravels are truncated by poorly sorted ice proximal glaciomarine sediments that record the pumping of large volumes of subglacial debris along the tunnel valley to a tidewater ice sheet margin the sedimentary succession is dominated by sediment gravity flow facies comprising interbedded diamict and massive poorly sorted gravel facies interpreted as subaqueous debris flow deposits gravel beds show local inverse and normal coarse tail graded facies recording the restricted development of turbulent flow sediment gravity flow deposits fill broad 2 km shallow 10 m and overlapping channels penetrative deformation structures e g dykes are common at the base of channels the same subglacially eroded topography and glaciomarine infill stratigraphy can be identified on high resolution seismic profiles across nearly 600 km2 of the western irish sea tunnel valleys are argued to have been exposed to glaciomarine processes by the rapid retreat of a calving tidewater ice sheet margin in response to marine flooding caused by glacio isostatic downwarping below the last british ice sheet the facies associations described in this paper comprise an event stratigraphy that may be found on other glaciated continental shelves

understanding the history of extreme wave events in the tuamotu archipelago of french polynesia from large carbonate boulders on makemo atoll with implications for future threats in the central south pacific abstract numerous large carbonate boulders up to 164 tonnes in mass were investigated on the reef flat and beaches of makemo atoll in the tuamotu archipelago of french polynesia to reveal the past occurrence and to anticipate the future potential threat of extreme wave events possibly generated by tropical cyclones and tsunamis the modern reef edge and emerged mid holocene coastal landforms were identified as sources of boulders mobilized during extreme wave events in the past the minimum flow velocities produced by extreme wave events were estimated to exceed 5 4 15 7 m s at the reef edge on different parts of the atoll comparison of uranium thorium ages of boulder coral fabric with written historical records indicates that two large boulders 77 and 68 tonnes were possibly emplaced on the reef flat by a powerful cyclone in february 1878 although most boulder dates are older than the earliest historical cyclone and tsunami records in french polynesia their ages concur with the following a periods of storminess i e increased cyclone activity compared to today in the central south pacific over the last millennium and b periods of high sea surface temperature sst at the great barrier reef possibly associated with higher than normal ssts pacific wide that facilitated the generation of cyclones affecting the central south pacific ocean none of the boulders on makemo were dated younger than ce1900 implying that the last century has not experienced extreme waves of similar magnitude in the past nevertheless the findings suggest that waves of comparable magnitudes to those that have transported large boulders on makemo may recur in the tuamotus and threaten island coasts across the central south pacific in the future