steep beach morphology changes due to energetic wave forcing abstract the three dimensional variability of the sub aerial beach is examined for waimea bay hawaii a steep slope pocket beach subject to energetic winter swell events the beach is mapped using 32 real time kinematic global positioning system rtk gps surveys collected from march 1996 to july 1997 the survey method provides 4 m horizontal spacing and 2 3 cm vertical accuracy the primary morphology change is the episodic removal and re establishment of a foreshore dune during the winter swell season the average sand volume flux between surveys reaches 8 and 4 m 2 day during peak erosion and accretion periods the sand volume of the sub aerial beach is found to be highly correlated 0 96 with the position of the shoreline longshore variations in morphology include beach cusps with typical peak to trough amplitudes of 0 5 1 5 m and longshore wavelengths of 30 70 m the relationships between the energetic swell forcing and the volume and flux of sand on the sub aerial beach are examined the highest correlation 0 88 is found between the total sand volume and the wave energy flux after the latter is filtered following wright et al wright l d short a d green m o 1985 short term changes in the morphodynamic states of beaches and surf zones an empirical predictive model mar geol 62 339 364 the filter is effective at capturing slow accretion phases following energetic erosion events

geologic implications of gas hydrates in the offshore of india krishna godavari basin mahanadi basin andaman sea kerala konkan basin gas hydrate resource assessments that indicate enormous global volumes of gas present within hydrate accumulations have been one of the primary driving forces behind the growing interest in gas hydrates gas hydrate volumetric estimates in recent years have focused on documenting the geologic parameters in the gas hydrate petroleum system that control the occurrence of gas hydrates in nature the primary goals of this report are to review our present understanding of the geologic controls on the occurrence of gas hydrate in the offshore of india and to document the application of the petroleum system approach to the study of gas hydrates national gas hydrate program of india executed the national gas hydrate program expedition 01 nghp 01 in 2006 in four areas located on the eastern and western margins of the indian peninsula and in the andaman sea these areas have experienced very different tectonic and depositional histories the peninsular margins are passive continental margins resulting from a series of rifting episodes during the breakup and dispersion of gondwanaland to form the present indian ocean the andaman sea is bounded on its western side by a convergent margin where the indian plate lithosphere is being subducted beneath southeast asia nghp 01 drilled logged and or cored 15 sites 31 holes in the krishna godavari basin 4 sites 5 holes in the mahanadi basin 1 site 2 holes in the andaman sea and 1 site 1 hole in the kerala konkan basin holes were drilled using standard drilling methods for the purpose of logging while drilling and dedicated wireline logging as well as through the use of a variety of standard coring systems and specialized pressure coring systems nghp 01 yielded evidence of gas hydrate from downhole log and core data obtained from all the sites in the krishna godavari basin the mahanadi basin and in the andaman sea the site drilled in the kerala konkan basin during nghp 01 did not yield any evidence of gas hydrate most of the downhole log inferred gas hydrate and core recovered gas hydrate were characterized as either fracture filling in clay dominated sediments or as pore filling or grain displacement particles disseminated in both fine and coarse grained sediments geochemical analyses of gases obtained from sediment cores recovered during nghp 01 indicated that the gas in most all of the hydrates in the offshore of india is derived from microbial sources only one site in the andaman sea exhibited limited evidence of a thermogenic gas source the gas hydrate petroleum system concept has been used to effectively characterize the geologic controls on the occurrence of gas hydrates in the offshore of india

attenuation measurements from sonic waveform logs in methane hydrate bearing sediments at the nankai trough exploratory well off tokai central japan 1 i have used full waveform logs from the nankai trough exploratory well off central japan to estimate both compressional and shear attenuation in sediments containing methane hydrate mh the attenuation estimates are based on a median frequency shift to the amplitude spectrum of the recorded waveforms this paper is concerned with attenuation at sonic frequencies of 10 20 khz for compressional waves and 500 1000 hz for shear waves i observed that the presence of mh increases the host sediments seismic attenuation and shear attenuation may be more helpful than compressional attenuation in detecting or characterizing mh bearing sediments as compressional attenuation is affected by the presence of gas moreover the ratio of compressional to shear attenuation is found to be a more sensitive indicator of the presence of low saturation gas than the corresponding velocity ratio

india national gas hydrate program expedition 02 operational and technical summary abstract the india national gas hydrate program is being steered by the government of india s ministry of petroleum and natural gas mopng with participation of directorate general of hydrocarbons dgh oil and natural gas corporation limited ongc and the national oil companies and research institutes of india the india national gas hydrate program expedition 01 nghp 01 established the presence of gas hydrate in the krishna godavari kg and mahanadi basins and in the offshore area of the andaman sea basin however the gas hydrates discovered during nghp 01 were mainly distributed as fracture filling material in fine grained clay rich sediments the india national gas hydrate program expedition 02 nghp 02 was carried out with an objective to discover gas hydrate in sand rich sediment along the eastern offshore margin of india ongc planned and executed nghp 02 on the behalf of the mopng nghp 02 started on march 3 2015 and was completed on july 28 2015 total 147 days using the japanese scientific drilling vessel chikyu d v chikyu during nghp 02 42 holes at 25 sites were drilled cored and or surveyed with downhole logging tools these sites were located in four areas along the eastern margin of india and formally named area a mahanadi basin three sites area b northern part of the kg basin twelve sites area c central part of the kg basin six sites and area e southern part to the kg basin four sites all 25 sites established during nghp 02 were first drilled and logged with logging while drilling lwd tools and an additional 17 holes were then drilled and or cored with conventional coring tools hpcs escs or pressure coring tools pctb wireline logging was conducted in 10 holes and formation tests using a dual packer modular formation dynamics tester mdt tool were carried out in two holes the onboard science team used the laboratory facilities on the d v chikyu to examine and analyse the physical properties geochemistry and sedimentology of all the cores collected during the expedition core samples were also analysed in additional post expedition shore based studies conducted in numerous domestic and international gas hydrate research laboratories the nghp 02 sediment cores were archived at the national gas hydrate core repository in mumbai india which is associated with the ongc gas hydrate research and technology centre ghrtc the necessary data for characterizing the occurrence of gas hydrate such as interstitial water chlorinities core derived gas chemistry physical and sedimentological properties thermal images of the recovered cores pressure core and downhole measured logging data lwd and or conventional wireline log data were obtained from most of the drill sites established during nghp 02 almost all the drill sites yielded evidence for the occurrence of gas hydrate however the inferred in situ concentration of gas hydrate varied substantially from site to site for the most part the interpretation of downhole logging data core thermal images interstitial water analyses and pressure core images from the sites established during nghp 02 indicate that the occurrence of concentrated gas hydrate is mostly associated with coarser grained sand rich sediments this paper presents the operational and technical summary of nghp 02

swell impact on reef sedimentary processes a case study of the la reunion fringing reef two surface sediment sampling campaigns were carried out in november and december 2003 before and after a strong swell event in the back reef area of a microtidal fringing reef on the western coast of la reunion indian ocean the spatial distributions of the mean grain size sorting and skewness parameters are determined and grain size trend analysis is performed to estimate the main sediment transport pathways in the reef the results of this analysis are compared with hydrodynamic records obtained in the same reef area during fair weather conditions and during swell events sediment dynamics inferred from the hydrodynamic records show that significant sediment erosion and transport occur only during swell events and under strongly agitated sea states under normal wave conditions there is a potential for onshore sediment transport from the reef flat to the back reef but this transport is episodic and occurs principally during high tide stages sediment transport trends revealed by the grain size trend analysis method show onshore and alongshore low energy transport processes that are in agreement with the hydrodynamic records the grain size trend analysis method also provides evidence of an offshore high energy transport trend that could be interpreted as a real physical process associated with return flow from the shore to the reef the impact of swell on the reef sediment dynamics is clearly demonstrated by onshore and alongshore transport considering different combinations of the vector transport trends computed through the grain size trend analysis approach more realistic and pertinent results can be obtained by applying an exclusive or operation xor case on the vectors the main results presented here highlight a trend towards the accumulation of carbonate sands in the back reef area of the fringing reef these sediments can only be resuspended during extreme events such as storms or tropical cyclones

residual sediment transport paths on a tidal sand bank a comparison between the modified mclaren model and bedform analysis abstract in order to evaluate the validity of the modified mclaren model for sand transport on a tidal sand bank 42 grab samples taken from the northern part of the kwintebank were decalcified sieved and analyzed for statistical parameters the areal distribution of mean grain size standard deviation and skewness were defined and used to determine the residual transport directions the grain size trends taken into consideration were that the sediment becomes finer better sorted and more negatively skewed along the transport pathways f b and the sediment becomes coarser better sorted and more positively skewed along the transport pathways c b these were compared with the transport paths inferred from bedform asymmetries obtained by side scan sonar records there were major differences between the sediment transport paths resulting from the two techniques when the f b trend and small dune asymmetries are compared only 5 out of 24 cases showed agreement 30 whereas in 9 cases the trends were 180 30 different there was even less agreement between the c b trend and the asymmetry of the small dunes only 1 out of 24 cases agreed 30 and almost half of the cases were 90 30 different the sediment transport directions deduced from the morphological analysis of the large dunes all point in the direction of the peak flood current the large dunes seem to be more suitable indicators of the sediment transport paths than the small ones however they conflict with the vectors resulting from the f b trend only one out of 20 cases agrees 30 while in 13 cases the vectors are 180 30 different and in three cases 90 30 neither do the transport directions from the c b trend agree with those deduced from the large dunes only one case agrees 30 while in four out of 20 cases the vectors point in opposite directions in four cases the vectors are 90 30 different the asymmetric cross section of the sand bank suggests sediment transport in a northwest direction it does not seem probable however that sediment transport occurs by migration of the whole sand bank the transport directions inferred from the bank morphology are quite different from the f b trend in 12 out of 42 cases the vectors agree 30 in four cases the vectors point in opposite directions and in 15 cases they are 90 30 different there is slightly more agreement between the c b trend and the transport directions deduced from the sand bank 16 out of 42 cases agree 30 in nine cases the vectors point in opposite directions and three cases are 90 30 different from this study it seems that the residual sediment transport directions can best be deduced from the morphological characteristics of the large dunes the departures between the results of the sediment trend analysis according to the modified mclaren model and the morphology of the subaqueous bedforms are partly explained by the location of the study area near the edge of the sand bank probably better results of the sediment trend analysis would be obtained if samples over the whole length of the sand bank were analyzed and compared perhaps a smaller spacing between the samples would improve the results as well and maybe the samples should not have been decalcified possibly the different transport patterns are attributed to different sediment transport processes which makes a comparison virtually impossible

application of grain size trend analysis for the determination of sediment transport pathways in intertidal areas abstract in this paper we apply the gao and collins procedure of grain size trend analysis for the first time in an intertidal sedimentary system our purpose is to evaluate a reliable method to determine residual transport directions in intertidal environments where sediment movement is not well understood residual transport patterns can be determined by grain size trend analysis if the following criteria are applied 1 a single sediment transport unit must be precisely defined and investigated 2 the thickness of sampling has to be chosen in order to investigate the most recent sedimentary event and 3 a regular mesh grid is sampled to avoid bias in the calculation of grain size trends the gao and collins method was undertaken simultaneously with a topographic survey and a tracer experiment during consecutive meteorological conditions of fair weather and a storm event the topographic changes observed between these two situations and the directions of sediment movement deduced from tracer tracking are coherent with the residual transport pattern calculated from the grain size trend analysis the method was tested on a ridge and runnel system which corresponds to the intertidal part of a macrotidal beach called la salie beach located along the southwest french coast in a high wave energy environment this study permits us to recognize two different residual transport patterns for this intertidal ridge and runnel system one for fair weather and a second for storm conditions during fair weather specific sites are subject to sand accretion while during storm conditions these sand stocks are subsequently spread out over the whole area and remain partly on the beach

growth trishear model and its application to the gilbertown graben system southwest alabama abstract fault propagation folding associated with an upward propagating fault in the gilbertown graben system is revealed by well based 3 d subsurface mapping and dipmeter analysis the fold is developed in the selma chalk which is an oil reservoir along the southern margin of the graben area depth strain analysis suggests that the cretaceous strata were growth units the jurassic strata were pregrowth units and the graben system is detached in the louann salt the growth trishear model has been applied in this paper to study the evolution and kinematics of extensional fault propagation folding models indicate that the propagation to slip p s ratio of the underlying fault plays an important role in governing the geometry of the resulting extensional fault propagation fold with a greater p s ratio the fold is more localized in the vicinity of the propagating fault the extensional fault propagation fold in the gilbertown graben is modeled by both a compactional and a non compactional growth trishear model both models predict a similar geometry of the extensional fault propagation fold the trishear model with compaction best predicts the fold geometry

multi measurement approach for establishing the base of gas hydrate occurrence in the krishna godavari basin for sites cored during expedition nghp 02 in the offshore of india abstract the 2015 national gas hydrate program of india s second expedition nghp 02 acquired logging and coring datasets for constraining the base of the gas hydrate occurrence zone deepest gh and the theoretical base of gas hydrate stability zone bghs these data are used here for two primary goals to constrain the deepest occurrence of gas hydrate relative to predicted stability limits and the observed bsr and to characterize the nature of the contact between gas hydrate bearing sediment and the underlying gas hydrate free sediment a consensus depth for the deepest gh is derived for each nghp 02 coring site from downhole indicators of gas hydrate occurrence obtained from well log electrical resistivity and acoustic data pressure core compressional wave velocity measurements and conventional core measurements of anomalously low temperatures to establish the theoretical bghs models of gas hydrate phase stability with depth are compared with downhole temperature profiles derived from 1 assuming a constant geothermal gradient consistent with downhole temperature measurements and 2 assuming constant heat flow using a geotherm through the downhole temperature measurements and incorporating thermal conductivity calculated from borehole logging data although the deepest nghp 02 gh occurrences are controlled at several sites by a lithologic boundary most sites have deepest gh occurrences within a single coarse grained lithology cutoffs within a single coarse grained lithology which occur for the primary nghp 02 area b gas hydrate reservoir will inhibit pore pressure drawdowns used to extract methane from gas hydrate as an energy resource

the relative contribution of processes driving variability in flow shear and turbidity over a fringing coral reef west maui hawaii high frequency measurements of waves currents and water column properties were made on a fringing coral reef off northwest maui hawaii for 15 months between 2001 and 2003 to aid in understanding the processes governing flow and turbidity over a range of time scales and their contributions to annual budgets the summer months were characterized by consistent trade winds and small waves and under these conditions high frequency internal bores were commonly observed there was little net flow or turbidity over the fore reef and over the reef flat net flow was downwind and turbidity was high when the trade winds waned or the wind direction deviated from the dominant trade wind orientation strong alongshore flows occurred into the typically dominant wind direction and lower turbidity was observed across the reef during the winter when large storm waves impacted the study area strong offshore flows and high turbidity occurred on the reef flat and over the fore reef over the course of a year trade wind conditions resulted in the greatest net transport of turbid water due to relatively strong currents moderate overall turbidity and their frequent occurrence throughout the period of study near surface current directions over the fore reef varied on average by more than 41 from those near the seafloor and the orientation of the currents over the reef flat differed on average by more than 65 from those observed over the fore reef this shear occurred over relatively short vertical order of meters and horizontal order of hundreds of meters scales causing material distributed throughout the water column including the particles in suspension causing the turbidity e g sediment or larvae and or dissolved nutrients and contaminants to be transported in different directions under constant oceanographic and meteorologic forcing

sediment transport pathways in a dredged ria system southwest england abstract the fowey ria system southwest england comprises the river fowey catchment the fowey estuary the cliffs and bays adjacent to the ria mouth and part of the inner continental shelf of the english channel previously large quantities of sediment were introduced into the upper ria by ore mining activity today in common with other rias the fowey receives a low riverine sediment input material from maintenance dredging in the lower ria is dumped in a spoil ground outside the ria mouth the sediments of the system are investigated using an integrated approach to determine sediment distribution and sediment transport pathways surface sediments are analysed for grain size and mineralogy grain size trend analysis is used to examine sediment dispersal patterns away from the locus of deposition in the spoil ground archived data are used to investigate the seabed morphology and to determine long term 100 year bathymetric changes within the ria mixing of sediment from several sources occurs in the upper reaches riverine and locally eroded sediment is transported seawards towards the main area of commercial activity sand and finer grained material moves into the ria from offshore the bed of the inner continental shelf comprises interfluves covered by a thin veneer of sediment with a natural composition of locally derived lithic fragments and biogenic material the area is mainly low non depositional in character except within the partially infilled palaeovalley and its tributaries sediments dumped in the spoil ground disperse in a complex pattern coarse grained material is moved by the action of waves and tidal currents towards the southwest and northeast fine grained material is transported either to the east or the west depending upon the prevailing wave and tidal current regime because of its geomorphology the lower ria acts as an efficient sediment trap retaining a riverine material and sediment eroded from the upper reaches and b sediment entering the ria from offshore despite being subjected to major anthropogenic disturbance from past mining and present day dredging activities the fowey ria conforms to the general sediment model for southwest england rias castaing p guilcher a 1995 geomorphology and sedimentology of rias in perillo g m e ed geomorphology and sedimentology of estuaries developments in sedimentology no 53 elsevier science amsterdam pp 69 111 a conceptual model of sediment transport pathways for the fowey ria system is presented as the basis for further investigations

a comparison of settling and sieve techniques for the analysis of bioclastic sediments this paper examines differences in the use of sieve and settling techniques for the determination of textural parameters of grain size distributions for 30 bulk bioclastic reefal deposits and examines the interpretive use of the results a comparison of results of the key textural parameters shows that sieve size estimates deviate from settled size determinations of mean grain size and dispersion values by up to 2 and up to 1 5 phi units respectively these differences are explained by the different grain properties measured by the two techniques exacerbated by the heterogeneous character of bioclastic deposits changes in sample components which control grain shape and grain bulk sample density also influence the magnitude of size and dispersion differences observed differences are discussed in relation to interpretation of the depositional environment and hydraulic regime leading to the conclusion that sieve results can grossly distort depositional and energy processes operating within bioclastic environments in contrast settled size estimates an index of deposit hydraulic behaviour show that bioclastic sediment transport systems operate within a much narrower energy regime than sieve sizes suggest hydraulic size estimates are considered to provide a better tool with which to interpret sedimentary processes in bioclastic environments

an alternative approach to the identification of net sediment transport paths based on grain size trends abstract progressive changes in grain size parameters have long been linked to net sediment transport paths however the methods employed to date suffer from limitations potentially leading to serious interpretational errors which necessitate the formulation of an integrated quantitative technique the approach advocated here is a step in this direction as it eliminates some of the problems inherent in the older methods previously trend vectors were obtained by comparing the grain size parameters of only two sampling stations at a time which gives a low probability of identifying the actual transport direction in the proposed method groups of five stations comprising a central station and four satellite stations are used for each trend vector grain size parameters are first combined in such a way that bias towards any one of them is climated the resultant dimensionless numbers are then substituted for the proportional frequencies of recorded directions in conventional vector analysis the satellite stations must be located equally far from the central station on radials 90 from each other which is seldom the case an iterative trigometric technique is therefore employed to determine the combined grain size parameters at these localities conventional vector analysis adapted to the situation of using four raials instead of 10 sectors allows the calculation of a vector mean azimuth and vector magnitude

temporal and spatial variability in the flow and dispersal of suspended sediment on a fringing reef flat molokai hawaii abstract a multi year study was conducted on a shallow fringing reef flat on molokai hawaii to determine the temporal and spatial dispersal patterns of terrigenous suspended sediment during this study trade wind conditions existed for the majority of the year on the reef flat the trade wind conditions produced strong currents and resuspended moderate amounts of sediment on the reef flat on a daily basis during the year of study resulting in an overwhelming contribution to the total sediment flux the magnitude and direction of the trade winds relative to the orientation of the coastline the shallow relief and broad morphology and tidal elevation provided the primary control of the physical processes that resuspended and transported sediment on the reef flat over the period of record spatial data indicate that much of the terrigenous sediment resuspended on the reef flat is transported predominantly alongshore and is confined to the inner to mid reef flat evidence for the limited across shore mixing and transport is provided by the dominantly alongshore wind driven currents during trade wind conditions and the well defined across shore gradient in percentage calcium carbonate of the suspended sediment regions of slightly offshore suspended sediment transport along the reef flat can be attributed to the circulation pattern set up by the interaction between the trade winds coastal morphology and anthropogenic coastal structures i e fish ponds and wharf the regions in which sediment were seen to move offshore provide the strongest link between the sediment dynamics on reef flat and fore reef and qualitatively appears to be correlated with low coral coverage on the fore reef

strength characteristics of sediments from a gas hydrate deposit in the krishna godavari basin on the eastern margin of india abstract knowledge of the strength of sediments overlying sub seafloor gas hydrate deposits is crucial for predicting borehole and seafloor stability during hydrate extraction ideally sediment strength should be determined along a continuous downhole profile from the seafloor to the hydrate reservoir but few such profiles have been obtained in this study we used cores retrieved at site nghp 02 23 in the krishna godavari basin in unconfined penetration tests on split cores and in triaxial deformation experiments on hydrate free sediment samples although penetrometer tests identified relatively low strength 70 250 kpa likely due to hydrate dissociation in the hydrate bearing interval 90 300 m below seafloor mbsf sediment strength exceeded 350 kpa in the intervals 140 170 and 250 270 mbsf each of which lies just above a zone of high gas hydrate concentration the average stress ratio of triaxial strength at 4 axial strain to effective mean stress qe 4 p of hydrate free silts was about 0 67 throughout the hole an exception to this trend was in fine sands from 280 mbsf in the deeper gas hydrate zone where the stress ratios were greater than 1 0 the stress ratios of hydrate bearing sediments in the deeper gas hydrate zone that were reported from the pressure core measurements were far greater than those of any hydrate free sediments for a given effective mean stress the high strength intervals in silty sediments we identified by the penetration tests could be associated with zones of high hydrate concentration because high strength layers in fine grained silty sediments commonly exhibit lower permeability than sandy layers potential hydrate host they may act as seals that assist the precipitation of hydrate below them

spatial and temporal variations in wave characteristics across a reef platform warraber island torres strait australia a field experiment was conducted at warraber island torres strait australia to investigate spatial and temporal variations in wave characteristics and energy across a mesotidal coral reef platform measurements of water depth were obtained using five pressure sensors deployed across a 2 7 km section of reef flat from july 3 5 2001 the reef surface was uneven and consisted of an outer reef flat a central reef flat depression an inner reef ramp a palaeo reef surface and the shoreline water levels decreased landward across the platform with tide ranges at the shoreline being almost 50 lower than at the outer reef flat rising and falling tides were characterised by a bimodal energy distribution with both short period 0 3 s and wind 3 8 s waves present higher water levels were dominated by wind waves the highest waves occurred at high tides associated with nocturnal tidal cycles with hs decreasing from 0 5 to 0 2 m from the outer reef flat to the shoreline wave energy at swell 8 20 s and infragravity 20 s frequencies was negligible across the reef platform although there was evidence of wave groups at higher water levels reef geometry and changes in water level determine the magnitude of wave energy on the reef platform up to 85 95 of incident wave energy is attenuated by the central reef flat depression at high and low tide respectively and strong linear relationships exist between hs and h at all locations both wave height and wave type are strongly depth dependent critical reef rim depths required to produce hs of a given size vary spatially across the reef rim due to variations in reef topography a distinct depth related threshold exists at which short period and wind wave dominance reverses over a 14 day spring neap tidal cycle the time of occurrence of wave action diminishes across the reef platform to the shoreline larger waves hs 0 2 m occur for only 9 of time at the outer reef flat and for less than 0 5 over the remaining reef platform this implies that on mesotidal reef platforms sediment entrainment and transport are severely constrained under normal wave energy conditions and significant change is likely restricted to extreme events

nearshore circulation in a tropical fringing reef system 1 the role of waves tide and wind on the circulation of a fringing reef system was investigated using data collected during a 6 week field experiment in a section of ningaloo reef off western australia the high correlation observed between current velocities and wave height throughout the system revealed the dominant role wave breaking plays in driving the overall reef lagoon circulation whereas the modulation of the currents at tidal frequencies suggested that the wave driven currents responded to tidal variations in the mean water level over the reef the influence of the various forcing mechanisms on the current field was investigated for both high and low frequency bands wave breaking was found to be the dominant forcing mechanism for the low frequency subtidal currents with the subtidal flow pattern consisting of a cross reef flow over the reef alongshore flow in the lagoon and water exiting back to the ocean through the main channel the tides controlled the high frequency current variability via two mechanisms one associated with the ebb flood cycle of the tides and the second associated with tidal modulations of the wave driven currents wind forcing and buoyancy effects were both found to be negligible in driving the circulation and flushing of the system during the observation period flushing time scale estimates varied from as low as 2 h to more than a day for the wide range of observed incident wave heights the results suggest that the circulation of ningaloo reef will be strongly influenced by even a small mean sea level rise

sediments from fringing reefs of reunion island indian ocean abstract on reunion island fringing reefs comprise the following physiographical zones from the open sea landwards outer sandy spread spur and groove zone reef flat backreef zone sixty two samples collected from the various zones have been analyzed by using correspondence factor analysis to determine variations in sediment composition and grain size five sediment facies and three foraminiferal subfacies can be recognized on the basis of component composition and three sediment types can be defined using the grain size data alcyonaria terrigenous fine sand facies and calcarina subfacies occur in the outer sandy spread whereas foraminiferal coarse sand facies characterizes the spur and groove system the outer margin of the reef flat exhibits coral coralline algal and coral molluscan coarse sand facies and the inner part of the reef flat exhibits a coral terrigenous mediumsand facies the whole reef flat also presents a miniacina subfacies the backreef area displays a coral coralline algal medium sand facies and a marginopora textularia subfacies factor axes seem to reflect physiographical or hydrodynamical gradients

wave set up on coral reefs 2 set up on reefs with various profiles abstract all available laboratory data for wave set up on two dimensional reef profiles of various shapes have been compared with data from an idealised horizontal reef with a steep reef face gourlay 1996 the data is generally well represented by a relationship between the relative set up parameter gh r t o and the submergence parameter g h r h r h o and the relative set up on reef profiles of natural form is found to be less than that observed on the idealised horizontal reef the important influences of reef rim slope and variable water depths on the reef top have been investigated and some methods for allowing for them are suggested comparison of data for irregular waves with that for regular waves has led to the development of a simple method for estimating the effects of wave groups upon the magnitude of the steady state mean wave set up gh r the results of the analyses are applied to the determination of wave set up and its effects at three specific coral reef sites

wave generated flow on coral reefs an analysis for two dimensional horizontal reef tops with steep faces waves breaking on the seaward rim of a coral reef generate a flow of water from the exposed side of the reef to the sheltered side and or to either channels through the reef rim or lower sections of the latter this wave generated flow is driven by the water surface gradient resulting from the wave set up created by the breaking waves this paper reviews previous approaches to modelling wave generated flows across coral reefs and discusses the influence of reef morphology and roughness upon these flows laboratory measurements upon a two dimensional horizontal reef platform with a steep reef face provide the basis for extending a previous theoretical analysis for wave set up on a reef in the absence of a flow gourlay m r 1996b wave set up on coral reefs 2 set up on reefs with various profiles coastal engineering 28 1755 to include the interaction between a unidirectional flow and the wave set up the laboratory model results are then used to demonstrate that there are two basic reef top flow regimes reef top control and reef rim control using open channel flow theory analytical relationships are derived for the reef top current velocity in terms of the offreef wave conditions the reef top water depth and the physical characteristics of the reef top topography the wave set up and wave generated flow relationships are found to predict experimental values with reasonable accuracy in most cases the analytical relationships are used to investigate wave generated flows into a boat harbour channel on heron reef in the southern great barrier reef c 2005 elsevier b v all rights reserved

evidence of paleo cold seep activity from the bay of bengal offshore india 1 we report evidence of paleo cold seep associated activities preserved in methane derived carbonates in association with chemosynthetic clams calyptogena sp from a sediment core in the krishna godavari basin bay of bengal visual observations and calculations based on high resolution wet bulk density profile of a core collected on board r v marion dufresne may 2007 show zones of sharp increase in carbonate content 10 55 vol within 16 20 meters below seafloor mbsf the presence of calyptogena clam shells chimneys shell breccias with high mg calcite cement and pyrite within this zone suggest seepage of methane and sulfide bearing fluid to the seafloor in the past highly depleted carbon isotopic values 13c ranges from 41 to 52 vpdb from these carbonates indicate carbon derived via anaerobic oxidation of methane extrapolated mean calendar age 58 7 ka b p of the clastic sediments at a depth of 16 mbsf is close to the upper limit of the u th based depositional age 46 2 3 7 and 53 0 1 6 ka of authigenic carbonates sampled from this level thereby constraining the younger age limit of the carbonate deposition methane expulsion events the observed carbonate deposition might have resulted from the flow of methane enriched fluids through the fracture network formed because of shale diapirism

wave breaking hydrodynamics within coral reef systems and the effect of changing relative sea level this paper considers the hydrodynamics of wave driven flow across a coral reef and the resultant flushing of its lagoon current depth coefficients are introduced that describe the fractional change of across reef and lagoonal current with change in the relative local sea level i e the depth of water over the reef flat the coefficients are derived from an analytical hydrodynamic model and compared with data from two reefs the first is ningaloo reef in northwest australia which is a typical barrier reef with a narrow coastal lagoon and the second is kaneohe bay in oahu hawaii where the reef is both unusually deep and wide the current depth coefficients are shown to be sensitive to the form of the frictional law on the reef flat and can be deduced from measurements of the astronomical tidal currents in the lagoon both quadratic and linear friction laws are considered for the reef flat and good agreement obtained with a linear law based on the high frequency motion due to surface gravity waves

modern fringing reef carbonates from equatorial se asia an integrated environmental sediment and satellite characterisation study abstract fringing reefs of se asia may conservatively comprise 30 of the world s coral reef area but remain almost unstudied white 1987 tomascik et al 1997 this study provides insights into the primary sedimentological and early alteration characteristics of an isolated fringing reef system kaledupa hoga from the tukang besi archipelago se asia a combined multispectral satellite imagery field and petrographic study allowed for the generation of an environmental facies map which acts as a model for the distribution of primary sedimentological characteristics in relation to the primary environmental facies the islands of the tukang besi archipelago are mesotidal 71 accuracy when compared with field and sedimentary data with the exception of the reef crest and reef slope that commonly have widths on a sub imaging resolution although field and satellite imagery observations reveal ten environmental facies sedimentological characterisation results in a lower number of distinctive categories due to the similarity of many deposits foreshore backshore and bare intertidal deposits are distinctive and are composed of reef derived material that has been reworked shorewards seagrass associated facies all show some fine silt clay sized material

wave transformation on a coral reef wave transformation of regular waves was measured in a laboratory model of a fringing reef with a steep face and an outer reef top slope gradually decreasing in the landward direction data was obtained for various wave conditions and water levels a nonlinearity parameter fco g1 25ho 0 5t2 5 hc 1 75 based upon one proposed by swart and loubser 1979 is proposed as a suitable parameter for classifying wave transformation regimes on this reef in particular when fco 150 waves plunge on the reef edge and the amount of wave energy reaching a shore or structure is small 16 when fin co 100 waves spill on the reef top but the greater part of their energy is transmitted over the reef top the maximum values of the wave height to water depth ratio on the reef top were found to be consistent with nelson s analyses for laboratory and field data which indicate that the maximum stable wave height to depth ratio h d on a horizontal bottom never exceeds 0 55 for shallow water waves fc 500 the experimental data confirms that the maximum value of h d decreases when fc decreases but that it also increases when the bottom slope increases

physical property characteristics of gas hydrate bearing reservoir and associated seal sediments collected during nghp 02 in the krishna godavari basin in the offshore of india abstract india s national gas hydrate program expedition 02 nghp 02 was conducted to better understand geologic controls on gas hydrate occurrence and morphology targeting coarse grained sediments along the lower continental slope offshore eastern india this study combines seismic logging while drilling data and a petroleum system approach to provide a regional geologic and lithologic context for 1 gas hydrate morphology and distribution and 2 effects of fine grained sediments clays and other grains smaller than 63 m on gas production in nghp 02 area b in the krishna godavari basin area b seismic data show a buried anticline syncline structure with strong reflectors r1 and r2 that delineate two of the five lithologic units unit i shallowest ii r1 iii iv r2 and v below the bas of gas hydrate stability throughout area b gas hydrate morphology depends on its placement within these units specifically core and grain scale measurements indicate fines content exerts a primary control on the gas hydrate distribution and morphology units i ii and iii are generally fine grained on the anticline crest these units host primarily grain displacing gas hydrate veins linked to pore occupying gas hydrate in thin localized coarser grained deposits diatoms in unit iii increase porosity with depth reaching 70 where it contacts unit iv the gas hydrate reservoir associated with reflector r2 the unit iii lithology and porosity allow fluid and dissolved phase methane to escape unit iv and form gas hydrate in the fine grained overburden within unit iv fine grained layers are interbedded with coarser grained gas hydrate reservoir sands and the fines content even in the sands is high enough to impact hydraulic and mechanical properties during gas production fluid motion during gas production can mobilize fines which can then clog pore throats limiting production rates pore water freshening during gas hydrate dissociation can increase fines mobilization particularly given the smectite identified in the fine grained interbeds

an interpretation of trends in grain size measures abstract the mean grain size sorting and skewness of a sedimentary deposit are dependent on the sediment grain size distribution of its source and the sedimentary processes of i winnowing erosion ii selective deposition of the grain size distribution in transport and iii total deposition of the sediment in transport if a source sediment undergoes erosion and the resultant sediment in transport is deposited completely the deposit must be finer better sorted and more negatively skewed than the source this trend is referred to as case i the lag remaining after erosion on the other hand must be coarser better sorted and more positively skewed case ii if sediment in transport undergoes selective deposition the resultant deposit can either be finer case iiia or coarser cas iiib than the source but the sorting will be better and the skew more positive although exceptions to these trends may occur they suggest that comparison of one sediment must be made with another for the proper identification of the sedimentary process and therefore it is not possible for a single grain size distribution to identify the depositional environment the trends also suggest that the skewness of a grain size distribution has been widely misinterpreted and implies neither the truncation of one of the tails nor the mixing of more than one mode rather a skewed sediment is the natural result of the sedimentary process in a system of related environments these trends can be used to identify both the probable source and the probable deposit and by inference the net sediment transport paths among sedimentary deposits such an analysis provides a rapid understanding of the sedimentary processes identifies patterns of erosion and accretion and may suggest transport processes

the hydrodynamic and sedimentary setting of nearshore coral reefs central great barrier reef shelf australia paluma shoals a case study the great barrier reef gbr shelf contains a range of coral reefs on the highly turbid shallow inner shelf where interaction occurs with terrigenous sediments the modern hydrodynamic and sedimentation regimes at paluma shoals a shore attached turbid zone coral reef and at phillips reef a fringing reef located 20 km offshore have been studied to document the mechanisms controlling turbidity at each reef waves currents and near bed turbidity were measured for a period of 1 month bed sediments were sampled at 135 sites on the inner shelf muddy sands are widespread with admixed terrigenous and carbonate gravel components close to the reefs and islands except on their relatively sheltered sw side where sandy silty clays occur at paluma shoals the coral assemblage is characteristic of inner shelf or sheltered habitats on the gbr shelf dominated by galaxea fascicularis up to 50 coral cover and is broadly similar to that at phillips reef further offshore and in deeper water the sediments of the paluma shoals reef flats consist of mixed terrigenous and calcareous gravels and sands with intermixed silts and clays whereas the reef slope is dominated by gravelly quartz sands the main turbidity generating process is wave driven resuspension and turbidity ranges up to 175 nephelometric turbidity units ntu in contrast at phillips reef turbidity is 40 ntu probably occurs for a total of 40 days each year and relatively little time is spent at intermediate turbidities 15 50 ntu the extended time spent at either low or high turbidities is consistent with the biological response of some species of corals to adopt two alternative mechanisms of functioning autotrophy and heterotrophy in response to different levels of turbidity sedimentation rates over periods of hours may reach the equivalent of 10 000 times the mean global background terrigenous flux btf of sediment to the sea floor i e 10 000 btf over three orders of magnitude greater than the holocene average for halifax bay of 3 btf as elsewhere along the nearshore zone of the central gbr dry season hydrodynamic conditions form a primary control upon turbidity and the distribution of bed sediments the location of modern nearshore coral reefs is controlled by the presence of suitable substrates which in halifax bay are pleistocene and early holocene coarse grained and relatively stable alluvial deposits

seismic imaging of a fractured gas hydrate system in the krishna godavari basin offshore india gas hydrate was discovered in the krishna godavari kg basin during the india national gas hydrate program nghp expedition 1 at site nghp 01 10 within a fractured clay dominated sedimentary system logging while drilling lwd coring and wire line logging confirmed gas hydrate dominantly in fractures at four borehole sites spanning a 500 m transect three dimensional 3d seismic data were subsequently used to image the fractured system and explain the occurrence of gas hydrate associated with the fractures a system of two fault sets was identified part of a typical passive margin tectonic setting the lwd derived fracture network at hole nghp 01 10a is to some extent seen in the seismic data and was mapped using seismic coherency attributes the fractured system around site nghp 01 10 extends over a triangular shaped area of 2 5 km2 defined using seismic attributes of the seafloor reflection as well as seismic sweetness at the base of the gas hydrate occurrence zone the triangular shaped area is also showing a polygonal nearly hexagonal fault pattern distinct from other more rectangular fault patterns observed in the study area the occurrence of gas hydrate at site nghp 01 10 is the result of a specific combination of tectonic fault orientations and the abundance of free gas migration from a deeper gas source the triangular shaped area of enriched gas hydrate occurrence is bound by two faults acting as migration conduits additionally the fault associated sediment deformation provides a possible migration pathway for the free gas from the deeper gas source into the gas hydrate stability zone it is proposed that there are additional locations in the kg basin with possible gas hydrate accumulation of similar tectonic conditions and one such location was identified from the 3d seismic data 6 km nw of site nghp 01 10

a currents of removal approach for interpreting carbonate sedimentary processes abstract this study develops a currents of removal methodology to examine and quantify the nature of physical transport processes affecting the formation of bioclastic deposits in the cocos keeling islands an indian ocean atoll this approach is based on the hydraulic settling and threshold of entrainment characteristics of bioclastic deposits and measured current energy potential mobility pm analysis of 157 samples quantifies the proportion of deposits able to be transported in each geomorphic zone results show that under mean energy conditions wave induced currents entrain and transport sediment within the atoll and show that transport of sediment is not solely reliant on storm energy conditions gradients of pm values are used to reconstruct sediment transport pathways from the reef flat 85 100 pm through shallow passages 75 100 pm to sand aprons 50 75 pm and shallow 0 20 pm and deep lagoon 0 pm comparison of settling velocity distributions of bed material and sediment retained in sediment trap experiments show that actual mobility levels correspond with pm estimates potential mobility analysis also identifies the immobile portions of deposits which increase lagoonward constituent analysis of immobile fractions and analysis of settling frequency distributions are used to differentiate the importance of physical and biological processes in the formation of deposits throughout cocos and identify the role of each geomorphic zone in the transport system the pattern of sediment is controlled by physical processes between the reef flat the primary sediment production zone with sediment transported through the shallow passage conduits to the sand aprons the formation of shallow and deep lagoon deposits is controlled by autochthonous sediment production and storm deposition potential mobility analysis is a powerful tool enabling physical transport processes within bioclastic sedimentary environments to be quantified the ability to examine an individual deposit s hydraulic behaviour and development also enables depositional processes to be examined at a much finer resolution than previously attempted using conventional textural approaches

unravelling the influence of water depth and wave energy on the facies diversity of shelf carbonates carbonate sequence stratigraphy is founded on the principle that changes in relative sea level are recorded in the rock record by the accumulation of sediment with relative water depth dependent attributes while at the scale of a shelf to basin transect facies clearly arrange by water depth the relation blurs for depths 40 m the most vigorous zone of carbonate production the reason for this change in behaviour is two fold firstly in shallow water the intrinsic processes of storm and wave reworking influence the seabed through submarine erosion and sediment redistribution secondly facies diversity tends to be greater in shallow water than deep water because of a greater diversity in grain producers remote sensing imagery field observations and hydrodynamic models for two reef rimmed shore attached carbonate platforms in the red sea show neither water depth nor energy regime to be reliable indicators of facies type when considered in isolation considered together however the predictive power of the two variables rises significantly the results demonstrate it to be an oversimplification to assume a direct link between palaeo water depth and depositional diversity of subtidal lithofacies while highlighting the importance of hydrodynamics in directing the accumulation of carbonate sediments in the shallow photic zone while the size distributions of facies extents in the two focus areas follow power laws no direct relation between the lateral continuity of the facies belts and water depth or wave height is reported the work is relevant for the interpretation of metre scale subtidal carbonate cycles throughout the geological record by demonstrating how caution must be applied when inferring palaeowater depths from depositional facies

regional stratigraphic framework and gas hydrate occurrence offshore eastern india core log seismic integration of national gas hydrate program expedition 02 nghp 02 area b drill sites abstract the indian national gas hydrate program expedition 02 nghp 02 was designed to study the occurrence of gas hydrate along the passive continental margin of the indian peninsula in the bay of bengal twelve holes were logged and measured with logging while drilling lwd and five holes were cored in area b of nghp 02 the lwd and coring results in area b helped to understand the geological significance of sequence stratigraphy in krishna godavari basin and identified the occurrence of gas hydrate this study summarized the log and litho units in area b and establish three integrated units based on the core log seismic integration most of the downhole log and core inferred gas hydrate occurrences are in the late miocene integrated unit b with several sets of reservoir sections exhibiting favorable conditions for hosting gas hydrate the gas hydrates reservoirs associated with reflectors r1 and r2 were identified and the r1 reservoirs are characterized by fracture and pore filling gas hydrate and the r2 is in sand rich sediments with pore filling gas hydrate at high saturations the thickness variations associated with the r1 and r2 are possibly associated with the development anticlinal structure and are likely related to syn sedimentary growth of the folding structures major gas hydrate zones exist in and around the r1 and r2 near the bsr depth and mostly have coincident with the fractures and mass transport deposits the spatial distribution of gas hydrate in the r1 and r2 reservoirs is highly influenced by the anticlinal structure this study can be considered a good case for the future gas hydrate studies and explorations in the nearby areas

wave set up on coral reefs 1 set up and wave generated flow on an idealised two dimensional horizontal reef wave set up may be significant in determining water levels on coral reefs particularly in microtidal environments and hence is an important factor for the design of reef top structures and for the stability of reef top islands laboratory experiments have been made on a two dimensional model of an idealised horizontal reef under two different conditions corresponding to a fringing reef or closed lagoon situation and a platform reef or open lagoon situation both wave set up on the reef top and the wave generated flow across the reef were measured and related to wave and tide level conditions all other factors being the same wave set up is greatest at low tide levels whereas wave generated flow is greater at higher tide levels the magnitude of the set up on a platform reef with a wave generated flow is less than on a fringing reef without any net flow by an amount equal to the velocity head of the flow across the reef dimensionless parameters ghrt o and q gho3 are found to be functions of relative submergence parameters hrho or r hr ho for values of ghr hr ho 1 waves break on the reef top and radiation stress theory can be used to calculate set up for ghr hr ho 0 7 waves break on the reef face and set up is determined by broadcrested weir control at the reef edge the symbols are defined as follows g is gravitational acceleration hr is still water depth over horizontal reef top ho is offreef wave height equivalent deep water value q is discharge per unit length of reef edge t is wave period and ghr is maximum wave set up on reef top

the use of grain size trend analysis in macrotidal areas with breakwaters implications of settling velocity and spatial sampling density abstract in a macrotidal environment with offshore breakwaters elmer west sussex a new approach for the identification of the sediment transport pathways with grain size trend analysis gsta was undertaken using statistical parameters mean sorting and skewness directly derived from settling velocities distributions the same samples were analysed with sieving quarter and half phi resolution and gsta was performed again in order to directly compare the resultant sediment transport directions derived with the two analytical techniques furthermore both regular and irregular sampling distributions were used to recalculate gsta hydrodynamic data were collected in different locations around the breakwaters and net sediment transport directions were calculated in order to assess the accuracy of the sediment transport pathway directions derived with the different analytical techniques the accuracy of settling velocity in determining the statistical parameters of the grain size distribution is identified especially for the fine medium sand sediments settling velocities produced better results than the sieving the quarter phi resolution producing the poorer results in comparison with the coarser half phi resolution the results for the different spatial sampling strategies are found to depend upon the number of samples utilised that shows that the accuracy of the gsta is based upon the ability of representing adequately the spatial distribution of the sediment parameters

gas hydrate occurrence and distribution controlled by regional geological structure off eastern india estimates from logging while drilling in area b national gas hydrate program expedition 02 nghp 02 abstract the national gas hydrate program expedition 02 nghp 02 was designed to examine gas hydrate occurrences off the eastern margin of the indian peninsula twelve holes were logged with logging while drilling lwd tools and nine holes at five sites were cored in area b of nghp 02 five logging units were defined based on the characteristics in logging data responses distinctive logging units r1 and r2 characterized by high gamma ray log values and composed of quartz and biotite rich medium sized sand grain units that act as gas hydrate resevoirs and correlated to strong seismic reflectors hydrate bearing intervals can be identified by resistivity and sonic velocity logs and classified into pore filling type fracture filling type and a mixture of pore and fracture filling types based on borehole image characteristics pore filling type gas hydrate is typically developed in the case where the depths of r1 and or r2 is close to the seismic inferred bottom simulating reflector bsr fracture filling type hydrates associated the r1 section occur above the bsr associated with the anticline in area b the occurrence of pore filling and fracture filling gas hydrate represent different processes of hydrate formation related to the regional geological structure the stratigraphic layered pore filling gas hydrate occurrences are generated along often dipping sand layers which are also conduits for methane bearing fluid migrating from below the bsr in many settings fracture filling type gas hydrate is an alternative mechanism for the occurrence of gas hydrate in mudstone rich sediments above the bsr and found associated with the anticline in area b this structural constraint of the hydrate bearing fractures in the area b anticline suggest that the fracture dominated reservoirs possibly formed by anticlinal flexure and the upward flow of methane bearing fluids along porous sedimentary layers and the subsequent formation of pore filling gas hydrate occurrences account for the range of gas hydrate accumulations discovered during nghp 02

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

net sediment transport patterns inferred from grain size trends based upon definition of transport vectors reply abstract a new approach to the analysis of the grain size trends associated with net sediment transport directions in shallow marine environments is developed here two specific trends modified from mclaren and bowles 1985 on the basis of a literature review are used to define a grid of trend vectors such vectors are filtered and transformed into transport vectors it is suggested that an ordered pattern of the transport vectors represents net transport paths the orderliness of the derived pattern is examined on the basis of a significance test using the average length of the transport vectors as a criterion both the filtering operation and the significance test procedure are based upon the assumption that the trend vectors which are not associated with net transport have the same probability of being in any direction the technique is applied to data from yangpu harbour southern china the technique can be applied to inner continental shelf and coastal environments for such an analysis the area under investigation should be sampled at an interval large enough to reflect the real grain size trends resulting from net sediment transport but small compared with the dimensions of the sedimentary environment the time scale of the results depends upon the sampling depth applicability of the technique is likely to be somewhat limited where the environment is highly variable over short distances furthermore due to its statistical character the analysis may fail to identify net transport patterns

improving recovery from mature oil fields producing from carbonate reservoirs upper jurassic smackover formation womack hill field eastern gulf coast u s a reservoir characterization modeling and simulation were undertaken to improve production from womack hill field eastern gulf coast united states this field produces oil from upper jurassic smackover carbonate shoal reservoirs these reservoirs occur in vertically stacked heterogeneous depositional and porosity cycles the cycles consist of lime mudstone and wackestone at the base and ooid grainstone at the top porosity has been enhanced through dissolution and dolomitization porosity is chiefly interparticle solution enlarged interparticle grain moldic intercrystalline dolomite and vuggy pores dolostone pore systems and flow units have the highest reservoir potential petroleum trapping mechanisms include a fault trap footwall uplift with closure to the south against a major west southeast trending normal fault in the western area a footwall uplift trap associated with a possible southwest northeast trending normal fault in the south central area and a salt cored anticline with four way dip closure in the eastern area potential barriers to flow are present as a result of petrophysical differences among and within the cycles as well as the presence of normal faulting reservoir performance analysis and simulation indicate that the unitized western area has less than 1 mmstb of oil remaining to be recovered and that the eastern area has 2 3 mmstb of oil to be recovered a field scale reservoir management strategy that includes the drilling of infill wells in the eastern area of the field and perforating existing wells in stratigraphically higher porosity zones in the unitized western area is recommended for sustaining production from the womack hill field

sedimentation processes in a coral reef embayment hanalei bay kauai oceanographic measurements and sediment samples were collected during the summer of 2006 as part of a multi year study of coastal circulation and the fate of terrigenous sediment on coral reefs in hanalei bay kauai the goal of this study was to better understand sediment dynamics in a coral reef lined embayment where winds ocean surface waves and river floods are important processes during a summer period that was marked by two wave events and one river flood we documented significant differences in sediment trap collection rates and the composition grain size and magnitude of sediment transported in the bay sediment trap collection rates were well correlated with combined wave current near bed shear stresses during the non flood periods but were not correlated during the flood the flood s delivery of fine grained sediment to the bay initially caused high turbidity and sediment collection rates off the river mouth but the plume dispersed relatively quickly over the next month the flood deposit was reworked by mild waves and currents and the fine grained terrestrial sediment was advected around the bay and collected in sediment traps away from the river mouth long after the turbid surface plume was gone the reworked flood deposits due to their longer duration of influence and proximity to the seabed appear to pose a greater long term impact to benthic coral reef communities than the flood plumes themselves the results presented here display how spatial and temporal differences in hydrodynamic processes which result from variations in reef morphology and orientation cause substantial variations in the deposition residence time resuspension and advection of both reef derived and fluvial sediment over relatively short spatial scales in a coral reef embayment

sediment characteristics in reef areas influenced by eutrophication related alterations of benthic communities and bioerosion processes abstract this study investigated sediment deposits and suspended particulate matter in three reef areas of reunion island characterized by varying benthic communities and bioerosion processes as a result of different eutrophication levels the sediments were sampled using two different methods hand collecting directly on the reef bottom and sampling by traps this approach allowed a comparison between the composition of reefal bottom sediments and suspended particles in locations where algal communities prevailed over corals as a result of nutrification a shift from coral to coralline algae dominated sediments could be observed in addition a decrease in sediment production and a prevalence of very fine sand to mud sized grains over medium to fine sands existed in the nutrient enriched areas this grain size difference probably is caused by a decrease in grazing activity in the enriched areas high proportions of coralline algal debris and sponge spicules were specifically found in the sediments within areas receiving high nutrient input these two diagnostic components were abundant in both the suspended particulate matter and in the fine fractions

structure and evolution of north choctaw ridge field alabama a salt related footwall uplift along the peripheral fault system gulf coast basin abstract north choctaw ridge ncr field is in a structural trap that produces from the jurassic smackover formation in the gilbertown graben system near the updip limit of the louann salt the field is in a footwall uplift below the southernmost of the three faults that form the northern boundary of the graben system the top seal is anhydrite in the overlying buckner member of the haynesville formation and the boundary fault provides a lateral seal the geometry and evolution of the structure has been determined from a three dimensional interpretation of the graben system and from a balanced and sequentially restorable cross section the cross section is both area and length balanced with a lower detachment in the louann salt significant structural growth began in early cretaceous time when three major south dipping down to the gulf faults formed creating an imbricate system of half grabens the melvin fault system regional subsidence in the hangingwall of the melvin fault system indicates contemporaneous salt deflation with the ncr field subsiding the least the north dipping boundary fault of the gilbertown graben system east gilbertown fault developed in the late cretaceous late cretaceous and tertiary extension produced a full graben between the east gilbertown and melvin c faults

structural framework and fault analysis in the east central gulf of mexico shelf implications for offshore co2 storage abstract a vast co2 storage resource exists offshore in cretaceous through neogene sandstone in the desoto canyon salt basin in the east central gulf of mexico continental shelf understanding the structural styles the likelihood of reactivation and seal properties of the faults in this area is essential for selecting safe carbon storage sites and minimizing the risk of injected co2 migrating beyond the confines of the storage complex the desoto canyon salt basin has variable structural styles in the basin with different insights for co2 storage the mobile viosca knoll shelf contains stable shelf and a large four way structural closure where provide favorable storage opportunities the destin dome region contains three groups of peripheral faults of the destin fault system faults that strike along shmax dip at 60 and steeply dipping faults are predicted to have elevated risk of slip and dilation the w e striking fault group has an overall higher slip and dilation tendency than the other two groups under the same injection conditions fault seal analysis shows that elevated risk along faults occurs at sandstone sandstone juxtaposition zones and zones with high fault throw and low sgr values storage plans should avoid the faults with elevated risk to ensure that the injectate will not flow into or pressurize the fault zones ideal injection sites within the destin fault system in the destin dome region are in hanging wall rollovers that contain low fault throw and shale sandstone juxtapositions future research should focus on geomechanical pressure and flow simulation of the potential reservoirs and associated seals in the area of the peripheral faults