high pressure eclogites in northern jiangsu southern shandong province eastern china abstract eclogites are distributed for more than 500 km along a major tectonic boundary between the sino korean and yangtze cratons in central and eastern china these eclogites usually have high p assemblages including omphacite kyanite and or coesite or its pseudomorph and form a high p eclogite terrane they occur as isolated lenses or blocks 10 cm to 300 m long in gneisses type i serpentinized garnet peridotites type ii and marbles type iii type i eclogites were formed by prograde metamorphism and their primary metamorphic mineral assemblage consists mainly of garnet pyrope prp 15 40 mol omphacite jadeite jd 34 64 mol pargasitic amphibole kyanite phengitic muscovite zoisite an sio2 phase apatite rutile and zircon type ii eclogites characteristically contain no sio2 phase and are divided into prograde eclogites and mantle derived eclogites the prograde eclogites of type ii are petrographically similar to type i eclogites the mantle derived eclogites have high mgo feo fe2o3 and cr2o3 compositions in bulk rock and minerals and consist mainly of pyrope rich garnet prp 48 60 mol sodic augite jd 10 27 mol and rutile type iii eclogites have an unusual mineral assemblage of grossular rich grs 57 mol garnet omphacite jd 30 34 mol pargasite rutile pargasitic and taramitic amphiboles calcic plagioclase an68 epidote zoisite k feldspar and paragonite occur as inclusions in garnet and omphacite in the prograde eclogites this suggests that the prograde eclogites were formed by recrystallization of epidote amphibolite and or amphibolite facies rocks with near isothermal compression reflecting crustal thickening during continent continent collision of late proterozoic age equilibrium conditions of the prograde eclogites range from p 26 kbar and t 500 750 c in the western part to p 28 kbar and t 810 880 c in the eastern part of the high p eclogite terrane the prograde eclogites in the eastern part are considered to have been derived from a deeper position than those in the western part subsequent reactions manifested by 1 narrow rims of sodic plagioclase or paragonite on kyanite and 2 symplectites between omphacite and quartz are interpreted as an effect of near isothermal decompression during the retrograde stage the conditions at which symplectites re equilibrated tend to increase from west p 9 kbar and t 680 c equilibrium temperatures of type ii mantle derived eclogites and type iii eclogite are 730 750 c and 680 c respectively

discontinuity surfaces clinoforms and facies architecture in a wave dominated shoreface shelf parasequence abstract detailed outcrop analysis of a wave dominated shoreface shelf parasequence exposed in the book cliffs utah reveals minor stratigraphic discontinuities which define clinoforms two types of discontinuity are recognized each with a distinctive lithologic character and geometry nondepositional discontinuities are marked by an abrupt decrease in the thickness and amalgamation of storm generated event beds and are interpreted to record hiatuses in sedimentation these discontinuities define clinoforms with a concave upward geometry that dip gently 0 02 0 58 over distances of 800 6000 m down depositional dip erosional discontinuities are marked by an abrupt increase in event bed amalgamation grain size and sand content and are interpreted as enhanced storm wave scours these discontinuities define more steeply dipping 0 22 0 95 concave upward clinoforms that extend over 100 1600 m down depositional dip and 500 1500 m along depositional strike the distribution and amalgamation of minor stratigraphic discontinuities defines linear zones of distinctive facies architecture that are oriented parallel to the paleoshoreline trend using the simple assumption that the shoreface shelf equilibrium profile remained approximately constant for each type of discontinuity throughout shoreface migration the bruun rule intra parasequence facies architecture can be speculatively interpreted in terms of shoreline trajectory which reflects the balance between sediment supply and accommodation the resulting interpretations support the notion that shoreline trajectory exerts a strong control on intra parasequence facies architecture and preservation of the shoreface shelf profile

clinoforms and clinoform systems review and dynamic classification scheme for shorelines subaqueous deltas shelf edges and continental margins abstract clinoforms are inclined and normally basinward dipping horizons developed over a range of spatial and temporal scales in both siliciclastic and carbonatic systems the study of clinoform successions underpins sequence stratigraphy and all efforts to reconstruct the relative partitioning of reservoir seal and source rocks along shoreline to basin floor profiles here we review clinoform research and propose a more systematic description and classification of clinoforms this is a crucial step to improve predictions of facies and lithology distribution within shoreline to continental shelf and abyssal plain successions together with the genesis drivers and dynamics of their constituent sedimentary units four basic clinoform types are here distinguished in delta shorelines lacustrine and marine environments on the basis of their overall spatial and temporal scale morphology outbuilding dynamic and geodynamic and depositional setting 1 2 delta scale clinoforms which in turns are sub divided into shoreline and delta scale subaqueous clinoforms 3 shelf edge clinoforms and 4 continental margin clinoforms delta scale clinoform sets are tens of metres high and typically represent 1 103 kyr with progradation rates ranging from 1 000 100 000 m kyr for shorelines and subaerial deltas to 100 20 000 m kyr for subaqueous deltas shelf edge clinoform sets are hundreds of metres high and are nucleated and accreted in 0 1 20 myr usual progradation rates of 1 100 m kyr by successive cross shelf transits of delta scale clinoforms continental margin clinoform sets are thousands of metres high hallmark key geodynamic crustal boundaries e g continent ocean transition and slowly prograde basinwards in ca 5 100 myr with typical rates of 0 1 10 m kyr as a consequence of the very different progradation rates and of the difficulty of large scale clinothems to backstep during transgressions shorelines are the most dynamic clinoforms with regards to position continental margins the least and shelf edges are intermediate shortly after a transgression therefore the four clinoform types may prograde synchronously along shoreline to abyssal plain transects forming compound clinoform systems during the subsequent regressive cycle however due to the dissimilarity in progradation rates different clinoform types will normally merge progressively with each other giving rise to hybrid clinoforms e g shelf edge deltas and fewer depositional breaks in slope are distinguished along a single shoreline to abyssal plain transect overall all clinoform systems are the result of the dynamic evolution of compound and hybrid clinoforms along a temporal and spatial continuum regulated by the cyclical backstepping of the smaller scale system within natural progradational retrogradational cycles of larger scale clinothem outbuilding all clinothem types may show either an accretionary active or draping passive style depending on the proximity to the sediment source draping clinothems are nearly always composed of condensed fine grained sediments while actively accreting clinothems can be composed of predominantly coarse grained i e reservoir forming or predominantly fine grained i e non reservoir lithotypes a novel hierarchical classification scheme for both recent and ancient clinoforms is here proposed consisting of 12 classes the four basic clinoform types delta scale shoreline delta scale subaqueous shelf edge and continental margin are sub divided into eight accretionary active and draping passive sub types 8 division each accretionary sub type is then sub divided into a sandstone prone and mudstone prone variant 12 division which can be at least tentatively predicted on the basis of the clinoform morphology even in the absence of direct stratigraphic logs

the influence of bottom topography on baroclinic transports abstract a new and reduced set of governing equations is proposed for the modeling of baroclinic motions in a two layer system with variable bottom topography the reduction of the equations which eliminates all barotropic is based on the assumption of almost vertically compensated transports the resulting equations differ somewhat from those obtained with a rigid lid approximation the limitations are topography variability only on horizontal scales greater than the wavelength and wavelengths shorter than the barotropic radius of deformation these are not critical in many problems numerical solutions to the reduced equations are shown to be close to those obtained from the primitive equations in one and two dimensional cases in view of their relative simplicity the new governing equations have also been applied to the analytical study of coastal upwelling in the presence of variable topography it is shown then that the presence of a canyon enhances coastal upwelling the success of the reduced e

three dimensional modeling of clinoforms in shallow marine reservoirs part 2 impact on fluid flow and hydrocarbon recovery in fluvial dominated deltaic reservoirs permeability contrasts associated with clinoforms have been identified as an important control on fluid flow and hydrocarbon recovery in fluvial dominated deltaic parasequences however they are typically neglected in subsurface reservoir models or considered in isolation in reservoir simulation experiments because clinoforms are difficult to capture using current modeling tools a suite of three dimensional reservoir models constructed with a novel stochastic surface based clinoform modeling algorithm and outcrop analog data upper cretaceous ferron sandstone member utah have been used here to quantify the impact of clinoforms on fluid flow in the context of 1 uncertainties in reservoir characterization such as the presence of channelized fluvial sandbodies and the impact of bed scale heterogeneity on vertical permeability and 2 reservoir engineering decisions including oil production rate the proportion and distribution of barriers to flow along clinoforms exert the greatest influence on hydrocarbon recovery equivalent models that neglect these barriers overpredict recovery by up to 35 continuity of channelized sandbodies that cut across clinoform tops and vertical permeability within distal delta front facies influence sweep within clinothems bounded by barriers sweep efficiency is reduced when producing at higher rates over shorter periods because oil is bypassed at the toe of each clinothem clinoforms are difficult to detect using production data but our results indicate that they significantly influence hydrocarbon recovery and their impact is typically larger than that of other geologic heterogeneities regardless of reservoir engineering decisions clinoforms should therefore be included in models of fluvial dominated deltaic reservoirs to accurately predict hydrocarbon recovery and drainage patterns

early cretaceous sediment failure in the southwestern sable subbasin offshore nova scotia conventional cores from lower cretaceous outer shelf and upper slope prodelta facies in the alma and glenelg fields of the scotian basin show a wide range of synsedimentary deformation storm dominated prodelta sandstone and mudstone beds have common load casts and structureless sandstone beds overlain by deformed sediment and sandstone dykes that are caused by storm or earthquake induced local liquefaction blocks of sediment 5 15 m 15 50 ft thick principally on the outer shelf have foliated mudstone at their base common internal shear zones in mudstone shear deformation of sandstone and are capped by intraclast conglomerates that are interpreted as debris flow deposits these are all features observed in shallow slides on the modern mississippi prodelta at the paleoshelf edge and upper slope larger slide blocks are recognized with zones of intense internal deformation and high angle thrusts near their base the lack of a basal foliated mudstone may be the result of more rapid slide motion than on the shelf resulting in hydroplaning in addition there is early postdepositional interstratal deformation as a result of loading by sandy delta distributaries and by slide blocks on the upper slope the scale of many deformation structures is below the limits of three dimensional seismic vertical resolution yet they are likely to substantially influence reservoir properties

delamination of eclogitized lower crust control on the crust mantle boundary in the central fennoscandian shield abstract the crustal structure of the central part of the fennoscandian shield is dominated by a high velocity lower crust hvlc vp 7 3 7 5 km s at the depth of 40 63 km in an area of ca 400 km 600 km formed in the palaeoproterozoic svecofennian orogen at 1 91 1 87 ga in the area of the hvlc the moho is deeper than 50 km and attains depths of up to 63 km in eastern finland at the archaean proterozoic boundary zone we suggest that the present moho dates back to late svecofennian time and was determined by delamination of high density eclogitized lower crust after tectonic collisional thickening of crust densities deduced from seismic and gravity data suggest a very small or completely lacking density contrast between lower crust and uppermost mantle new geological evidence from kimberlite hosted garnet xenocrysts supports the presence of a garnet population with compositions in agreement with crustal eclogitic garnets in addition small clinopyroxene garnet mineral aggregates microxenoliths show omphacitic clinopyroxene compositions therefore the presence of eclogites in the high velocity lower crust is implied although the eclogite proportion as estimated from seismic velocity data is only a few percent in the present hvlc with results on near incidence and wide angle seismic studies and geological and geochemical data on heat producing elements we modeled the svecofennian collision and the thermal evolution of the crust to provide temperature constraints for the delamination model the constructed thermal model simulates the genesis of svecofennian synkinematic at 1 89 1 88 ga and postkinematic 1 88 1 87 ga granitoids as well as the general metamorphic grade of the surface rocks and lower crustal xenoliths moreover the narrow distribution of the ages of the svecofennian mafic ultramafic magmatism ca 1 89 1 87 ga dispersed around the hvlc area is explained by the homogeneous warming of the lithosphere the conditions of lower crustal delamination were estimated with a rayleigh taylor convective instability model constrained with lower crustal and upper mantle rheological data delamination of a lower crustal eclogite layer 5 30 km thick takes place in about 7 50 ma if the rock dynamic viscosity is 1 1021 pa s it requires temperatures of 1000 c in the lower crust and upper mantle in the svecofennian crust such temperatures were attained at about 1860 1850 ma i e after the orogenic peak we conclude that the moho of the hvlc area was controlled by delamination of a ca 5 10 km thick layer of high density lowermost crust into the mantle such a density controlled process may have controlled the moho depth also in other proterozoic shield areas

the oligocene succession in the eastern north sea basin development and depositional systems the oligocene sedimentary succession in the eastern north sea is revised and re interpreted by applying new state of the art reflection seismic data integrated with new bio and sr stratigraphy data from three key wells in the study area the oligocene succession in the eastern north sea is divided into four transgressive regressive t r sequences characterized by non accretional and or aggradational transgressive systems tracts and prograding regressive systems tracts detailed studies of three wells including biostratigraphy and sr analysis constrain the age relationships between the t r sequences internal clinoform geometry indicates that the sediments were sourced from the present southern norwegian mainland to the north of the depositional area the direction of progradation shifted from being se directed in the earliest rupelian early oligocene to s and sw directed during chattian time late oligocene rapid basin subsidence is indicated by the development of non accretionary transgressive systems tracts with subsequent progradation into water depths of hundreds of metres the creation of accommodation space was out of phase relative to eustatic sea level changes and mainly controlled by regional scale differential vertical movements where uplift and exposure of landmasses of the hinterland southern norway occurred concurrently with basin subsidence halokinesis had an intra basinal influence on the main sediment transport direction but probably did not contribute much in creation of accommodation space

sea level and initiation of predynastic culture in the nile delta predynastic occupation of the nile valley and delta dating back to at least 5000 bc has been attributed by most archaeologists to environmental factors primarily regional climate change and fluctuating nile flood stages1 5 here we propose instead that initiation of farming settlements in the nile delta was closely related to eustatic sea level we present geological analyses of late quaternary subsurface sections throughout the delta which reveal that the deceleration in sea level rise that occurred at about 6500 5500 bc was a prime factor in the accumulation of nile silt and the creation of the widespread and fertile delta plain as rising sea level reduced the gradient of the river course a system of meandering nile distributaries evolved with increased overbank deposition burying the former early holocene partially vegetated sandy plain the broadening seasonally flooded fecund plain with its increasing plant cover provided a setting that was conducive to evolving agricultural activity and was therefore instrumental in the development of predynastic communities in the nile delta

deltaic morphodynamics and stratigraphic evolution of middle barataria bay and middle breton sound regions louisiana usa implications for river sediment diversions abstract river sediment diversions have been recognized as a key strategy for offsetting land loss in coastal louisiana recently much attention has been focused on sediment capture from the main stem river and conveyance of that material through diversion outflows yet the performance and long term feasibility of diversions as land building agents also hinges upon the subsurface stratigraphic architecture of receiving basins a concept that has largely been unexplored a major core collection and analysis program was undertaken to study the geological properties of substrates in the middle barataria bay and middle breton sound diversion receiving basins louisiana usa over a region of 200 square kilometers in both basins 50 vibracores up to 5 5 m in length were collected in spring and summer of 2015 cores were logged for bulk density and imaged with a geotek multi sensor core logger split cores were then subsampled for granulometry organic content and 14c dating both receiving basins are characterized by 1 2 m of organic rich surficial strata underlain by 2 m of mineral rich sand and silt beds that display a greater bulk density additionally some cores contain deeper peaty strata intercalated within muds and sands 14c dates of these buried peats range between 1910 and 3203 calendar years before present demonstrating that relatively old deltaic strata exist at shallow depths age comparisons of stratigraphically similar peat beds from this study and previous delta lobe chronological models indicate that the st bernard lobe prograded eastward at a time averaged rate of 75 m yr from a geotechnical standpoint the surficial uncompacted

a 5200 year paleoecological and geochemical record of coastal environmental changes and shoreline fluctuations in southwestern louisiana implications for coastal sustainability abstract this study presents a 5200 year history of coastal environmental changes and shoreline fluctuations based on a multi proxy sedimentary record developed from the eastern end of louisiana s chenier plain palynological loss on ignition grain size and x ray fluorescence data for a 525 cm sedimentary core indicate five stages of ecosystem development in the rockefeller wildlife refuge since the mid holocene between 5190 and 4240 cal yr bp the relative sea level was much lower than the present level and our study area was occupied by a baldcypress swamp when the sale cypremont subdelta complex formed at a western position approximately 4600 years ago our study area was transformed to a maritime forest about 4240 3440 cal yr bp suggesting shoreline progradation when the mississippi river delta lobe switched to more easterly positions during the teche st bernard lafourche and plaquemine balize complexes our study site was transformed back to a freshwater swamp between 3440 and 1520 cal yr bp and then to a coastal marsh between 1520 and 300 cal yr bp after the atchafalaya wax lake subdelta complex formed at a more westerly position again the modern day beach form at 300 cal yr bp these coastal ecosystem developments suggest that shoreline retreat started at 3440 cal yr bp and persisted to the present day in addition evidence of at least four possible paleohurricane events was found during the late holocene our multi proxy record demonstrates that shoreline fluctuation in southwestern louisiana was tied to the mississippi river delta switch since the mid holocene shoreline progradation occurred during the sale cypremont subdelta phase 5200 3500 years ago when the sediment supply was high retrogradation occurred after 3500 cal yr bp when the mississippi river subdelta complexes occupied more easterly position resulting in diminished sediment supply a significant increase in the delivery of water and total suspended sediment load from the atchafalaya river to the gulf of mexico is needed in order to sustain the southwestern louisiana coastal wetlands

significant effect of sediment cohesion on delta morphology delta morphology is thought to be controlled by factors such as river discharge tides and waves numerical modelling shows that sediment cohesion also strongly influences the development of a delta s characteristics the morphologies of the world s deltas are thought to be determined by river discharge tidal range and wave action 1 more recently sea level rise 2 3 and human engineering4 have been shown to shape delta evolution the effects of factors such as sediment type and the overall amount of sediment carried by rivers are considered secondary4 5 6 in particular the role of sediment cohesion which is controlled by sediment size and type of vegetation is unclear here we use a numerical flow and transport model7 8 9 10 to show that sediment cohesiveness also strongly influences the morphology of deltas we find that holding all other factors constant highly cohesive sediments form bird s foot deltas with rugose shorelines and highly complex floodplains whereas less cohesive sediments result in fan like deltas with smooth shorelines and flat floodplains in our simulations sediment cohesiveness also controls the number of channels that form within the deltas and the average angle of bifurcation of those channels as vegetation generally acts as a cohesive agent we suggest that deltas that formed before the expansion of land plants in the devonian period should show fan like characteristics a finding consistent with the limited data from the sedimentological record11

impact of deltaic clinothems on reservoir performance dynamic studies of reservoir analogs from the ferron sandstone member and panther tongue utah subsurface reservoir models are typically limited by a lack of spatially accurate geometric data on bedform architecture and geometry these factors are key controls on fluid flow outcrop analogs have long been used as a source of such data but the capture of sufficiently precise outcrop data is a challenge the study presented in this article used highly accurate geometrical digital geological outcrop data collected using ground based laser scanning light detection and ranging lidar to build and test three dimensional geocellular models of deltaic reservoir analogs two well exposed ancient river dominated delta systems the panther tongue and the ferron sandstone member which both crop out in central utah were digitally mapped to precisely recreate their clinothem and clinoform geometries in geocellular reservoir modeling software such clinoforms are commonly draped with low permeability mudstones that produce reservoir heterogeneity by subdividing the deltaic sand body into a series of dipping sandstone beds clinothems a key aspect of the modeling was to accurately capture these geometries and their effect on simulated fluid flow portions of the two deltaic systems were dynamically analyzed in a reservoir modeling software by simulating production in 41 models these models tested a range of mudstone barrier continuities and permeabilities results quantify how the continuation of the heterogeneities governed the production rate and recovery factor in the panther tongue models mudstone permeability values were more important in the ferron sandstone models with steeper dipping and closer spaced clinothems although production was still influenced by the continuation of the heterogeneities

delta distributary dynamics in the skagit river delta washington usa extending testing and applying avulsion theory in a tidal system article i nfo analysis of historical aerial photos shows that skagit delta washington usa distributary dynamics are consistent with the slingerland and smith model of avulsion dynamics where the ratio of the water surface slopes of the two branches of a bifurcation predicts avulsion stability this model was extended to predict distributary inlet upstream width and bankfull cross sectional area the water surface gradient ratio for a bifurcation pair predicted distributary width well the lowest r 2 was 0 61 for the 1937 data points but r 2 ranged from 0 83 to 0 90 for other year specific regression lines gradient ratios were not constant over the historical record from 1937 to 1972 the mainstem river channel lengthened by 1250 m in the course of marsh progradation while distributary lengthening was comparatively negligible consequently the gradient advantage of the distributaries increased and their channels widened after the mainstem river terminus stabilized from 1972 to the present the distributaries continued to lengthen with marsh progradation so that distributary gradient advantage steadily declined and the distributaries narrowed while distributary cross sections were not available for the historical period they were surveyed in 2007 near the distributary inlets gradient ratio was more closely related to distributary inlet bankfull cross sectional area r 2 0 95 than to minimum distributary width for any photo year examined applying this form of analysis to skagit delta distributaries that have been dammed in the course of agricultural development suggests that their restoration to stabilize eroding marshes at their outlets and recover salmon migration pathways would be feasible without significant risk of full river avulsion

atmospheric forcing of interannual variability in the northeast pacific ocean connections with el nino the nature and causes of the observed interannual variability of oceanic conditions in the northeast pacific were investigated using a variety of meteorological and oceanographic data sets an examination of a long series of seasonal mean atmospheric sea level pressure slp charts showed that when the winter average slp pattern in the north pacific varies significantly from climatology it tends to do this in one of two characteristic ways in particular in some winters there is an anomalously strong circulation which differs from climatology mainly in having an intensified aleutian low in other winters there is an anomalously weak atmospheric circulation this is almost invariably associated with the westward displacement of the aleutian low and the production of a separate but much weaker low in the gulf of alaska the north pacific winter slp appears to have some relation to the southern oscillation so and oceanic temperatures in the tropics in particular el nino southern oscillation enso episodes are generally coincident with strong north pacific slp patterns and often follow winters with weak slp patterns however this relationship is far from being perfectly regular and predictable interannual variations in the intensity of the north pacific atmospheric surface circulation were found to be strongly correlated with the anomalies of both sea surface temperature sst and sea level height slh at stations along the british columbia coast an intense aleutian low is invariably associated with warm coastal waters and high coastal sea levels by comparing a large number of pacific slp and sst maps it was possible to verify that the relation between north pacific slp and oceanic surface temperature actually applies to the sst over much of the northeast pacific at least as far west as 150 w the relationship of north pacific slp with the so together with the relationship between north pacific slp and oceanic conditions in the northeast pacific can account for the observed general tendency for sst and slh along the west coast of north america to be anomalously high during tropical enso episodes on the other hand the lack of a truly predictable relation between the southern oscillation and north pacific slp explains the fact that not all enso events are associated with wanning of the northeast pacific

a quasi geostrophic circulation model of the northeast pacific part i a preliminary numerical experiment abstract a limited area quasi geostrophic numerical model with mesoscale resolution is developed to study the circulation in the northeast ne pacific ocean the model domain extends from the british columbia alaska coast out to 170 w and down to 45 n and incorporates the coastline geometry and bottom topography of the region a long term integration was conducted using a steady climatological wind stress curl field to drive the circulation several statistical properties of the solution are determined and compared with observations a cyclonic circulation develops in the model basin with a meandering alaska current feeding at the head of the gulf of alaska into an intense boundary current corresponding to the alaskan stream the head of the gulf is a region where anticyclonic closed streamline features are occasionally generated with characteristics resembling those of the sitka eddy in the downstream region the boundary current separates and is subject to lateral meandering due to topographic wave

analysing the origin of the upper cretaceous lower tertiary rio capim semi flint para state brazil under a sedimentologic perspective abstract the rio capim kaolin one of the largest kaolin reserves in the world currently under exploration is typified by a lower and an upper unit represented of a soft well structured kaolin and a semi flint kaolin respectively the latter term been applied here for a flint like fire clay consisting of indurated kaolinite which develops no plasticity when ground up the latter is characterized by its elevated hardness and massive nature which has been preliminarily attributed to stronger weathering relative to the underlying soft kaolin despite the overall massive aspect a detailed sedimentologic investigation of freshly exposed sections along open mines revealed a variety of structures in the semi flint kaolin that are attributed to primary sedimentary features the features include channel like forms having distinct lags of quartz sandstones at their bottoms these deposits intergrade with strata displaying a series of inclined lines defining lobed bodies that are locally highlighted by distinctively soft massive mud layers the lobes are internally truncated by undulating surfaces attributed to wave erosion the features described in this work are related to deposition of the semi flint kaolin unit in either distributary channels and mouth bar or tidal inlet and tidal delta areas associated with deltaic or wave dominated estuarine settings respectively the recognition of these deposits in the semi flint unit has large implications to analyze its composition which must have primarily included sand grain sizes at least in the case of the lobed strata the apparent muddy nature of the semi flint kaolin might be due at least in part to post depositional modification of a sandy unit composed most likely by grains of previously formed kaolinite derived from reworking of the underlying soft kaolin unit

hydrodynamic sorting and transport of terrestrially derived organic carbon in sediments of the mississippi and atchafalaya rivers abstract over the course of two years four cruises were conducted at varying levels of discharge in the lower mississippi and atchafalaya rivers mr and ar where grab samples were collected from sand and mud dominated sediments the tetramethylammonium hydroxide tmah thermochemolysis method was used to determine sources of terrestrially derived organic carbon oc in these two sediment types to examine the effects of hydrodynamic sorting on lignin sources in river sediments average lignin concentrations in the lower mr were 1 4 1 1 mg goc 1 at english turn et and 10 4 27 4 mg goc 1 at venice using these concentrations annual lignin fluxes to the gulf of mexico from tidal and estuarine mud remobilization at et and venice were 3 1 2 5 10 5 kg and 11 4 30 0 10 5 kg respectively much of the lignin derived materials in muddy sediments appeared to be derived from non woody grass like sources which should decay more quickly than the woody materials typically found in the sandy deposits the average total oc 1 93 0 47 of english turn sands yields an annual flux of 0 34 0 09 10 9 kg lignin flux in the english turn sands 3 6 2 6 mg gc 1 using the numbers above would be 12 2 9 4 10 5 kg the extensive amounts of sand sized woody materials coffee grinds found in the sandy sediments in both the ar and mr are likely derived from woody plant materials this is the first time it has been demonstrated that sandy sediments in the mr provide an equally important pathway compared to muds for the transport of terrestrially derived organic matter to the northern gulf of mexico using the ar average oc in sand 1 16 0 72 we estimated an annual flux of oc to the shelf of 0 13 0 07 10 9 kg lignin flux for ar sands was estimated to be 12 4 12 1 10 5 kg despite the high error associated with these numbers we observe for the first time that the flux of lignin in sandy sediments in the ar to the northern gulf of mexico is comparable to that found in the mr these results further support the likelihood of grain size related hydrodynamic sorting of terrestrially derived organic carbon in the lower mississippi and atchafalaya rivers suggesting that there is a distinct sandy sediment organic fraction contributed by major rivers to the global carbon cycle

the northeast pacific ocean response to the 1982 1983 el nino the ocean s response to atmospheric forcing and to forcing along the coast by kelvin waves is examined in light of nearshore seasonal variability and the major 1982 1983 el nino in addition to driving the northeast pacific gyre and local currents the wind modifies the depth to the main thermocline changing the apparent westward phase speed of rossby waves excited by passing kelvin waves the amplitude of the passing kelvin wave determines whether the rossby wave depresses or raises the thermocline while propagating westward along the northeast pacific coast from oregon to washington model results suggest that the wind raises the main thermocline during the 1982 1983 el nino generally the coastal response off oregon and washington appears to be strongly driven by the large scale atmosphere while along the california coast and south to the equator the dominant el nino signal has an oceanic origin that signal with periods between 2 and 5 years originates in the western equatorial pacific ocean and is tracked eastward through the equatorial waveguide and then poleward along the coast to 50 n using data from two reduced gravity primitive equation models coupled at 18 n at shorter seasonal time scales the acceleration of the wind appears to be an important mechanism in driving coastal currents

thermodynamic modelling of sodic pyroxene solid solution and its application in a garnet omphacite kyanite coesite geothermobarometer for uhp metamorphic rocks a garnet omphacite kyanite coesite geothermobarometer is constructed to estimate the peak metamorphic pressure of ultrahigh pressure uhp eclogites for this we use a quaternary regular solution model for garnet and propose a new model for sodic pyroxene that assumes double site solid solution na ca m2 al fe3 fe2 mg m1si2o6 where cations in the m2 and the m1 sites mix randomly but with inter site interactions not only between nearest neighboring cations but also between next nearest neighboring cations in the new model overall excess interaction parameters are quantitatively deduced from the previous experimental data and critical temperature and the activity of the jadeite component agrees reasonably with that based on the landau theory furthermore the relations of the calculated order parameter to temperature and composition are consistent with other experimental works these facts support the usefulness of the new model application of our geothermobarometer to kyanite eclogite gave metamorphic conditions around 3 4 gpa and 800 c for both samples from the dora maira massif western alps and from rongcheng county in the su lu region of eastern china

eastern mississippi delta late wisconsin unconformity overlying transgressive facies sea level and subsidence abstract analysis of 92 engineering core logs located in the balize sector of the eastern mississippi delta focuses on the late wisconsin unconformity and lithofacies of strata lying immediately below and above this stratigraphic horizon this major sequence boundary is a key feature used to correlate strata across shelf and slope to the basin observations emphasize lithofacies distributions of the latest pleistocene sediments underlying the unconformity the late pleistocene to early holocene transgressive facies and the immediately overlying deltaic deposits maps and a cross section compiled with this information highlight the critical relation between lithofacies distributions and late wisconsin sea level oscillations core analysis reveals that the transgressive facies comprises distinct environments of deposition offshore to onshore findings identify criteria to determine the approximate position of the shoreline at the late wisconsin maximum sea level lowstand and at the extent of early holocene maximum marine inundation in the balize complex mapping of lithologies along the late wisconsin unconformity serves to improve correlation of sediment facies with changes in acoustic response along high resolution seismic profiles an estimate of long term averaged land subsidence suggests lowering of at least 1 mm year near the shelfedge during the past 18 000 years this mapping also refines sea level response models for the mississippi delta including criteria to locate key paleogeographic features such as shelfedges and maximum flooding surfaces in other recent marine deltas and in older stacked deltaic sequences

geologic conditions underlying the 2005 17th street canal levee failure in new orleans a careful program of subsurface sampling and cone penetration test soundings was employed to characterize the geologic conditions beneath the failed portion of the 17th street canal levee in new orleans where a 150 m long section of the levee and floodwall translated up to 16 m when flood waters rose to 1 2 m of the wall s crest on august 29 2005 during hurricane katrina the subsurface conditions are characterized by discrete layers of fill placed upon the historic cypress swamp which is underlain by a deeper prehistoric cypress swamp these swamp deposits were consolidated beneath the levee and in the area of the 2005 failure the swamp materials infilled a natural depression believed to be an old slough which dipped below the sheetpile tips for a distance of about 50 m which corresponds to where the breach appears to have initiated detailed examination of the recovered soils suggest that recent hurricanes periodically inundated the swamps with saline and or brackish water which cause a mass

recent observations of variability in the path and vertical structure of the alaskan stream abstract current records were recently obtained from two sites on the continental slope southwest of kodiak island at the inshore site 10 month record flow mainly resembled the weak shelf break flow typical of the gulf of alaska except for two periods each of 3 months duration the offshore site 31 mouth record was in the path of the alaskan stream during the alaskan stream segments flow characteristics low eddy energy high vertical coherence and high stability were similar to those in the stream at other locations when the stream was absent from the offshore site it made a seaward excursion of 50 km as evidences by satellite tracked drifters the cause of this migration is unclear during a period of 6 months a subsurface velocity maximum was measured at 165 m flow near 1000 m was very weak for almost two years geostrophic flow estimates however suggest this is a rare situation

sedimentology stratigraphy and reservoir properties of an unconventional shallow frozen petroleum reservoir in the cretaceous nanushuk formation at umiat field north slope alaska numerous oil and gas accumulations exist in the brooks range foothills of the national petroleum reserve in alaska npra we use cores and well logs from 12 abandoned legacy wells at umiat field near the southeastern boundary of the npra to characterize the sedimentology and stratigraphy of unconventional shallow frozen reservoirs in sandstones of the cretaceous albian cenomanian nanushuk formation the nanushuk formation at umiat has five facies associations offshore and prodelta lower shoreface upper shoreface delta front and delta plain three stratigraphically distinct regionally extensive nanushuk formation depositional systems at umiat contain several potential petroleum reservoirs the lower nanushuk formation including a reservoir interval known informally as the lower grandstand primarily consists of marine mudstone and shoreface sandstones the middle nanushuk formation is dominantly deltaic and contains a second major reservoir interval in the informal upper grandstand sandstone both the upper grandstand and lower grandstand are regressive the transgressive upper nanushuk formation contains an additional potential reservoir interval in shoreface sandstones of the informal ninuluk interval the primary reservoir intervals at umiat field are upper shoreface and delta front sandstones in the upper grandstand and lower grandstand where increased sorting and decreased bioturbation in high energy depositional environments affect overall permeability and permeability anisotropy

the role of sea level rise monsoonal discharge and the palaeo landscape in the early holocene evolution of the pearl river delta southern china abstract the early holocene history of the pearl river delta is reconstructed based on a series of sediment cores obtained from one of the main palaeo valleys in the basin sedimentary and microfossil diatom analyses combined with radiocarbon dating provide new evidence for the interactions between sea level rise antecedent topography and sedimentary discharge changes within the deltaic basin since the last glacial these new records show that river channels of last glacial age incised down to c 40 m into an older possibly mis5 age marine sequence which forms the floor of the deltaic basin and exists primarily at c 10 m 15 m below present mean sea level rapid postglacial sea level rise flooded the incised valleys by the beginning of the holocene and prior to c 9000 cal years bp marine inundation was largely confined within these incised valleys the confined available accommodation space of the incised valleys combined with strong monsoon driven freshwater high sediment discharge and a period of rapid rising sea level meant that sedimentation rates were exceptionally high towards c 8000 cal years bp as sea level rose to about 5 m marine inundation spilled out of the incised valleys and the sea flooded the whole deltaic basin as a result the mouth of the pearl river was forced to retreat to the apex of the deltaic basin water salinity within the basin increased markedly as the previously confined system dispersed across the basin and the sedimentation changed from fluvial dominated to tidal dominated sea level continued to rise albeit at a much reduced rate between 8000 and 7000 cal years bp and deltaic sedimentation was concentrated around the apex area of the basin during the last 7000 cal years bp the delta shoreline moved seawards and the sedimentary processes changed gradually from tidal dominated to fluvial dominated

coastal morphodynamics and chenier plain evolution in southwestern louisiana usa a geomorphic model abstract using 28 topographic profiles air photo interpretation and historical shoreline change data coastal processes were evaluated along the chenier plain to explain the occurrence distribution and geomorphic hierarchy of primary landforms and existing hypotheses regarding chenier plain evolution were reconsidered the chenier plain of sw louisiana classified as a low profile microtidal storm dominated coast is located west and downdrift of the mississippi river deltaic plain this late holocene marginal deltaic environment is 200 km long and up to 30 km wide and is composed primarily of mud deposits capped by marsh interspersed with thin sand and shell rich ridges cheniers that have elevations of up to 4 m in this study the term ridge is used as a morphologic term for a narrow linear or curvilinear topographic high that consists of sand and shelly material accumulated by waves and other physical coastal processes thus most ridges in the chenier plain represent relict open gulf shorelines on the basis of past movement trends of individual shorelines ridges may be further classified as transgressive regressive or laterally accreted geomorphic zones that contain two or more regressive transgressive or laterally accreted ridges are termed complexes consequently we further refine the chenier plain definition by otvos and price otvos e g and price w a 1979 problems of chenier genesis and terminology an overview marine geology 31 251 263 and define chenier plain as containing at least two or more chenier complexes based on these definitions a geomorphic hierarchy of landforms was refined relative to dominant process for the louisiana chenier plain the chenier plain is defined as a first order feature 5000 km2 composed of three second order features 30 to 300 km2 chenier complex beach ridge complex and spit complex individual ridges of each complex type were further separated into third order features chenier beach ridge and spit to understand the long term evolution of a coastal depositional system primary process response mechanisms and patterns found along the modern chenier plain coast were first identified especially tidal inlet processes associated with the sabine calcasieu and mermentau rivers tidal prism and quantity of littoral transport mtotal are the most important factors controlling inlet stability greater discharge and or tidal prism increase the ability of river and estuarine systems to interrupt longshore sediment transport maintain and naturally stabilize tidal entrances and promote updrift deposition thus prior to human modification and stabilization efforts the mermentau river entrance would be classified as wave dominated sabine pass as tide dominated and calcasieu pass as tide dominated to occasionally mixed hoyt hoyt j h 1969 chenier versus barrier genetic and stratigraphic distinction am assoc petrol geol bull 53 299 306 presented the first detailed depositional model for chenier genesis and mudflat progradation which he attributed to changes in mississippi river flow direction i e delta switching caused by upstream channel avulsion however hoyt s model oversimplifies chenier plain evolution because it omits ridges created by other means thus the geologic evolution of the chenier plain is more complicated than channel avulsions of the mississippi river and it involved not only chenier ridges i e transgressive but also ridges that are genetically tied to regression beach ridges and lateral accretion recurved spits a six stage geomorphic process response model was developed to describe chenier plain evolution primarily as a function of i the balance between sediment supply and energy dissipation associated with mississippi river channel avulsions ii local sediment reworking and lateral transport iii tidal entrance dynamics and iv possibly higher than present stands of holocene sea level consequently the geneses of three different ridge types transgressive regressive and laterally accreted typically occur contemporaneously along the same shoreline at different locations

the influence of the alaskan gyre on the coastal circulation in the gulf of alaska a wind driven nonlinear reduced gravity primitive equation model is used to simulate the circulation of the northeast pacific ocean including the northeast gulf of alaska the model includes the affects of bottom topography model geometry encompasses the entire gulf of alaska region from vancouver island to west of kodiak island this region is traditionally beyond the latitude limits of the reduced gravity model imposed by a weakening thermocline away from the equator the model resolution 0 025 in latitude and longitude is very fine this is the first time that a model of this type and resolution has been successfully run at these latitudes although we expected that such resolution would allow the mesoscale eddy field to develop it did not one reason may be the coarse spatial and temporal winds twenty year of comprehensive ocean atmosphere data set pseudo wind stress data used to drive the model are statistically analyzed to obtain a wind stress climatology after model spin up the monthly stresses for 1986 1989 are used to drive the model the model reproduces many of the regional oceanographic features such as the alaskan gyre the alaska current the alaska coastal current the sitka eddy and an intense cyclonic eddy that has not yet been reported in the literature northwest of the queen charlotte island in the spring in addition the model displays seasonal and interannual variability model results are validated through comparisons with national ocean service coastal sea level records and a multilayer oceanic basin scale model being run at the institute for naval oceanography

assessing levee stability with geometric parameters derived from airborne lidar abstract a methodology to assess levee structural integrity using high resolution airborne light detection and ranging lidar data is investigated for a 16 km reach of the sacramento river within the sacramento san joaquin river delta california levee geometric parameters levee crown width height and water and landside slopes were extracted from 0 5 m resolution lidar derived digital ground models deviation of these parameters from minimum levee design standards was used to calculate a levee stability index stability maps were generated and those areas that did not meet usace geometric shape standards were identified results show that 2 out of the 4 geometric parameters do not meet the minimum value required in 48 and 43 of profiles on the east urban adjacent and west farmland adjacent margins respectively most importantly the crown width in 99 of the levee profiles located on the urban side was below the minimum required the paper also points out the importance of evaluating all four geometric parameters not just the elevation of the levee by assessing its level of performance through a geometric assessment

interannual variability of the equatorial pacific revisited a linear numerical model forced by monthly shipboard wind estimates used to study the interannual response of the tropical pacific ocean for 1961 1970 busalacchi and o brien 1981 is extended through december 1978 the additional 8 years include the 1972 and 1976 los ninos and the aborted event of 1975 model pycnocline variations at several locations are compared with observed sea level fluctuations el nino events are depicted as periods when the pycnocline is persistently deep along the eastern boundary remotely forced equatorial kelvin waves are responsible for this response the character of each simulated el nino is strongly dependent on the relation between zonal wind stress changes in the western and central equatorial pacific there are important differences in the location and timing of the wind changes associated with each el nino during the 1970 s the easterlies in the central equatorial pacific had more of an active role in the evolution of el nino than in the previous decade in the western tropical pacific a rapid shoaling of the pycnocline during each el nino is caused by westward propagating rossby waves interannual pycnocline displacements in the central equatorial pacific are determined by the superposition of kelvin waves excited to the west and first horizontal mode rossby waves generated to the east

new evidence on the spatial temporal distribution of superlobes in the yellow river delta complex abstract unraveling the spatial temporal distribution of delta superlobes precisely is particularly important and challenging in the yellow river delta complex yrdc previous research on this issue can be dated back to the early 1990s when the paleoenvironmental reconstructions mainly hinged on the historical documents and geomorphologic analysis of well developed cheniers from the west coast of bohai bay and only few drilled cores with scant radiocarbon dates were available to build a refined model of the holocene stratigraphic architecture and reconstruct the sedimentary evolution of the yrdc detailed sedimentological investigation of 12 boreholes including 59 new ams 14c radiocarbon dates was combined with other published 25 cores and 174 ams 14c dates therein age depth curves were grouped by stratigraphic positions and facies characteristics of these 233 radiocarbon dated samples across different sectors of the yrdc exhibiting consistent patterns that can be used to identify distinct phases of delta superlobe activities eight new superlobes with relatively accurate dating spans were therefore proposed in the yrdc our results demonstrate that very high aggradation rates almost invariably correlate with the onset of deltaic deposition age depth patterns thus may be very useful to elucidate the complex sedimentary evolution of delta systems with multiple lobes

correlating terrestrial signatures from biomarker distributions δ13c and palynology in fluvio deltaic deposits from nw australia triassic jurassic abstract a multidisciplinary study using molecular and organic isotope geochemistry petrology and palynology has been used to establish palaeoenvironmental conditions of fluvio deltaic deposits from the delambre 1 well western australia triassic jurassic changes in higher plant biomarker distributions correlate with 1 brackish water environments 2 major changes in composition of spore and pollen assemblages 3 variations in types of sedimentary facies and 4 stable carbon isotopic composition of higher plant biomarkers these changes are all consistent with the occurrence of climatic shifts in northwestern australia during triassic jurassic periods established by parrish j t bradshaw m t brakel a t mulholland s m totterdell j m yeates a n 1996 palaeoclimatology of australia during the pangean interval palaeoclimates 1 241 281 the combustion marker benzo e pyrene is abundant in samples that contain pollen from falcisporites australis the decline of f australis and the rapid emergence of assemblages dominated by corollina spp at the end of the triassic marks a rapid pollen spore extinction event at the triassic jurassic boundary there is an increase in relative abundance of the higher plant biomarkers cadalene and simonellite in a prodeltaic facies the 13 c values of between 26 9 and 24 9 for retene are consistent with a source from class i conifer resinites and relate to samples abundant in araucariacian conifers in the early middle jurassic where facies are characterized as pro distal deltaic

low pressure temperature stability of pyrope quartz relative to orthopyroxene kyanite a new model for aluminous orthopyroxene with vacancies determination of the stability of pyrope with quartz could provide theoretical pressure temperature p t constraints on silica saturated eclogites as well as near end member pyrope bearing terrains the lower p t stability of pyrope in the presence of quartz in the system mgo al2o3 sio2 can be modeled by the reaction 3 enstatite 2 kyanite 2 pyrope 2 quartz reaction reversals were experimentally obtained using a in diameter piston cylinder press and a 1000 t multi anvil press besides natural quartz all other starting materials including orthopyroxene pyrope and kyanite were synthesized the reaction has been bracketed at 1 50 gpa at 1040 1080 c 1 69 1 79 gpa at 1000 c 2 26 gpa at 920 940 c 2 90 gpa at 840 860 c the bracketed boundary is higher in temperature and pressure than that calculated using the newest dataset of holland et al j petrol 59 881 900 https doi org 10 1093 petrology egy048 2018 particularly at higher pressures aluminum is usually thought to be taken into orthopyroxene in the form of mg tschermak s pyroxene mgts mgal2sio6 under these experimental p t conditions in contrast the observed orthopyroxene composition indicated the involvement of a non stoichiometric component mg eskola pyroxene mges mg0 5 0 5alsi2o6 an aluminous orthopyroxene with octahedral vacancies end member thermodynamic properties for mges as well as a mixing model for the ternary enstatite mgts mges solid solution have been derived the thermodynamic calculations employing the mixing model are in good agreement with the experimental brackets the new model has potential applications to constrain p t conditions of tectonic settings such as ultrahigh pressure and ultrahigh temperature metamorphisms

sedimentary evidence of deglacial megafloods in the northern gulf of mexico pigmy basin abstract cored sediments from the pigmy basin northern gulf of mexico were analyzed in order to better constrain late deglacial and early holocene paleoenvironmental and sedimentary changes in response to north american climate evolution mineralogical and geochemical proxies indicate the succession of two sedimentary regimes dominantly detrital during the deglaciation 15 12 9 cal ka bp whereas biogenic contribution relatively increased later on during the younger dryas and early holocene 12 9 and 10 cal ka bp geochemical data reveal that the deglacial record mainly reflects variations of terrigenous supply via the mississippi river rather than modifications of redox conditions in the basin specific variations of almost all the parameters measured in this paper are synchronous with the main deglacial meltwater episode meltwater spike described or modeled in previous marine or continental studies during this episode most parameters display stair step like pattern variations highlighting three successive steps within the main meltwater flow variations in grain size and clay mineral assemblage recorded in the pigmy basin indicate that the erosional regime was very strong on land during the first part of the meltwater spike and then milder inducing more subtle modifications in the sedimentary regime in this part of the gulf specific geochemical and mineralogical signatures notably clay minerals and trace metal geochemistry pinpoint a dominant origin from nw north america for detrital particles reflecting meltwater outflow from the south western laurentide ice sheet lis margin during the most intense freshwater discharge the observed decrease of the sedimentation rate from about 200 to 25 cm ka at ca 12 9 ka evidenced a drastic decrease of erosional processes during late phase of discharge consistently with the hypotheses of major reduction of meltwater flow the major modification at 12 9 cal ka bp is interpreted to result from both modifications of the main mississippi fluvial regime due to eastward and northward rerouting of meltwater flow at the onset of the younger dryas and the increase of sea surface temperature linked to insolation finally slight grain size modifications suggest that some freshwater discharges may have episodically reached the gulf of mexico after the younger dryas reflecting possible small adjustments of the postglacial hydrological regime

evolution of the moose lake delta british columbia implications for holocene environmental change in the canadian rocky mountains abstract reconstruction of the geomorphic history of the moose lake delta is used to infer environmental change in the uppermost fraser river watershed british columbia delta top changes are interpreted from surface channel morphology riverbank exposures hand auger data vibracores and other borehole records river channel and overbank sediments are related to source area contributions in terms of granule lithology and fine

coexisting retrograde jadeite and omphacite in a jadeite bearing lawsonite eclogite from the motagua fault zone guatemala coexisting jadeite and omphacite were found as retrograde minerals in a jadeite bearing lawsonite eclogite from the motagua fault zone guatemala the lawsonite eclogite is characterized by the occurrence of garnet porphyroblasts up to 2 5 cm in size and the eclogite facies parageneses almandine rich garnet impure jadeite lawsonite rutile quartz garnet contains inclusions of impure jadeite phengite ferroglaucophane chlorite lawsonite rutile ilmenite and quartz textural relations and parageneses and compositions of minerals indicate that the lawsonite eclogite experienced two stages of metamorphism prograde eclogite facies stage m 1 and retrograde stage m 2 the impure jadeite jd i of the m 1 eclogite facies occurs in both the matrix and as inclusions in garnet and contains considerable amounts of augite and aegirine components jd 6 1 7 5 aug 1 6 2 4 ae 0 1 8 it is partly recrystallized to retrograde m 2 jadeite jd ii jd 7 4 8 7 aug 9 1 6 ae 0 1 1 and omphacite jd 4 2 5 0 aug 3 6 4 6 ae 7 1 6 some of these two sodic pyroxenes may have crystallized from fluids both m 2 jadeite and omphacite show textural equilibrium and are believed to have grown concurrently based on the observed compositions and the phase relations of sodic pyroxenes from carpenter 1980 the m 1 impure jadeite jd i may have had a disordered c2 c symmetry at t ca 450 c and p ca 1 8 2 4 gpa and was subsequently crystallized into jadeite jd ii plus ordered p2 n omphacite during retrogression with infiltration of fluids at t ca 300 c and p ca 0 7 gpa m 2 the extreme low t conditions during retrogression may have prevented reaction between eclogitic jadeite and adjacent minerals instead eclogitic impure jadeite plus fluid has recrystallized into the retrograde jadeite omphacite pair with a wide compositional gap

distribution of discontinuous mudstone beds within wave dominated shallow marine deposits star point sandstone and blackhawk formation eastern utah deposits of wave dominated shorelines are typically considered to act as relatively simple hydrocarbon reservoirs and are commonly modeled as tanks of sand however important heterogeneities that can act as barriers to fluid flow occur at the parasequence bedset and bed scales especially in viscous oil or low permeability oil fields heterogeneities at the parasequence and bedset scales have been well studied but discontinuous mudstone beds occurring within the shoreface have received little attention the book cliffs and wasatch plateau are among the best exposed and best studied deposits of wave dominated shallow marine systems in the world two parasequences within these outcrops have been studied in detail to investigate the distributions of intrashoreface shales and to propose models for the controls on their distribution a data set consisting of 30 km 18 6 mi of virtual outcrops derived from oblique helicopter mounted light detection and ranging lidar scanning with supporting stratigraphic sections makes it possible to collect a large quantity of accurate geometric data of depositional elements from inaccessible cliffs nine hundred and twenty one discontinuous mudstone beds were measured these occur as ellipses with long axes oriented normal to the paleoshoreline lengths and widths of these mudstone beds exhibit a lognormal distribution with means of 21 9 and 13 8 m 71 9 and 45 3 ft respectively within the shoreface succession the number of mudstone beds increases downward whereas size does not vary significantly with stratigraphic height an average of 100 m 328 ft cumulative length of shale exists per 100 m 328 ft of horizontal outcrop this increases threefold near both wave dominated deltas and bedset boundaries that reflect minor sea level fluctuations during progradation

paleopedologic and paleohydrologic records of precipitation seasonality from early pennsylvanian underclay paleosols u s a underclays in the crooked fork group lower pennsylvanian atokan langsettian in eastern tennessee u s a are paleosols associated with fourth order depositional sequences that record changing paleohydrologic conditions during their formation climate changes possibly milankovitch driven resulted in evolution of soil landscapes from well drained seasonally wet floodplains and delta plains dominated by vertic vertisol like paleosols to very poorly drained everwet swamps dominated by sideritic gley paleosols coals paleohistosols cap most underclays and record peat swamp development during everwet conditions followed by marine submergence pedogenic slickensides and angular blocky ped structures in conjunction with illuviated clay pore fillings and sepic plasmic microfabric indicate an initial better drained phase of paleosol development stage i gley overprinting characterized by drab low chroma paleosol colors fe reduction in upper portions of paleosols sideritic rhizocretions sphaerosiderite and pyrite nodules extensive leaching and translocation of alkali and alkaline earth elements and kaolinitization of smectites and hydroxy interlayer vermiculite hiv indicate a later poorly drained stage of paleosol development characterized by saturated conditions moderate to low eh and low ph stage ii as well as peat swamp development lastly burial and juxtaposition of marine facies on top of terrestrial deposits terminated paleosol and peat development stage iii paleosols likely formed under conditions of marked seasonality of rainfall judging from both modern analog systems in sumatra and pennsylvanian paleoclimate models the chemical index of alteration without potash cia k was used as a proxy for atokan paleoprecipitation estimated as 1300 mm yr this estimate is comparable with mean annual precipitation map in modern tropical to subtropical rainy environments

constraining uncertainty in interpretation of seismically imaged clinoforms in deltaic reservoirs troll field norwegian north sea insights from forward seismic models of outcrop analogs forward seismic modeling of outcrop analogs has been used to characterize the seismic expression of clinoforms in different deltaic depositional environments and thus constrain uncertainty in interpretation of intra reservoir clinoforms imaged in seismic data from the troll field norwegian north sea three outcrop analogs from the cretaceous western interior seaway united states were studied to quantify the geometry distribution and lithologic character of clinoforms in fluvial dominated and mixed influence deltaic deposits outcrop derived geometric data were calibrated to sedimentological and petrophysical data from the krossfjord and fensfjord formations in the troll field and then used to create a suite of forward seismic models for comparison with real seismic reflection data from the troll field clinoforms were imaged in the forward seismic models in which they were 1 spaced wider than the tuning thickness 10 m 33 ft 2 marked by pronounced interfingering of facies associations with different acoustic properties and or 3 lined by relatively thick 50 cm 20 in carbonate cemented layers however where clinothems are thinner than the vertical resolution limit of seismic data destructive interference occurred creating misleading geometrical relationships furthermore our ability to image clinoforms is dependent on 1 the frequency of the seismic wavelet 2 the overburden velocity and or 3 the acoustic impedance contrast at the boundary between the overburden and the clinoform bearing target the established methodology has allowed characterization of deltaic clinoformal architectures in reservoir seismic data from the troll field and has facilitated a more robust interpretation by bridging the critical gap in resolution between well and seismic data

cambrian stratigraphy and depositional history of the northern indian himalaya spiti valley north central india recent work on himalayan tectonics indicates that prior to the cenozoic collision of india and asia an enigmatic cambrian ordovician event may have strongly infl uenced the regional geology of the himalaya stratigraphic and sedimentological analyses of well preserved cambrian deposits are critical for understanding the nature of this early tectonic event and its infl uence on the later tectonic evolution of the himalaya the parahio formation defi ned herein of the parahio valley spiti region in the tethyan himalaya of india is the best biostratigraphically resolved section of cambrian strata in the entire himalaya this formation consists of 1350 m of dominantly siliciclastic deltaic deposits the formation ranges from uppermost lower cambrian lungwangmiaoan stage to middle middle cambrian hsuchuangian stage representing a time span of 5 10 m y it contains numerous mediumscale shoaling cycles that range from storminfl uenced offshore deposits to thick trough cross bedded fl uvial facies many thin carbonate beds with abundant trilobite fossils directly overlie the fl uvial facies and represent transgressive systems tract deposits the cycles are interpreted to have resulted from delta lobe switching based on a lack of systematic stratigraphic changes in cycle or facies thicknesses this paleoenvironmental reconstruction contradicts previous interpretations of this unit that range from deep sea fl ysch to shallow marine tidalites in addition our paleoenvironmental analysis and paleocurrent data suggest that the uppermost lower to middle cambrian deposits of the lesser and tethyan himalaya are parts of the same ancient northward prograding fl uvial deltaic depositional system of the paleo tethys margin of india an angular unconformity with overlying ordovician conglomeratic rocks has considerable local relief with meter scale scours and a valley fi ll 100 m thick the scours have northeast southwest orientations which parallel both the paleocurrents in the underlying parahio formation as well as published paleocurrent readings from the coarse red beds of the overlying ordovician strata the cambrian ordovician unconformity is of regional extent and our recent biostratigraphic database indicates that the minimum hiatus associated with the unconformity in spiti is 15 m y our sedimentological analysis and associated paleocurrent data from the parahio formation along with additional data from units both above and below the unconformity indicate that published models portraying foreland basin development at this time with southward directed thrusting are problematic an alternate possibility that uplift took place south of the tethyan himalaya is also problematic because no published stratigraphic or structural evidence exists for such an uplift to the south for either the greater or the lesser himalaya lithotectonic zones

facies architecture and stratigraphic evolution of a river dominated delta front turonian ferron sandstone utah u s a abstract facies architectural analysis of a river dominated deltaic parasequence in the turonian ferron sandstone member near factory butte utah was conducted to determine the hierarchical spatial arrangement of mouth bars and their role in constructing the delta five architectural elements were identified using 21 measured sections paleocurrent measurements and bedding diagrams they are 1 prodelta pf 2 frontal splay fs 3 detached distal bars dbs 4 distributary mouth bars dmbs and 5 terminal distributary channels tdcs lower in the parasequence detached bars consist of proximally located cross bedded and quasi parallel laminated subaqueous bars that onlap the delta front slope and grade distally into finer grained distal delta front splays these bars translate downstream in a progradational aggradational degradational trajectory and are overlapped by adjacent bars forming a bar assemblage these bars are interpreted to have been deposited by descending hyperpycnal flows as a decelerating axial jet deposition of these bars occurs at the delta front to prodelta chokepoint presumably due to flow deceleration the distal bar assemblage is capped by an extensive but discontinuous shale drape suggesting local abandonment upper facies assemblages show a distinct switch to predominantly cross bedded distributary mouth bars corresponding to a decrease in water depth an increase in friction and a likely transition into planar versus axial jets this is indicated by aggrading cross bedded distributary mouth bars that overlie the distal bars laterally the mouth bar deposits are interstratified with terminal distributary channel deposits with prominent scour surfaces at the base separate distributary channels and their bars coalesce ultimately to build the entire delta lobe the detached distal bars prograde locally west to northwest and lack fair weather wave formed sedimentary structures suggesting a local embayment along the regionally northeast prograding shoreline low levels of ichnofaunal diversity indicate a stressed river dominated setting at the base of the section frontal splays and detached bars dominated by storm driven river flood deposits are deposited over muddy prodelta facies detached bars are likely initiated about 500 meters distal of the distributary channel in water depths of 10 30 meters based on the thickness of the parasequence once this subaqueous platform is constructed by the distal bar assemblage more proximal distributary mouth bars fill the remaining shallow water accommodation as the system continues to shallow distributary channels override and scour the bars reflecting reduced accommodation

backwater controls on the evolution and avulsion of the qingshuigou channel on the yellow river delta abstract as rivers approach base level their water and sediment dynamics are affected by a transitional reach known as the backwater zone at low flows backwater zones cause flow deceleration and in channel sedimentation but at high flows they cause flow acceleration and erosion over many floods the dynamics of deposition and erosion in the backwater zone are thought to control the locations of avulsions on some large deltaic channels however in various studies the role of the backwater is often inferred or modeled and directly observed evidence of how backwater affects channel dynamics at avulsion sites remains scarce in this study we show how the backwater zone impacts the evolution and avulsion of the qingshuigou channel a recent lobe on the yellow river delta using four decades 1976 2015 of data from systematic surveys of water discharge sediment load cross sectional profiles and water surface elevation the results show that the channel was commonly eroded during flood seasons and aggraded during nonflood seasons erosion rates generally decreased in the downstream direction along the lower channel reach during flood seasons primarily due to downstream channel widening and the subsequent decrease in sediment transport capacity the erosion rate reached zero at the cross sections farthest downstream which is contrary to expectations under hydrodynamic backwater effects where drawdown causes erosion to increase downstream during high flows during nonflood seasons maximum sedimentation occurred upstream of the backwater zone possibly due to impacts of local topography of meandering bends or constriction from dikes morphodynamic backwater accompanied by the deposition and gradual progradation of a mouth bar resulted in downstream increasing sedimentation superelevation and lateral migration rates along the lower channel reach from 1985 to 1996 the predicted avulsion location was near cross sections q6 or q7 with an avulsion length of 20 30 km upstream of the shoreline which was consistent with those for historical avulsions we emphasize the close interplay between backwater effects and channel geometry and argue that morphodynamic backwater may play a more important role than hydrodynamic backwater in setting up and triggering avulsions on the yellow river delta

sediment infilling and wetland formation dynamics in an active crevasse splay of the mississippi river delta abstract crevasse splay environments provide a mesocosm for evaluating wetland formation and maintenance processes on a decadal time scale site elevation water levels vertical accretion elevation change shallow subsidence and plant biomass were measured at five habitats along an elevation gradient to evaluate wetland formation and development in brant pass splay an active crevasse splay of the balize delta of the mississippi river the processes of vertical development vertical accretion elevation change and shallow subsidence were measured with the surface elevation table marker horizon method there were three distinct stages to the accrual of elevation capital and wetland formation in the splay sediment infilling vegetative colonization and development of a mature wetland community accretion elevation gain and shallow subsidence all decreased by an order of magnitude from the open water lowest elevation to the forest highest elevation habitats vegetative colonization occurred within the first growing season following emergence of the mud surface an explosively high rate of below ground production quickly stabilized the loosely consolidated sub aerial sediments after emergent vegetation colonization vertical development slowed and maintenance of marsh elevation was driven both by sediment trapping by the vegetation and accumulation of plant organic matter in the soil continued vertical development and survival of the marsh then depended on the health and productivity of the plant community the process of delta wetland formation is both complex and nonlinear determining the dynamics of wetland formation will help in understanding the processes driving the past building of the delta and in developing models for restoring degraded wetlands in the mississippi river delta and other deltas around the world

the geometry and internal architecture of stream mouth bars in the panther tongue and the ferron sandstone members utah u s a abstract clinothems are seaward dipping beds which are deposited during the progradation of delta front mouth bars measurements taken from clinothems in the field and from geospatially constrained photo realistic virtual outcrops were used to record clinothem dip maximum bed thickness and bed thickness every 10 m along a series of depositional dip oriented profiles from two ancient river dominated delta successions which crop out in central utah usa these data show systematic changes in bed dip and bed thinning which highlight discrete packaging of the beds into bedsets interpreted to represent the progradation of stream mouth bars in the delta front individual bedsets are characterized by a progressive steepening of beds coupled with a more rapid thinning systematic collection of 2800 locations along 73 separate clinothems from the panther tongue sandstone member and parasequence 1f from the ferron sandstone were used to study the relationship between bed thickness dip and decay gradient parameter which describes the down dip bed thinning clinothems in the panther tongue are much longer and more gently dipping than the clinothems in the ferron sandstone in both systems beds can be clustered into groups bedsets which show a systematic decrease in values and an increase in dip angle boundaries between the groups are defined by a sudden increase in values and a concurrent decrease in dip angle these bedsets are interpreted to represent individual stream mouth bars which amalgamate to form mouth bar complexes within the delta front sand bodies the use of virtual outcrops was essential for the collection of the large volumes of thickness data and the recognition of very subtle 1 changes in dip angle which have made these interpretations possible

spatial and temporal patterns of land loss in the lower mississippi river delta from 1983 to 2016 abstract the mississippi delta in coastal louisiana has some of the highest rates of land loss in the world this land loss crisis might become a global problem because most major deltas are expected to be vulnerable to land loss during the remainder of the 21st century and beyond despite this predicament we do not understand how land loss in a deltaic environment proceeds in time and space here we evaluate the spatial and temporal trends of land loss in the lower mississippi river delta lmrd region using spatial statistics and landscape metrics we used nearly 4800 landsat images to construct a series of three year cloud free composites from 1983 to 2016 from these data we created a stability index si which is a dimensionless measure of the number of land to water transitions that a land pixel makes before being considered lost our results indicate that on the lmrd 75 of land loss is a single transition from land to water while about 25 of land pixels have two or more transitions before being considered lost using a local indicator of spatial association we show that pixels with similar si tend to cluster together single transition clusters low si form elongated shapes they are densely packed and they are predominantly but not always found on marsh edges on the other hand multi transition clusters high si form square like shapes they are more fragmented and they are usually found in marsh interiors our analysis further shows that the land loss area within the spatial patches with both high and low stability is strongly related to the density of land patches and their shape r2 of 0 717 and 0 545 respectively our analysis suggests that land loss pixels on the marsh edges undergo different temporal patterns of land loss compared to those in the marsh interior we hypothesize that this arises because wave edge erosion drives land loss on marsh edges whereas subsidence related flooding drives land loss in marsh interiors the stability index provides a useful way to characterize the processes causing land loss

observation of mesoscale ocean features in the northeast pacific using geosat radar altimetry data in this paper geosat altimetry data from the northeast pacific are examined the data are 1 binned data on 1 latitude by 2 longitude blocks and 2 collinear track data the binned data cover the region from 20 n to 60 n from the north american coast westward to 150 w and span from december 15 1986 to june 1 1989 to examine the data for evidence of westward propagation of sea level anomalies three zonal transects 45 n 49 n and 57 n are made complex empirical orthogonal function analysis of the data transects at these latitudes reveals phase speed and amplitude information the first eigenmode at each latitude has a very strong annual signal two dimensional spectral analysis of the first eigenmode at 45 n and 57 n shows westward propagation of sea level anomalies at 45 n only the propagating features are annual in period and of order 1000 km in length at 57 n westward propagation is evident as at 45 n but there is also an eastward component to examine the variability of the coastal sea level signal collinear track data from three ascending tracks crossing the gulf of alaska are analyzed revealing mesoscale features of the order of 100 km that parallel the canadian and alaskan coast the most notable feature is the sitka eddy westward propagation of several of these features is observed the results from the analysis of both types of geosat data are compared with other observational data

petrology of very high pressure eclogitic rocks from the brossasco isasca complex dora maira massif italian western alps petrographical and mineral chemical data are given for the eclogites which occur in the garnet kyanite micaschists of the penninic dora maira massif between brossasco isasca and martiniana italian western alps and for a sodic whiteschist associated with the pyrope coesite whiteschists of martiniana the brossasco isasca bi eclogites are fine grained foliated and often mica rich rocks with a strong preferred orientation of omphacite crystals and white micas porphyroblasts of hornblende are common in some varieties whilst zoisite and kyanite occur occasionally in pale green varieties associated with leucocratic layers with quartz jadeite and garnet these features differentiate the bi eclogites from the eclogites that occur in other continental units of the western alps which all belong to type c garnet sodic pyroxene and glaucophane are the major minerals in the sodic whiteschist sodic pyroxene in the eclogites is an omphacite often close to jd50di50 with very little acmite and virtually no aliv and impure jadeite in the leucocratic layers and in the sodic whiteschist garnet is almandine with 20 30 mol for each of the pyrope and grossular components in the eclogites and a pyrope rich variety in the sodic whiteschist white mica is a variably substituted phengite and paragonite apparently only occurs as a replacement product of kyanite amphibole is hornblende in the eclogites but the most magnesian glaucophane yet described in the sodic whiteschist quartz pseudomorphs of coesite were found occasionally in a few pyroxenes and garnets the p t conditions during the vhp event are constrained in the eclogites by reactions which define a field ranging from 27 28 kbar to 35 kbar and from 680 to 750 c these temperatures are consistent with the results of garnet pyroxene and garnet phengite geothermometry which suggest that the eclogites may have equilibrated at around 700 c in the sodic whiteschist pressures ranging from 29 to 35 kbar can be deduced from the stability of the jadeite pyrope garnet glaucophane compatibility as in the eclogites water activity must have been low such conditions are close to the p t values estimated for the early alpine recrystallization of the pyrope coesite rock and like petrographical and mineralogical features set aside the bi eclogites from the other eclogites of the western alps instead indicating a close similarity to some of the eclogite bodies occurring in the adula nappe of the central alps an important corollary is that glaucophane stability at least in na and mg rich compositions and under very high pressures may extend up to 700 c in agreement with the ht stability limit suggested by experimental studies

modeling river delta formation a model to simulate the time evolution of river delta formation process is presented it is based on the continuity equation for water and sediment flow and a phenomenological sedimentation erosion law different delta types are reproduced by using different parameters and erosion rules the structures of the calculated patterns are analyzed in space and time and compared with real data patterns furthermore our model is capable of simulating the rich dynamics related to the switching of the mouth of the river delta the simulation results are then compared with geological records for the mississippi river

variability in sedimentological and ichnological signatures across a river dominated delta deposit peay sandstone member cenomanian of the northern bighorn basin wyoming u s a abstract incorporation of ichnological trace fossil data into facies models for deltaic systems and their deposits has yielded useful new criteria for discriminating between alternative interpretations nevertheless despite the recognition that trace fossil suites may vary spatially across an individual delta system few spatially resolved datasets are currently available to inform these interpretations we present a new sedimentological and ichnological analysis of the upper cretaceous cenomanian peay sandstone member of the frontier formation in the northern bighorn basin wyoming u s a based on three dimensional mapping of surface exposures and subsurface drilling data both down depositional dip and across depositional strike trends can be determined and quantified prima facie from this dataset the peay sandstone member is a crudely coarsening upward sandstone body that has an elongate planform shape projecting southeastward into the basin based on a facies analysis the vertical facies succession in the core of the body represents from base to top deposits of prodelta stratified siltstone distal delta front thinly interbedded siltstone and sandstone through medial proximal delta front thickly interbedded siltstone and sandstone to bioturbated fine grained sandstone to mouth bar amalgamated largely unbioturbated fine to medium grained sandstone environments this complete progradational succession persists for at least 40 km in the depositional dip direction thinning and fining abruptly over a few kilometers south of the town of greybull wyoming transects from the delta axial core to the peripheral flanks reveal changes in facies reflecting a transition from a high energy river dominated mouth bar environment to a tide and wave influenced medial proximal delta flank and ultimately to a low energy storm and wave influenced distal delta flank setting on the peripheries of the delta lobe the trace assemblage in the axial core is interpreted as a highly stressed expression of the skolithos ichnofacies this passes gradationally down depositional dip into stressed expressions of the cruziana ichnofacies and along depositional strike into an archetypal unstressed expression of the cruziana ichnofacies on the delta flanks this spatial variation in bioturbation intensities and trace fossil assemblages is interpreted to reflect dissipation of physico chemical stresses from the axial core to peripheral flanks the outcomes of this study emphasize the point that data acquired on an ancient deltaic deposit in isolation of their paleogeographic context may give rise to a misleading impression of that system and potentially a less than parsimonious interpretation of its process balance and planform geometry

morphological adjustment of the qingshuigou channel on the yellow river delta and factors controlling its avulsion abstract the avulsion time scale of channels on the yellow river delta yrd is about a decade due to the large sediment load and rapid channel aggradation and progradation nevertheless the qingshuigou channel has been maintained for about four decades since 1976 this channel provides an ideal opportunity to study channel evolution following avulsion and to examine different avulsion criteria in this study we analyzed the geomorphic adjustment of the lower qingshuigou channel during 1976 2015 and calculated normalized gradient advantage and superelevation at the channel to estimate how close the channel was to avulsion results showed that channel evolution processes may be divided into four phases i 1976 1980 rapid aggradation ii 1980 1985 channel widening and enlargement iii 1985 1996 main channel aggradation and shrinkage and iv 1996 2015 main channel incision and deepening evolution phases i ii and iii are similar to the avulsion cycle observed in natural and experimental fluvial systems the calculated values of normalized gradient advantage and superelevation in early 1990s exceeded the critical values suggested by previous studies implying that the channel was prone to avulsion nevertheless avulsion was prevented mainly due to limited overbank flows constriction from artificial dikes and slowed channel extension as a result of reduced sediment load the evolution of the qingshuigou channel confirms previous arguments that superelevation and gradient advantage are not sufficient for avulsion and multiple factors should be considered including flood frequency lateral mobility sediment diameter and human interruptions

sequence stratigraphic analysis of thick coal seams in paralic environments a case study from the early permian shanxi formation in the anhe coalfield henan province north china abstract to study the possible role of base level oscillations in the formation of thick coal seams in coastal plain paralic environments the early permian shanxi formation no 21 thick coal seam was investigated in 3 cores spanning a distance of 29 km in the anhe anyang hebi coalfield henan province using sedimentology sequence stratigraphy and coal petrology the accommodation condition and origin of the peatland can be interpreted from maceral and mineral composition in the no 21 coal seam coals that accumulated in a low accommodation peat of ombrotrophic origin are characterized by relatively high inertinite content and relatively low mineral matter abundance coals accumulated in a balanced accommodation peat of rheotrophic origin are characterized by high vitrinite content and low abundances of inertinite and mineral matter coals with relatively high vitrinite content and relatively low inertinite content are interpreted to have accumulated in a high accommodation peat of rheotrophic origin the no 21 coal seam was developed as part of a transgressive systems tract tst and displays maximum thickness in the central anhe coalfield due to the local rapid subsidence of the formative delta plain six types of key stratigraphic surfaces are recognized in the coal seam including terrestrialization tes paludification pas give up transgressive guts accommodation reversal ars exposure es and flooding fs surfaces the no 21 coal seam consists of at least three drying up and wetting up cycles defined by these surfaces with each cycle spanning from 20 ka to 30 ka the variation of peatland type from rheotrophic through ombrotrophic and back to rheotrophic peat in the landward area implies the role of high frequency climatic fluctuations and the water level changes in the central and seaward areas may reflect sea level fluctuations due to the hydrological connection to the sea and the change in rainfall to evaporation rates these cycles arrived at a period close to that of climatic precession for milankovitch cycles during the early permian the oscillating high and low summer insolation would have caused the alternating wet and dry climate periods that were then recorded as the wet dry cycles in the coal seams the results of this study can provide insights for research addressing hydrological conditions in ancient peatlands and paleoclimate and sea level fluctuations recorded in thick paralic coal seams

a unifying framework for shoreline migration 1 multiscale shoreline evolution on sedimentary coasts 1 a unifying framework for shoreline migration is presented which synthesizes problems from coastal engineering geomorphology and stratigraphy into a common quantitative basis consideration of characteristic problems from these fields reveals that multiscale shoreline evolution problems naturally break into three classes on the basis of the morphologic unit of evolution shoreface bed versus shoreline planform versus stratigraphic shoreline trajectory shoreline evolution models correspondingly break into morphodynamic morphokinematic and hybrid approaches a generalized shoreline continuity equation is derived the shoreline exner equation which subsumes equilibrium profile models commonly used in geomorphology and engineering and provides a natural framework for interpreting shoreline trajectories preserved in the sedimentary record the shoreline exner equation provides a rigorous basis for geometric and moving boundary models which have significant untapped potential for shoreline migration problems recent advances in computational methods for evolving interface problems make hybrid models particularly attractive for problems of large scale planform shoreline dynamics such as delta evolution

degradation of the plaquemines sub delta and relative sea level in eastern mississippi deltaic coast during late holocene abstract the stratigraphic architecture of plaquemines sub delta lobe is identified from sedimentary cores and sub bottom seismic data collected at lower breton sound louisiana usa four lithofacies were identified in cores from bottom to top 1 organic poor mud 2 organic poor silty sand 3 massive mud 4 organic rich peat and root rich soft mud overall the lithofacies displays a typical progradational deltaic deposit at bottom with upward coarsening feature and then an upward fining deposit overlying on top stratigraphic position of the organic rich peat facies indicates that it is formed after the fluvial sediment source moves away from this region and it is recognized as a termination of progradation of the plaquemines sub delta dated peat samples show that sub delta progradation stops between 876 and 1384 yr ad during which a 20 70 cm relative sea level rise is detected the geological framework reported in this study provides critical information for future modeling on river diversions the stratigraphic architecture underlying lower breton sound implicates that top three facies of root rich soft mud organic rich peat and massive mud are likely to be eroded away before the development of new crevasse splay or sub delta when sediment diversion is in operation the deeper organic poor silty sand lithofacies however can serve as a firm foundation to build new land

basic building blocks and process variability of a cretaceous delta internal facies architecture reveals a more dynamic interaction of river wave and tidal processes than is indicated by external shape abstract although delta building processes and the resultant facies and facies associations have been studied for over a century there remains a lack of well documented facies architectural studies of ancient deltas in this study architectural element analysis is applied to determine the basic building blocks of a cretaceous delta at the top of the upper turonian wall creek member exposed along the western flanks of the powder river basin wyoming we document the bed scale basic building blocks of this ancient delta and show them in the context of their facies and stratal variability and their hierarchical spatial arrangement within a single deltaic parasequence we also test the idea that external sand body shape may not reflect the internal facies complexity as has recently been suggested in studies of several modern deltas including the burdekin in australia the brazos in the gulf of mexico and the baram trusan in borneo five orders of bounding surfaces separate six facies architectural elements in the prodelta and delta front deposits these elements are prodelta fines pf frontal splay fs channel ch storm sheet ss tidally modulated deposit tm and bar accretion ba seasonal to decadal river floods are thought to represent the main building phases of the delta producing channels bars and frontal splay elements during intervening periods the delta was reworked by waves storms and tides producing tidally modulated and storm sheet elements due to the complex interactions of river effluents with waves storms and tides the delta is interpreted as mixed influenced regional sandstone isolith facies and paleocurrent maps help to reconstruct the paleogeography and show how the various architectural elements varied across the delta front the channels bars frontal splays and tidally modulated elements are found only near the distributary mouth whereas the storm sheets occur extensively away from the distributary mouth the plan view morphology of the studied delta shows a smooth fronted arcuate to cuspate shape which should indicate wave dominance in contrast our analysis of the internal facies architecture shows that the delta was constructed rapidly during major river floods with significant tidal reworking additional outcrop mapping shows that storm wave reworked sands are attached to the flanks of the system previously published delta models predict incorrectly that the tidal reworking of a river flood dominated system should result in a more bird foot shape versus the lobate geometry that is actually mapped our analysis of internal facies versus external shape matches similar observations on several modern deltas and suggests that external shape is a poor indicator of internal facies complexity

quantitative outcrop data for flow simulation abstract an architectural analysis documents variations in bedding geometry and rock properties within a tide influenced deltaic sandstone exposed in the cretaceous frontier formation of central wyoming usa digital maps of bedding lithofacies and diagenetic cements as well as vertical logs of grain size lithofacies and permeability describe rock properties that potentially influence fluid flow behavior these records are used to construct simulation models that assess the relative importance of different types of geologic variability on prediction of subsurface fluid flow two 25 meter thick tide influenced deltaic sandstone bodies coarsen upward and contain inclined beds that reflect episodic delta front progradation decimeters to meters thick beds within bodies alternate between cross stratified sandstones formed during rapid flows and shales deposited during more quiescent conditions down depositional dip bed draping shales are more continuous and lithofacies within sandstone beds become finer grained and increasingly heterolithic as sandstone beds fine down dip mean permeability values decrease and coefficients of variation increase permeability values change from nearly normal distributions to highly right skewed and permeability values become more strongly spatially correlated nodular cements also affect permeability all of these variations were modeled using stratigraphic cornerpoint grids that preserve stratal geometry and gridblocks with properties assigned using a combination of rock property maps and statistical models based on rock property logs simulations predict effects on fluid flow of geologic heterogeneity at different scales the influences of process variables and the effects of different methods of grid construction and rock property assignment flow simulations of water flooding through a 22 m thick by 360 m long segment of a deltaic sandstone oil reservoir predict that 1 rapid flow through coarser grained deposits at the top of the sandstone body tends to draw water upward 2 thin shales draping sandstone beds shunt downdip directed flow downward and updip directed flow upward 3 cement nodules cause more tortuous flow patterns but have little effect on recovery efficiency 4 methods of predicting intrafacies correlation of permeability have little effect on flow behavior at this scale a simulation model constructed using a high resolution cartesian grid did not resolve the effects of inclined shales demonstrating the usefulness of stratigraphic cornerpoint grids for modeling flow through complex geologic deposits flow simulations of tracer flow through a meter thick cross stratified bed within the deltaic sandstone body showed that at this scale shale drapes and models of the intrafacies distribution of permeability have statistically significant effects

correlation techniques perforation strategies and recovery factors an integrated 3 d reservoir modeling study sirikit field thailand production in the sirikit oil field of the phitsanulok basin thailand commenced in 1982 the field has an stoiip stock tank oil initially in place of approximately 800 mmbbl million barrels to date more than 130 wells have been drilled and over 100 mmbbl produced reservoir management studies into optimizing recovery and identifying unswept oil volumes are ongoing so as to maximize the venture s profitability this work includes 3 d three dimensional static and dynamic modeling this study is one such exercise whereby different geological correlation techniques and perforation strategies were analyzed for their potential impact on recovery factors the sirikit field and adjacent satellite fields are composed of predominantly lacustrine mouth bar and fluvial deposits two correlation techniques lithostratigraphy and chronostratigraphy were employed to generate two 3 d reservoir architectures using the shell proprietary 3 d static reservoir modeling system geocap significantly different recovery factors are derived from 3 d dynamic flow simulation of these architectures no vertical upscaling 2 x 2 areal upscaling within the shell proprietary reservoir simulator mores when good quality sands observed on well logs are perforated in both models the lithostratigraphic correlation model results in an absolute 3 higher recovery factor than that of the chronostratigraphic correlation model in relative terms this represents a 43 higher recovery factor this suggests that if a lithostratigraphic correlation model is assumed then for this perforation strategy the recovery factor would be overestimated by 3 absolute and 43 relative if the chronostratigraphic interpretation represents the actual subsurface architecture in addition the architecture of the chronostratigraphic model results in the lateral correlation of the thicker upper mouth bar sands with good quality thin bedded toeset sands and shales heterolithics these thin bedded sands are only marginally resolvable on wireline logs and have not generally been perforated in the sirikit field when these thin bedded heterolithics are additionally perforated in the 3 d model an absolute increase in recovery factor of 2 is observed over the same model that has only the upper mouth bar sands perforated in relative terms this represents a 28 improvement in the recovery factor this work confirms and partially quantifies the impact that the choice of mouth bar correlation style can have on recovery factors as predicted by 3 d dynamic reservoir models however the chronostratigraphic model described in this paper represents an end member connectivity scenario whereby sand body continuity is relatively low due to continuous dipping shale barriers further work is required to quantify the recovery factors for the whole spectrum of potential chronostratigraphic model connectivity scenarios

autostratigraphy a framework norm for genetic stratigraphy abstract autostratigraphy is the stratigraphy generated by large scale autogenic processes and needs to be heeded because of a current overreliance on allogenic controls in sequence stratigraphy key principles of autostratigraphy emerging from the theory of autoretreat and a new understanding of alluvial grade derive from the non equilibrium stratigraphic response i e the general lack of equilibrium configuration of depositional systems the non equilibrium behavior of fluvial deltas during times t of steady dynamic forcing leads to variable stratigraphic response that is the inevitable result of length d and time scaling particular to the depositional system rather than necessarily reflecting any sudden or unsteady change in the rate of allogenic forcing some abrupt breaks in the stratigraphic record are not necessarily associated with changes in allogenic conditions but can result from purely autogenic processes of the system when t is comparable to or longer than 1 the depositional system takes the non equilibrium large scale autogenic response 2 the superposition of autogenic and allogenic components of the forcing is prominently nonlinear and thus 3 sequence stratigraphic models that have been built on the assumption of equilibrium response are incorrect autostratigraphic analysis makes it possible to detect and identify complex autogenic responses and unsteady allogenic events in the stratigraphic record by quantifying a temporal change in the magnitude of d autostratigraphy thus functions as a norm for genetic stratigraphy

holocene avulsion styles and sedimentation patterns of the saskatchewan river cumberland marshes canada abstract this paper describes the styles and sedimentation patterns of holocene avulsions of the saskatchewan river at the cumberland marshes predating the most recent 1870 s avulsion holocene avulsions involved two major styles 1 progradation of lacustrine deltas and splay complexes and 2 local reoccupation or appropriation of preavulsive channels most avulsions were progradational and occurred in floodplain lakes occupying floodbasin areas between elevated alluvial ridges the two most recent avulsions old channel and 1870 s diverted mainly into inundated peatland progradational avulsions were accompanied by deposition of avulsion belt sediments associated with multiple channel networks the characteristics of avulsion belt deposits include 1 sediments dominated by poorly sorted silt and very fine sand 2 lateral continuity in transverse and longitudinal directions with subhorizontal upper and lower boundaries 3 predominantly nonerosional contacts with underlying sediments 4 coarsening upward successions 5 consistent radiocarbon dates for the tops of preavulsive substrates and 6 occurrence beneath levee and overbank deposits of the associated major channel belt indicating that avulsion belt deposition occurs prior to the development of a new master channel the width of ancient avulsion belts reaches 18 km with typical thicknesses of 2 3 m avulsion belt deposition accompanied by many small channels was followed by flow reversion to a few larger channels and eventually to one single channel accompanied by deposition of levee and channel deposits reoccupational avulsions were not accompanied by deposition of widespread avulsion belt sediments and led mainly to the modification of pre existing channel belts the sedimentation patterns of holocene avulsions of the saskatchewan river reveal that avulsion belt sediments represent major components of the floodplain deposits supporting the model developed from observations of the 1870 s avulsion

the anticyclonic baroclinic eddy off sitka alaska in the northeast pacific ocean abstract among the many mesoscale eddies found in the northeast pacific ocean is a well developed anticyclonic baroclinic eddy situated within a few hundred kilometers of sitka alaska 57 n 138 w it has definitely been observed during spring and summer 1958 summer 1960 and summer 1961 observations made at other times show some evidence of its occurrence also the trajectories of three norpax drifting buoys for april may 1977 also indicated the probable presence of an eddy there the eddy whose diameter ranges from 200 to 300 km and whose depth extends to 100 m and probably to as much as 2000 m recurs at the same location the center of the eddy is characterized by the following features the surface water is less saline and only somewhat warmer than at its periphery at depths within and below the halocline it is warmer less saline and contains more dissolved oxygen than at the periphery and a warm core is situated within the halocline the halocline is usually depressed by less than 100 m but

natural controls of fluvial denudation rates in major world drainage basins we present a new compilation of estimates of modern rates of mechanical and chemical denudation for externally drained basins exceeding 5 105 km2 in area these estimates are based on sediment and solute load data selected in order to represent natural rates as far as possible chemical denudation rates have been calculated by deducting the nondenudational component of solute load mechanical denudation rates range from 1 mm kyr 1 for the st lawrence and dnepr basins to 670 mm kyr 1 for the brahmaputra basin chemical denudation rates vary from 1 mm kyr 1 kolyma niger nile and rio grande basins to 27 mm kyr 1 chiang jiang basin the kolyma basin has the lowest 4 mm kyr 1 and the brahmaputra basin the highest overall rate of denudation 688 mm kyr 1 relationships between denudation rates and a range of morphometric hydrologic and climatic variables are investigated through correlation and regression analysis morphometric variables such as mean local relief are accurately calculated for large basins for the first time by using the national geophysical data center 10 minute topographic database variables expressing basin relief characteristics and runoff are found to be most strongly associated with both mechanical and chemical denudation rates with more than 60 of the variance in total denudation being accounted for by basin relief ratio and runoff basin area runoff variability and mean temperature however are only weakly associated with rates of denudation although direct comparisons cannot be made it appears that rates of basin denudation derived from present day mass flux estimates are not overall significantly different from estimates of long term rates based on sediment volume and thermochronologic data it therefore appears that the key factors identified as controlling denudation rates here are also applicable to the geological time spans relevant to the interaction between tectonic and denudational processes

characterization of stratigraphic architecture and its impact on fluid flow in a fluvial dominated deltaic reservoir analog upper cretaceous ferron sandstone member utah fluviodeltaic stratigraphic architecture and its impact on fluid flow have been characterized using a high resolution three dimensional reservoir scale model of an outcrop analog from the upper cretaceous ferron sandstone member of central utah the model contains two parasequence sets delta complexes each with five or six parasequences separated by an interval of coastal plain strata each parasequence contains one or two laterally offset teardrop shaped delta lobes that are 6 to 12 km 4 7 mi long 3 to 9 km 2 6 mi wide 5 to 29 m 16 95 ft thick and have aspect ratios width length of 0 4 to 0 8 delta lobes have a wide range of azimuthal orientations 120 around an overall east northeastward progradation direction in plan view delta lobes in successive parasequences exhibit large as much as 91 clockwise and counterclockwise rotations in progradation direction which are attributed to autogenic lobe switching in cross sectional view parasequence stacking is strongly progradational but a small component of aggradation or downstepping between parasequences reflects relative sea level fluctuations we use flow simulations to characterize the impact of this heterogeneity on production in terms of the sweep efficiency which is controlled by 1 the continuity orientation and permeability of channel fill sand bodies 2 the vertical permeability of distal delta front heteroliths 3 the direction of sweep relative to the orientation of channel fill and delta lobe sand bodies and 4 well spacing distributary channel fill sand bodies terminate at the apex of genetically related delta lobes and provide limited sand body connectivity in contrast fluvial channel fill sand bodies cut into and connect multiple delta lobe sand bodies low but non zero vertical permeability within distal delta front heteroliths also provides connectivity between successive delta lobe sand bodies

dynamic changes and processes in the mississippi river delta research in the modern delta of the mississippi river has revealed short term changes and processes that are of significant magnitude deltaic lobes each lobe covering an area of 30 000 sq km and having an average thickness of 35 km switch sites of deposition on an average of every 1 500 yr through short periods of geologic time this process results in a relatively thick accumulation of stacked deltaic cycles covering extremely large areas within a single delta lobe and operating on an even higher frequency are bay fills and overbank splays bay fills having areas of 250 sq km and thickness of 15 m require only 150 yr to accumulate four major events have taken place in the modern balize delta since 1838 overbank splays are much smaller covering areas of less than 2 sq km and having thicknesses of 3 m but are associated with high floods on the river at the river mouth continued progradation of the distributary channel can form distributary mouth sand bodies that have dimensions of 17 km long 8 km wide and a thickness of 80 m in a period of only 200 yr differential sedimentary loading at the river mouth results in formation of diapirs that display vertical movements in excess of 100 m in a period of 20 yr on the subaqueous delta platform sediment instabilities operate nearly continuously mass moving large quantities of shallow water deposits to deeper water environments via arcuate rotational slides and mudflow gullies and depositional lobes all of these changes and processes operate at differing spatial and temporal scales but all result in deposition of large volumes of sediment over extremely short periods of time

alluvial pedogenesis in pleistocene and holocene mississippi river deposits effects of relative sea level change comparison of pleistocene and holocene soils developed in mississippi river meander belt deposits in louisiana illustrates the influence of relative sea level change on pedogenesis holocene and pleistocene meander belts have similar landscape morphologies lithofacies and soil characteristics and probably formed under similar hydrologic regimes the pleistocene avoyelles prairie meander belt is now terraced but it was originally graded to a lower relative sea level position than the holocene flood plain holocene alluvial soils are generally weakly expressed cumulative profiles with abundant redoximorphic features and formed on an aggrading flood plain with a shallow fluctuating water table the soil morphology varies with respect to landscape position and overbank lithofacies pleistocene alluvial paleosols show evidence for two stages of pedogenesis during the first stage of pedogenesis water table fluctuations and flood plain aggradation produced profiles with color mottles iron and carbonate nodules and weak b and c horizons similar to holocene flood plain soils the second stage of pedogenesis occurred after the avoyelles prairie was terraced and the regional water table fell a minimum of 30 m improved soil drainage created oxidizing and acidic conditions removed free carbonates dehydrated iron oxides and transformed clay minerals this stage produced pleistocene profiles with brighter matrix and mottle hues lower ph values larger and harder iron nodules and greater kaolinite contents than comparable holocene flood plain soils the primary influence on regional water table lowering in the southern lower mississippi valley was relative sea level fall mississippi river flood plain lowering adjacent to the avoyelles prairie most likely occurred between the end of oxygen isotope stage 3 and the maximum period of valley entrenchment during oxygen isotope stage 2 water table fall affected pedogenic processes a minimum of 400 km upvalley of the continental shelf margin pleistocene mississippi river paleosols represent excellent analogs for interpreting ancient alluvial paleosols formed during episodes of base level fall and valley incision as fluvial entrenchment terraced the meandering avoyelles prairie a pedogenic threshold was crossed that altered the pathway of chemical weathering the complexity of a multiple step pedogenic history also highlights the fact that interpretation of relative profile development as a function of time can be problematic

geology and stratigraphy of fluvio deltaic deposits in the ivishak formation applications for development of prudhoe bay field alaska significant remaining reserves in prudhoe bay field are confined within deltaic rocks at the base of the triassic ivishak sandstone the initial stratigraphic characterization of the prudhoe bay reservoir was lithostratigraphically based and it depicted this basal reservoir interval as tabular zones between marine shale and overlying coarse grained fluvial sandstones a reassessment of this interval based on cores and genetic stratigraphic correlations depicts en echelon offlapping fluvially dominated deltaic wedges reservoir quality rocks occur in distributary mouth bar distributary channel and fluvial facies associations a paleogeographic reconstruction of one delta lobe includes an alluvial plain crossed by channels of possibly braided or low sinuosity rivers this alluvial plain graded into a delta plain cut by distributary channels that fed distributary mouth bars on a broad delta front river dominance is inferred from the abundance of unidirectional current structures normally graded beds soft sediment deformation and general absence of wave formed tidal and biogenic structures slumping and growth faulting locally replaced coarsening upward deltaic successions with sharp based overthickened mouth bar and distributary channel deposits mudstones deposited following delta lobe abandonment form laterally extensive flow barriers between lobes compartmentalization is most pronounced distally where deltaic sandstones are overlain by and pass laterally into marine shale proximally fluvial and deltaic sandstones are juxtaposed across erosional contacts improving reservoir continuity this stratigraphic interpretation is corroborated by production and surveillance data plus an interference test locally stratigraphy and poor waterflood performance reflect completions in diachronous sandstones that originated in separate deltaic lobes previously poor well performances were attributed to sandstone pinch outs in some cases production can be enhanced with recompletions rather than infill drilling nonconventional wells planned and completed with the benefit of detailed facies association correlations currently are recovering millions of barrels of previously bypassed oil

improved understanding of mixed oil in nigeria based on pyrolysis of asphaltenes abstract crude oil from reservoirs in the onshore niger delta is a mixture of low and high maturity charge aromatic biomarkers in these oils such as alkylphenanthrenes and alkylnaphthalenes show relatively high thermal maturity whereas the saturated sterane and hopane biomarkers indicate lower maturity close to the peak of the oil window the high predicted maturity of the crude oils based on alkylphenanthrene and alkylnaphthalene indices is probably caused by mixing of high maturity condensate with less mature black oil this correlates with the gas washing phenomenon of studied nigerian oils caused by migrating condensate stream the results of our study indicate that asphaltenes can be used to infer the organofacies of the low maturity petroleum charge in mixed crude oils compositional characteristics of the asphaltene pyrolysates indicate an origin of the related oils from type ii iii or type iii source rock kerogen the n alkyl chain length distributions of the asphaltene pyrolysates predict source rocks that generated high wax paraffinic naphthenic aromatic oils or paraffinic oils the n alkyl chain length of asphaltene pyrolysates changes in proportion to oxicity and the relative input of terrigenous organic matter to the source rock

shelf edge delta and reef development on a mixed siliciclastic carbonate margin central great barrier reef the great barrier reef gbr is the world s largest extant mixed silicilastic carbonate margin previous research on the great barrier reef has suggested that the extensive barrier reef system may act as an impermeable barrier and limit the development of delta systems during lowstands but sufficient geophysical data to support this hypothesis are lacking we use dense sparker seismic and sub bottom profiler data to better understand the structure of a large lobe shaped feature 10 km 10 km on the shelf edge of the central gbr and the interactions between siliciclastic and carbonate sedimentary systems interpreted sparker seismic contains prograding clinoforms and suggest that the lobe shaped feature was a river dominated shelf edge delta a delta on the shelf edge implies that the presence of an exposed barrier reef was not a major impediment to deposition and that other adjacent lobe shaped features are also deltaic deposits the shelf edge deltas were deposited onto a broad upper slope terrace that allowed continued progradation and limited incision when sea level fell below the shelf edge delta foresets are commonly colonized by coral reefs but the spatial and temporal relationship between reefs and some deltaic units remains unclear the presence of multiple shelf edge deltas that link to previously mapped burdekin river paleo channels indicates a complex history of sedimentation with the burdekin river delta migrating up to 100 km along the gbr margin during the late quaternary regional bathymetric data suggest that large modern or recent shelf edge deltas are rare on the gbr and that there was a broad range of sedimentary processes operating along the margin of the gbr during periods of low sea level

perspectives on the geoarchaeology of the lower mississippi valley abstract the impact of harold n fisk s work on the archaeology and geoarchaeology of the lower mississippi valley lmv has been monumental as a result of his landmark publications on the geology of the alluvial valley of the mississippi river our comprehension of the interplay between geological geomorphic and human actions is relatively well developed however geologists and archaeologists still need to work together more closely to appreciate and understand the contributions each field has to offer examination of the interplay between geologists and archaeologists in the realm of dating and landscape evolution provides the basis for an investigation of the state of geoarchaeology in the lmv today integration of research demands an appreciation of scale which must be approached from an historical perspective humans have both in the past and the present impacted the natural environment of the mississippi river and its floodplain only when this fact is fully appreciated by archaeologists and geologists alike will it be possible to forge a new synthesis of the relationship between the dynamic alluvial valley and its human occupants

the mississippi delta region past present and future the mississippi delta region of south louisiana houses a wealth of resources within a dynamic subsiding landscape foundations for the delta region reflect neogene evolution of the depocenter whereas details of the modern landscape reflect late pleistocene to holocene evolution of the alluvial deltaic plain the holocene delta plain was constructed by cyclical growth of deltaic headlands followed by avulsion and relocation of the fluvial sediment source abandoned headlands were then submerged and reworked while a new headland was created at the site of active fluvial sediment input historic period levees have decoupled the delta plain from its fluvial sediment source at the same time global sea level rise was accelerating which has accelerated delta plain submergence diversions of mississippi river water and sediment are necessary to achieve delta plain sustainability but upstream dams trap 50 of the total sediment load and there is not enough supply to keep pace with subsidence and accelerated

estuarine controls on fine grained sediment storage in the lower mississippi and atchafalaya rivers observations of the lower mississippi river channel in 1999 2003 with side scan and subbottom seismic profilers multibeam bathymetry core radiotracers 7be 137cs 210pb and 234th and water column profiles of fluid and suspended sediment properties are utilized to constrain the timing location and intensity of the seasonal storage of fine grained sediments in the estuarine channel reach below venice louisiana unlike earlier studies that suggested little or no estuarine sedimentation was taking place in the river the present study demonstrates that the river channel above the head of passes seasonally stores as much as 10 of the annual suspended sediment discharge during periods of falling to low mississippi water discharge associated with salt stratification in the channel thalweg mud deposits are up to 3 2 m thick with 7be derived sediment deposition rates of up to 8 9 mm day water column profiling and 234th 7be ratios suggest that 1 particles are transported and settled mainly as flocs and 2 riverine flocs are settling through the strong salt wedge halocline and are protected from re erosion by the salt stratification with onset of the spring freshet and the corresponding seaward retreat of the saltwater wedge the entire volume of fine grained material stored in the lower river except in low freshet years is remobilized and transported to the gulf of mexico in the turbid freshwater plume this tidal hysteresis strongly influences the timing of sediment supply to the ocean high turbidities in the shelf plume during rising water discharge spikes of 1 to 2 week duration are the product of local channel floor remobilization as well as increased supply from the drainage basin pulsed resupply of sediments and the pore water products of early diagenesis potentially have major implications for issues such as continental margin carbon budgets and coastal eutrophication companion surveys conducted in the lowermost 12 km reach of the atchafalaya distributary of the mississippi show no evidence of saltwater wedge intrusion at low discharge or seasonal fine grained sediment storage likely due to the shallow 7 m river mouth sill that impedes the upstream movement of gulf water

topographically induced baroclinic eddies near a coastline with application to he northeast pacific abstract a mathematical model is developed to describe the interaction between variable bottom topography and a steady horizontally sheared baroclinic coastal current the topography modeled in this study consists of an offshore seamount and a seaward protrusion of the continental slope the fluid motions are assumed to conserve potential vorticity on the f plane and expressions for the pressure density velocity and mass transport fields are obtained using a normal mode analysis and the appropriate green s function for the horizontal problem the theory is applied to the northeast pacific ocean in an attempt to model the anticyclonic eddy which has been observed by tabata west of sitka alaska the numerical calculations of the model and the observed location dimensions velocities and transports of the sitka eddy are in good agreement the axial velocities and dimensions of the calculated eddy field are largest for upstream surface and bottom currents of approximately 5 7 and 1 2 cm s 1 respectivel

synthesis and characterization of amphiboles along the tremolite glaucophane join actinolite and glaucophane are the principal amphiboles in greenschist and blueschist facies metamafic rocks respectively and constitute an important mineral pair for deducing the conditions of medium and high pressure metamorphism here we present the crystal chemical properties of amphiboles synthesized along the tremolite glaucophane join as an important starting point for the more chemically complex samples occurring in nature amphiboles were synthesized in 10 mol increments at conditions ranging from 840 c and 0 6 gpa for tremolite rich to 750 c and 2 5 gpa for glaucophane rich amphiboles the amphibole yields were generally high 95 wt though minor quartz pyroxene and amorphous material either glass or quenched solute were often present electron microprobe analysis of the amphibole showed that deviations from the nominal or intended compositions occurred with the observed compositions showing solid solution primarily toward the katophorite component and reaching a maximum near the middle of the join unit cell dimensions showed a pronounced positive deviation from ideality even after linear correction for the non join components suggesting a strong tendency toward exsolution single crystal refinements of a couple of selected amphiboles confirmed the deviation from nominal composition and confirmed the presence of ana tal and cal the latter disordered between the m 2 and m 3 sites infrared spectra in the oh stretching region were measured on samples that were heated to 250 350 c to remove absorbed moisture the spectra consist of a main band centered in the 3675 3660 cm 1 region and two minor absorptions on both sides of the dominant central peak which are centered at 3720 and 3640 cm 1 and can be attributed to oh next to ana and cal respectively the main band is evidently composed of several overlapping components due to local arrangements of b cations typical of tremolite caca glaucophane nana and cummingtonite mgmg examination of several intermediate amphiboles by both single crystal xrd and by high resolution tem analysis could not identify evidence of reflections or ordered domains that would violate the c 2 m symmetry of the end member amphiboles comparing the compositions of the synthetic amphiboles from this study with winchite rich amphiboles in nature shows that deviations from the tremolite glaucophane join are common the inability to make pure winchite or even winchite rich amphiboles on the tremolite glaucophane join suggests that this structure is unstable