ammonium in granites and its petrogenetic significance abstract ammonium is present as a trace constituent in all granites with an average concentration of 45 ppm nh4 equivalent to 35 ppm of elemental n it shows wide variations related to petrography and region but the only significant correlation between ammonium and other geochemical parameters is that it is most abundant in peraluminous granites and least abundant in peralkaline granites these variations can be related to a the amount of sedimentary material in the magmatic source region and b redox conditions in the source region the ammonium content of granitic magmas can also be modified by fractionation or contamination hydrothermal alteration has a major effect on the ammonium content of granitic rocks and variation due to this cause may exceed the magmatic variation most hydrothermally altered granites are enriched in ammonium as a result of the transfer of ammonium from sedimentary country rocks by the hydrothermal fluids

nitrogen isotopic composition of ammoniated phyllosilicates case studies from precambrian metamorphosed sedimentary rocks ammonium concentrations in phyllosilicates from archean and proterozoic schists and carbonates were evaluated by fourier transform infrared microspectrometry aftir the y 15 nair values of structural nitrogen in these phases were subsequently measured by laser mass spectrometry a rapid estimate of the concentration of nh4 in biotite by aftir allows the preselection of the samples to be analyzed for their isotopic composition micas from 1 90 2 09 ga metasediments from finland and from 1 025 1 500 ga biotite schists from the moine succession in scotland have high concentrations of structural ammonium between 176 and 1549 ppm suggestive of a biological origin for the nitrogen the heavy nitrogen isotopic signatures y 15 n 4 9x to 19 7x of structural nh4 in these micas are considered consistent with biological denitrification in operation at the time of sedimentation evidence for denitrification in the mesoproterozoic is in agreement with geological and geochemical data for abundant free oxygen in the atmosphere facilitating the stability of marine no3 sequences of early archean ca 3 8 ga garnet mica schists from the isua supracrustal belt isb in southern west greenland contain biotite rich in nh4 between 233 and 512 ppm and nitrogen isotopic signatures y 15 n 1 9x to 5 9x which possibly point to an early evolution of ammonium assimilation and or nitrogen fixation this result appears to be consistent with molecular phylogenetic studies in the bacterial and archaeal domains which suggest that nitrogen fixation and ammonium assimilation were metabolic features of the last common ancestor lca of all organisms d 2004 elsevier b v all rights reserved

identification of possible recent water lava source vents in the cerberus plains stratigraphic and crater count age constraints 1 in order to investigate sources of lava and water to the cerberus plains of mars geomorphological mapping on high resolution imaging science experiment hirise images was carried out to reveal the history of activity of fissures and pits which lie upstream of channels and deposits associated with a wrinkle ridge near cerberus fossae the fissures and pits are superbly exposed and imaged and flows and channels emanate directly from them interpreted as clear evidence that these are vents the mapping establishes stratigraphic relationships between the plains and the channels and deposits originating from the vents establishing the vent history for example to the south of the wrinkle ridge both incised channels and leveed flows extend onto the southern plain and are clearly the final phase of plains forming activity conversely to the north vent sourced channels only incise the plain close to the ridge beyond that they are overlain by large scale regional flows that appear to have originated from the direction of athabasca valles in the southeast there is evidence of contemporaneity between vent sourced activity and large scale plains forming flow that was not sourced from the vents indicating that activity here was part of a broader process of cerberus plains formation from multiple sources crater counts show all the activity to be late amazonian with the latest activity tentatively dating to circa 11 ma thus this study implies that very recent outflows from these vents contributed to the formation of the cerberus plains and constrains the timing and local flow direction of plains forming deposits from other sources

light element distributions n b li in baltic basin bentonites record organic sources abstract distributions of nitrogen boron and lithium were studied in illite smectite from ordovician silurian k bentonites in the baltic basin these trace elements are linked to thermal maturation of organic matter creating fluid signatures that are distinct from those in regionally buried sediments the fluid chemistry is ideally recorded in authigenic illite within the k bentonite because b substitutes in tetrahedral sites of illite li in octahedral sites and n is fixed in the interlayers as nh 4 three nanometric size fractions of illite 10 among these size fractions relate mainly to changes in fluid composition during illite growth bentonite volcanic ash layers mark stratigraphic timelines while illitization of the bentonite k bentonite varies as a function of burial and tectonic temperature gradients in the central baltic basin bentonites were deposited across a carbonate platform near estonia grading to deep basin shales near denmark and poland compositional variations in illite reflect fluids from different sources high n illite 2000 ppm in the southwest basin transitions to high b 250 ppm and high li 100 ppm illite to the northeast these trends follow a thermal gradient decreasing from southwest 200 c to northeast 90 c isotope ratios of b and li show opposing trends in samples across this thermal gradient the bisotopes decrease from southwest to northeast 18 to 4 while li isotopes increase from 5 to 32 the cambrian alum shale a regional hydrocarbon source rock was studied as a potential source of b and li as more than 50 of its b and li was associated with organic matter with increasing thermal maturity illite 11b decreased from 0 to 13 while 7li increased from 20 to 5 these opposing trends are similar to those observed in the k bentonites this suggests that organic sources of n b and li dominate fluids in bentonites from the southwestern baltic basin whereas basement derived fluids dominate in the northeastern baltic basin these trace elements record paleofluid changes during illite crystal growth and can identify pathways of chemically distinct oil and gas related fluids

classification of paraglacial barrier systems coastal new england usa the new england coast harbours a wide variety of barrier forms which we organize into six barrier coastline types the barriers develop in response to the relative importance of several spatially and temporally variable parameters particularly antecedent topography and geology sediment abundance and size exposure to wave and tidal energy and sea level history the six coastline types can also be identified in other paraglacial regions existing barrier coastline classification schemes do not allow consistent subdivision of paraglacial barrier coasts this paper presents a new scheme that is applicable to paraglacial and non paraglacial barrier coasts alike aside from hydrodynamic regime which forms the basis of the barrier classification most commonly used to date it includes a compartmentalization factor sediment starved isolated type 1 barrier coastlines are characterized by short widely spaced barriers small localized updrift and offshore sources have provided sediment for short barriers along clustered headland separated type 2 barrier coastlines various amounts of sediment from larger updrift and offshore glaciofluvial deposits or directly from rivers have formed the longer barriers along wave dominated mainland segmented type 3a mixed energy mainland segmented type 3b wave dominated inlet segmented type 4a and mixed energy inlet segmented type 4b barrier coastlines geomorphic form grain size and stratigraphy can be used to characterize individual barriers along barrier coastlines most paraglacial barriers form as spits but many are transformed subsequently welded barriers are common along type 1 and type 2 coasts baymouth barriers are characteristic of type 3 coasts and barrier islands occur exclusively along type 4 coasts the coarsest grained barriers are located along type 1 and type 2 coasts progradational barrier sections are concentrated along type 3 and type 4 coasts with abundant sediment supply but are also present along type 2 coasts temporary increases in sediment supply common in paraglacial regions result in transitions between retrogradational and progradational barrier behaviour which may be recognized on shore perpendicular stratigraphic cross sections

morphology and seismic stratigraphy of the inner continental shelf off nova scotia canada evidence for a 65 m lowstand between 11 650 and 11 250 c14 yr b p abstract nova scotia s position near the margin of large pleistocene ice sheets makes the scotian shelf region critical for evaluation of glaciation models and sea level change the sea floor of the inner scotian shelf was mapped using multibeam bathymetry a combination of conventional seismic and sonar techniques and sampling multibeam bathymetry provides an areal image of the sea floor combining this unique image with sub bottom seismic imaging the relationships between sea floor topography and the underlying strata were explored the inner continental shelf of nova scotia can be subdivided into five major terrain zones these are the 1 truncation zone 2 morainal zone 3 outcrop zone 4 basin zone and 5 scotian shelf end moraine complex the scotian shelf end moraine complex and basin zone are glacial depositional zones at the seaward edge of the inner shelf landward of these zones is a region of high relief bedrock with ridges and valleys largely devoid of surficial sediments extending from 80 to 120 m water depth outcrop zone this zone is interpreted as a relict bedrock surface preserved under frozen bed glacier conditions to the east of the outcrop zone in similar water depths are unmodified till ridges overlying bedrock morainal zone the truncation zone is a region of the inner shelf from 90 m to the present shoreline characterized by muted acoustic topography and planar erosional surfaces truncating bedrock and surficial sediments the truncation zone is subdivided into the valley subzone the transition subzone the platform subzone and the estuarine subzone the valley subzone is typified by sediment infilled valleys occurring in 75 to 90 m water depths these valleys contain seismic facies with a ponded style of deposition planed off at the sea floor or by erosional unconformities near the sea floor the transition subzone is marked by a relatively steep ramp and terraces the ramp at the type section extends from 75 to 65 m water depth the surface of the ramp can be either an erosional unconformity or a depositional surface formed by clinoform beds the 65 m former shoreline is interpreted as the top of the transition subzone ramp surface at one ramp locality clinoform beds form part of a progradational sequence called the sambro delta a mussel valve fragment mytilus edulis was obtained from a core in the foresets and radiocarbon dated an age of 11 650 110 yr b p was obtained adjusted for isotopic fractionation above 65 m the sea floor forms a low relief gently sloping erosional surface platform subzone estuarine deposits have been found above 50 m the new sea level curve constructed with the dated 65 m shoreline and recently published data is at variance with calculated rsl curves based on geophysical models primarily in the amplitudes and rates of rsl change reasons for the discrepancies may be late melting ice and regional variations in lithospheric strength and thickness

sedimentary framework of the southern maine inner continental shelf influence of glaciation and sea level change abstract although the tidally influenced shoreline of maine is longer than that of virtually any other state almost no research on its geology has been published in order to go some way towards remedying this 1500 km of high resolution seismic reflection data and 800 km of sidescan sonar imagery have been collected on the basis of these data and observations made during ten submersible dives more than 800 bottom samples were collected and evaluated for texture and composition the understanding of the sedimentary framework of the southern maine shelf and the processes that maintain it are summarized and future research directions to evaluate the strategic mineral potential are indicated in the past 14 000 years the maine shelf has experienced a deglaciation and two marine transgressions separated by a regression the deglaciation was accompanied by the first transgression and deposited till interbedded with up to 40 m of glaciomarine sediment the presumpscot formation across the shelf the first transgression culminated about 12 500 yrs b p and its landward limit is marked by large glaciomarine deltas 50 100 km landward of the present day coast sea level fell until about 9500 yrs b p when shorelines were cut at about the 65 m depth and some large lowstand deltas were deposited sea level has risen since then and in the general absence of modern river sediment input marine processes have reworked the older sediment five shelf environments have been defined in terms of their surficial sediment and stratigraphy nearshore ramps are sandy regions extending to about 30 m deep offshore of sandy beaches these may be reworked lowstand deltas and possess the thickest bodies of sand in the region nearshore basins are mud filled troughs seaward of coastal areas lacking significant river input slumping glaciomarine deposits provide most of the holocene mud that floors these basins rocky zones are extensive areas of exposed rock most common in the 30 50 m depth range these are areas of high carbonate productivity and provide shell fragments to adjacent areas the outer basins are muddy regions that begin at the 65 m shoreline and extend beyond the 100 m isobath to the deep gulf of maine finally shelf valleys are former stream courses that connect nearshore ramps and basins to the outer basins these bedrock framed valleys are filled with sand and mud and are apparently still active conduits for the offshore movement of sediment the mineralogy of the shelf sediment is complex and it is not yet clear whether glacial homogenization has obliterated distinctions between river drainage basins and the adjacent shelf studies are continuing into northern maine and analysis of the heavy mineralogy of the shelf sediment utilizing a 2 m humphrey spiral to process large grab samples and cores has begun

nitrogen isotope geochemistry of organic matter and minerals during diagenesis and hydrocarbon migration the magnitude of isotopic variations between organic and inorganic nitrogen was examined in samples from three stacked hydrocarbon reservoirs in the fordoche field louisiana gulf coast basin usa measurements were made of 15n in kerogen bitumen oil formation water and fixed nh4 extracted from mudstones nonproductive sandstones and productive sandstones nitrogen isotope fractionation occurs because 14n is released preferentially to 15n from organic molecules during thermal maturation released 14n goes into solution or may be adsorbed by minerals leaving crude oil enriched in 15n diagenetic clay minerals e g illite commonly form in the temperature range of hydrocarbon generation and nh4 may be fixed in clay interlayers with an isotopic ratio similar to that of the migrating fluids results indicate that the influence of organic matter on mineral 15n depends on the timing of authigenic mineral formation relative to fluid migration the average 15n of kerogen 3 2 0 3 and fixed nh4 from mudstones 3 0 1 4 is similar while bitumen increases from 3 5 to 5 1 with depth in deep reservoir sandstones 100 c the 15n of crude oil averages 5 2 0 4 similar to the 15n of bitumen in the proposed source rocks formation waters are 14n enriched with an average 15n of 2 2 2 6 fixed nh4 15n values lie between that of the oil and water the average 15n of fixed nh4 is 3 0 1 2 in productive sandstones and 0 2 2 4 innonproductive sandstones in the shallower reservoir sandstones 90 c fixed nh4 is apparently not influenced by the presently associated fluids productive and nonproductive sandstones have distinctly low average 15n values 1 2 0 8 yet crude oil 11 1 0 3 and water 3 8 0 1 have been 15n enriched by 6 relative to the deeper reservoirs this suggests that the present fluids migrated into the reservoir after authigenic illite had formed fluids become enriched in 15n during migration and the amount of enrichment may be a function of the amount of interaction with argillaceous sediments

holocene shoreline progradation and coastal evolution at guichen and rivoli bays southern australia prograded barrier systems record shoreline behaviour and palaeoenvironmental information the guichen bay holocene embayment fill succession in south australia has been subject to several prominent

sediment transport and dispersion in a cool temperate estuary and embayment saco river estuary maine usa abstract the saco river flows through a rock bound mid latitude estuary recognized as the primary source of sand to the saco bay barrier beach system to better constrain the conditions under which the saco river contributes sand to saco bay three moorings equipped with current meters and a ctd were deployed inside and outside the saco river jetty system from april to june 2005 these measurements characterized high discharge events and their competence for transporting sand outside the jetty system discharge values from 125 175 m 3 s 1 were identified as the threshold envelope at which the saco river transports sand in its bedload to saco bay put in an 89 year historical context with usgs stream gauge data the saco river is expected to contribute sand annually to the embayment but the amount of transport varies significantly from year to year the moored hydrographic data were augmented by geophysical langrangian drifter data and local wind observations to better ascertain nearshore dispersal patterns once sand exits the jettied river mouth these data suggest that transported sand responds to seasonably variable shelf conditions reacts to artifacts of the jetty system or exits saco bay the results and methods of this study suggest that relatively small rock bound estuaries are potentially significant sources of sand to adjacent beach systems and the inner shelf although the pathway for sand from river to shoreface to beach or inner shelf is complex and mediated by local meteorological and oceanographic conditions

ammonium contents of biotites from precambrian rocks in finland the significance of nh4 as a possible chemical fossil abstract the ammonium contents of biotites in precambrian rocks from finland have been determined to examine the possibility that ammonium in biotites represents a chemical fossil if biologic activity existed in precambrian sedimentary environments biotites formed from the sediments should contain distinctly larger quantities of nh 4 than biotites from igneous rocks biotites from svecokarelidic metasediments which were originally products of sedimentation about 2400 1900 ma ago have high nh 4 contents hundreds of ppm while biotites from svecokarelidic plutonic rocks of 1800 1900 ma old and postsvecokarelian rapakivi granites of 1650 1700 ma old have low nh 4 contents tens of ppm the results may indicate that biologic activity was plentiful during sedimentation of the svecokarelian strata this agrees with evidence for ancient life found in dolomites and greywacke slates of the svecokarelides biotites from presvecokarelidic schists of more than 2600 2800 ma old have only tens of ppm of nh 4 this value is at the same level as those of biotites from the rapakivi granites and the svecokarelidic plutonic rocks considering the rarity of fossils in presvecokarelidic rocks the low nh 4 content of biotite from a presvecokarelidic pelitic schist may indicate less biologic activity during the sedimentation of the original sediments these data emphasize that ammonium in biotites of precambrian metasediments may be a useful chemical fossil for identifying the geologic sites of ancient life

volumetric analysis of a new england barrier system using ground penetrating radar and coring techniques ground penetrating radar gpr profiles calibrated with core data allow accurate assessments of coastal barrier volumes we applied this procedure successfully to the barrier system along saco bay maine usa as part of a sediment budget study that focused on present day sand volumes in various coastal shoreface and inner shelf lithosomes and on sand fluxes that have affected the volume or distribution of sand in these sediment bodies through time on gpr profiles the components of the barrier lithosome are readily differentiated from other facies except where the radar signal is attenuated by brackish or salty groundwater significant differences between dielectric properties of the barrier lithosome and other units commonly result in strong boundary reflectors the mostly sandy barrier sediments allow deep penetration of gpr waves in contrast to finer grained strata and till covered bedrock within the saco bay barrier system 22 pm 3 times 10 6 m 3 of sediment are unevenly distributed

nitrogen in future biosphere studies this article suggests a theme for future nitrogen studies involving the functioning and evolution of the biosphere together with certain aspects of human biology it is hoped that this theme could be developed into a multi authored book at some point in the future although numerous new case studies may be required the biosphere can be considered to be a single interactive system comprised of numerous component parts including the atmosphere rain rivers lakes oceans continental ecosystems marine ecosystems soils and sediments in order to study the internal complexity of each of the components and the relationships that exist between them one can choose a common theme the author believes that nitrogen is a good prospect because of its ubiquitous nature and complex chemistry the burial of sedimentary volatiles in the continental crust has contributed to the long term chemical evolution of the exterior environments of the earth the most marked effects notably the accumulation of atmospheric oxygen have been due to the burial of reduced carbon an understanding of the passage of sedimentary volatiles through the crust will provide important constraints on the evolution of the biosphere and may lead to a more meaningful comparative planetology carbon is difficult to trace through crustal processes because its high temperature form graphite is incompatible with the crystal structures of silicate minerals however the high temperature form of sedimentary nitrogen ammonium readily enters into potassic minerals and it can be easily traced through crustal processes herein the fate of sedimentary nitrogen is traced from wet sediments through metamorphic rocks into granites and other crustal melts without the trapping of nitrogen in the crust and the liberation of oxygen that is a consequence of biological nitrogen fixation the n2 o2 of the atmosphere may have been about 82 9 to 16 3 and the total atmospheric pressure about 1 2 atm most of the changes in the oxygen content is due to dilution by nitrogen with only about 5 of the present atmospheric oxygen being a consequence of nitrogen fixation the ancient continental surfaces would have been volcanic deserts containing little 1 ppm or no nitrogen today nitrogen rich soils support continental ecosystems one can use nitrogen as a window to speculate on the colonisation of the continents by land plants herein nitrogen fixation by legumes is considered in detail and by drawing analogies with the present day the author speculates on the colonisation of the continents by land plants having speculated on the co evolution of the atmosphere soils and continental ecosystems one can place a human being in the centre of a tropical forest and begin to examine how they relate to the modern biosphere the chosen example is the metabolism of plant protein and the roles of glutamate dehydrogenase gdh vitamin b2 and flavin mononucleotide fmn the realisation of this theme would imply numerous new case studies notably those concerning the continental crust where nitrogen studies were linked to mineralogy petrology and other geochemical tracers including sr o al and k and where the short range order of 15n were taken into consideration

the significance of fixed ammonium in palaeozoic sediments for the generation of nitrogen rich natural gases in the north german basin in contrast to predominantly hydrocarbon rich natural gases in the western part of the central european basin ceb accumulations of natural gases from the eastern part of the north german basin ngb are nitrogen rich with up to 90 n2 this study is focused on the behaviour of fixed ammonium in clay minerals of organic rich palaeozoic sediments in the eastern part of the ngb as a major source of nitrogen rich natural gases carboniferous shales have been investigated for a better understanding of nitrogen fixing during diagenesis storage during burial and release during devolatilization processes or fluid rock interactions the total nitrogen contents in the studied carboniferous shales of the ngb reach up to 2700 ppm with an inorganic fixed portion in the form of nh4 n of more than 60 the results of this study indicate an increasing proportion of the mineralogically fixed ammonium with increasing thermal maturity and storage up to catagenetic conditions the isotopic composition of fixed nh4 is relatively homogeneous in the majority of the shales and ranges from 1 to 3 5 in contrast samples from the basin centre show a significant decrease in ammonium contents down to 460 ppm coupled with a shift in 15n up to 5 6 suggesting a release of nitrogen on a large scale calculation of nitrogen loss and isotopic fractionation indicate that more than 30 of nitrogen was released as ammonium probably as a consequence of fluid rock interaction with highly saline brines

hyperspectral imaging of drill core from the steen river impact structure canada implications for hydrothermal activity and formation of suevite like breccias

petrology and geochemistry of diagenetically altered tuffaceous rocks from the middle triassic of central spain abstract petrographical and geochemical analysis of altered tuffaceous rocks of the middle triassic from the iberian range in central spain shows that pedogenic processes and subsequent diagenesis have strongly modified the original mineralogy and textures these rocks are related to a magmatic episode that occurred at the buntsandstein muschelkalk unconformity in this region during the evolution of the iberian trough the tuffaceous rocks accumulated in saline ponds in an open and terminal flood plain setting their alteration is typified by neoformation of k feldspar and illite precipitation of chert and carbonate cements and replacements were also important processes resulting in intercalated chert beds and nodules much of the silica appears to be derived from extensive devitrification and weathering of glassy volcanic ash x ray diffraction analysis microscopic observations and edx microanalysis reveal that the chert consists of various types of chalcedony tridymite micro and megaquartz illite k feldspar and small amounts of albite in some of the nodules dolomite ankerite is also common enclosing anhydrite and barite relicts which are partially silicified different levels of ammonium enrichment have been found in each petrofacies type tuffs and tuffaceous rocks contain from 27 to 326 ppm mean 139 of nh4 underlying arkosic sandstones with authigenic k feldspar contain nh4 ranging from 48 ppm to 191 ppm mean 124 the nh4 was probably derived from decay of organic matter in the evaporitic environment of deposition and its incorporation into feldspar and illite as they formed from unstable volcanic glass sanidine plagioclase and vitric volcanic fragments this transformation could have occurred via the intermediate phases of smectite and zeolites the tuffaceous rocks also have a high content of b ranging from 61 ppm to 170 ppm mean 101 however high levels of b are not positively correlated with high levels of nh4 in the samples both b and nh4 can be contained in either k feldspar or illite but it is not possible to know how much is present in each mineral without separating the minerals comparison of spidergrams of the tuffaceous rocks with those in the underlying arkosic sandstones indicates similar patterns with positive anomalies in la sm and y and negative in nb p ti and yb although the tuffaceous rocks are slightly richer in total ree these data suggest that the distribution of ree must also be controlled by weathering and diagenetic reactions and cannot be used for discrimination between volcanic and nonvolcanic sandstones

the measurement of δ15n in crustal rocks by static vacuum mass spectrometry application to the origin of the ammonium in the cornubian batholith southwest england the release of ammoniacal nitrogen from muscovite biotite orthoclase microcline and a whole rock granite by vacuum pyrolysis has been investigated under the heating regimes employed it was found that micas lose most of their nitrogen below the temperature at which the powders begin to sinter ca 1100 c the peak release of n occurring in either the 900 c or 1000 c heating step it is possible that the loss of ammonium is linked to the loss of h2o and perhaps f for the feldspars there was insignificant release of n below the melting point of the minerals about 1150 c suggesting that diffusion of ammonium or ammonia is the principal control for both micas and feldspars there was significant kinetic fractionation of the nitrogen isotopes during stepped heating from these results a technique has been devised for the routine determination of 15n and ammonium concentration in whole rock granites by static vacuum mass spectrometry the ammonium concentrations and 15n values have been determined in whole rock samples from the cornubian batholith southwest england the ammonium concentrations were in the range 8 to 187 ppm and the 15n values were in the range 5 1 to 10 2 most of the granite samples had 15n values between 8 4 and 10 2 and are within the range that have been obtained from amphibolite facies metasediments these granites are also typified by high 87sr86srinit 0 7130 to 0 7166 and high normative corundum 2 31 to 2 55 taken together the data suggest that the ammonium present within these granites is of biological origin and that it was incorporated via the anatexis of metasediments which originally contained organic material the samples were collected over a distance of 120 km and the limited range in 15n suggests either 1 1 the 15n values within the metasedimentary protolith were rather homogeneous or 2 2 the nitrogen isotopes were homogenised during the incorporation of ammonium into the granite magmas two of the granites had lower 15n values of 5 1 and 7 0 these granites also have lower ammonium concentrations 8 and 15 ppm lower 87sr86srinit 0 7094 0 7095 and lower normative corundum 1 44 and 1 63 the preferred explanation is that they were derived from or have had a contribution from a second crustal source containing sedimentary or metasedimentary material with a lower proportion of pelitic to other constituents

recent hydrocarbon alteration sulfate reduction and formation of elemental sulfur and metal sulfides in salt dome cap rock abstract geochemical analysis of hydrocarbons and scanning electron microscopy sem provide insight to recent alteration of crude oil microbial sulfate reduction and mineral deposition in carbonate cap rock at damon mound brazoria county texas u s a previous work showed that intense aerobic biodegradation of hydrocarbons occurs in shallow cap rock where s 0 and metal sulfides are not abundant the present study focuses on some deeper carbonate cap rock characterized by more limited oxygen availability the c 1 c 4 hydrocarbons in deeper cap rock are a biodegraded residue of hydrocarbons derived from crude oil alteration of higher molecular weight crude oil components is best explained by the effects of water washing accompanied by some biodegradation sem of cavities in carbonate cap rock shows microbes in association with globular masses of solid crude oil and sulfate minerals late forming minerals in cavities include s 0 pyrrhotite pyrite sphalerite and aragonite the presence of s 0 and sulfide minerals indicates that microbial sulfate reduction is associated with limited hydrocarbon biodegradation in this deeper cap rock environment similar processes could explain the origin of some s 0 and metal sulfides at damon mound in the geologic past

organic geochemistry of the san vicente zinc lead district eastern pucara basin peru abstract isotopic and chemical studies of organic matter of the san vicente mississippi valley type zn pb district hosted in the dolomitic units of the eastern pucara basin peru provide insight into the source of organic matter and of the organic matter ore relationship a large scatter exists in the 13c and 15n values of the highly mature kerogens these bulk data were combined with 13c covariations of the saturated and aromatic fractions of the rock extracts to indicate a contribution of continental higher plant lipids to the marine algal source of the organic matter disseminated in the host carbonate rocks an enrichment in 15n of the kerogens of mineralized samples compared to barren samples suggests that isotopically heavy nitrogen compounds were introduced to the ore fluid the fluid likely leached these compounds from the underlying clastic rocks and other detrital units of the pucara the extracts from mineralized samples are enriched in 13c compared to the associated kerogens this suggests that the rocks in the mineralized areas were stained by a mixture of extrinsic and indigenous bitumens by the use of novel instrumentation such as a gas chromatograph gc coupled to a stable isotope ratio mass spectrometer irms through a combustion c interface gc c irms stable carbon isotope analyses of individual hydrocarbons were also obtained both the molecular and isotopic signatures of the individual hydrocarbons are related to mineralization the variability in the organic molecular parameters and the 13c values of the individual n alkanes and isoprenoids indicate mixing of indigenous hydrocarbons with extrinsic 13c depleted microbially derived hydrocarbons the extrinsic source hydrocarbons were introduced to the mineralization site by the ore fluid or later fluids using the same porosity network oxidative alteration of the migrating hydrocarbons was involved in the thermochemical reduction of sulfate to h2s and precipitation of pyrobitumen large differences 12 in the carbon isotope compositions of long chain c20 n alkanes can be utilized in distinguishing sources of organics in the barren and mineralized samples

sediment production on sediment starved continental margins the interrelationship between hardbottoms sedimentological and benthic community processes and storm dynamics abstract modern sediment starved continental shelves represent developing condensed sections analogous to those considered key stratigraphic markers in many stratigraphic models condensed sections and their associated hardbottoms on the modern high energy north carolina continental margin provide important benthic habitats that are modified on time scales of days to centuries by interrelated sedimentological biological and physical processes outcropping upper cenozoic strata of varying lithologies form distinct hardbottom morphologies that through differential bioerosion contribute significant volumes of new sediment to the surficial sand regime of the continental shelf 1 vertical and sloped mudstone to muddy sandstone hardbottoms of the miocene pungo river formation are dominated by the endolithic fauna jouanettia quillingi bivalve and upogebia sp shrimp 2 vertical and sloped hardbottoms consisting of harder miocene and pleistocene limestone are dominated by the endolithic bivalves lithophaga bisulcata gastrochaena stimpsoni and g ovata 3 the highly lithified flat hardbottoms of plio pleistocene limestone are dominated by the epifloral macroalgal species dictyopteris hoytii zonaria tournefortii and sargassum filipendula these three groups of bioeroders physically and or chemically degrade their respective lithologies develop relief on hardbottom surfaces produce large scale morphological features on the shelf and recycle ancient sediment into the modern surficial sediment system the rate of sediment production resulting from bioerosion varies from 5 5 kg m2 yr on the vertical and sloped miocene mudstone hardbottoms to 0 4 kg m2 yr on vertical and sloped pleistocene limestone to 0 03 kg m2 yr on the flat highly lithified plio pleistocene limestone hardbottoms depending on lithology and associated bioerosional processes bioeroders excavate exposed hardbottom surfaces and develop relief ranging from millimeters to meters whereas differential rates of bioerosion between different lithologic units results in relief ranging from meters to tens of meters recession rates measured on miocene mudstones at the chapel site range from 2 to 4 cm per year for the outcrop exposure which is 132 m long this would produce a ten meter overhang of the overlying pleistocene limestone in 250 500 years by removing 13 400 metric tons of eroded sediment 25 fine sand that would be contributed to the surficial sediments the overhang would ultimately break off during a storm to produce the next row of the limestone rubble blocks that form a ramp in front of the receding mudstone scarp these rates of sediment production are rapid enough to bury the hardbottoms producing the sediment however surface sediment is generally not accumulating on the shelf it is present only as thin 0 1 m highly variable and ephemeral sand bodies major storms modify the abundance and distribution of surface sediment on hardbottom habitats and routinely export large volumes of these sediments from the shelf system depositing them as fine sand clinoforms off the prograding shelf edge exposed hardbottom habitats free of sand are dominated by highly diverse communities of endolithic fauna and epilithic fauna and flora those habitats with 2 6 cm of sand are generally dominated by scattered epilithic fauna with small growths of epilithic flora irregularly distributed on topographic highs and those habitats with 6 cm of sand are generally dominated by softbottom benthic communities storms modify the distribution of bottom sediments which either exposes or buries additional hardbottom surfaces and controls the expansion or contraction of hardbottom benthic communities thus the intensity frequency and character of individual storms and the seasonal storm pattern determine the amount and location of sand accumulation which controls the benthic community structure in turn the benthic community determines the type rate and volume of hardbottom bioerosion and resulting sediment production

late quaternary relative sea level change in the western gulf of maine evidence for a migrating glacial forebulge new radiocarbon dated cores obtained by vibracorers in the western gulf of maine confirm that a short lived relative sea level lowstand of 55 m occurred at 11 10 5 ka these cores and younger salt marsh data also reveal that rates of transgression varied throughout the holocene probably due to local variations in glacial isostasy the isostatic component is resolved by subtracting published approximations of eustatic sea level from our well determined observations of local relative sea level a large peak in the isostatic curve coincides with the lowstand and is interpreted as a forebulge 20 25 m in amplitude forebulge migration is estimated at 7 11 km 100 yr based on the timing of lowstands across the region

a method to estimate the longshore sediment transport at ebb tidal deltas based on their volumetric growth application to the guadiana spain portugal border

ammonium halos in lithogeochemical exploration for gold at the horse canyon carbonate hosted deposit nevada u s a use and limitations abstract rock samples taken from the oxidized open pit to depths of 55 m of the carbonate hosted horse canyon gold deposit contain no nh4 samples from the unoxidized zone at the bottom of the pit in the protore however contain as much as 1 44 nh4 1 12 n the presence of nh4 was confirmed by mass spectrometry from these results it is concluded that samples from any oxidized environment e g outcrops soils likely will have lost all or most of any nh4 originaly present in minerals such as buddingtonite of nh4 containing clays this limits the use of nh4 halos in lithogeochemical exploration programs the most reliable application of lithogeochemical studies based on nh4 halos will likely be based on samples from drill cores and other situations where the samples have always been in a reducing environment analysis for nh4 by ir spectroscopy the method preferred by most previous workers is subject to several inherent problems the main one being the presence of the co32 ion whose absorbance at about 1430 cm 1 coincides with that used to determine nh4 the removal of co32 and other phases e g organic matter which may cause analytical difficulties by chemical treatment is not recommended because it is not possible to predict the effect of such treatment on any one of several possible minerals which may contain nh4 it is suggested that the most efficient method of analysis of rock samples for nh4 or n which can be assumed to represent nh4 will be to analyze the samples after heating to 550 c at which temperature all organic nh4 and n is removed by oxidation any remaining nh4 n determined on this residue can be assumed to originate in nh4 containing mineral structures

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

mineralization of organogenic ammonium in the monterey formation santa maria and san joaquin basins california usa abstract inorganic fixed ammonium nh4 contents as high as 0 28 wt were measured in organicrich quartz grade siliceous rocks of the miocene monterey formation from the santa maria and san joaquin basins california the greatest amount of fixed nh4 was found in rocks associated with hydrocarbons in the point arguello and lost hills oil fields where the nh 4 nh 4 k molar ratio of bulk samples ranges from 0 17 0 35 the formation of nh4 illite is suggested by the parallel increase in the percent of illite in the mixed layered illite smectite i s and in the nh 4 nh 4 k molar ratio of the clay sized fraction with increasing burial depth mineralization of nh4 appears to be promoted by the coincident timing of the smectite to illite clay mineral transformation and the release of nh4 during catagenesis nh4 feldspar may form at shallow burial depths in rocks from the point arguello field that contain a greater amount of detrital k feldspar and in which the i s contains only 10 20 illite quartzgrade siliceous monterey rocks from coastal outcrops in the lions head area lack significant amounts of hydrocarbons and have nh 4 nh 4 k molar ratios of 0 14 0 21 rocks from the lions head area show a strong positive correlation between diagenetic illite and fixed nh4 contents with nh4 constituting 18 21 mol of the fixed interlayer cations in the i s low grade opal a and opal ct siliceous miocene rocks from coastal outcrops in the pt pedemales area have low fixed nh4 contents 0 01 wt because these rocks contain minor amounts of diagenetic k bearing minerals i s contains 10 illite and they lack significant amounts of generated or migrated hydrocarbons the increase in the organic c n ratio with burial depth most likely reflects the preferential release of n compared to c and suggests that nh4 release is greatest during shallow burial bacterial degradation and deep burial catagenesis oil generation the results of this study support the suggestion of williams et al 1989 that high fixed nh4 contents may provide a long term geologic record of low temperature

shallow water pockmark formation in temperate estuaries a consideration of origins in the western gulf of maine with special focus on belfast bay abstract a systematic mapping program incorporating more than 5000 km of side scan sonar and seismic reflection tracklines in the western gulf of maine has identified more than 70 biogenic natural gas deposits occupying 311 km2 in nearshore muddy embayments many of these embayments also contain pockmark fields with some exhibiting geologically active characteristics including the observance of plumes of escaping fluids and sediment pockmarks hemispherically shaped depressions of various size and depths formed through fluid escape of gas and or pore water are sometimes found within or outside gas fields although many gas fields lack pockmarks altogether although the origin of the natural gas remains unclear if coastal environments at times of lower sea level were similar to the present numerous lake wetland valley fill and estuarine sources of organic rich material may have formed on the inner shelf if these deposits survived transgression and remain buried they are potential gas sources intensive mapping of the belfast bay pockmark field in 1998 produced the first nearly continuous side scan sonar mosaic of a gulf of maine pockmark field with a corresponding 3 dimensional geological model generated from seismic data statistical analysis of pockmark geometry gas deposit loci and subsurface evidence for gas enhanced reflectors suggest that gas migration from deeper lateral sources along permeable subsurface strata may be the mechanism for pockmark formation in areas lacking gas curtain seismic reflections the coarse grained transgressive ravinement unconformity between pleistocene glacial marine mud and holocene mud may act as a conduit for distributing methane to the field s margins

distribution of ammonium in minerals of metamorphic and granitic rocks abstract sixty nine analyses are given for nh4 in minerals of metamorphic and granitic rocks mostly from the ryoke belt japan the distribution of nh4 in coexisting minerals is quite systematic suggesting that nh4 is one of the stable geochemical components in high temperature processes biotite has the highest content of nh4 followed by muscovite k feldspar and plagioclase pure quartz is almost free from nh4 calcic plagioclase contains less nh4 than does sodic plagioclase the partition coefficients d pl bi d kf bi and d kf bi are on the average 0 11 0 38 and 0 43 respectively the fractionation of nh4 in these minerals is quite similar to that of rb but much smaller than that of cs distribution of nh4 as well as those of rb and cs appears to be explained by its ionic radius and the shortest cation o distances in alkali positions of minerals

sea level change and inner shelf stratigraphy off northern ireland new seismic stratigraphic vibracore and ams c 14 dates from two sites off the northern ireland coast yield information on the deglacial to present sea level history and shelf evolution of the region a lowstand of sea level at about 30 m below present sea level recorded by fossils in a lowstand shoreline deposit occurred around 13 4 cal ka b p following a period of rapid isostatic uplift associated with a rsl fall of 6 7 cm yr following the lowstand contrasting styles of sedimentation characterized the two study sites in the sheltered environment of belfast lough the lowstand shoreline was overtopped and buried by transgressive facies of intertidal and shallow sub tidal mud and sandy mud on the high energy portrush coast the inner shelf sedimentary sequence is characterized by a basal conglomerate overlain by well sorted sands with occasional interbedded gravel c 2006 elsevier b v all rights reserved

stratigraphic evolution of the inner continental shelf in response to late quaternary relative sea level change northwestern gulf of maine accumulations of deltaic and littoral sediments on the inner continental shelf of maine gulf of maine preserve a record of postglacial sea level changes and shoreline migrations the depositional response of coastal environments to a cycle of regression lowstand and transgression was examined with seismic reflection profiles vibracores and radiocarbon dates collected from sediments at the mouths of the kennebec and penobscot rivers sequence stratigraphic analysis of these data reveals two distinctly different successions of late quaternary deposits that represent end members in an evolutionary model for this glaciated coast seaward of the kennebec river coarse grained shorelines with foreset beds occur at depths of 20 60 m and outline the lobate margin of the kennebec river paleodelta a complex rock framed accumulation of glaciomarine and deltaic sediments capped by estuarine and marine deposits sand derived from this system today supports large barrier spits and extensive salt marshes in contrast the mouth of the penobscot river is characterized by thick deposits of glaciomarine mud overlain by marine mud of holocene age including gas charged zones that have locally evolved into fields of pockmarks the distinct lack of sand and gravel seaward of the penobscot river and its abundance seaward of the kennebec river probably reflect differences in sediment sources and the physiography of the two watersheds the contrasting stratigraphic framework of these systems demonstrates the importance of understanding local and regional differences in sediment supply sea level change bedrock structure and exposure to waves and tides in order to model river mouth deposition on glaciated coasts evolution of shelf deposits was largely controlled by relative sea level which locally fell from a highstand 60 to 70 m at 14 ka contemporary with deglaciation to a lowstand 55 m at 10 8 ka the sea level lowering was accompanied by fluvial incision of older deposits producing a regressive basal unconformity major rivers deposited abundant sediment over this surface sea level then rose at varying rates extensively reworking formerly emergent parts of the shelf and producing a shoreface ravinement surface in areas exposed to waves a tidal ravinement surface has developed in sheltered embayments where erosion is due mainly to tidal currents incised valleys in both settings preserve transgressive estuarine deposits that contain lagoonal bivalves and salt marsh foraminifera at depths of 15 30 m these deposits accumulated ca 9 2 7 3 ka locally a period of relatively slow sea level rise

the framework of hydrocarbon generation and migration gulf of mexico continental slope abstract the occurrence of large volumes of crude oil and thermogenic gas in plio pleistocene reservoirs and holocene seeps of the gulf of mexico slope argues that the process of hydrocarbon generation and migration continues at the present time calculated thermal maturity models based on deep seismic stratigraphy indicate that cretaceous and possibly early tertiary sediments are presently within the thermal maturity range for generation and expulsion of crude oil the cretaceous and early tertiary sediments are suggested as possible source rocks because younger sediments are thermally immature for crude oil generation and older sediments are thermally overmature for crude oil preservation the calculated thermal maturity profile for the slope indicates that some generation of crude oil could occur as shallow as 6 km and that liquid hydrocarbons could be preserved as deep as 9 km thermogenic gas is stable at even greater depths migration with a strong vertical component must be invoked to explain thermogenic hydrocarbons in shallow reservoirs and seeps of the slope the great depth at which liquid hydrocarbons and dry gas can be preserved in reservoirs of the gulf of mexico salt basin indicates that huge volumes of prospective section remain essentially unexplored

inorganic nitrogen in anthracite from eastern pennsylvania usa abstract up to 20 of the total nitrogen content of anthracite rank coal from eastern pennsylvania occurs in authigenic nh 4 rich illite this enrichment is due to the concurrence of two independent reactions in the coal and surrounding organic rich shale during late stage organic maturation and diagenesis t 200 c 1 the release of n from organic matter by devolatilization reactions and 2 the formation of illite from kaolinite our estimates of inorganically bound n are conservative because minerals in fractures which can be volumetrically important were removed prior to analysis inorganic n estimates using x ray diffraction analysis are similar to those obtained by elemental analysis of combusted material the occurrence of inorganically bound n in organic rich rocks has important implications for geochemical characterizations of high rank coal n content and isotopic composition and laboratory investigations of the kinetics of n loss from organic material during thermal maturation in addition because nh 4 rich illite authigenesis is temporally linked to coalification the radiometric age of this mineral can theoretically be used to determine the absolute age of coalification in this region for detailed characterization of high rank coal we recommend that mineral matter be isolated by low temperature ashing and analyzed by x ray diffraction or c h n elemental analysis for inorganically bound n

near infrared detection of ammonium minerals diagnostic near infrared spectral features have been identified for minerals with ammonium nh4 bound in the crystal structure spectral bands near 2 12 2 02 and 1 56 m are characteristic of synthetic and natural nh4 bearing minerals laboratory spectra of nh4 bearing minerals are distinct from spectra of oh bearing minerals and have diagnostic shifts in band position among different mineral types nh4 bearing minerals were detected at several mineralized hot spring deposits in the western u s by means of hand held and airborne instruments near infrared detection of nh4 bearing minerals may provide useful information for prospecting for certain ore deposits and may provide a better understanding of the nitrogen cycle within geologic environments

the distribution of ammonium in granites from south west england the ammonium contents of granites pegmatites and hydrothermally altered rocks from sw england have been measured ammonium levels in the granites are generally high compared with those from other regions averaging 36ppm and they differ markedly between intrusions the pegmatites show higher ammonium contents than any other igneous rocks which have yet been investigated ammonium contents are strongly enriched in the hydrothermally altered rocks including greisens and kaolinized granites there is a good correlation between the average ammonium content of the intrusions in sw england and their initial 87 sr 86 sr ratios and peraluminosity this relationship supports the hypothesis that the ammonium in the granites is derived from a sedimentary source either in the magmatic source region or via contamination of the magma

holocene coastal evolution of the transition from transgressive to regressive barrier in southern brazil abstract in this study the evolution of a holocene coastal barrier was determined based on a basal transgressive unit followed by a regressive unit standard penetrating test vibrocore and ground penetrating radar profiles were used to acquire stratigraphic data sedimentological paleontological and geochronological analyses were performed to describe and interpret the sedimentary facies the base of the holocene record indicates the existence of pre transgression continental and coastal environments basal peat which resulted from the initial flooding of the antecedent topography pleistocene substrate due to rising sea levels during this period the continental environments were flooded by lagoon environments that occupied the landward displacement of the transgressive barrier which had channels that connected the lagoon and the ocean at this time the coastal barrier had a transgressive configuration indicated by its morphology and characterized by washover fans as the backbarrier accommodation space decreased due to the displacement of the barrier transgressive maximum the transition of the transgressive regressive record began at approximately 7 200 years bp restricting the overwash events and the dynamics of the inlets however before the highest level eustatic maximum of the postglacial marine transgression pmt was reached this transgressive barrier stopped its migration toward the continent causing an inversion of the depositional record which became a normal regression later at the end of the pmt sea levels began to fall causing a forced regression that persists to the present day

calculating shoreline erosion potential using nearshore stratigraphy and sediment volume outer banks north carolina 1 despite the acknowledged influence of coastal geological framework on the behavior of beaches and barrier islands and a wealth of geological and bathymetric observations from the inner shelf quantitatively connecting those observations to shoreline behavior has been difficult nearshore geologic and morphologic variability described by recent research is not well represented by conventional geologic parameters such as mean grain size and shoreface slope used in most shoreline change models we propose that total nearshore sediment volume as calculated to a continuous seismic reflection surface provides a flexible and robust metric for use in the prediction of shoreline change this method of determining the volume of sediment in the nearshore accounts for three dimensional sandbar morphologies and heterogeneous seafloor sediments the decadal scale shoreline change rate for northeastern north carolina is significantly correlated to the volume of sediment in the nearshore when a geologically defined base is used in volume determinations suggesting that the shallow stratigraphic framework of transgressive coasts is an important influence on decadal shoreline behavior nearshore sediment volume was overestimated when an arbitrary depth constant baseline was used and was not correlated to decadal shoreline change this implies that a volume metric which accounts for both framework geology and variable seafloor morphology better represents the geologic character of the shoreface and may help to improve existing models of shoreline change an empirical model of regional shoreline erosion potential demonstrates the importance of incorporating nearshore sediment volume shallow framework geology and surface morphology when predicting seasonal to decadal shoreline evolution

nitrogen geochemistry as a tracer of fluid flow in a hydrothermal vent complex in the karoo basin south africa abstract we have investigated the n geochemistry of minerals and rocks from contact metamorphic aureoles and hydrothermal vent complexes hvc in the karoo basin in south africa the hvc formed during phreatic eruptions associated with rapid devolatilization and pressure build up in contact aureoles around early jurassic sill intrusions by combining outcrop data from a hvc and core data from contact aureoles we investigate the relationship between light element release during metamorphism and vertical fluid migration sandstone and breccia from the hvc contain early diagenetic ammonium nh 4 bearing feldspar buddingtonite and illite ammonium occupies up to 95 of the a site in feldspar corresponding to concentrations up to 5 2 wt n bulk rock n isotope data for rocks from inside and outside the hydrothermal vent complex fall into two distinct groups background samples have 15nair between 1 5 and 4 9 whereas minerals from the vent complex have 15n in the range 7 5 to 10 6 the n geochemistry of contact metamorphic shale from the lower stratigraphic units of the karoo basin shows that the vitrinite reflectance and 15n values are positively correlated shale with reflectivity values 4 ro are enriched in 15n with 15n values between 6 and 14 implying the release of isotopically light n into metamorphic fluids probably as n2 we suggest that the relatively high 15n values of the early diagenetic buddingtonite in the hvc reflect exchange of buddingtonite with n bearing fluids ascending from greater depth after their release during contact metamorphism and dehydration we present a qualitative model whereby hydrothermal vent complexes represent fluid flow structures after their formation focusing n bearing metamorphic fluids sourced in deeper levels of the basin the release of organic n from sediments at depth in volcanic basins could play a role in the geochemical cycle of n becoming particularly important during periods of intense volcanic activity

anthropogenic effects on shoreface and shoreline changes input from a multi method analysis agadir bay morocco abstract in many situations the links between shoreline fluctuations and larger scale coastal change embracing the shoreface are not always well understood in particular meso scale years to decades sand exchanges between the shoreface and the shoreline considered as important on many wave dominated coasts are rather poorly understood and difficult to identify coastal systems where sediment transport is perturbed by engineering interventions on the shoreline and shoreface commonly provide fine examples liable to throw light on these links this is especially so where shoreface bathymetric datasets which are generally lacking are collected over time enabling more or less fine resolution of the meso scale coastal sediment budget agadir bay and the city of agadir together form one of the two most important economic development poles on the atlantic coast of morocco using a combined methodological approach based on wave current modelling bathymetric chart differencing determination of shoreline fluctuations and beach topographic surveying we highlight the close links between variations in the bed of the inner shoreface and the bay shoreline involving both cross shore and longshore sand transport pathways sediment budget variations and new sediment cell patterns we show that the significant changes that have affected the bay shoreline and shoreface since 1978 clearly reflect anthropogenic impacts notably blocking of alongshore sand transport by agadir harbour completed in 1988 and the foundations of which lie well beyond the depth of wave closure construction of the harbour has led to the creation of a rapidly accreting beach against an original portion of rocky shoreline updrift and to a net sand loss exceeding 145 000 m 3 year between 1978 and 2012 over 8 5 km 2 of the bay shoreface downdrift shoreline retreat has been further exacerbated by sand extraction from aeolian dunes and by flattening of these dunes to make space for tourist infrastructure digital elevation models of part of the bay beach between 2012 and 2014 confirm this on going sand loss these changes have involved the establishment of two divergent longshore bay sediment cells instead of the original single unidirectional cell a prospective view of these changes suggests that perturbation of longshore drift and the on going bay sediment budget deficit will eventual directly pose threats to the harbour access and to coastal tourism on which the economic growth of agadir has been built

natural bathymetric change as a control on century scale shoreline behavior identification of the relevant forcing factors behind coastal change is a major societal demand in the face of rising sea level changes in the patterns of coastal erosion and accretion at a century scale in dundrum bay northern ireland are here attributed to natural changes in the nearshore bathymetry of sufficient magnitude to alter incident wave energy dispersal simulations of wave propagation across the nearshore reveal a marked change in the nearshore patterns of energy dispersal and related sediment transport pathways between 1861 and 1968 the 1861 bathymetry is associated with a simulated longshore drift divide in the middle of the bay and with sediment dispersal to the southeast and northeast whereas the 1968 bathymetry is associated with a consistent northeastward drift throughout the bay these changes are consistent with recorded shoreline changes sediment accumulation and foredune accretion in the northeast and northeastward spit elongation across a tidal inlet this study reveals a case in which purely natural changes in the seafloor at a century scale can be related to long term shoreline changes similar changes during relative sea level rise during the holocene were potentially capable of significant modification of shoreline morphology and dynamics near shore extraction of sand for beach nourishment purposes may have consequences of similar magnitude for adjacent beaches

large scale reversals in shoreline trends along the u s mid atlantic coast robust regression modeling of shoreline data spanning 1930 to 1990 and covering 1055 km of the atlantic coast shows that nearly two thirds of the u s east coast shorelines have undergone a significant change in the long term rates of change between 1950 and 1980 the model results show that 62 of the shorelines have become more erosional or less accretional the average timing of these reversals 1967 corresponds to a peak in the record of extratropical northeast storm frequency and magnitude these results raise questions regarding the applicability of linear methods for interpreting historical long term trends and for predicting future shoreline positions

precambrian ammonium biogeochemistry a study of the moine metasediments scotland abstract the content and isotopic composition of ammoniacal nitrogen have been determined in a suite of amphibolite facies metasediments of precambrian age whole rock samples and mica separates from the moine succession proterozoic of scotland were analysed by a combination of capacitance manometry and static vacuum mass spectrometry prior to the analyses the presence of the ammonium ion was confirmed by obtaining infrared ir absorption spectra from the micas principally biotites whole rock ammonium contents are high for amphibolite facies metasediments 140 422 ppm the ammonium ion was not detected in the ir absorption spectra of biotites from one schist however this sample contains neither garnet nor white mica for most of the samples the 15n values are very positive between 12 4 and 16 6 with one sample having a lower value of 8 4 the major variations between samples can be interpreted in terms of original sedimentary features for the ammonium bearing samples muscovites have concentrations between 365 and 633 ppm biotites between 845 and 1739 ppm for individual samples nh4 mu nh4 bi varies between 0 31 and 0 43 a much narrower range than has been reported previously there are no significant or consistent differences in 15n between co existing biotite and white mica nor between the 15n values of the mineral separates and their respective whole rock values the latter suggests minimal selective partitioning of isotopes between micas and plagioclase feldspar the only other potential host for ammonium in the rocks assuming that the ammonium has been derived from organic matter originally present at the time of deposition and by comparison with previous studies it can be inferred that the original 15n value of the moine sediments was somewhere between 5 and 10 similar to recent sediments this suggests that the nitrogen cycle in the proterozoic shelf sea from which the moine sediments were deposited was broadly similar to the present day overall the study underlines how under developed the n system is compared to other stable isotope systems notably c and s and we use the opportunity to highlight some areas that could be developed in the future however one aspect is clear future ammonium studies of metamorphic rocks will need to be performed at high resolution visible scale of heterogeneity with strong mineralogical petrological and field controls

integrated high precision analyses of holocene relative sea level changes lessons from the coast of maine a suite of salt marsh peat samples from four sites along the coast of maine wells phippsburg gouldsboro and machiasport has been analyzed using high precision techniques to determine local relative sea level trends and to evaluate proposed along coast warping a spatially variable set of relative sea level records in maine would have important implications for geophysical models that predict the response of the lithosphere during deglaciation and postglacial isostatic relaxation the amplification of m sub 2 tidal range in the gulf of maine and the bay of fundy during the holocene is modeled and applied to the mean high water data yielding best estimate envelopes of mean tide level change for each location average long term thousands of years mean tide level rise did not exceed approx 2 mm yr at any time during the late holocene at wells phippsburg and machiasport between 4 5 and 3 ka calibrated cal the apparent rate of rise at gouldsboro was higher than at any other site studied this along coast variation in the rate of mean tide level rise may reflect time of deglaciation neotectonics or differential isostatic adjustments a slight acceleration of mean tide level rise has occurred during the past millennium in gouldsboro and machiasport if 12 m downwarping inmore easternmost maine occurred as suggested in other publications it must have happened prior to 5 7 ka cal 84 refs 13 figs 8 tabs less

ammonium loss and nitrogen isotopic fractionation in biotite as a function of metamorphic grade in metapelites from western maine usa abstract ammonium fixed in micas of metamorphic rocks is a sensitive indicator both of organic inorganic interactions during diagenesis as well as of the devolatilization history and fluid rock interaction during metamorphism in this study a collection of geochemically well characterized biotite separates from a series of graphite bearing paleozoic greenschist to upper amphibolite facies metapelites western maine usa were analyzed for ammonium nitrogen nh 4 n contents and isotopic composition 15nnh4 using the hf digestion distillation technique followed by the ea irms technique biotite separates sampled from 9 individual metamorphic zones contain 3000 to 100 ppm nh 4 n with a wide range in 15n from 1 6 to 9 1 average nh 4 n contents in biotite show a distinct decrease from about 2750 ppm for the lowest metamorphic grade 500 c down to 218 ppm for the highest metamorphic grade 685 c decreasing abundances in nh 4 are inversely correlated in a linear fashion with increasing k in biotite as a function of metamorphic grade and are interpreted as a devolatilization effect despite expected increasing 15nnh4 values in biotite with nitrogen loss a significant decrease from the garnet zones to the staurolite zones was found followed by an increase to the sillimanite zones this pattern for 15nnh4 values in biotite inversely correlates with mg mg fe ratios in biotite and is discussed in the framework of isotopic fractionation due to different exchange processes between nh 4 nh 3 or nh 4 n 2 reflecting devolatilization history and redox conditions during metamorphism

sand budgets at geological historical and contemporary time scales for a developed beach system saco bay maine usa abstract saco bay hosts one of the largest sand beach and salt marsh systems in northern new england usa unsuccessful remedies for chronic beach erosion have generated controversy and differing theories regarding 1 the source s of sand to the bay 2 the sand transport paths and 3 the role of jetties in beach erosion we constructed a sand budget for the bay by evaluating the past and present sand transport pathways fluxes and reservoir volumes side scan sonar and bottom samples were employed to map the offshore areas seismic reflection profiles and vibracores were used to measure the volume of offshore sand on land ground penetrating radar and cores constrained the sand volume and stratigraphy time series maps and aerial photographs provided data on historical sand movement and current meters and recent harbor dredge data allowed contemporary sand movement to be estimated in the saco river estuary at the present time 56 million m3 of sand reside in the shoreface and 22 million m3 of sand are beneath the barrier beach and dunes the saco river has been the major source of sand to the bay providing an estimated 10 000 16 000 m3 of sand per year the net direction of sand movement is to the north where river derived sand has historically fed growth of barrier spits construction of the north jetty at the saco river mouth profoundly altered the prehistoric patterns of sand movement and storage in the bay causing the northward migration of almost 6 million m3 of sand between 1867 and 1955 contemporary dredging of tidal inlets involves sand volumes approximately equal to the influx of sand delivered by the saco river

illite smectite structural changes during metamorphism in black cambrian alum shales from the baltic area illite smectite i s from cambrian black shale of both early diagenetic and anchimetamorphic grade was investigated to determine the mechanism of the clay transformation the layer sequences the distribution of thicknesses of coherent scattering domains csds and the three dimensional ordering were determined by x ray diffraction xrd the proportions of cis vacant cv and transvacant tv 2 1 layers were determined by thermal analysis and the proportion and distribution of interlayer ammonium by xrd and by infared spectroscopy ir the structural formulae were determined from total chemical analysis and mossbauer and 27al nmr spectroscopies and the particle shape and size investigated by atomic force microscopy afm in the early diagenetic samples the i s is composed of two phases one of which contains 0 05 and the other 0 25 smectite s interlayers the first phase does not change during metamorphism in the second phase 0 20 s are converted to tobelite t layers through fixation of formula 1 but the i layers are not changed simultaneously the proportion of cv layers changes from 0 18 to 0 02 and the tetrahedral substitution of al for si is parallel to the increase in t layers all i interlayers contain 0 75k per o10 oh 2 further more the metamorphism results in increasing mean thickness of csds from 5 1 6 8 nm for the low diagenetic samples to 6 7 8 4 nm for the anchimetamorphic samples we conclude that the tobelitization was accompanied by transformation of cv to tv 2 1 layers adjacent to the smectite interlayers and formation of tv layers adjacent to the newformed tobelite interlayers in otherwise intact crystallites this mechanism only partly resembles the tobelitization previously observed in the upper jurassic north sea oil source rocks i s in these rocks contained tv 2 1 layers and t interlayers formed through solid state al for si substitution in the tetrahedral sheet and by ammonium fixation in the corresponding interlayers these different mechanisms are probably because the north sea i s originated from weathered illite like the cambrian high illitic phase whereas the cambrian low illitic phase undergoing the transformation originated from cv smectite of volcanic origin the results indicate that the illitization in oil source rocks is linked to oil generation and that it deviates from the illitization in other rocks because of the supply of ammonium formed during oil generation and the fixation of this ammonium in the former smectite interlayers 1 embed tex math 1 gif

fixed ammonium in clays associated with crude oils abstract the association of ammonium nh 4 silicates with organic rich sedimentary environments has stimulated interest in the chemical cycle of n and its possible application as an indicator of in situ organic maturation reactions or crude oil migration fixed nh 4 in clay minerals was determined from three hydrocarbon occurrences of similar depositional environment but different ages depth and thermal maturity to determine whether anomalously high nh 4 substitution occurs near mature hydrocarbons results show higher fixed nh 4 concentrations in marginally mature mudstones than in immature sediments the highest fixed nh 4 concentrations were found in clays from sandstone reservoirs containing migrated crude oil fixed nh 4 in clays from holocene oil seep sediments in the gulf of mexico continental slope offshore louisiana averages 0 08 wt and increases with depth in shallow cores 420 cm reflecting an early diagenetic trend that is apparently not influenced by migrating crude oil programmed pyrolysis shows that the sediments are thermally immature av t max 419 c high hydrogen index values av 359mg g are the result of biodegraded crude oil and a high oxygen index av 182mg g reflects the presence of authigenic carbonate fixed nh 4 averages 0 16 wt in wilcox group eocene mudstones enclosing two sandstone reservoirs at fordoche field onshore louisiana in comparison to these mudstones anomalously high nh 4 fixation appears to occur in reservoir clay minerals pyrolysis shows that the sediments are marginally mature for crude oil generation av t max 432 c average hydrogen index 187 mg g and oxygen index values 75 mg g are consistent with oil prone type ii and type iii kerogen increased pyrolysis production index values and solvent extraction shows the presence of migrated crude oil this suggests that a reaction which releases nh 3 during crude oil generation or migration is recorded bynh 4 substitution in clays fixed nh 4 and total organic carbon toc at fordoche field show no statistically significant correlation suggesting that nh 4 substitution in clay minerals is not simply related to the amount of organic matter in the section but is also influenced by the presence of crude oil once nh 4 has been fixed in clays it is a more stable hydrocarbon proximity indicator than pore fluid tracers because it is less influenced by later chemical or geological changes

investigation of the pyrolytic liberation of molecular nitrogen from palaeozoic sedimentary rocks open system non isothermal pyrolysis up to 1 200 c in combination with elemental analysis was used to study the thermal liberation of molecular nitrogen n2 from sedimentary rocks and kerogen concentrates of palaeozoic age from the central european basin system and an eocene shale liaohe basin china with a high content 36 of ammonium feldspar buddingtonite the n corg atomic ratios of the kerogen concentrates ranged from 0 005 to 0 014 which represents the range commonly observed for coals bulk n corg ratios of the palaeozoic shales extended from 0 035 to 0 108 indicating the presence of significant amounts of inorganic nitrogen namurian a and a b cna cna b samples typically exhibited the earliest onset of n2 generation with intense characteristic peaks around 600 c n2 liberation from the buddingtonite rich sample occurred at higher temperatures with a broad peak around 700 c pyrograms of the kerogen concentrates showed no or strongly reduced n2 generation in the 500 700 c range on line isotope specific analysis of the pyrolytically liberated n2 on one sample revealed a variability of 10 in the 15n values and a steady increase in 15n with temperature during the main phase of n2 generation

origin of crude oil in the wilcox trend of louisiana and mississippi evidence of long range migration abstract geochemical characterization of crude oils from wilcox reservoirs in central louisiana and southwest mississippi suggests that they represent a single crude oil family that is distinct when compared to crude oils in deeper tuscaloosa and smackover reservoirs this observation is consistent with geologic constraints that suggest an origin of crude oil from within the wilcox group itself although shales of the shallow wilcox group in central louisiana and southwest mississippi contain gas prone kerogen and are thermally immature a more oil prone source facies is present in marine shales of the deep wilcox group in southcentral louisiana thermal maturity measurements based on pyrolysis suggest a broad area of effective wilcox source rock in southcentral louisiana migration distances from source to reservoir rocks of the downdip wilcox trend of southcentral louisiana appear to be relatively short however long range updip migration sometimes greater than 100 km from deeply buried wilcox source facies provides the best explanation for emplacement of crude oil in the shallow wilcox trend of central louisiana and southwest mississippi

the effects of storms and storm generated currents on sand beaches in southern maine usa storms are one of the most important controls on the cycle of erosion and accretion on beaches current meters placed in shoreface locations of saco bay and wells embayment me recorded bottom currents during the winter months of 2000 and 2001 while teams of volunteers profiled the topography of nearby beaches coupling offshore meteorological and beach profile data made it possible to determine the response of nine beaches in southern maine to various oceanographic and meteorological conditions the beaches selected for profiling ranged from pristine to completely developed and permitted further examination of the role of seawalls on the response of beaches to storms current meters documented three unique types of storms frontal passages southwest storms and northeast storms in general the current meter results indicate that frontal passages and southwest storms were responsible for bringing sediment towards the shore while northeast storms resulted in a net movement of sediment away from the beach during the 1999 2000 winter there were a greater percentage of frontal passages and southwest storms while during the 2000 2001 winter there were more northeast storms the sediment that was transported landward during the 1999 2000 winter was reworked into the berm along moderately and highly developed beaches during the next summer a northeast storm on march 5 6 2001 resulted in currents in excess of 1 m s 1 and wave heights that reached six meters the storm persisted over 10 high tides and caused coastal flooding and property damage topographic profiles made before and after the storm demonstrate that developed beaches experienced a loss of sediment volume during the storm while sediment was redistributed along the profile on moderately developed and undeveloped beaches two months after the storm the profiles along the developed beaches had not reached their pre storm elevation in comparison the moderately developed and undeveloped beaches reached and exceeded their pre storm elevation and began to show berm buildup characteristic of the summer months

diagenesis of ammonium during hydrocarbon maturation and migration wilcox group louisiana u s a abstract as organic matter matures n is released in the reduced form as nh4 and substitutes for k in clay minerals as oil forms an abundance of n is generated coincident with the formation of authigenic illite this study suggests that nh4 released from organic matter during maturation migrates through sandstones together with the pore fluids and volatile phases generated from the migrating crude oil this causes anomalously high nh4 substitution in authigenic illites fixed nh4 concentrations in illite are a product of both hydrocarbon maturation and migration concentrations of fixed nh4 from organic rich mudstones in two wilcox group oil fields show a general increase with depth coincident with increasing organic maturation reservoir sandstones containing crude oils have fixed nh4 concentrations as much as two times those of the mudstones when values are normalized to the quantity of clay minerals fixed nh4 concentrations in the gaseous portion of the reservoir are three times as high two out of five sandstones from a dry hole adjacent to a producing oil field contain anomalously high 2 above mean concentrations of fixed nh4 with respect to total organic centent this together with a high production index and hydrogen index in those units suggests that migrating hydrocarbons may have influenced the fixed nh4 concentrations

high primary productivity and nitrogen cycling after the paleoproterozoic phosphogenic event in the aravalli supergroup india the causes of atmospheric oxygenation in the paleoproterozoic are multifaceted yet poorly understood an increase in the level of primary productivity however may have been an important factor in producing large amounts of oxygen in the atmosphere a likely environmental consequence of atmospheric oxygenation is an increased abundance of seawater nitrate which would have resulted in a fundamental change from the archean nitrogen cycle in this study we investigate these questions using the carbon and nitrogen isotope compositions of carbonaceous shales from the paleoproterozoic aravalli supergroup india the shales occur stratigraphically above one of the oldest phosphogenic events that took place around 2 0 ga shales in the phosphate domain of the jhamarkotra formation from the lower aravalli group have distinct characteristics from coeval shales in the non phosphate domain carbonaceous shales of the phosphate domain contain relatively high v and u th typical of oxygen deficient environments these shales also have a high organic content of up to 14 wt generally homogeneous 13 corg values around 29 c nwr up to 360 and a large range of 15