Decrease In Sedimentation Rate Research Articles

Sedimentation in created freshwater riverine wetlands: 15 years of succession and contrast of methods

This study summarizes five separate sedimentation studies spanning 15 years (years 3–17 following wetland creation in 1994) of two 1ha experimental flow-through wetlands. Included are methods and analyses of the most recent (2009–2010) comparative study that attempted to quantify both erosion and bioturbation processes. Depending on techniques used, two distinct types of sedimentation rates were estimated—gross and net sedimentation. Gross sedimentation in 2004–2005 (years 11 and 12) using sediment trap bottles was 45kgm−2 for 4 months during and after spring flood pulsing conditions in 2004 and 39kgm−2 for the same 4 months during and after steady flow conditions in 2005. Annual sediment accretion using feldspar and other horizon markers was 31.7±4.4kgm−2yr−1 (4.2±0.6cmyr−1) in 1996 (year 3 after wetland creation) and 34.4±4.5kgm−2yr−1 (5.5±0.8cmyr−1) in 2009 (year 16 after wetland creation). Net sedimentation using soil cores to estimate accumulation of sediments over antecedent soil horizon layers was 4.7±0.3kgm−2yr−1 (0.9±0.07cmyr−1) in 2004 (year 11) and 6.0±0.4kgm−2yr−1 (0.9±0.06cmyr−1) in 2009 (year 16). Net sedimentation, using estimates of sedimentation and erosion with the sediment erosion table (SET) method in 2009–2010 (years 16–17) was 3.9±6.1–9.0kgm−2yr−1 (1.3±0.8–1.4cmyr−1). Bioturbation by macrofauna significantly decreased sedimentation rates during the 2009 (year 16) study. Spatial patterns, consistent among horizon marker and net sedimentation studies, showed that deep, open-water areas had higher rates of sedimentation than shallow areas with emergent vegetation, and that sedimentation rates were higher when closer to the inflow than at the outflow of these flow-through wetlands. Net sedimentation of these created riverine wetlands ranged from 1.2cm/yr to 1.4cm/yr, suggesting that these wetlands will accumulate about 30cm of sediments in a little more than two decades.

Taphonomy and ichnology: tools for interpreting a maximum flooding interval in the Berriasian of Tlemcen Domain (Western Tellian Atlas, Algeria)

During the Middle-Late Berriasian, a long-term climatic and eustatic change occurred, documented in the literature. However, data from the northern Gondwana paleomargin are scarce. This research analyzes the Lamoriciere Clay Formation at the Ouled Mimoun section, focusing on fossil assemblages and using taphonomic and ichnological aspects to interpret a transgressive–regressive cycle. The section starts with mudstones and oolitic grainstones representing shallow-water environments in the top part of the Ouled Mimoun Marly Limestones Formation (Upper Tithonian p.p. to lowermost Berriasian). The base of the Lamoriciere Clay Formation is characterized by a high clay content but was still deposited in shallow water, as indicated by the record of the ostracod Asciocythere, dasyclad green algae, and the sponge Cladocoropsis. The subsequent record of fossil-rich calcareous beds at the beginning of the Upper Berriasian (Boissieri Zone) with ammonoids and calpionellids is congruent with an increase in water depth. The sedimentation rate in the Late Berriasian was reduced, as indicated by the increment of fossil remains and trace fossils. Ammonoid moulds show taphonomic features pointing to long-lasting exposure on the sea floor prior to burial with corrasion and encrustation by sessile organisms such as serpulids, thecideidinids, and bryozoans. During calm periods, crustaceans and worms intensely burrowed the sea floor. The record of Thalassinoides and Rhizocorallium indicates bottom conditions ranging from soft to firm. The low sedimentation rate and sediment by-passing probably favored early lithification. The increasing carbonate content as well as decreasing sedimentation rate is compatible with the maximum distance to emerged areas during maximum flooding. High-energy events, probably related to storms, favored the exhumation and extreme corrasion of ammonite moulds and trace fossils. In the resulting substrate, limonitic films developed and encrusting organisms proliferated (serpulids, bryozoans, and thecideidinids), colonizing both the bottom surface (hardground) and exhumed moulds of ammonoids and Thalassinoides. The uppermost 0.7 m of the section represents the return to shallow conditions, with increasing sedimentation rate and terrigenous detrital content, along with the disappearance of hemipelagic forms (ammonoids); hence it is interpreted as having developed at the beginning of a regressive context.

A Holocene palynological record from the northeastern Laptev Sea and its implications for palaeoenvironmental research

A 844 cm long core PS51/118-3 (77°53.54′ N; 132°11.92′ E) recovered from the upper slope (122 m water depth) of the Laptev Sea (Russian Arctic) has been studied for pollen, spores and aquatic palynomorphs, including freshwater green algae and cysts of marine dinoflagellates. The age model was established on the basis of radiocarbon dates obtained on marine bivalve mollusk shells. The available dates suggest that the analyzed sediment was accumulated during the last ca. 10.8 cal. ka and reveal two intervals with markedly different sedimentation rates, reflecting the sedimentary regime changes of the Laptev Sea shelf during postglacial sea-level rise. Very high sedimentation rates (ca. 4.7 mm per year) in the lower part of the core (120–866 cm) between ca. 9.2 and 10.8 cal. ka BP reflect lower-than-present sea levels, high erosion activity and much closer position of the palaeo-shoreline with the Lena and Yana river mouths to the core site. Dramatic decrease in sedimentation rates (ca. 0.1 mm per year) during the middle and late Holocene interval reflects high sea-level and decreased amount of suspended material transported to the outer shelf by rivers. Despite the location of the core site at the continental slope and far away from the modern coastline pollen, spores and fresh-water algae constitute a major part of the microfossils throughout the whole record, indicating great impact of the Lena and Yana rivers and possibly prevalent wind regime on the pollen and non-pollen-palynomorph (NPP) assemblages. Although a number of short-term (decadal to multi-century) oscillations deviate from the mean Holocene values, pollen taxa percentages and pollen-based numerical biome reconstructions do not show very clear trends. The latter is likely a result of the mixed environmental signal and complex pollen contribution of several large environmental regions and vegetation zones of Siberia drained by the Lena and Yana rivers. The greater pollen contribution of the forested regions to the PS51/118-3 record reflects higher pollen production of the boreal trees and shrubs over the low-productive Arctic vegetation. The intervals of the relative increase in the tundra biome scores in the PS51/118-3 record reflect decreased arboreal pollen production or/and increased landscape openness within the pollen source area and can be correlated (within the uncertainty of the age models) with the cold episodes observed in the Greenland ice and North Atlantic sediment records.

Carbonyl iron suspension with halloysite additive and its magnetorheology

The magnetorheological (MR) characteristics of a micron-sized soft magnetic carbonyl iron-based MR fluid were examined using halloysite nanoclay mineral, as an additive. The flow curves measured from a rotational rheometer revealed non-Newtonian Bingham fluid behavior under an applied magnetic field. The sedimentation of the MR fluid with and without the halloysite additive was also measured using a Turbiscan. It was found that the added rod-like hollow nanotubular-structured halloysite improved the sedimentation problem despite the decrease in MR behavior, as determined from the significant decrease in sedimentation rate.

Magnetostratigraphy and Anisotropy of Magnetic Susceptibility of the Lulehe Formation in the Northeastern Qaidam Basin

Abstract:The timing of onset of deposition of the Lulehe Formation is a significant factor in understanding the genesis of the Qaidam basin and the evolution of the Tibetan Plateau. Here, we describe a detailed magnetostratigraphic and magnetic fabric study of the middle and lower parts of the Lulehe Formation. A total of 234 samples were collected from 117 sites throughout a thickness of almost 460 m of fluvial and lacustrine deposits at the Xitieshan section in the northeastern Qaidam basin. Out of these sites, 94 sites yielded well‐defined characteristic remanent magnetization components by stepwise thermal demagnetization and were used to establish the magnetostratigraphy of the studied section. Based on correlation with the geomagnetic polarity timescale, the studied section spans the period from 53.8 Ma to 50.7 Ma. Our results show a three‐fold decrease in sedimentation rates as well as marked change in facies from braided river to delta and shore–shallow lake around 52.6 Ma, which suggests tectonic uplift of the northeastern Qaidam basin margin ridge was rapid at the onset of formation of the Qaidam basin and subsequently weakened after 52.6 Ma. The anisotropy of magnetic susceptibility results indicate that tectonic compression stress had reached the northeastern Tibetan Plateau by the early stages of Indo–Eurasian plate collision and that the direction of stress in the study area was NE–SW. Furthermore, a weakening of tectonic compression stress around 52.6 Ma is consistent with sedimentary records. The age of initial deposition of the Qaidam basin (around 53.8 Ma) was almost synchronous with that of the Qiangtang, Hoh Xil, Xining, and Lanzhou basins, which implies that stress was transferred rapidly through the Tibetan Plateau during or immediately after the onset of Indo–Eurasian collision.

Therapeutic Vaccination of Treatment-Failed TB Patients on “Palliative” Support Consisting of Isoniazid and Rifampicin

Open label phase 2b retrospectively controlled trial was conducted in 72 treatment-failed TB patients on socalled palliative support consisting of isoniazid (H) and rifampicin (R) with or without adjunct immunotherapy. The intervention group (N=36) received once-daily pill of V-5 Immunitor (V5) and comparison control (N=36) received HR only. The subjects in V5 and control groups had miliary: cavitary: MDR-TB: DR-TB: TB/HIV at 10: 26: 5: 4: 1 and 14: 22: 6: 6: 2 ratios, respectively. After 3 months 69.4% of V5-treated patients experienced negative sputum smear conversion (P<0.0001) vs. 16.7% (P=0.02) in comparison group who were treated for 3.5 months on average. 9 out of 10 V5 recipients with drug-resistant TB and TB/HIV became sputum negative, whereas none of 14 patients with same diagnosis converted (P<0.0001; OR 1732; 100-30008 at 95% CI). TB-associated inflammation was downregulated by V5 as shown by normalization of leukocytosis 7.9 vs. 6.2 x109/L (P=0.005) and decreased erythrocyte sedimentation rate 22.7 vs. 13.3 mm/h (P<0.0001), whereas among HR recipients changes were smaller, i.e., 7.2 vs. 7.5 x109/L (P=0.49) and 26.4 vs. 22.5 mm/h (P<0.0001). The body °C temperature was reduced from 37.4 ± 0.5 to 37.1 ± 0.3 (P=0.001) and from 37.7 ± 0.5 to 37.2 ± 0.5 (P=0.0002) in V5 and control respectively. In V5 arm average body weight accrual 2.2 ± 1.7 kg (P<0.0001) was higher than 0.08 ± 1.1 kg in control. No adverse effects or reactivation of disease were seen at any time. V5 is safe and in combination with simple two-drug regimen was highly effective as an immune adjunct for management of treatment-failed and/or drug-resistant TB.

Adjunct Immune Therapy of First-Diagnosed TB, Relapsed TB, Treatment-Failed TB, Multidrug-Resistant TB and TB/HIV

To evaluate the effect of an adjunct immunotherapy in randomized double-blind, placebo-controlled Phase IIb trial involving 123 TB patients. Patients were randomly allocated into two arms: one (n = 62) received a once-daily pill of V-5 Immunitor™ (V5) and the other (control; n= 61) received placebo for 30 days in addition to first- or second-line TB drugs administered under directly observed therapy. The subjects in V5 and placebo arms had first-diagnosed, relapsed, treatment-failed and multidrug-resistant TB at ratios of 17:21:11:13 and 20:19:14:8, respectively; among them, ten and seven had HIV coinfection, respectively. After 1 month, 55 out of 62 patients (88.7%) became sputum smear-negative in the V5 arm (p < 0.0001), whereas in the placebo group, nine out of 61 (14.8%) had converted. The conversion rate among V5 recipients was similar, regardless of whether TB was drug-sensitive, drug-resistant or with HIV. V5 downregulated TB-associated inflammation, as shown by the normalization of elevated leukocyte counts (8.7 vs 6.3 × 10 (9)/l; p < 0.0001) and decreased erythrocyte sedimentation rate (22.8 vs 12.6 mm/h; p < 0.0001), whereas among placebo recipients, changes were smaller (8.9 vs 8.2 × 10 (9)/l and 25.1 vs 19.9 mm/h). Thirty three (54.1%) placebo patients gained on average 0.8 kg (p = 0.0002); by contrast, 57 (91.9%) out of 62 patients in the V5 group gained a mean weight of 2.9 kg (p < 0.0001). No adverse side effects or reactivation of TB were seen at any time. V5 is safe and effective as an immune adjunct to chemotherapy for TB and can potentially reduce the treatment duration down to 1 month.

Holocene sea‐level change and Antarctic melting history derived from geological observations and geophysical modeling along the Shimokita Peninsula, northern Japan

A Mid to Late Holocene sea‐level record based on combined geomorphological, geological and micropaleontological observations was obtained from well‐developed wave cut benches subaerially exposed along the Shimokita Peninsula, northern Japan. Results indicate that the benches were formed during mid to late Holocene sea‐level transgressions, reaching a maximum highstand level of 2 m above present at about 4,000 years ago. This timing corresponds to an abrupt, order of magnitude decrease in sedimentation rate as recorded in a core recovered from proximal Mutsu Bay. In addition, glacio‐hydro‐isostatic adjustment due to crustal deformation in response to postglacial sea‐level rise was modeled, and results are consistent with the reconstructed local 2 m highstand. Given that meltwater contributions from the major North American and European ice sheets had largely ceased by 7,000 years ago, these independent lines of evidence, taken together, indicate that melting of the Antarctic ice sheet ended by 4,000 years ago.

Clinical analysis of macrophage activation syndrome in pediatric patients with autoimmune diseases

Macrophage activation syndrome (MAS) belongs to secondary hemophagocytic lymphohistiocytosis (HLH) syndrome. It is usually associated with rheumatic diseases. We retrospectively reviewed our hospital's medical records of 102 HLH/MAS patients from the past 20 years. Demographics, clinical data, treatment, and outcomes were analyzed. Among 102 patients, eight patients with underlying juvenile systemic lupus erythematous (two patients), mixed connective tissue disease (one patient), primary anti-phospholipid syndrome (one patient), and systemic type juvenile rheumatoid arthritis (sJRA; four patients) with 13 episodes of MAS were studied. Clinical manifestations of MAS included fever (100 %), hepatosplenomegaly (77 %), lymphadenopathy (38 %), skin rash (62 %), and neurological involvement (31 %). Laboratory features included leukopenia (54 %), anemia (46 %), thrombocytopenia (77 %), jaundice (27 %), hypofibrinogenemia (40 %), decreased erythrocyte sedimentation rate (67 %), and elevated liver enzymes (77 %), lactate dehydrogenase (100 %), ferritin (88 %), triglycerides (91 %), C-reactive protein (85 %), plasma D-dimer (50 %), and hemophagocytosis in bone marrow (83 %). The Epstein-Barr virus and adenovirus infection triggered MAS in two patients with sJRA. Methylprednisolone pulse therapy was effective in two out of three patients, and high-dose intravenous immunoglobulin (IVIG) was effective in two out of six patients. Patients with sJRA responded well to corticosteroids and cyclosporine. Complications included opportunistic infection with Pneumocystis jiroveci, multiple organ failure, and intensive care unit myopathy. The mortality rate was one out of eight (12.5 %). Our results showed that MAS could be fatal and complicate various pediatric autoimmune diseases. It generally has a good response to corticosteroids and IVIG. Prompt recognition and timely treatment can result in good outcomes.

Comparative efficacy of infliximab and adalimumab in patients with ankylosing spondylitis

Система комплексной поддержки и сопровождения научного журнала Elpub позволяет запустить двуязычный сайт журнала со встроенной системой электронной редакции в соответствии с лучшими издательскими практиками, а так же предусматривает техническую и методическую поддержку со стороны специалистов НЭИКОН.

Long-term outcome of tumor necrosis factor alpha antagonist's treatment in pediatric Crohn's disease

BackgroundAnti tumor necrosis factor alpha (TNFα) agents have become widely used in pediatric inflammatory bowel disease (IBD). So far, only few studies examined the long-term results of anti-TNFα treatment in children with IBD. MethodsThe long-term outcome of pediatric patients with IBD was assessed retrospectively in a multicenter cohort of children treated with anti-TNFα beyond induction treatment. Short- and long-term response rates, predictors for loss of response, data on growth and laboratory parameters were assessed. Results120 patients [101 crohn's disease (CD), 19 ulcerative colitis (UC) or indeterminate colitis (IC)] received either infliximab or adalimumab. The mean age at initiation of anti-TNFα was 13.4±3.9 years and the median duration of anti-TNFα treatment was 15 months (range: 2–90). Overall, 89% of the cohort experienced short-term response following induction. Response was associated with improvement in weight and BMI Z-scores (p<0.001) but not with linear growth. Responders experienced a significant decrease in erythrocyte sedimentation rate (ESR) and C reactive protein (CRP) during treatment (p<0.001). Albumin and hemoglobin both improved but only albumin increased significantly (p<0.001).The cumulative probability of losing response to anti-TNFα treatment was 17%, 38%, and 49% after 1, 3, and 5years, respectively. Responders had a significantly lower weight and BMI Z-scores at initiation of anti-TNFα treatment in compared to non-responders (p=0.04 and 0.02 respectively). ConclusionsOur long term cohort supports the current evidence on the effectiveness and safety of anti-TNFα treatment in children with IBD. Response to treatment was interestingly associated with lower weight and BMI.

Glauconite Composition and Morphology, Shocked Quartz, and the Origin of the Cretaceous(?) Main Fossiliferous Layer (MFL) in Southern New Jersey, U.S.A.

Abstract The Main Fossiliferous Layer (MFL) is a concentration of vertebrate and invertebrate fossils, 20 to 30 cm thick, preserved in a sequence of glauconitic sand at or near the Cretaceous–Paleogene boundary in the New Jersey (USA) coastal plain. Several hypotheses have been proposed to explain the origin and age of the MFL, including: marine transgression and formation of lag deposits of reworked bones and shells, formation of a condensed section and attritional accumulation of fossil material, and catastrophic collapse of Late Cretaceous ecosystems following the end-Cretaceous bolide impact at Chicxulub. We use new data on glauconite morphology, concentrations, geochemistry, and presence of shocked quartz, coupled with previous data on sedimentology, taphonomy, and rare-earth-element geochemistry of fossil vertebrates to interpret the genesis of the MFL. Glauconite concentration and maturity steadily increases from latest Cretaceous sediments of the Navesink–New Egypt Formation, through the MFL and into the Paleogene upper Hornerstown Formation, suggesting that marine transgression and decreasing sedimentation rates were a factor in the formation of the glauconite, but not the MFL. Rare-earth-element patterns in fossil bones from the MFL, which are acquired during fossilization, are different from those of Cretaceous and Paleogene specimens, indicating that vertebrate remains in the MFL fossilized in situ and were not reworked from older, underlying units. Vertebrate fossils from the MFL are preserved as isolated to articulated specimens. While isolated specimens would be common in a transgressive lag, articulated specimens would not. Articulated specimens could be concentrated by attritional accumulation along a defined surface during a period of slow sedimentation, but the lack of a distinct increase in glauconite maturity or concentrations of elements associated with heavy-mineral accumulations at the Navesink–New Egypt–Hornerstown contact or MFL, which would be expected during a period of reduced sedimentation, hiatus, or unconformity, are absent at the localities studied. Shocked quartz was identified in a burrow fill directly beneath the MFL, at the contact of the Navesink and Hornerstown formations. Clay clasts with latest Cretaceous microfossils, along with reworked invertebrate fossils with infills of latest Cretaceous sediment, have been recovered from the MFL. The association of shocked quartz, mixture of isolated and articulated vertebrates with distinct rare-earth signatures, lack of a punctuated period of increased glauconite maturity, and presence of reworked Late Cretaceous invertebrates and clay clasts with Late Cretaceous microfossils suggests that the MFL may represent a thanatocoenosis that was the direct result of environmental disturbance associated with the end-Cretaceous impact event at Chicxulub.

Paleoecology of mangroves along the Sibun River, Belize

This study examines a sediment core (SR-63) from a mangrove ecosystem along the Sibun River in Belize, which is subject to both changes in sea-level and in the characteristics of the river's drainage basin. Radiocarbon dates from the core show a decreased sedimentation rate from ~ 6 ka to 1 cal ka BP and a marked change in lithology from primarily mangrove peat to fluvial-derived material at ~ 2.5 cal ka BP. Changes in the sedimentation rates observed in mangrove ecosystems offshore have previously been attributed to changes in relative sea-level and the rate of sea-level rise. Pollen analyses show a decreased abundance of Rhizophora (red mangrove) pollen and an increased abundance of Avicennia (black mangrove) pollen and non-mangrove pollen coeval with the decreased sedimentation rates. Elemental ratios ([N:C] a) and stable isotope analyses (δ 15N and δ 13C) show that changes in the composition of the organic material are also coeval with the change in lithology. The decrease in sedimentation rate at the site of core SR-63 and at offshore sites supports the idea that regional changes in hydrology occurred during the Holocene in Belize, influencing both mainland and offshore mangrove ecosystems.

Kerogen to oil conversion in source rocks. Pore-pressure build-up and effects on seismic velocities

Abstract The aim of this work is to obtain a model for source rocks relating to kerogen–oil conversion and pore pressure to seismic velocity and anisotropy. The source rock is described by a porous transversely isotropic medium composed of illite/smectite and organic matter. The rock has a very low permeability and pore-pressure build-up occurs. We consider a basin-evolution model with constant sedimentation rate and geothermal gradient. Kerogen–oil conversion starts at a given depth in a volume whose permeability is sufficiently low so that the increase in pressure due to oil generation greatly exceeds the dissipation of pressure by flow. Assuming a first-order kinetic reaction, with a reaction rate satisfying the Arrhenius equation, the kerogen–oil conversion fraction is calculated. Pore-pressure changes affect the dry-rock stiffnesses, which have an influence on seismic velocities. The properties of the kerogen–oil mixture are obtained with the Kuster and Toksoz model, assuming that oil is the inclusion in a kerogen matrix. We use Gassmann's equations generalized to the anisotropic case to obtain the seismic velocities of the source rock as a function of depth, pressure and oil saturation. The procedure is to obtain the dry-rock stiffnesses by assuming a Poisson medium for the mineral material constrained by the physical stability conditions at the calibration confining pressures. The example considers a sample of the North-Sea Kimmeridge shale. At a given depth, the conversion increases with increasing geothermal gradient and decreasing sedimentation rate, and the porosity increases with depth due to the conversion. As expected, the horizontal velocities are greater than the vertical velocities and the degree of anisotropy increases with depth. The analysis reveals that the vertical P-wave velocity is the main indicator of overpressure.

Reconstruction of floodplain sedimentation rates: a combination of methods to optimize estimates

AbstractReconstruction of overbank sedimentation rates over the past decades gives insight into floodplain dynamics, and thereby provides a basis for efficient and sustainable floodplain management. We compared the results of four independent reconstruction methods – optically stimulated luminescence (OSL) dating, caesium‐137 (137Cs) dating, heavy metal analysis, and flood bed interpretation – applied at three embanked floodplain sites along lower Rhine River distributaries in the Netherlands.All methods indicate significant sedimentation rates on the floodplains, varying between 2–7 mm/a in the distal zones and 3–9 mm/a in the proximal zones. On a rapidly developing sand bar along a natural levee sedimentation rates of 9 to 25 mm/a were found. Except for some minor inconsistencies in 137Cs dating results, all methods show decreasing sedimentation rates with increasing distance from the river channel.Intercomparison of the results of the different dating methods revealed the potential errors associated with each method, particularly where disagreement among the results were found. Uncertainties may arise due to (1) grain‐size dependent downward migration of 137Cs, (2) smoothing of the vertical heavy metal and 137Cs profiles, (3) delayed sediment‐associated input of 137Cs in addition to direct atmospheric fall‐out, (4) overestimation of the burial age in OSL dating due to incomplete resetting of the OSL signal, or (5) non‐linear relationships between sediment deposition and flood magnitude in the count‐from‐the‐top correlation between sediment lamination and past observed flood records. Still, taking the uncertainties associated with each method into account, the results are generally in good agreement.Using the results we indicate the optimal spatial range of application of each method, depending on sediment texture and sedimentation rate. The optimal spatial and temporal ranges differ for each method, but show significant overlap. A combination of the methods will thus provide maximum information for accurate estimation of sedimentation rates on a decadal time scale. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Passive margin evolution and its controls on natural gas leakage in the southern Orange Basin, blocks 3/4, offshore South Africa

Using a 2D seismic dataset that covers part of the southern Orange Basin offshore South Africa, we reconstructed the geological evolution of the basin. This evolutionary model was then used to investigate the occurrence of natural gas within the sedimentary column and the distribution of gas leakage features in relation to the observed sedimentary and tectonic structures developed in the post-rift succession since the Early Cretaceous. The Cretaceous succession has been subdivided into five seismic units. The highest sedimentation rates occur within the Barremian/Aptian (unit C1) and the Turonian/Coniacian (unit C3). Two Cenozoic units (T1 and T2) have been distinguished. These show a sudden decrease in sedimentation rate for the whole of the Cenozoic. Three phases of gravitational tectonics, with two Late Cretaceous phases of mass movement in the northern study area and Cenozoic slumping in the southern study area, have been related to sedimentation rates, sea-level changes, paleoenvironmental evolution and regional tectonics. The occurrence of natural gas leakage follows a coast-parallel distribution within the study area. In the near shore part at water depths shallower than 400 m, massive gas chimneys penetrate through the sediment layers and reach the (near-) surface. Within an intermediate narrow band, between 300 and <500 m water depth, the gas migrates more diffusely through sub-vertical faulted Cretaceous sediments, while in the outer part of the basin, through the Cretaceous and Cenozoic gravitational wedges, only very few signs of gas accumulation and migration can be seen along the faults. A conceptual model has been established with the Aptian source rock generating gas in the outer part of the basin. This source rock underlies the Cenozoic wedge in the south and the thick Cretaceous wedge in the north and is a postulated source for the natural gas within the sedimentary column. This thermogenically generated gas does not migrate directly through the gravitational faults and the above lying sediments, but moves buoyancy driven up-dip along stratigraphic layers, to escape through the sediments to the sea-floor in the inner shelf area.

Trends in Total Phosphorus Loadings and Concentrations Regarding Surface Waters of the Baltic Sea, 1968-2007

The Baltic Sea, a large estuarine sea in northern Europe, has for many decades displayed obvious signs of an- thropogenic eutrophication. This study relates long-term trends in total phosphorus (TP) loadings and TP concentrations in surface waters regarding five major sub-basins of the Baltic Sea; the Bothnian Bay, the Bothnian Sea, the Baltic Proper, the Gulf of Finland and the Gulf of Riga. The longest time series ever published on these variables was developed and used for this purpose. TP loadings to these waters have decreased greatly and significantly since the 1980s. However, TP concentrations have only decreased slightly in one of the sub-basins while concentrations have increased in the other four basins. Four possible hypotheses about the weak connection between TP loadings and concentrations are 1) increasing TP concentration is a delayed effect from many decades of intensive TP loading, 2) fewer saline inflows of high intensity have decreased sedimentation rates and increased TP concentrations, 3) fewer oxygen-rich saline inflows of high intensity have increased TP diffusion from deep sediments to the whole water column and 4) less ice in the winter has increased the erosion and resuspension of shallow sediments and increased TP concentrations.

Geophysical evidence for Holocene lake‐level change in southern California (Dry Lake)

Bird, B. W., Kirby, M. E., Howat, I. M. &amp; Tulaczyk, S. 2009: Geophysical evidence for Holocene lake‐level change in southern California (Dry Lake). Boreas, 10.1111/j.1502‐3885.2009.00114.x. ISSN 0300‐9483.Ground penetrating radar (GPR) data are used in combination with previously published sediment cores to develop a Holocene history of basin sedimentation in a small, alpine lake in southern California (Dry Lake). The GPR data identify three depositional sequences spanning the past 9000 calendar years before present (cal. yr BP). Sequence I represents the first phase of an early Holocene highstand. A regression between &lt;8320 and &gt;8120 cal. yr BP separates Sequence I from Sequence II, perhaps associated with the 8200 cal. yr BP cold event. Sequence II represents the second phase of the early‐to‐mid Holocene highstand. Sequence IIIa represents a permanent shift to predominantly low lake stands beginning ∼5550 cal. yr BP. This mid‐Holocene shift was accompanied by a dramatic decrease in sedimentation rate as well as a contraction of the basin's area of sedimentation. By ∼1860 cal. yr BP (Sequence IIIb), the lake was restricted to the modern, central basin. Taken together, the GPR and core data indicate a wet early Holocene followed by a long‐term Holocene drying trend. The similarity in ages of the early Holocene highstand across the greater southern California region suggests a common external forcing – perhaps modulation of early Holocene storm activity by insolation. However, regional lake level records are less congruous following the initial early Holocene highstand, which may indicate a change in the spatial domain of climate forcing(s) throughout the Holocene in western North America.

Relationship of diagenetic chlorite rims to depositional facies in Lower Cretaceous reservoir sandstones of the Scotian Basin

The relationship between diagenetic chlorite rims and depositional facies in deltaic strata of the Lower Cretaceous Missisauga Formation was investigated using a combination of electron microprobe, bulk geochemistry and X-ray diffraction data. The succession studied comprises several stacked parasequences. The delta progradational facies association includes: (i) fluvial or distributary channel sandstones (some with tidal influence); (ii) thick-bedded delta-front graded beds of sandstone interpreted as resulting from fluvial hyperpycnal flow during floods and storms; and (iii) more distal muddier delta-front and prodeltaic facies. The transgressive facies association includes lag conglomerate, siderite-cemented muddy sandstone and mudstone, and bioclastic sandy limestone. Chlorite rims are absent in the fluvial facies and best developed in thick sandstones lacking mudstone baffles. Good quality chlorite rims are well correlated with Ti in bulk geochemistry. Ti is a proxy for Fe availability, principally from the breakdown of abundant detrital ilmenite (FeTiO3). Under conditions of sea floor diagenesis, the abrupt decrease in sedimentation rate at transgressive surfaces caused progressive shallowing of the sulphate-depletion level and of the overlying Eh-controlled diagenetic zones, resulting in conditions suitable for diagenetic formation of berthierine to migrate upwards through the packet of reservoir sandstones. This early diagenetic berthierine suppressed silica cementation and later recrystallized to chlorite. Thick euhedral outer chlorite rims were precipitated from formation water in sandstone lacking muddy baffles on this chlorite substrate and inhibited late carbonate cementation. This study thus shows that the preservation of porosity by chlorite rims is a two-stage process. Rapidly deposited delta-front turbidite facies create early diagenetic conditions that eventually lead to the formation of chlorite rims, but the best quality chlorite rims are restricted to sandstones with high permeability during burial diagenesis.

Methane sources and production in the northern Cascadia margin gas hydrate system

The oceanographic and tectonic conditions of accretionary margins are well-suited for several potential processes governing methane generation, storage and release. To identify the relevant methane evolution pathways in the northern Cascadia accretionary margin, a four-site transect was drilled during Integrated Ocean Drilling Program Expedition 311. The δ 13C values of methane range from a minimum value of − 82.2‰ on an uplifted ridge of accreted sediment near the deformation front (Site U1326, 1829 mbsl, meters below sea level) to a maximum value of − 39.5‰ at the most landward location within an area of steep canyons near the shelf edge (Site U1329, 946 mbsl). An interpretation based solely on methane isotope values might conclude the 13C-enrichment of methane indicates a transition from microbially- to thermogenically-sourced methane. However, the co-existing CO 2 exhibits a similar trend of 13C-enrichment along the transect with values ranging from − 22.5‰ to +25.7‰. The magnitude of the carbon isotope separation between methane and CO 2 ( ε c = 63.8 ± 5.8) is consistent with isotope fractionation during microbially mediated carbonate reduction. These results, in conjunction with a transect-wide gaseous hydrocarbon content composed of > 99.8% (by volume) methane and uniform δD CH 4 values (− 172‰ ± 8) that are distinct from thermogenic methane at a seep located 60 km from the Expedition 311 transect, suggest microbial CO 2 reduction is the predominant methane source at all investigated sites. The magnitude of the intra-site downhole 13C-enrichment of CO 2 within the accreted ridge (Site U1326) and a slope basin nearest the deformation front (Site U1325, 2195 mbsl) is ~ 5‰. At the mid-slope site (Site U1327, 1304 mbsl) the downhole 13C-enrichment of the CO 2 is ~ 25‰ and increases to ~ 40‰ at the near-shelf edge Site U1329. This isotope fractionation pattern is indicative of more extensive diagenetic alteration at sites with greater 13C-enrichment. The magnitude of the 13C-enrichment of CO 2 correlates with decreasing sedimentation rates and a diminishing occurrence of stratigraphic gas hydrate. We suggest the decreasing sedimentation rates increase the exposure time of sedimentary organic matter to aerobic and anaerobic degradation, during burial, thereby reducing the availability of metabolizable organic matter available for methane production. This process is reflected in the occurrence and distribution of gas hydrate within the northern Cascadia margin accretionary prism. Our observations are relevant for evaluating methane production and the occurrence of stratigraphic gas hydrate within other convergent margins.