Dewatering Of Sediments Research Articles

A Late Cretaceous polygonal fault system in central North America

Research Article| May 01, 2017 A Late Cretaceous polygonal fault system in central North America Andy St-Onge Andy St-Onge 1PFS Interpretations Ltd., 427 28 Avenue NW, Calgary, Alberta T2M 2K7, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information Andy St-Onge 1PFS Interpretations Ltd., 427 28 Avenue NW, Calgary, Alberta T2M 2K7, Canada Publisher: Geological Society of America Received: 23 May 2016 Revision Received: 28 Oct 2016 Accepted: 04 Dec 2016 First Online: 06 Jul 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 2017 Geological Society of America GSA Bulletin (2017) 129 (5-6): 582–593. https://doi.org/10.1130/B31582.1 Article history Received: 23 May 2016 Revision Received: 28 Oct 2016 Accepted: 04 Dec 2016 First Online: 06 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Andy St-Onge; A Late Cretaceous polygonal fault system in central North America. GSA Bulletin 2017;; 129 (5-6): 582–593. doi: https://doi.org/10.1130/B31582.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Polygonal fault systems (PFS) have been interpreted worldwide using seismic data imaging sedimentary strata. Normal faults initiate over a large area in fine-grained subaqueous strata soon after deposition. As they continue to grow laterally and vertically, their fault traces intersect to form polygons in plan view. These polygons are difficult to image without three-dimensional (3-D) seismic data. The faulting is initiated during sediment dewatering and mud particle consolidation that can be independent of external stresses. In the past 20 years, hundreds of basins worldwide have been interpreted to contain polygonal faults.This paper presents a PFS interpretation for fine-grained sediments deposited in the Late Cretaceous Western Interior Seaway of the Great Plains of North America. The faulted strata have been observed as a PFS at depths ranging from ∼2750 m subsurface to outcrop. Seismic dataset interpretations and borehole analyses corroborate previously published outcrop analyses and seismic interpretations. The larger observed faults are mesoscale in size, with throws up to 80 m, and strike lengths up to ∼1.5 km. Potentially encompassing over 2,000,000 km2, observational averages imply 107 or more mesoscale-size faults, with an order of magnitude greater number of smaller faults. At shallow depth and outcrop, the PFS model of extensive normal faulting could help to explain Late Cretaceous shale faulting attributed to other causes such as deeper sediment dissolution or glacial processes. In the subsurface, faulting and fracturing consistent with a PFS model can help to explain fault geometries observed in well control and 3-D seismic data. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Formation Pore Pressure Variation of the Neocomian Sedimentary Succession (the Fahliyan Formation) in the Abadan Plain Basin, SW of Iran

The Neocomian Fahliyan Formation is one of the important oil reservoirs in the Abadan Plain Basin, SW of Iran. To evaluate the pore pressure regime of the Fahliyan reservoir, 164 in situ pressure data points (MDT, XPT, and RFT) were analyzed from seven wells belonging to six oilfields. The pressure versus depth plot revealed that the Fahliyan reservoir is highly overpressured in all fields. The formation was characterized as a multilayered stacked reservoir with different pore pressure decreasing downward in a step-wise manner. Also, there is a major pressure step in the middle part of the reservoir, suggesting the presence of a regional efficient seal dividing the reservoir into two stacked compartments, where the upper compartment is more overpressured than the lower one. The stepped pressure pattern of the Fahliyan Formation is a regional phenomenon controlled by a factor governed regionally, the depositional condition, and facies lateral changes during the deposition of shallowing upward sequence of the Fahliyan reservoir. In addition, direct relationship is observed between the reservoir pressure and burial depth. This matter could amplify the initially generated overpressure state more possible due to dewatering of sediments and by-pass product of oil migration from Garau source rock to the Fahliyan reservoir.

The thermal effect of fluid circulation in the subducting crust on slab melting in the Chile subduction zone

Fluids released from subducting slabs affect geochemical recycling and melt generation in the mantle wedge. The distribution of slab dehydration and the potential for slab melting are controlled by the composition/hydration of the slab entering a subduction zone and the pressure–temperature path that the slab follows. We examine the potential for along-strike changes in temperatures, fluid release, and slab melting for the subduction zone beneath the southern portion of the Southern Volcanic Zone (SVZ) in south central Chile. Because the age of the Nazca Plate entering the subduction zone decreases from ∼14 Ma north of the Guafo Fracture Zone to ∼6 Ma to the south, a southward warming of the subduction zone has been hypothesized. However, both north and south of Guafo Fracture Zone the geochemical signatures of southern SVZ arc lavas are similar, indicating 3–5 wt.% sediment melt and little to no contribution from melt of subducted basalt or aqueous fluids from subducted crust. We model temperatures in the system, use results of the thermal models and the thermodynamic calculation code Perple_X to estimate the pattern of dehydration-derived fluid release, and examine the potential locations for the onset of melting of the subducting slab. Surface heat flux observations in the region are most consistent with fluid circulation in the high permeability upper oceanic crust redistributing heat. This hydrothermal circulation preferentially cools the hottest parts of the system (i.e. those with the youngest subducting lithosphere). Models including the thermal effects of fluid circulation in the oceanic crust predict melting of the subducting sediment but not the basalt, consistent with the geochemical observations. In contrast, models that do not account for fluid circulation predict melting of both subducting sediment and basalt below the volcanic arc south of Guafo Fracture Zone. In our simulations with the effects of fluid circulation, the onset of sediment melting occurs under the volcanic arc, but dewatering of the subducting sediment and basalt is focused farther seaward (below the landward boundary of the stagnant mantle wedge corner). Thus, the sediment melt could enter the mantle wedge, contributing to the composition of the southern SVZ magmas, yet remain separate from the fluid derived from sediment dewatering which could migrate updip within the slab or into the wedge corner. Preferential hydrothermal cooling of the hottest segments of the system can help explain how there can be fairly uniform magma composition along the arc, despite large along-arc differences in the age of the subducting plate.

Seepage in Isfjorden and its tributary fjords, West Spitsbergen

Abstract This study analyses pockmark morphology and their spatial distribution in Isfjorden relative to seabed morphology, bedrock geology, fault systems, glacial landforms and processes using multibeam bathymetric data. It provides insight into the possible mechanisms of pockmark formation, high density pockmark field evolution, and fluid migration pathways. A total of 1304 pockmarks occur in the Isfjorden at water depths of 40 to 320 m, varying from circular to elongate in plan-view. Their diameter ranges from 14 to 265 m and their depths from 1 to 11 m. Elongate pockmarks are dominant in the Isfjordbanken and outer Isfjorden where the seafloor is influenced by the West Spitsbergen Current. The West Spitsbergen fold-and-thrust belt and other fault systems sub-cropping at the Isfjorden seafloor correlate spatially with the high density pockmark zones. The pockmarks are preferentially located on the marine sediments draping the bedrock of Isfjorden fjord system. They are most abundant in the areas underlain by Jurassic–Cretaceous and the Triassic–Lower Jurassic bedrock. Pockmarks found ahead of submarine slope failures may have formed due to dewatering of soft sediments as a result of rapid increase of overpressure caused by deposition of glacigenic debris lobes. Fault conduits, potential source rock and thin postglacial sediment layers are found to be crucial for the formation of pockmarks. Modeling results of the near-shore subsea permafrost and potential gas hydrate stability zone imply thawing permafrost and gas hydrate dissociation as additional possible mechanisms for pockmark formation in Isfjorden.

Facies Controlled Synaeresis Cracks in Mixed Siliciclastic-Carbonate Sediments of Middle Jurassic of Patcham Island, Kachchh, Western India

Abstract: Synaeresis cracks are observed at different stratigraphic levels in shallow marine mixed siliciclastic-carbonate sediments of the Middle Jurassic rocks of the Patcham Island, Kachchh, Western India. Cracks are preserved as cast or grooves in micritic sandstone of the Kuar bet member of Kaladongar Formation and sandy allochem limestone of the Raimalro Limestone member of Goradongar Formation. It bear distinct morphology of simple, straight to gently curved, spindle-shaped, irregular, unbranched to branched at acute angle; interconnected curlicue forms of non-orthogonal pattern. The X-radiography shows sharp margin and tapering twigs which support to nullify the possible biogenic origin. These cracks are developed at sediment-water interface and sediment-sediment interface in aqueous conditions, where partial dewatering of sediments causes reduction of sediment volume and loss of plasticity. Formation of cracks are also post-depositional phenomenon operated during initial phase of diagenesis where induced stress is generated due to compaction of sediments and neomorphism/recrystallisation of the susceptible carbonate grains.

Interaction between deformation and magma extraction in migmatites: Examples from Kangaroo Island, South Australia

Migmatite terranes are structurally complex because of strong rheological contrast between layers with different melt contents and because of magma migration leading to irregular volume changes. Migmatite deformation is intimately linked with magma extraction and the origin of granitoids. We investigate here the relationships between evolving deformation and magma extraction in migmatites formed during the ca. 500 Ma Delamerian orogeny, exposed on Kangaroo Island, South Australia. Here, several phases of deformation occurred in the presence of melt. During an early upright, noncylindrical folding event, magma was channeled toward the hinge zones of antiforms. Funnel-shaped networks of leucosomes formed a root zone that linked up toward a central axial planar channel, forming the main magma extraction paths during folding. Extraction was associated with fold limb collapse, and antiformal hinge disruption by magma accumulation and transfer. During a later deformation phase, melt-rich diatexites were deformed, and schollen, blocks or rafts of source rock, were disaggregated into smaller blocks and schlieren, and these were deformed into asymmetric, sigmoidal shapes indicative of dextral shearing flow. During flow, magma accumulated preferentially along shear planes, indicating a dilatational component during shearing (transtension) and in strain shadows of schollen. At the waning stages of deformation, magma extraction from these diatexites gave rise to N-trending, steeply dipping, funnel-shaped channels not associated with any externally imposed deformational feature. The funnel shape of these structures indicates the direction of magma flow. Structures developed during this phase are comparable with those formed during dewatering of soft sediments. Despite a high degree of complexity, magma migration and extraction features record distinct responses to the evolving deformation that can be used to understand deformation, and the nature and direction of magma extraction. The oldest and youngest magmatic rocks from migmatites were dated by U-Pb SHRIMP (sensitive high-resolution ion microprobe) dating techniques. Both reveal a continuous age spread between ca. 495 and 465 Ma. The age range is interpreted to indicate the duration of anatexis (order of 30 m.y.), with the older ages marking onset of monazite growth as the system approached peak metamorphism and younger ages representing final growth close to the solidus during cooling.

The Paleozoic Ozbak-Kuh carbonate-hosted Pb-Zn deposit of East Central Iran: Isotope (C, O, S, Pb) geochemistry and ore genesis

Lead and zinc mineralization occurs in dolostones of the Middle Devonian Sibzar Formation at Ozbak-Kuh, which is located 150 km north of Tabas city in East Central Iran. The ore is composed of galena, sphalerite and calcite, with subordinate dolomite and bitumen. Wall-rock alterations include carbonate recrystallization and dolomitization. Microscopic studies reveal that the host rock is replaced by galena and sphalerite. The Pb–Zn mineralization is epigenetic and stratabound. The δ13C values of hydrothermal calcite samples fall in the narrow range between −0.3‰ and 0.8‰. The δ18O values in calcite display a wider range, between −14.5‰ and −11.9‰. The δ13C and δ18O values overlap with the oxygen and carbon isotopic compositions of Paleozoic seawater, indicating the possible important participation of Paleozoic seawater in the ore-forming fluid. The δ18O signature corresponds to a spread in temperature of about 70 °C in the ore-bearing fluid. The δ13C values indicate that the organic materials within the host rocks did not contribute significantly in the hydrothermal fluid. The δ34S values of galena and sphalerite samples occupy the ranges of 12.2‰–16.0‰ and 12.1–16.8‰, respectively. These values reveal that the seawater sulfate is the most probable source of sulfur. The reduced sulfur was most likely supplied through thermochemical sulfate reduction. The sulfur isotope ratios of co-precipitated sphalerite–galena pairs suggest that deposition of the sulfide minerals took place under chemical disequilibrium conditions. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of the galena samples represent average values of 18.08, 15.66, and 38.50, respectively. These ratios indicate that galena Pb likely originated from an orogenic source in which supracrustal rocks with high 238U/204Pb and 232Th/204Pb ratios are dominant. The average lead isotope model age portrays Cambrian age. This model age is not coeval with the host rocks, which are of middle Devonian age. It is probable that the pre-Middle Devonian model age shows the derivation of Pb from older sources either from host rocks of Cambrian age or from deposits previously formed in these rock units. The Pb isotopic composition of galena accords with the occurrence of an orogenic activity from Late Neoproterozoic to Lower Cambrian in Central Iran. The proposed genetic model considers the fact that mineralization formed in fractured and brecciated host rocks along shear zones and faults from metal-bearing connate waters that were discharged due to deformational dewatering of sediments.

Salt tectonics on passive margins: examples from Santos, Campos and Kwanza basins

Abstract Salt flows downslope, irrespective of overburden. In salt basins on passive margins, the salt will tilt and flow towards the ocean immediately after continental rifting has ended due to thermal subsidence. Using real examples, as well as physical and numerical models, tilting is shown to be relatively rapid, enhanced by isostatic rebound updip and loading downdip where salt pools and inflates behind an outer high. In the Santos, Campos and Kwanza basins, this outer high is represented by an embryonic mid-Atlantic ridge, amplified in height by the differential weight of the inflating salt. Widespread extension and translation of overburden, utilizing both seaward- and landward-dipping normal faults, characterizes the early evolution of the inboard region. Inflation and contraction occur outboard, the effects of which tend to expand in a landward direction over time. Rapid accumulation of salt implies wholesale dewatering of pre-salt sediments, the water possibly permeating the salt once it has reached a burial depth of c. 3 km. The process of thermal subsidence, salt drainage and isostatic amplification is an efficient mechanism for moving sediment on passive margins tens of kilometres seaward during a relatively short period and helps explain why great thicknesses of salt can accumulate there in the first place.

Influences of sediment dessication on phosphorus transformations in an intertidal marsh: Formation and release of phosphine

This study investigated the effects of sediment dewatering on the phosphorus transformations concerning about the production and emission of phosphine in the intertidal marsh of the Yangtze Estuary. The concentrations of matrix-bound phosphine ranged from 18.62–72.53 ng kg −1 and 31.14–61.22 ng kg −1 within the August and January exposure incubations, respectively. The responses of matrix-bound phosphine concentrations to sediment dessication demonstrate that the production (or accumulation) of matrix-bound phosphine significantly increased with water loss at the start of the emersion incubations. However, further dehydration inhibited the formation of matrix-bound phosphine in sediments. The significant correlations of matrix-bound phosphine with the organic-P bacteria abundance and alkaline phosphatase activities implicate that the production of matrix-bound phosphine within the dessication incubations was linked closely to the microbial decomposition of organic P. The emissions of phosphine generally decreased with sediment dewatering, with the fluxes of 7.51–96.73 ng m −2 h −1 and 5.34–77.74 ng m −2 h −1 over the exposure incubations of both August and January, respectively. Also, it is observed that the releases of phosphine during the entire exposure periods were affected not only by its production but also by sediment water and redox conditions.

DEVELOPMENT OF SUSTAINABLE TECHNOLOGY OF RECYCLING AND REDUCING THE AMOUNT OF WASTE BOTTOM DEEPENING OF URBAN RESERVOIRSWITH THE USE OF DEHYDRATION IN GEOSYNTHETIC CONTAINERS

A complex of technological and managerial solutions to reduce the volumes of sediments of urban reservoirs is developed. The environmental efficiency of low-temperature dewatering of sediments in geosynthetic containers of the proposed design is shown.

Deepwater Exmouth Plateau, North Carnarvon Basin: preliminary investigations into ridge and furrow features

Numerous fields of long, shallow subsurface linear ridge and furrow features were mapped during the interpretation of a 3D seismic dataset covering Hess Exploration Australia Pty Ltd’s WA–390–P deepwater Exmouth Plateau permit. These kilometre scale features are often slope parallel and have separations of between 100 to 400 metres between ridge crests. Heights range from the limit of seismic resolution up to approximately nine metres. Similar linear shallow subsurface features have been interpreted in the North Falkland Basin in Desire Petroleum’s Tranches C and D permits. Initial investigations suggest that these features appear similar to the Holocene and older mega furrows/palaeo-mega furrows identified along the lower slope/rise in the Gulf of Mexico, most notably along the base of the Sigsbee Escarpment, and along other continental slope/rise settings. Evidence of seabed and shallow sub-seabed sediment instability in the form of slumps and slides together with the effects of shallow sediment deformation and dewatering are also visible across the WA-390-P area. Ridge and furrow features from the deepwater Exmouth Plateau area are described in detail alongside examples from the North Falkland Basin. It is suggested that interaction between gravity driven downslope processes, sediment dewatering and alongslope sedimentary processes could be a possible mechanism of formation for these features. Horizontal and vertical delineation of these features can contribute towards regional understanding of subsurface sediment instability.

Effects of desiccation on the photosynthetic activity of intertidal microphytobenthos biofilms as studied by optical methods

Due to the periodic exposure to air during periods of low tide, desiccation can be expected to cause important limiting effects on the photosynthetic activity of intertidal microphytobenthos biofilms. This work addresses the study of the short-term effects of desiccation on microphytobenthos using a new, simple methodological approach to non-destructively estimate the water content of muddy intertidal sediments. The method is based on the non-destructive measurement of the specular reflectance in the visible spectral region, shown to be linearly related to the water content of the uppermost 200 µm of the sediment. During air exposure, water loss by the surface sediment layers was shown to induce marked decreases in both the photosynthetic activity, as measured by the maximum quantum yield of photosystem II, F v/ F m, and the surface microalgal biomass, as estimated from the diffusive reflectance biomass index NDVI. The effects of desiccation were largely dependent on the rate of sediment de-watering. For a same level of desiccation, samples under fast desiccation (exposed to wind of 4.2 m s − 1 ) showed much larger effects on F v/ F m and NDVI comparatively to samples under slow desiccation (maintained under still air). By showing the rapid and significant effects of desiccation on microphytobenthos biofilm functioning, the results of this study have potentially important implications for the modelling of primary productivity of estuarine intertidal areas, as desiccation and factors inducing it may result in previously unaccounted effects on photosynthetic performance and productive biomass.

Pore pressure development beneath the décollement at the Nankai subduction zone: Implications for plate boundary fault strength and sediment dewatering

Despite its importance for plate boundary fault processes, quantitative constraints on pore pressure are rare, especially within fault zones. Here, we combine laboratory permeability measurements from core samples with a model of loading and pore pressure diffusion to investigate pore fluid pressure evolution within underthrust sediment at the Nankai subduction zone. Independent estimates of pore pressure to ∼20 km from the trench, combined with permeability measurements conducted over a wide range of effective stresses and porosities, allow us to reliably simulate pore pressure development to greater depths than in previous studies and to directly quantify pore pressure within the plate boundary fault zone itself, which acts as the upper boundary of the underthrusting section. Our results suggest that the time‐averaged excess pore pressure (P*) along the décollement ranges from 1.7–2.1 MPa at the trench to 30.2–35.9 MPa by 40 km landward, corresponding to pore pressure ratios of λb = 0.68–0.77. For friction coefficients of 0.30–0.40, the resulting shear strength along the décollement remains <12 MPa over this region. When noncohesive critical taper theory is applied using these values, the required pore pressure ratios within the wedge are near hydrostatic (λw = 0.41–0.59), implying either that pore pressure throughout the wedge is low or that the fault slips only during transient pulses of elevated pore pressure. In addition, simulated downward migration of minima in effective stress during drainage provides a quantitative explanation for down stepping of the décollement that is consistent with observations at Nankai.

Seep-carbonates in a thrust-related anticline at the leading edge of an orogenic wedge: The case of the middle–late Miocene Salsomaggiore Ridge (Northern Apennines, Italy)

Seep-carbonates are important indicators of submarine fluid expulsion and dewatering of sediments along convergent margins and accretionary prisms. In the Northern Apennine compressional wedge, seep-carbonates usually occur in pelitic successions from different settings of the middle late Miocene foreland basin system. In Serravallian foredeep deposits of the Salsomaggiore area, seep-carbonates cemented and/or encrusted coarse-grained sandstones and conglomerates. Fluid expulsion, strictly related to variable intensities in tectonic stresses, generated seep-carbonate facies and sediment instabilities, depending on the position of the fluid-pathway feeders within the Salsomaggiore Ridge, a middle–late Miocene intra-basinal high, at the leading edge of the Apenninic orogenic wedge. This site provides a unique opportunity for analyzing depositional characters, and the three-dimensional distribution and evolution of a seepage system in a thrust-related anticline. The resulting evolutionary model shares common features with recent ridges in other accretionary wedges. In this model a strict relationship between tectonics, seepage and sediment instability during a major tectonic phase is outlined.

The use of plant tissue silica content for estimating transpiration

Dewatering of saturated soils, sediments, and similar substrates is an emerging issue that requires a low cost solution. Plants have the ability to remove water from the substrate in which they grow through transpiration and could be used to aid in moisture removal. However, the need exists for a rapid screening tool to identify plant species with high transpiration rates that can grow in high water content substrates. This study examines the relationship between plant silica content and plant transpiration rate. A variety of plant species and types were grown in two soils to understand the relationship between silica and transpiration. Using an Infrared Gas Analyzer (IRGA) to quantify transpiration rate and acid-insoluble ash to quantify silica, a statistically significant relationship ( p < 0.01) between plant silica content and plant transpiration rate was determined. Plant type (wetland, grass, or forb) also was a significant ( p < 0.01) indicator of plant transpiration rate. These tools combined with knowledge of plant growth characteristics can be used in identifying plant species well-suited for particular dewatering applications.

Electroosmotic dewatering of dredged sediments: Bench-scale investigation

The Indiana Harbor (Indiana, USA) has not been dredged since 1972 due to lack of a suitable disposal site for dredged sediment. As a result of this, over a million cubic yards of highly contaminated sediment has accumulated in the harbor. Recently, the United States Army Corps of Engineers (USACE) has selected a site for the confined disposal facility (CDF) and is in the process of designing it. Although dredging can be accomplished rapidly, the disposal in the CDF has to be done slowly to allow adequate time for consolidation to occur. The sediment possesses very high moisture content and very low hydraulic conductivity, which cause consolidation to occur slowly. Consolidation of the sediment is essential in order to achieve adequate shear strength of sediments and also to provide enough air space to accommodate the large amount of sediment that requires disposal. Currently, it has been estimated that if a one 3-foot (0.9-m) thick layer of sediment was disposed of at the CDF annually, it would take approximately 10 years to dispose of all the sediment that is to be dredged from the Indiana Harbor. This study investigated the feasibility of using an electroosmotic dewatering technology to accelerate dewatering and consolidation of sediment, thereby allowing more rapid disposal of sediment into the CDF. Electroosmotic dewatering essentially involves applying a small electric potential across the sediment layer, thereby inducing rapid flow as a result of physico-chemical and electrochemical processes. A series of bench-scale electrokinetic experiments were conducted on actual dredged sediment samples from the Indiana Harbor to investigate dewatering rates caused by gravity alone, dewatering rates caused by gravity and electric potential, and the effects of the addition of polymer flocculants on dewatering of the sediments. The results showed that electroosmotic dewatering under an applied electric potential of 1.0 VDC/cm could increase the rate of dewatering and consolidation by an order of magnitude as compared to gravity drainage alone. Amending the sediment with polymers at low concentrations (0.5–1% by dry weight) will enhance this dewatering process; however, the optimal polymer concentration and the cost-effectiveness of using polymers should be investigated further.

Development of a Jurassic rocky shore complex (Zohar Formation, Makhtesh Qatan, southern Israel)

Wilson, M.A., Wolfe, K.R., and Avni, Y. 2005. Development of a Jurassic rocky shore complex (Zohar Formation, Makhtesh Qatan, southern Israel). Isr. J. Earth Sci. 54: 171–178. The Zohar Formation (Callovian, Middle Jurassic) is exposed as a sequence of limestones, dolomites, siltstones, and shales near the center of Makhtesh Qatan in the Negev Desert of southern Israel. Two dolomite units near the top of these faultbounded exposures are deeply incised by two perpendicular sets of relatively straight channels. Bivalve borings (Gastrochaenolites) in these dolomites show that they were cemented limestones when they were exposed and eroded; dolomitization came later. The dimensions of the channels, along with their orientations and stratigraphic context (they contain later Jurassic sediment), show that they are a series of joints that were widened by bioerosion and erosive currents, most likely from tides and wave action within a rocky shore context. Other trace fossils in these units track the earlier lithification history of these sediments. The soles of the beds show a fabric of Planolites, tunnels excavated by deposit-feeding worms that require soft sediments, cut by a large network of Thalassinoides burrows, which were created by crustaceans in firm sediments. The Zohar Formation at Makhtesh Qatan thus shows the firming, dewatering, and early cementation of sediments that were then exposed and eroded as part of a rocky shore. This new hypothesis updates previous models, which interpreted these rocks as the products of sabkha deposition.

残留性有機汚染物質を含んだ底質の造粒加熱処理に関する基礎検討

In this study, a calcination process was applied to destroy dioxins in sediments highly contaminated with them on a pilot scale (10 kg sediment/hr of treatment capacity). Treatment process involved apparatus of dewatering, size classification and aggregation of sediments, rotary kiln, secondary burner and bag filter. A remarkable reduction of the dioxin content (2, 900 and 11, 000 pg-TEQ/g for two test samples) in sediments to less than 0.033 pg-TEQ/g was achievable. In addition, from a physical point of view, the treated sediments possessed appropriate strength and water permeability comparable to those of sand, which leads to use of the treated sediments construction materials. The applied process could comply with dioxin emission limits in Japan for air and residual samples (i. e., treated sediments and fly ashes). Through a treatment system, high destruction efficiency (DE) values of greater than 99.99 percent were demonstrated for dioxins and their TEQs. DEs of greater than 99.4 percent were also found for PCBs (>99.91%), chlorobenzens (>99.97%), chlorophenols (>99.93%), polychlorinated naphthalenes (>99.96%) and polyaromatic hydrocarbons (>99.4%).

Investigation of Microearthquakes, Macroseismic Data, and Liquefaction Associated with the 1867 Wamego Earthquake in Eastern Kansas

Historical felt earthquakes and instrumentally recorded microseismicity in eastern Kansas and western Missouri have been attributed to the movement of the Nemaha Ridge and Humboldt fault zone (nrhf). Our investigations of the nrhf have concentrated on relocation of microearthquakes in the Kansas catalog, re-evaluation of the 1867 earthquake felt reports, and field studies to determine the presence or absence of sedimentary evidence of earthquake-induced liquefaction. Microearthquakes in the Kansas catalog have been relocated in a joint inversion with 3D seismic velocity variations. This improved set of hypocenters affirms the loose association of seismicity with the basement nrhf structure, even though seismicity does not seem to follow a single, well-defined fault feature. Overall, the association of microearthquakes with the nrhf suggests that it remains a potential source of large earthquakes. Our field investigations confirm that sedimentary deposits with moderate liquefaction susceptibility are present in the vicinity of Wamego and Wabaunsee, Kansas. Soft-sediment deformation features, including flame and dish structures, are present in the late Holocene floodplain deposits of the Kansas River. These features may have formed by liquefaction or by processes unrelated to seismic activity, such as sediment dewatering. We found several clastic dikes that may be attributed to seismically induced liquefaction. Our initial results suggest that liquefaction features are present but may not be pervasive in this region. These data imply that the 5.2 magnitude of the 1867 Wamego earthquake may characterize the seismic source in this location. However, additional field investigations are still necessary to complete the assessment for liquefaction features.

Impacts of sediment dewatering and rehydration on sediment nitrogen concentration and macrophyte growth

River sediments were experimentally dewatered via exposure to air from an initial moisture content of 75% to 61% (~20% dewatered), 32% (~60% dewatered), and 4% (~95% dewatered). Sediments dewatered by 20% and 60% and rehydrated exhibited a lower exchangeable ammonium-N (NH4-N) concentration and a lower rate of nitrate/nitrite-N and NH4-N release from sediments compared with controls. In contrast, sediments dewatered by 95% and rehydrated exhibited a marked increase in exchangeable sediment NH4-N and a much higher rate of nitrate/nitrite-N (under oxic conditions) and NH4-N (under oxic and anoxic conditions) release from sediments. Sediment dewatered by 60% and 95% and rehydrated lost total N (18%), suggesting denitrification. Growth of Potamogeton pectinatus responded to changes in the exchangeable sediment NH4-N concentration; it was lower on partially dewatered and rehydrated sediments that exhibited lower exchangeable sediment NH4-N and elevated on sediment that was dewatered by 95%. Our results suggest that sediment N may be altered via sediment dewatering and rehydration to affect macrophyte growth.