拜耳法赤泥放射性特征及应用途径研究

赤泥是氧化铝生产过程中的工业固体废弃物,具有强碱性和高放射性两个特点。目前赤泥的处置方法主要是建设赤泥堆场，供长期堆放，尚没有对其进行大规模利用的成熟技术。 随着铝工业的发展，亟需开发赤泥处置与资源化利用的新工艺技术。本论文运用环境地球化学的理论方法，采用化学分析、选矿分离、放射性测试等技术手段，对贵州铝厂拜耳法赤泥的放射性特征进行了矿物学研究，并利用铁钛着色机理生产赤泥墙体装修材料进行了应用试验研究，指明了赤泥规模化综合利用的途径。 通过研究，得到以下主要结论： 1）初步确定了赤泥放射性元素主要来源于铝土矿原矿，并赋存于原矿残留的锆石和独居石中。 2) 贵州铝厂拜耳法赤泥所含放射性偏高，倘若利用赤泥制作建筑主体材料，需要慎重考虑。 3）探讨了不同选矿方法对赤泥放射性强度的变化情况，重选、磁选、加磁粉磁选所得赤泥组分与赤泥原样放射性相比较，没有显著性差异。采用现有选矿技术，难以达到分离富集赤泥中含放射性组分。 4）利用拜耳法赤泥中富含Fe2O3和TiO2的着色机理，加入一定量的页岩可以制得金红-褐色系列颜色的彩色墙体装修材料。采用现有烧结砖厂一般生产工艺，利用拜耳法赤泥生产烧结制品，是规模化处理赤泥的一条可行途径。 本论文的研究结果指明了赤泥可行的利用途径是用于建材领域，为制定赤泥大规模资源化利用的技术路线提供了一定的理论基础。

A cultural study on communication and technology with specific reference to media in China

This dissertation examines the role of communications technology in social change. It examines secondary data on contemporary China arguing that many interpretations of events in China are unsuitable at best and at worst conceptually damages our understanding of social change in China. This is especially the case in media studies under the ‘democratic framework’. It proposes that there is an alternative framework in studying the media and social change. This alternative conceptual framework is termed a zone of interpretative development offering a means by which to discuss events that take place in a mediated environment. Taking a theoretical foundation using the philosophy of Mikhail Bakhtin this dissertation develops a platform with which to understand communication technology from an anthropological perspective. Three media events from contemporary China are examined. The first examines the Democracy Wall event and the implications of using a public sphere framework. The second case examines the phenomenon of the Grass Mud Horse, a symbol that has gained popular purchase as a humorous expression of political dissatisfaction and develops the problems seen in the first case but with some solutions. Using a modification of Lev Vygotskiĭ’s zone of proximal development this symbol is understood as an expression of the collective recognition of a shared experience. In the second example from the popular TV talent show contests in China further expressions of collective experience are introduced. With the evidence from these media events in contemporary China this dissertation proposes that we can understand certain modes of communication as occurring in a zone of interpretative development. This proposed anthropological feature of social change via communication and technology can fruitfully describe meaning-formation in society via the expression and recognition of shared experiences.

Isotopic imprints of mountaintop mining contaminants.

Mountaintop mining (MTM) is the primary procedure for surface coal exploration within the central Appalachian region of the eastern United States, and it is known to contaminate streams in local watersheds. In this study, we measured the chemical and isotopic compositions of water samples from MTM-impacted tributaries and streams in the Mud River watershed in West Virginia. We systematically document the isotopic compositions of three major constituents: sulfur isotopes in sulfate (δ(34)SSO4), carbon isotopes in dissolved inorganic carbon (δ(13)CDIC), and strontium isotopes ((87)Sr/(86)Sr). The data show that δ(34)SSO4, δ(13)CDIC, Sr/Ca, and (87)Sr/(86)Sr measured in saline- and selenium-rich MTM impacted tributaries are distinguishable from those of the surface water upstream of mining impacts. These tracers can therefore be used to delineate and quantify the impact of MTM in watersheds. High Sr/Ca and low (87)Sr/(86)Sr characterize tributaries that originated from active MTM areas, while tributaries from reclaimed MTM areas had low Sr/Ca and high (87)Sr/(86)Sr. Leaching experiments of rocks from the watershed show that pyrite oxidation and carbonate dissolution control the solute chemistry with distinct (87)Sr/(86)Sr ratios characterizing different rock sources. We propose that MTM operations that access the deeper Kanawha Formation generate residual mined rocks in valley fills from which effluents with distinctive (87)Sr/(86)Sr and Sr/Ca imprints affect the quality of the Appalachian watersheds.

English Channel towed sledge seabed images. Phase 2: Analysis of selected tow images

During the 1970s and 1980s, the late Dr Norman Holme undertook extensive towed sledge surveys in the English Channel and some in the Irish Sea. Only a minority of the resulting images were analysed and reported before his death in 1989 but logbooks, video and film material has been archived in the National Marine Biological Library (NMBL) in Plymouth. A study was therefore commissioned by the Joint Nature Conservation Committee and as a part of the Mapping European Seabed Habitats (MESH) project to identify the value of the material archived and the procedure and cost to undertake further work (Phase 1 of the study reported here: Oakley & Hiscock, 2005). Some image analysis was undertaken as a part of Phase 1. Phase 2 (this report) was to further analyse selected images. Having determined in Phase 1 that only the 35 mm photographic transparencies provided sufficient clarity to identify species and biotopes, the tows selected for analysis were ones where 35mm images had been taken. The tows selected for analysis of images were mainly in the vicinity of Plymouth and especially along the area between Rame Head and the region of the Eddystone. The 35 mm films were viewed under a binocular microscope and the taxa that could be recognised recorded in note form. Twenty-five images were selected for inclusion in the report. Almost all of the images were of level sediment seabed. Where rocks were included, it was usually unplanned and the sled was hauled before being caught or damaged. The main biotopes or biotope complexes identified were: SS.SMU.CSaMu. Circalittoral sandy mud. Extensively present between the shore and the Eddystone Reef complex and at depths of about 48 to 52 m. At one site offshore of Plymouth Sound, the turret shell Turritella communis was abundant. In some areas, this biotope had dense anemones, Mesacmaea mitchelli and (more rarely) Cerianthus lloydii. Queen scallops, Aequipecten opercularis and king scallops, Pecten maximus, were sometimes present in small numbers. Hard substratum species such as hydroids, dead mens fingers Alcyonium digitatum and the cup coral Caryophyllia smithii occurred in a few places, probably attached to shells or stones beneath the surface. South of the spoil ground off Hilsea Point at 57m depth, the sediment was muddier but is still assigned to this biotope complex. It is notable that three small sea pens, most likely Virgularia mirabilis, were seen here. SS.SMx.CMx. Circalittoral mixed sediment. Further offshore but at about the same depth as SS.SMU.CSaMu occurred, coarse gravel with some silt was present. The sediment was characterised must conspicuously by small queen scallops, Aequipecten opercularis. Peculiarly, there were ‘bundles’ of the branching bryozoan Cellaria sp. – a species normally found attached to rock. It could not be seen whether these bundles of Cellaria had been brought-together by terebellid worms but it is notable that Cellaria is recorded in historical surveys. As with many other sediments, there were occasional brittle stars, Ophiocomina nigra and Ophiura ophiura. Where sediments were muddy, the burrowing anemone Mesacmaea mitchelli was common. Where pebbles or cobbles occurred, there were attached species such as Alcyonium digitatum, Caryophyllia smithii and the fleshy bryozoan Alcyonidium diaphanum. Undescribed biotope. Although most likely a part of SS.SMx.CMx, the biotope visually dominated by a terebellid worm believed to be Thelepus cincinnatua, is worth special attention as it may be an undescribed biotope. The biotope occurred about 22 nautical miles south of the latitude of the Eddystone and in depths in excess of 70 m. SS.SCS.CCS.Blan. Branchiostoma lanceolatum in circalittoral coarse sand with shell gravel at about 48m depth and less. This habitat was the ‘classic’ ‘Eddystone Shell Gravel’ which is sampled for Branchiostoma lanceolatum. However, no Branchiostoma lanceolatum could be seen. The gravel was almost entirely bare of epibiota. There were occasional rock outcrops or cobbles which had epibiota including encrusting calcareous algae, the sea fan Eunicella verrucosa, cup corals, Caryophyllia smithii, hydroids and a sea urchin Echinus esculentus. The variety of species visible on the surface is small and therefore identification to biotope not usually possible. Historical records from sampling surveys that used grabs and dredges at the end of the 19th century and early 20th century suggest similar species present then. Illustrations of some of the infaunal communities from work in the 1920’s is included in this report to provide a context to the epifaunal photographs.

The Partitioning Of Secondary Production Among Species In Benthic Communities

The way in which total secondary production is partitioned amongst species in various macrofauna communities (Amphiura, Venus, Abra, Modiolus) around the British Isles is discussed. When the proportion of total production is plotted for each species, ranked in order of productive importance, curves are produced which are characteristic of particular physical conditions. The shapes of the curves are independent of the actual species involved, but depend on the proportion of individuals in the community which adopt a particular feeding behaviour, and the scope for diversification within trophic groups. The form of these curves correlates closely with bottom currents and associated bed-stresses, since these affect both the nature of the food supply to bottom animals and the nature of the substrate. These observations have important implications for the structure and functioning of benthic communities. Comparison of production partitioning in the meiofauna of mud and sand substrates indicates a remarkable similarity within trophic groups although the partitioning of production between trophic groups is very different. The shapes of production-rank curves again appear to depend on the scope for diversification within trophic groups. In the meiofauna resources are partitioned more equitably than in the macrofauna. There is a marked discontinuity in the lognormal distribution of body sizes within integrated benthic communities at the meiofauna-macrofauna size boundary.

New genus and two new species of the family Ethmolaimidae (Nematoda: Chromadorida), found in two different cold-seep environments

This study describes a new genus Dystomanema gen. nov. with two new species, D. cadizensis sp. nov. and D. brandtae sp. nov. within the family Ethmolaimidae, subfamily Neotonchinae, based on specimens from two low-activity cold-seep environments at distant geographical locations. The new genus was first identified in samples from the Darwin mud volcano (1100 m depth) in the Gulf of Cadiz and later on also found in samples from a low-activity seep in the Larsen B embayment (820m depth) off the eastern Antarctic Peninsula. Until now, the family Ethmolaimidae contained nine genera: Ethmolaimus and Paraethmolaimus in the subfamily Ethmolaiminae, and Comesa, Filitonchoides, Filitonchus, Gomphionchus, Gomphionema, Nannolaimus, and Neothonchus in the subfamily Neotonchinae. The most important family characteristics are: an annulated cuticle bearing transverse rows of dots, cephalic sensilla arrangement of 6+6+4, a spiral amphid, an oesophagus with muscular posterior bulb, paired gonads and males with cup-shaped precloacal supplements. The new genus resembles Comesa and Neotonchus, but is typified by a ventrally displaced oral opening with three very small teeth that are easily overlooked. D. cadizensis gen. nov. sp. nov. is characterized by the 1401-2123 mu m long body; cuticle transversally striated with fine punctation; head conical; low lips; amphid spiralled 3 turns, oral opening ventrally displaced, male with outstretched testes; spicules of equal size; gubernaculum plate-like and ten to twelve conspicuous cup-shaped precloacal supplements with external longitudinal articulated flange. D. brandtae gen. nov. sp. nov. can be distinguished by the 2438-3280 mu m long body; cuticle transversally striated with fine punctuation; head conical; low lips; amphid spiraled 3+ turns; oral opening ventrally displaced; male with anterior testes outstretched and posterior one smaller and reflexed; spicules of equal size; gubernaculum plate-like and twenty conspicuous cup-shaped precloacal supplements with external longitudinal articulated flange. Notes on the ecology and habitat of the new genus are provided in light of its discovery in cold-seep environments.

Structure and diversity of intertidal benthic diatom assemblages in contrasting shores: a case study from the Tagus estuary1

The structure of intertidal benthic diatoms assemblages in the Tagus estuary was investigated during a 2-year survey, carried out in six stations with different sediment texture. Nonparametric multivariate analyses were used to characterize spatial and temporal patterns of the assemblages and to link them to the measured environmental variables. In addition, diversity and other features related to community physiognomy, such as size-class or life-form distributions, were used to describe the diatom assemblages. A total of 183 diatom taxa were identified during cell counts and their biovolume was determined. Differences between stations (analysis of similarity (ANOSIM), R=0.932) were more evident than temporal patterns (R=0.308) and mud content alone was the environmental variable most correlated to the biotic data (BEST, rho=0.863). Mudflat stations were typically colonized by low diversity diatom assemblages (H' similar to 1.9), mainly composed of medium-sized motile epipelic species (250-1,000 mu m(3)), that showed species-specific seasonal blooms (e.g., Navicula gregaria Donkin). Sandy stations had more complex and diverse diatom assemblages (H' similar to 3.2). They were mostly composed by a large set of minute epipsammic species (<250 mu m(3)) that, generally, did not show temporal patterns. The structure of intertidal diatom assemblages was largely defined by the interplay between epipelon and epipsammon, and its diversity was explained within the framework of the Intermediate Disturbance Hypothesis. However, the spatial distribution of epipelic and epipsammic life-forms showed that the definition of both functional groups should not be over-simplified.

Impacts of bioturbation on temporal variation in bacterial and archaeal nitrogen-cycling gene abundance in coastal sediments

In marine environments, macrofauna living in or on the sediment surface may alter the structure, diversity and function of benthic microbial communities. In particular, microbial nitrogen (N)-cycling processes may be enhanced by the activity of large bioturbating organisms. Here, we study the effect of the burrowing mud shrimp Upogebia deltaura upon temporal variation in the abundance of genes representing key N-cycling functional guilds. The abundance of bacterial genes representing different N-cycling guilds displayed different temporal patterns in burrow sediments in comparison with surface sediments, suggesting that the burrow provides a unique environment where bacterial gene abundances are influenced directly by macrofaunal activity. In contrast, the abundances of archaeal ammonia oxidizers varied temporally but were not affected by bioturbation, indicating differential responses between bacterial and archaeal ammonia oxidizers to environmental physicochemical controls. This study highlights the importance of bioturbation as a control over the temporal variation in nitrogen-cycling microbial community dynamics within coastal sediments.

RRS Discovery DY021 Cruise Report, March 2015

The Shelf Sea Biogeochemistry research programme directly relates to the delivery of the NERC Earth system science theme and aims to provide evidence that supports a number of marine policy areas and statutory requirements, such as the Marine Strategy Framework Directive and Marine and Climate Acts. The shelf seas are highly productive compared to the open ocean, a productivity that underpins more than 90 per cent of global fisheries. Their importance to society extends beyond food production to include issues of biodiversity, carbon cycling and storage, waste disposal, nutrient cycling, recreation and renewable energy resources. The shelf seas have been estimated to be the most valuable biome on Earth, but they are under considerable stress, as a result of anthropogenic nutrient loading, overfishing, habitat disturbance, climate change and other impacts. However, even within the relatively well-studied European shelf seas, fundamental biogeochemical processes are poorly understood. For example: the role of shelf seas in carbon storage; in the global cycles of key nutrients (nitrogen, phosphorus, silicon and iron); and in determining primary and secondary production, and thereby underpinning the future delivery of many other ecosystem services. Improved knowledge of such factors is not only required by marine policymakers; it also has the potential to increase the quality and cost-effectiveness of management decisions at the local, national and international levels under conditions of climate change. The Shelf Sea Biogeochemistry research programme will take a holistic approach to the cycling of nutrients and carbon and the controls on primary and secondary production in UK and European shelf seas, to increase understanding of these processes and their role in wider biogeochemical cycles. It will thereby significantly improve predictive marine biogeochemical and ecosystem models over a range of scales. The scope of the programme includes exchanges with the open ocean (transport on and off the shelf to a depth of around 500m), together with cycling, storage and release processes on the shelf slope, and air-sea exchange of greenhouse gases (carbon dioxide and nitrous oxide). The DY021 cruise is the first of the 2015 Benthic SSB cruises to investigate the 4 main ‘representative’ sites in the Celtic Sea that will represent all the various sediment types found in the whole area, these being Mud, San, Sandy-Mud and Muddy-Sand. The cruise will also carry out complimentary sampling at the Pelagic SSB programme main site called CANDYFLOSS in the central Shelf area in order to better link the Benthic and Pelagic programmes.

Lamellibrachia anaximandrin. sp., a new vestimentiferan tubeworm (Annelida) from the Mediterranean, with notes on frenulate tubeworms from the same habitat

A new species of lamellibrachiid vestimentiferan, Lamellibrachia anaximandri n. sp., has been found in the Eastern Mediterranean, close to cold seeps of fluid carrying dissolved methane and sources of sulfide in superficial sediments. It occurs at about 1100 to 2100 m depth, on some of the mud volcanoes on the Anaximander Mountains, south of Turkey, on the Mediterranean Ridge, south of Crete, and on the Nile deep-sea fan. In addition, it has been obtained from rotting paper inside a sunken ship, torpedoed in 1915 and lying at 2800 m depth, southeast of Crete. Some frenulate pogonophores also occur on the mud volcanoes (including a species of Siboglinum resembling S. carpinei and tubes of other unidentified genera). The new Lamellibrachia is the first vestimentiferan species to be described from the Mediterranean. It differs from L. luymesi taken from the Gulf of Mexico population in the very weak development of collars on its tube and in having a smaller number of pairs of branchial lamellae in the branchial plume. Sequencing of the COI and the mt16S genes confirms a difference at the species level between the new species and L. luymesi, and a difference between these two species and four described species of Lamellibrachia from the Pacific Ocean. The largest individuals of L. anaximandri n. sp. may be many years old, but there are numerous young individuals at some sites, showing that favourable conditions are available for settlement and early growth. The development of the branchial plume in a series of young stages reveals that the sheath lamellae, which are characteristic of the genus Lamellibrachia, begin to form only after the establishment of several pairs of branchial lamellae. Examination of the adult trophosome by transmission electron microscopy shows Gram-negative bacteria without internal stacked membranes, indicating that the symbionts are most probably sulfide oxidizing.

Simulated predator extinctions: Predator identity affects survival and recruitment of oysters

The rate of species loss is increasing at a global scale, and human-induced extinctions are biased toward predator species. We examined the effects of predator extinctions on a foundation species, the eastern oyster (Crassostrea virginica). We performed a factorial experiment manipulating the presence and abundance of three of the most common predatory crabs, the blue crab (Callinectes sapidus), stone crab (Menippe mercenaria), and mud crab (Panopeus herbstii) in estuaries in the eastern United States. We tested the effects of species richness and identity of predators on juvenile oyster survival, oyster recruitment, and organic matter content of sediment. We also manipulated the density of each of the predators and controlled for the loss of biomass of species by maintaining a constant mass of predators in one set of treatments and simultaneously using an additive design. This design allowed us to test the density dependence of our results and test for functional compensation by other species. The identity of predator species, but not richness, affected oyster populations. The loss of blue crabs, alone or in combination with either of the other species, affected the survival rate of juvenile oysters. Blue crabs and stone crabs both affected oyster recruitment and sediment organic matter negatively. Mud crabs at higher than ambient densities, however, could fulfill some of the functions of blue and stone crabs, suggesting a level of ecological redundancy. Importantly, the strong effects of blue crabs in all processes measured no longer occurred when individuals were present at higher-than-ambient densities. Their role as dominant predator is, therefore, dependent on their density within the system and the density of other species within their guild (e.g., mud crabs). Our findings support the hypothesis that the effects of species loss at higher trophic levels are determined by predator identity and are subject to complex intraguild interactions that are largely density dependent. Understanding the role of biodiversity in ecosystem functioning or addressing practical concerns, such as loss of predators owing to overharvesting, remains complicated because accurate predictions require detailed knowledge of the system and should be drawn from sound experimental evidence, not based on observations or generalized models.

The Casual Buttress:Certainty and Contingency in the Study of the Vernacular

Impromptu accretions such as the buttresses in Robin Walkers photograph are moments that are familiar in the architecture of the everyday. Indeed the buttress is a very common occurrence with these cottages in particular, their mud walls being poor at resisting concentrated lateral loading. While not always required the buttress emerges when requirements to create spaces to support inhabitation are at odds with the external form and construction of the buildings. These points of disjunction are resolved in an additive fashion externally. The location varies from structure to structure, occasionally the buttress is be used as a point of connection for further structures, becoming subsumed in outbuildings or walls. This preponderance to variety means that it is omitted from the reductive drawings of type that classify these buildings and yet it occurs in enough for it to have a fundamental and transformative relationship to the generality of cottages.
What is of interest is not so much what these structures hold in common, but rather what differentiates them. It is their capacity for variety within a defined range which allows them at once to speak at once of broader social structures and of a specific place and person.
Using the above observation this paper treats of the failure of architectural typological studies of the vernacular to derive anything other than formal exemplars, and posits an alternative approach based on a focus on the technical construction of such buildings.

A composite pollen-based stratotype for inter-regional evaluation of climatic events in New Zealand over the past 30,000 years (NZ-INTIMATE project)

Our review of paleoclimate information for New Zealand pertaining to the past 30,000 years has identified a general sequence of climatic events, spanning the onset of cold conditions marking the final phase of the Last Glaciation, through to the emergence to full interglacial conditions in the early Holocene. In order to facilitate more detailed assessments of climate variability and any leads or lags in the timing of climate changes across the region, a composite stratotype is proposed for New Zealand. The stratotype is based on terrestrial stratigraphic records and is intended to provide a standard reference for the intercomparison and evaluation of climate proxy records. We nominate a specific stratigraphic type record for each climatic event, using either natural exposure or drill core stratigraphic sections. Type records were selected on thebasis of having very good numerical age control and a clear proxy record. In all cases the main proxy of the type record is subfossil pollen. The type record for the period from ca 30 to ca 18 calendar kiloyears BP (cal. ka BP) is designated in lake-bed sediments from a small morainic kettle lake (Galway tarn) in western South Island. The Galway tarn type record spans a period of full glacial conditions (Last Glacial Coldest Period, LGCP) within the Otira Glaciation, and includes three cold stadials separated by two cool interstadials. The type record for the emergence from glacial conditions following the termination of the Last Glaciation (post-Termination amelioration) is in a core of lake sediments from a maar (Pukaki volcanic crater) in Auckland, northern North Island, and spans from ca 18 to 15.64±0.41 cal. ka BP. The type record for the Lateglacial period is an exposure of interbedded peat and mud at montane Kaipo bog, eastern North Island. In this high-resolution type record, an initial mild period was succeeded at 13.74±0.13 cal. ka BP by a cooler period, which after 12.55±0.14 cal. ka BP gave way to a progressive ascent to full interglacial conditions that were achieved by 11.88±0.18 cal. ka BP. Although a type section is not formally designated for the Holocene Interglacial (11.88±0.18 cal. ka BP to the present day), the sedimentary record of Lake Maratoto on the Waikato lowlands, northwestern North Island, is identified as a prospective type section pending the integration and updating of existing stratigraphic and proxy datasets, and age models. The type records are interconnected by one or more dated tephra layers, the ages of which are derived from Bayesian depositional modelling and OxCal-based calibrations using the IntCal09 dataset. Along with the type sections and the Lake Maratoto record, important, well-dated terrestrial reference records are provided for each climate event. Climate proxies from these reference records include pollen flora, stable isotopes from speleothems, beetle and chironomid fauna, and glacier moraines. The regional composite stratotype provides a benchmark against which to compare other records and proxies. Based on the composite stratotype, we provide an updated climate event stratigraphic classification for the New Zealand region. © 2013 Elsevier Ltd.

Predicting the predatory impacts of the “demon shrimp” Dikerogammarus haemobaphes, on native and previously introduced species

Biological invasions continue to exert pressure on ecosystems worldwide and we thus require methods that can help understand and predict the impacts of invasive species, on both native species and previously established invaders. Comparing laboratory derived functional responses among invasive and native predators has emerged as one such method, providing a robust proxy for field impacts. We used this method to examine the likely impacts of the Ponto–Caspian amphipod Dikerogammarus haemobaphes, known as the “demon shrimp”, a little investigated invader in European freshwaters that has recently established in the British Isles. We compared the functional responses on two prey species of D. haemobaphes with two other amphipod species: Dikerogammarus villosus, a congeneric invasive with well-documented impacts on macro-invertebrate communities and a native amphipod, Gammarus pulex. Prey species were native Chironomus sp. and the invasive Chelicorophium curvispinum, a tube-building amphipod also originating from the Ponto–Caspian region. D. villosus showed higher Type II functional responses towards both prey species than did D. haemobaphes and G. pulex, with the latter two predators exhibiting similar impacts on the native prey. However, D. haemobaphes had higher functional responses towards the invasive C. curvispinum than did G. pulex, both when prey individuals were tubeless and resident in their protective mud tubes. Thus, we demonstrate that functionally equivalent invasive congeners can show significantly different impacts on prey, regardless of shared evolutionary history. We also show that some predatory invaders can have impacts on native prey equivalent to native predator impacts, but that they can also exert significant impacts on previously introduced prey. We discuss the importance of invasion history and prey identity when attempting to understand and predict the impacts of new invaders.

Diagenetic Alterations and Reservoir Quality Evolution of Lower Cretaceous Fluvial Sandstones: Nubian Formation, Sirt Basin, North-Central Libya

Lower Cretaceous meandering and braided fluvial sandstones of the Nubian Formation form some of the most important subsurface reservoir rocks in the Sirt Basin, north-central Libya. Mineralogical, petrographical and geochemical analyses of sandstone samples from well BB6-59, Sarir oilfield, indicate that the meandering fluvial sandstones are fine- to very fine-grained subarkosic arenites (av. Q91F5L4), and that braided fluvial sandstones are medium- to very coarse-grained quartz arenites (av. Q96F3L1). The reservoir qualities of these sandstones were modified during both eodiagenesis (ca. <70oC; <2 km) and mesodiagenesis (ca. >70oC; >2km). Reservoir quality evolution was controlled primarily by the dissolution and kaolinitization of feldspars, micas and mud intraclasts during eodiagenesis, and by the amount and thicknessof grain-coating clays, chemical compaction and quartz overgrowths during mesodiagenesis. However, dissolution and kaolinitization of feldspars, micas and mud intraclasts resulted in the creation of intercrystalline micro- and mouldic macro-porosity and permeability during eodiagenesis, which were more widespread in braided fluvial than in meandering fluvial sandstones. This was because of the greater depositional porosity and permeability in the braided fluvial sandstones which enhanced percolation of meteoric waters. The development of only limited quartz overgrowths in the braided fluvial sandstones, in which quartz grains are coated by thick illite layers, retained high porosity and permeability (12-23 % and 30- 600 mD). By contrast, meandering fluvial sandstones underwent porosity loss as a result of quartz overgrowth development on quartz grains which lack or have thin and incomplete grain-coating illite (2-15 % and 0-0.1mD). Further loss of porosity in the meandering fluvial sandstones occurred as a result of chemical compaction (pressuredissolution) induced by the occurrence of micas along grains contacts. Otherdiagenetic alterations, such as the growth of pyrite, siderite, dolomite/ankerite and albitization, had little impact on reservoir quality. The albitization of feldspars may have had minor positive influence on reservoir quality throughthe creation of intercrystalline micro-porosity between albite crystals.The results of this study show that diagenetic modifications of the braided and meandering fluvial sandstones in the Nubian Formation, and resulting changes in reservoir quality, are closely linked to depositional porosity and permeability. They are also linked to the thickness of grain-coating infiltrated clays, and to variations in detrital composition, particularly the amounts of mud intraclasts, feldspars and mica grains as well as climatic conditions.