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Modeling Fluid Flow Effects on Shallow Pore Water Chemistry and Methane Hydrate Distribution in Heterogeneous Marine SedimentChatterjee, Sayantan 06 September 2012 (has links)
The depth of the sulfate-methane transition (SMT) above gas hydrate systems is a direct proxy to interpret upward methane flux and hydrate saturation. However, two competing reaction pathways can potentially form the SMT. Moreover, the pore water profiles across the SMT in shallow sediment show broad variability leading to different interpretations for how carbon, including CH4, cycles within gas-charged sediment sequences over time. The amount and distribution of marine gas hydrate impacts the chemistry of several other dissolved pore water species such as the dissolved inorganic carbon (DIC). A one-dimensional (1-D) numerical model is developed to account for downhole changes in pore water constituents, and transient and steady-state profiles are generated for three distinct hydrate settings. The model explains how an upward flux of CH4 consumes most SO42- at a shallow SMT implying that anaerobic oxidation of methane (AOM) is the dominant SO42- reduction pathway, and how a large flux of 13C-enriched DIC enters the SMT from depth impacting chemical changes across the SMT. Crucially, neither the concentration nor the d13C of DIC can be used to interpret the chemical reaction causing the SMT.
The overall thesis objective is to develop generalized models building on this 1-D framework to understand the primary controls on gas hydrate occurrence. Existing 1-D models can provide first-order insights on hydrate occurrence, but do not capture the complexity and heterogeneity observed in natural gas hydrate systems. In this study, a two-dimensional (2-D) model is developed to simulate multiphase flow through porous media to account for heterogeneous lithologic structures (e.g., fractures, sand layers) and to show how focused fluid flow within these structures governs local hydrate accumulation. These simulations emphasize the importance of local, vertical, fluid flux on local hydrate accumulation and distribution. Through analysis of the fluid fluxes in 2-D systems, it is shown that a local Peclet number characterizes the local hydrate and free gas saturations, just as the Peclet number characterizes hydrate saturations in 1-D, homogeneous systems. Effects of salinity on phase equilibrium and co-existence of hydrate and gas phases can also be investigated using these models.
Finally, infinite slope stability analysis assesses the model to identify for potential subsea slope failure and associated risks due to hydrate formation and free gas accumulation. These generalized models can be adapted to specific field examples to evaluate the amount and distribution of hydrate and free gas and to identify conditions favorable for economic gas production.
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A Study of the Social and Political Implication of Friedrich Schlegel’s ‘Comedy of Freude’Bhatti, Manjit Singh 01 December 2009 (has links)
Generally speaking, scholarship in the field of Germanistik has taken an interest in Friedrich Schlegel’s early publication, “Vom aesthetischen Werte der griechischen Komoedie” (1794), either because of its perceived influence on German Romantic Comedy [(Catholy 1982), (Kluge 1980), (Holl 1923), (Japp 1999)], or else because of its relevance as an example of Schlegel's still inchoate aesthetic philosophy [(Dierkes 1980), (Behrens 1984), (Schanze 1966), (Michel 1982), (Dannenberg 1993), (Mennemeier 1971)]. As a theory of comedy in its own right, Schlegel’s essay has garnered little attention, in part because of its supposed inapplicability to comedic praxis and at times utopian implications, in part because of its seemingly contradictory argument, and lastly in part because Schlegel himself abandoned the essay’s central premise soon after its publication. However, it is the central argument of the present study that Schlegel’s essay can be shown to be interesting and relevant precisely for the theory of comedy it contains. Through a close reading of Schlegel’s essay on Old Greek Comedy, as well as an examination of Schlegel’s early political and aesthetic beliefs, which will help render Schlegel’s theory more intelligible, it will be shown that Schlegel’s theory of comedy is novel in so far as it is one of the first aesthetic theories to claim that comedic practice is necessarily deprived of aesthetic validity unless it exists in a social atmosphere of freedom of expression, namely, such as that of the Athenians. The implication is that Schlegel here predicates an aesthetic theory upon one of society. Schlegel’s theory is also interesting for the peculiar type of comedy it advocates, namely a joyous comedy (Comedy of ‘Freude’), which stands in direct opposition to the ‘Satirische Verlachskomoedie’ of the Enlightenment and makes use of a comedic mechanism (joy) that is anathema to traditional negative comedic elements (satire, derision, mockery etc.). The conclusion discusses what the relevance and value of these implications might be for future research.
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Processes and architectures of deltas in shelf-break and ramp platforms : examples from the Eocene of West Spitsbergen (Norway), the Pliocene paleo-Orinoco Delta (SE Trinidad), and the Cretaceous Western Interior Seaway (S. Wyoming & NE Utah)Uroza, Carlos Alberto, 1966- 08 October 2012 (has links)
This research investigates different scenarios of deltaic deposition, both in shelfbreak and ramp settings. I address four ancient cases with particular characteristics: 1) A shelf-margin case from the Eocene Battfjellet Formation, West Spitsbergen, Norway, in which deltas were able to migrate to the shelf-edge during rising and sea-level highstand conditions despite the low-supply character of the system (low progradation/aggradation rates compared to analogous margins), with consequent sand starvation on the slope and deeper areas of the basin. The delta system was overall wave-dominated, with restricted tide-influence at the mouth of the distributaries and more accentuated tide-influence during the transgressive transit of the deltas; 2) A shelf-margin case from the Pliocene paleo-Orinoco Delta System, Mayaro Formation, SE-Trinidad, in which high rates of sediment supply from the paleo-Orinoco River and exceptionally high subsidence rates due to growth-faulting, produced a spectacular stacking of sandstones on the outer shelf and shelf-edge areas, but with apparently limited sand delivery into deeper waters. The delta system was overall storm-wave dominated, with fluvial-influence in the lower segment of the system and some tide-influence in association with the fluvial-influence; 3) A case from a shallow-water ramp, Campanian Rock Springs Formation (Western Interior Seaway), in which deltas accumulated along relatively straight, north-south oriented shorelines highly impacted by wave-storm processes. Tide-influence was limited to the mouth of the distributaries, and fluvial deposits mostly developed within the coastal-plain areas; and 4) A case from the same ramp setting as (3) but in an outer-ramp site, Campanian Haystack Mountains Formation, in which a lowering in sea-level translated the delta system tens of kilometers eastwards into the basin. As a consequence of a shallower and narrower seaway, southerly-oriented tidal currents were enhanced and subsequently skewed or re-aligned the delta system to the south. The key contributions of this research concern (1) the feasibility of shelf-margin accretion during rising and highstand of sea level, (2) the critical importance of shelf width and sediment supply (and not only sea-level behavior) to bring deltas to the shelfedge, and (3) the possible tendency for tides enhancement in the distal reaches of shallow seaway ramps, caused by narrowing of the seaway and fault-topography enhancement during falling sea level. / text
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From rifting to collision : the evolution of the Taiwan Mountain BeltLester, William Ryan 10 October 2013 (has links)
Arc-continent collisions are believed to be an important mechanism for the growth of continents. Taiwan is one of the modern day examples of this process, and as such, it is an ideal natural laboratories to investigate the uncertain behavior of continental crust during collision. The obliquity of collision between the northern South China Sea (SCS) rifted margin and Luzon arc in the Manila trench subduction zone allows for glimpses into different temporal stages of collision at different spatial locations, from the mature mountain-belt in central-northern Taiwan to the 'pre-collision' rifted margin and subduction zone south of Taiwan. Recently acquired seismic reflection and wide-angle seismic refraction data document the crustal-scale structure of the mountain belt through these different stages. These data reveal a wide rifted margin near Taiwan with half-graben rift basins along the continental shelf and a broad distal margin consisting of highly-extended continental crust modified by post-rift magmatism. Magmatic features in the distal margin include sills in the post-rift sediments, intruded crust, and a high-velocity lower crustal layer that likely represents mafic magmatism. Post-rift magmatism may have been induced by thermal erosion of lithospheric mantle following breakup and the onset of seafloor spreading. Geophysical profiles across the early-stage collision offshore southern Taiwan show evidence the thin crust of the distal margin is subducting at the Manila trench and structurally underplating the growing orogenic wedge ahead of the encroaching continental shelf. Subduction of the distal margin may induce a pre-collision flexural response along the continental shelf as suggested by a recently active major rift fault and a geodynamic model of collision. The weak rift faults may be inverted during the subsequent collision with the continental shelf. These findings support a multi-phase collision model where the early growth of the mountain belt is driven in part by underplating of the accretionary prism by crustal blocks from the distal margin. The wedge is subsequently uplift and deformed during a collision with the continental shelf that involves both thin-skinned and thick-skinned structural styles. This model highlights the importance of rifting styles on mountain-building. / text
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Patterns and dynamics of ocean circulation variability on the West Florida shelfLiu, Yonggang 01 June 2006 (has links)
Patterns of variability and the dynamics of the ocean circulation on the West Florida Shelf (WFS) are investigated using multi-year, shelf-wide oceanographic observations from moored Acoustic Doppler Current Profiler (ADCP) arrays,hydrographic cruises, High-Frequency (HF) radars, satellites, and coastal tide gauges.Novel neural network techniques, Self-Organizing Map (SOM) and Growing Hierarchical Self-Organizing Maps (GHSOM), are introduced as feature extraction methods in physical oceanography. The SOM is demystified and demonstrated to be a useful feature extraction method in a series of performance evaluations using artificial data sets comprising known patterns. It is then applied to velocity time series from moored ADCP arrays and to a joint HF-radar and ADCP data set, respectively, to extract patterns of ocean current variability, and it is shown to be a useful technique for extracting dynamically consistent ocean current patterns. The extracted characteristic patte
rns of upwelling/downwelling variability are coherent with the local winds on the synoptic weather time scale, and coherent with both the local winds and thecomplementary Sea Surface Temperature (SST) patterns on the seasonal time scale. Thecurrents are predominantly southeastward during fall-winter and northwestward during summer. The GHSOM is used to describe the SST seasonal variation. As feature extraction methods, both the SOM and the GHSOM have advantages over the conventional Empirical Orthogonal Function method.The circulation dynamics are examined, first through depth-averaged momentum balances at selected locations and then via sea surface height (SSH) estimates across the inner shelf. Dominant dynamics of the shelf circulation are diagnosed and a method is discussed for estimating along-shelf currents from coastal sea level and wind data. Nontidal coastal sea level fluctuations are related to both the offshore SSH and the dynamical responses of the inner shelf to wind and bu
oyancy forcing. The across-shelf distribution of the SSH is estimated from the velocity, hydrography, wind, and coastal sea level data.Subtracting the variability that may be accounted for by inner shelf dynamical responses yields a residual at the 50 m isobath that compares well with satellite altimetry data. This suggests the possibility of calibrating satellite SSH data on the continental shelf.
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Hållbarhetsrapportering inom bilindustrin : En komparativ studie av amerikanska och tyska bolag / Sustainability Reporting within the Car Industry – A Comparative Study of American and German CompaniesCarlsson, Sofia, Claesson, Sandra January 2015 (has links)
Hållbarhetsredovisning speglar företagens samhällsansvar vilket inom näringslivet idag benämns som Corporate Social Responsibility (CSR). Företagens samhällsansvar berör ekonomiska, miljömässiga och sociala aspekter. En ledande organisation som upprättar ramverk för hållbarhetsredovisning är Global Reporting Initiative (GRI). G3.1 är deras tredje version av riktlinjer som består av både redovisningsprinciper och vägledning samt standardupplysningar som ska anges i hållbarhetsrapporter. Standardupplysningarna omfattar företags strategi och profil, hållbarhetsstyrning och resultatindikatorer. GRI:s riktlinjer är inte lagstadgade utan endast rekommendationer som företag kan välja att tillämpa. Detta är en av många orsaker till att företags hållbarhetsrapporter kan skilja sig från varandra. Tidigare forskning har visat på att det finns internationella skillnader inom traditionell redovisning varav vissa kan kopplas till anglosaxisk respektive kontinental redovisningstradition. Denna studie inkluderar därför företag från länder tillhörande respektive redovisningstradition.Syftet med denna studie är att undersöka vilka internationella skillnader som förekommer inom hållbarhetsrapportering. En avsikt är att studera företags rapporterade resultat-indikatorer. Ytterligare en avsikt är att undersöka ett antal aspekter i hållbarhetsrapporterna på en djupare nivå, detta för att studera hur företagen delger information.Studien omfattar hållbarhetsrapporter utgivna av två amerikanska och två tyska företag inom bilsektorn. Hållbarhetsrapporterna är upprättade enligt G3.1 och utgivna för år 2012. Undersökningen genomfördes med innehållsanalys som tillvägagångssätt och inleds med en kvantitativ del där främst företagens rapporterade resultatindikatorer jämförs. Därefter presenteras en kvalitativ undersökning som berör hur informationen i hållbarhetsrapporterna är delgiven.Studiens resultat visar att det finns skillnader mellan de tyska och amerikanska företagens hållbarhetsrapporter. Resultatet i den kvantitativa undersökningen tyder på att de amerikanska företagen har en social inriktning i sina hållbarhetsrapporter då de fokuserar på samhälls- och anställningsfrågor framför andra frågor. För både de tyska och amerikanska företagen var området med flest rapporterade resultatindikatorer den miljömässiga aspekten, detta är dock en naturlig följd av att indikatorkategorin miljömässig påverkan omfattar flest resultat-indikatorer. Inom ekonomisk påverkan kunde ingen anmärkningsvärd skillnad utläsas bland de tyska och amerikanska företagens fördelning av indikatorkategorier. Den kvantitativa undersökningen visar vidare att de tyska företagen redovisar en större bredd av fullständigt redovisade aspekter inom samtliga kategorier av resultatindikatorer.Den mest utmärkande skillnaden som framkom i den kvalitativa undersökningen var att de tyska företagens hållbarhetsrapporter präglas av intressentmodellen medan fokus fanns på aktieägarna i de amerikanska företagens hållbarhetsrapporter. I undersökningen av hur företagen delger information i sina hållbarhetsrapporter framkom att de amerikanska företagen använde sig av mer finansiell information än de tyska vilket kan tänkas vara en följd av att de söker legitimitet hos aktieägarna. De tyska företagen å andra sidan vänder sig till en bredare intressentgrupp vilket framkommer av att de redovisar mer övergripande information. De amerikanska företagen i studien redovisar således en högre detaljnivå än de tyska företagen, som istället i sina hållbarhetsrapporter redovisar mindre detaljerat men om fler områden. / Sustainability reporting reflects the corporate commitments which are commonly known as Corporate Social Responsibility (CSR). The corporate commitments include economic, environmental and social aspects. Global Reporting Initiative (GRI) is a prominent organization which establishes frameworks for sustainability reporting. Their third version is called G3.1 and consists of guidelines regarding reporting principles and guidance, and standard disclosures. The standard disclosures are divided in the company´s strategy and profile, management approach, and performance indicators. A consequence of the framework from GRI not being statutory, but just optional for companies to use, is that the sustainability reports will differ from each other. Previously research has shown that international differences within traditional accounting exist, and it has to some extent been linked with the Anglo-Saxon and continental European accounting tradition. Therefore, this study includes companies from countries originating from correspondingly accounting tradition.This study aims to examine what international differences occur within sustainability reporting. One purpose is to compare companies´ reported performance indicators. Another intension is to do an in-depth examination of a number of aspects in the sustainability reports, with the ambition to find out how the companies communicate the information.The study includes sustainability reports from two North American and two German companies. The sustainability reports are all prepared regarding to G3.1 and published for the year of 2012. The examination was conducted with a content analysis and begins with a quantitative part, where the primarily objective is a comparison with the companies reported performance indicators. A qualitative inquiry about how the information in the sustainability reports is communicated is thereafter presented.The result of the study shows that differences exist between the American and the German companies´ sustainability reports. The quantitative examination indicates a social orientation among the American companies which emphasizes areas regarding community and employment conditions, in their reports. Environmental aspects are the ones most reported in both the American and German companies´ reports; an expected consequence considering that the environmental performance indicators are the most comprehensive area. No perceptible variations between the companies could be found for the economic performance indicators. Finally, the quantitative examination discloses that the German companies report a greater width of completely reported indicators in all categories of performance indicators.The most distinctive difference revealed in the qualitative examination was the presence of a stakeholder model within the sustainability reports from the German companies, while the American reports are affected by a shareholder model. It was discovered that the American companies use more financial information than the German ones, which may be due to a need of legitimization from the shareholders. Since the German companies reaches for a wider group of stakeholders, they present more general information. To conclude the qualitative examination, the American companies in this study report a higher level of details and depth in their reports compared to the German companies, who instead has less details but reports about more areas.(This thesis is written in Swedish)
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Observational and Numerical Modeling Studies of Turbulence on the Texas-Louisiana Continental ShelfZhang, Zheng 16 December 2013 (has links)
Turbulent dynamics at two sites (C and D) in a hypoxic zone on the Texas- Louisiana continental shelf were studied by investigating turbulence quantities i.e. turbulence kinetic energy (TKE), dissipation rate of TKE (E), Reynolds stress (τ ), dissipation rate of temperature variance (χ), eddy diffusivity of temperature (ν't), and eddy diffusivity of density (ν'p). Numerical models were also applied to test their capability of simulating these turbulence quantities.
At site D, TKE, E, and τ were calculated from velocity measurements in the bot- tom boundary layer (BBL), using the Kolmogorov’s -5/3 law in the inertial subrange of energy spectra of vertical velocity fluctuations in each burst measurement. Four second-moment turbulence closure models were applied for turbulence simulations, and modeled turbulence quantities were found to be consistent with those observed. It was found from inter-model comparisons that models with the stability functions of Schumann and Gerz predicted higher values of turbulence quantities than those of Cheng in the mid layer, which might be due to that the former stability functions are not sensitive to buoyancy.
At site C, χ, E, v’t, and ν’p were calculated from profile measurements throughout the water column, and showed high turbulence level in the surface boundary layer and BBL, as well as in the mid layer where shear stress was induced by advected non-local water above a hypoxic layer. The relatively high dissolved oxygen in the non-local water resulted in upward and downward turbulent oxygen fluxes, and the bottom hypoxia will deform due to turbulence in 7.11 days. Two of the four models in the study at site D were implemented, and results showed that turbulence energy resulting from the non-local water was not well reproduced. We attribute this to the lack of high-resolution velocity measurements for simulations. Model results agreed with observations only for χ and E simulated from the model with the stability function of Cheng in the BBL. Discrepancies between model and observational results lead to the following conclusions: 1) the stability functions of Schumann and Gerz are too simple to represent the turbulent dynamics in stratified mid layers; 2) detailed velocity profiles measurements are required for models to accurately predict turbulence quantities. Missing such observations would result in underestimation,
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Evolution des fonds sédimentaires sous l'influence de la divagation des chenaux aux abords du Mont- Saint-MichelGluard, L. 05 September 2012 (has links) (PDF)
Résumé La littérature concernant la divagation des chenaux sur le domaine intertidal est lacunaire, à fortiori sur la slikke. Ce phénomène est illustré dans ce travail avec l'exemple du chenal du Couesnon dans la partie interne de la baie du Mont-Saint-Michel. Un jeu de photographies aériennes et images satellitaires a permis l'étude des divagations du Couesnon, de 1969 à nos jours. Des relevés topographiques ont été réalisés avec des techniques laser terrestre et aéroporté, afin de caractériser les évolutions : i) des fonds sédimentaires sous l'influence des chenaux, de 1997 à 2010 ; ii) des bilans sédimentaires. Ces différentes évolutions sont corrélées avec différents forçages mesurés : marée, débit fluvial, conditions météorologiques et agitation. Il est ainsi mis en évidence le rôle du cycle à 18,6 ans de la marée sur la dynamique du chenal du Couesnon. En phase ascendante les apports sédimentaires contraignent le chenal vers l'Est, alors qu'en phase descendante, le Couesnon retrouve une position d'axe NNW, voire plus occidentale. En réponse à la diminution des apports sédimentaires, le chenal est principalement soumis à des paramètres externes : débits fluvial et solide, et interne : pente. Il est aussi montré que dans une tendance à l'accrétion globale du système, de +100 000 m3/an, l'évolution des bilans sédimentaires n'est pas linéaire, et montre parfois des phases érosives. Les bilans sédimentaires sont spatio-temporellement variables. L'érosion des surfaces est principalement due au renforcement du jusant induit par la présence des chenaux. Ce travail a permis de réaliser un schéma de fonctionnement hydrosédimentaire global de la partie interne de la baie du Mont-Saint-Michel.
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Regional Security, Early Warning and Intelligence Cooperation in AfricaLauren Angie Hutton January 2010 (has links)
<p>This dissertation explores the potential contributions of the mechanisms for early warning and intelligence sharing to regional security in Africa. The Continental Early Warning System (CEWS) and the Committee on Intelligence and Security Services of Africa (CISSA) are centrally concerned with the dissemination of information to enable decision-making on continental security. The main focus of the dissertation is on the manner in which the information generated by the CEWS and CISSA can contribute to regional security. In order to analyse the potential contribution of the CEWS and CISSA to regional security, a sound theoretical framework is proposed so as to explore how and why states choose to cooperate, as well as addressing multifaceted cooperation and integration at inter-state, government department and nonstate levels. Constructivist interpretations of international cooperation are utilised to explore the role of ideas, meanings and understandings in shaping behaviour. The focus is placed on the manner in which interaction as provided for by the CEWS and CISSA can shape understandings of reality and potentially impact on the definition of actors&rsquo / interests. This is based on the assumption drawn from security community and epistemic community theory that, enabling the creation of shared meanings and shared knowledge there is the potential for both the CEWS and CISSA to have a positive influence on the choices that stakeholders take in favour of peaceful change.</p>
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Sedimentology, coral reef zonation, and late Pleistocene coastline models of the Sodwana Bay continental shelf, Northern ZululandRamsay, Peter John. January 1991 (has links)
This geostrophic current-controlled Zululand/Natal shelf displays a unique assemblage of interesting
physical, sedimentological and biological phenomena. The shelf in this area is extremely narrow
compared to the global average of 75km, and is characterised by submarine canyons, coral reefs, and
steep gradients on the continental slope. A shelf break occurs 2.1km to 4.1km offshore and the shelf
can be divided into a northern region and a southern region based on the presence or absence of a
defined shelf break. The southern shelf has a poorly-defined shelf break whilst the northern shelf has
a well-defined break at -65m. The poor definition of the shelf break on the southern shelf can possibly
be attributed to the presence of giant, climbing sand dunes offshore of Jesser Point at depths of -37m
to -60m. The northern shelf has a series of coast-parallel oriented patch coral reefs which have
colonised carbonate-cemented, coastal-facies sequences.
The northern shelf can be divided into three distinct zones: inner-, mid-, and outer-shelf zones. The
inner-shelf is defined as the area landward of the general coral reef trend, with depths varying from
0m to -I5m and having an average gradient of 1.1. The mid-shelf is defined by the general coral reef
trend, varying from -9m over the shallow central axis of the reefs to -35m along the deep reef-front
environments. The outer-shelf is seaward of the coral reefs and occurs at a depth range of -35m to -
65m. Gradients vary from 1° in the south to 2.5° in the northern part of the study area, and are steep
compared to world average shelf gradient of 0.116°.
Four submarine canyons occur in the study area and are classified as mature- or youthful-phase
canyons depending on the degree to which they breach the shelf. The origin of these canyons is not
related to the position of modern river mouths but can probably be linked to palaeo-outlets of the
Pongola and Mkuze River systems. It is suggested that the canyons are mass-wasting features which
were exploited by palaeo-drainage during regressions. The youthful-phase canyons appear to be mass-wasting features associated with an unstable, rapidly-deposited, progradational late Pliocene sequence
and a steep upper continental slope. The mature-phase canyons were probably initiated by mass-wasting
but have advanced shoreward, breaching the shelf, due to their link with the palaeo-outlets
of the Pongola and Mkuze Rivers during late Pleistocene regressions.
Evidence of modem canyon growth has been noted on numerous SCUBA diving surveys carried out
on the canyon heads. These take the form of minor wall slumps and small-scale debris flows. The
canyons are also supplied with large quantities of sand in the form of large-scale shelf subaqueous
dunes generated and transported by the Agulhas Current. As these bedforms meet the canyons the
sediment cascades down the canyon thalweg and causes erosion and downcutting of the canyon walls
and floor thereby increasing the canyon dimensions.
Late Pleistocene beachrock and aeolianite outcrops with or without an Indo-Pacific coral reef veneer
are the dominant consolidated lithology on the shelf. These submerged, coast-parallel, carbonate cemented,
coastal facies extend semi-continuously from -5m to -95m, and delineate late Pleistocene
palaeocoastline events. The rock fabric of these high primary porosity lithologies shows grains floating
in a carbonate cement with occasional point-contacts. Grains are mostly quartz (80-90%), minor K-feldspar
and plagioclase (5-10%), and various lithic fragments. The rocks contain conspicuous organic
grains including foraminifera, bivalve, echinoid, bryozoan, red algal, and occasional sponge spicule
fragments; these commonly display replacement fabrics or iron-stained rims. The dominant
sedimentary structures found in these sandstone outcrops include high-angle planar cross-bedding and
primary depositional dip bedding. Palaeocurrent directions sngest a palaeoenvironment dominated
by a combination of longitudinal and transverse dunes with wind directions similar to those observed
forming the modem dune systems. Erosional features evident on the submerged beachrocks and
aeolianites include gullies trending in two different directions and sea-level planation surfaces with or
without the presence of potholes.
The unconsolidated sediment on the shelf is either shelf sand, composed mainly of terrigenous quartz
grains; or bioclastic sediment which is partially derived from biogenic sources.
The quartzose sand from the inner-shelf is generally fine-grained, moderately- to well-sorted, and
coarsely- to near symmetrically-skewed. Carbonate content is low, and varies between 4-13%.
Quartzose sand from the outer-shelf is fine-grained, moderately- to well-sorted, and coarsely- to very
coarsely-skewed. The inner-shelf quartzose sand is better sorted than the outer-shelf sand due to
increased reworking of this sediment by the high-energy swell regime. Sediment from the shallower
areas of the outer-shelf (< -50m) is better sorted than sediment from depths of greater than -50m.
Generally wave-reworking of quartzose shelf sand from the Sodwana Bay shelf results in greater
sediment maturity than that observed from geostrophic current effects or a combination of geostrophic
and wave-reworking. This sediment was derived by reworking of aeolian and beach sediments,
deposited on the shelf during the period leading up to the Last Glacial Maximum (15 000 - 18 000
years B.P.) when sea-level was -130m, during the Holocene (Flandrian) transgression.
Bioclastic sediment on the Sodwana Bay shelf is defined as having a CaC03 content of greater than
20% and is a mixture of biogeoically-derived debris and quartzose sand. The distribution of bioclastic
sediment in the study area is widespread, with reef-derived and outer-shelf-derived populations being
evident. This sediment consists of skeletal detritus originating from the mechanical and biological
destruction of carbonate-secreting organisms such as molluscs, foraminifera, alcyonaria, scleractinia,
cirripedia, echinodermata, bryozoa, porifera. The reef-derived bioclastic population is confined to
depths less than -40m in close proximity to reef areas, whereas the shelf-derived bioclastic population
occurs at depths greater than -40m and is derived from carbonate-producing organisms on deep water
reefs and soft-substrate environments on the shelf.
Large-scale subaqueous dunes form in the unconsolidated sediment on the outer-shelf due to the
Agulhas flow acting as a sediment conveyor. These dunes are a common feature on the Sodwana Bay
shelf occurring as two distinct fields at depths of -35m to -70m, the major sediment transport direction
being towards the south. The two dune fields, the inner- and outer subaqueous dune fields, are
physically divided by Late Pleistocene beachrock and aeolianites ledges. A bedform hierarchy has been
recognised. The larger, outer dune field appears to have originated as a system of climbing bedforms
with three generations of bedforms being superimposed to form a giant bedform, while the inner dune
field has a less complex construction. The largest bedforms are those of the outer dune field off Jesser
Point, being up to 12 m high, 4 km long and 1.2 km wide. A major slip face, with a slope of 8° is
present.
Bedload parting zones exist where the bedform migration direction changes from south to north.
Three bedload parting zones occur in the study area at depths of -60m, -47m and -45m; two in the
inner dune field and one in the outer dune field. These zones are invariably located at the southern
limits of large clockwise eddy systems. Such eddies appear to be the result of topographically induced
vorticity changes in the geostrophic flow and/or the response to atmospheric forcing caused by coastal
low-pressure system moving up the coastline.
It has been demonstrated that the inner subaqueous dune sediment conveyor is not active all the time
but only during periods . of increased current strength when the Agulhas Current meanders inshore.
The smaller bedforms in the outer dune field undergo continuous transport due to the current velocity
on the shelf edge outer dune field being higher than the velocity experienced on the inner dune field.
The very large 2·D dune which forms the outer dune field is probably not active at present: this is
inferred due to the shallow angle of the mega-crest lee slope (8°).
The very large Sodwana Bay subaqueous dune fields may be compared with the very large,
reconstructed, subaqueous dunes which occur in Lower Permian sediments of the Vryheid Formation,
northern Natal. These Permian dunes are represented, in section, as a fine- to medium-grained distal
facies sandstone with giant crossbeds. These large-scale bedforms are unidirectional, but rare
directionally-reversed, climbing bedforms do occur, this directional reversal may be related to bedload
parting zones. On the evidence presented in this thesis, it is proposed that these Permian subaqueous
dunes may be ancient analogues of the modem subaqueous dune field on the Sodwana Bay shelf.
Positive-relief hummocks and negative-relief swale structures are fairly common in the fine-grained,
quartzose shelf sand at depths of -30m to -60m. These appear to be transitional bedforms related to
the reworking by storms of medium 2-D subaqueous dunes. These hummocky structures may be the
modem equivalent of hummocky cross-stratification noted in the geological record, and if so, they are
probably the first to have ever been observed underwater.
The occurrences of ladderback ripples on the Sodwana Bay shelf at depths of -4m to -17m, suggest that
subtidal ladderback ripples may be more common than previously thought. Ladderback ripples are
common features of tidal flats and beaches where they form by late-stage emergence run-off during
the ebb tide. They are generally considered diagnostic of clastic intertidal environments. The mode
of formation on the Sodwana Bay shelf is different from the classic late-stage emergence run-off model
of intertidal occurrences, being a subtidal setting. Subaqueous observations indicate that ladderback
ripples are not environment-specific, and that additional evidence of emergence is therefore necessary
to support an intertidal setting in the rock record: ladderback ripples alone are insufficient to prove
an intertidal environment.
The coral patch reefs of the northern Natal coast are unique, being the most southerly reefs in Africa,
and totally unspoilt. The Zululand reefs are formed by a thin veneer of Indo-Pacific type corals which
have colonised submerged, late Pleistocene beachrocks and aeolianites. Two-Mile Reef at Sodwana Bay
has been used to develop a physiograpbic and biological zoning model for Zululand coral reefs, which
has been applied to other reefs in the region. Eight distinct zones can be recognised and differentiated
on the basis of physiographic and biological characteristics. The reef fauna is dominated by an
abundance of alcyonarian (soft) corals, which constitute 60-70% of the total coral fauna. The Two-Mile
Reef zoning model has been successfully applied to larger reefs such as Red Sands Reef, and smaller
patch reefs (Four-Mile and Seven-Mile Reefs) in the same general area.
In this thesis extensive use has been made of Hutton's uniformitarian principles. Hutton's doctrine
is particularly relevant to the study of depositional processes and relict shorelines. Coastal processes
and weather patterns during the late Pleistocene were broadly similar to modem conditions enabling
direct comparisons to be made. A computer-aided facies analysis model has been developed based on
textural statistics and compositional features of carbonate-cemented coastal sandstones. Many
attempts have been made to distinguish different ancient sedimentary depositional environments, most
workers in this field having little success. The new method of facies reconstruction is based on:
(1) underwater observations of sedimentary structures and general reef morphology;
(2) a petrographic study of the reef-base enabling flve facies: aeolianite, backbeach,
forebeach, swash, and welded bar facies to be recognised, which control the
geomorphology of Two-Mile Reef;
(3) cluster and discriminant analysis comparing graphic settling statistics of acid-leached
reef-base samples with those of modem unconsolidated dune/beach environments.
The results of this analysis demonstrated that the beachrocks and aeolianites on the shelf formed
during a regression and that late Pleistocene coastal facies are similar to modem northern Zululand
coastal environments, which have been differentiated into aeolian, backbeach, forebeach, swash, &
welded bar.
A late Pleistocene and Holocene history of the shelf shows that during the late Pleistocene, post
Eemian regressions resulted in deposition and cementation of coast-parallel beachrocks and
aeolianites, which define a series of four distinct palaeocoastline episodes with possible ages between
117 000 and 22 000 years B.P. The beachrock/aeolianites formed on the shelf during stillstands and
slow regressions, and the gaps between these strandline episodes represent periods of accelerated sealevel
regression or a minor transgressive phase which hindered deposition and cementation. The
formation of these lithologies generated a considerable sediment sink in the nearshore zone. This
reduced sediment supply and grain transport in the littoral zone during the Holocene, and probably
enhanced landward movement of the shoreline during the Flandrian transgression.
Prior to the Last Glacial Maximum, the beachrock/aeolianite sedimentary sequence was emergent and
blanketed by shifting aeolian sands. The Pongola River, which flowed into Lake Sibaya, reworked the
unconsolidated sediments on the shelf, and exploited the route of least resistance: along White Sands
and Wright Canyon axes. The erosion resulting from fluvial denudation in Wright Canyon has caused
this canyon to erode some of the beachrock/aeolianite outcrops which form palaeocoastline episode 2
and entrench the canyon to a deeper level; this eroded the shelf to a distance of 2km offshore.
During the Flandrian transgression the unconsolidated sediment cover was eroded, exposing and
submerging the beachrock/aeolianite sequence. Flandrian stillstands caused erosional features such
as wave-planed terraces, potholes, and gullies to be incised into beachrock and aeolianite outcrops;
these are seen at present depths of -47m, -32m, .26m, -22m, -17m to -15m, and -12m. High energy
sediment transfers, in an onshore direction, resulted in the deposition of sand bars across the outlet
of Lake Slbaya's estuary and the development of a 130m + coastal dune barrier on a pre-existlng,
remnant Plelstocene dune stub. Sea-level stabilised at its present level 7 000-6 000 years B.P. and coral
reef growth on the beachrock/aeolianite outcrops probably started at 5 000 years B.P. A minimum age
for the formation of the northern Zululand coral reefs has been established at 3780 ± 60 years B.P.
A mid Holocene transgression relating to the Climatic Optimum deposited a + 2m raised beach rock
sequence. This transgression eroded the coastal dune barrier and caused a landward shoreline
translation of approximately 40m. A minor transgression such as this can be used as a model for
coastal erosion which will result from the predicted 1.5m rise in sea-level over the next century. This
rise in sea-level could result in a 30m landward coastline translation of the present coastline, ignoring
the influence that storms and cyclones will have on the coastline configuration. / Thesis (Ph.D.)-University of Natal, Durban, 1991.
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