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Phosphorus Mobility in Lacustrine Sediments Upon Lake AcidificationMayer, Tatiana 09 1900 (has links)
<p> The forms of phosphorus in sediments of acid and non-acid shield lakes were determined in order to assess the effects of lake acidification on the mobility of sediment phosphorus. Sediment phosphorus is conveniently classified into three categories: non-apatite inorganic phosphorus (NAI-P), apatite-P and organic P. The distribution of P between different categories was found to be dependent on the lithology of the lake basin, the pH in the water column, and the redox conditions.</p> <p> More than 90% of inorganic P in shield lake sediments was in the NAI-P category, associated presumably with hydrated Fe and Al oxides. Organic P accounted for more than 40% of total P in sediments of acid lakes, which is proportionally higher than that found in sediments of neutral lakes. Bioavailable P, a measure of the fraction of sediment inorganic P readily available for biological utilization, amounted to ~70% of NAI-P, similar to that found in hard water lakes.</p> <p> A series of experiments was designed to investigate the immobilization of P from solution. The uptake of P by solid phase was explained by an adsorption mechanism. The quantitative estimates of phosphate sorption parameters for sediments of acid and non-acid lakes show that mineralogical and chemical characteristics of sediments are more important than the pH of water in determining their efficiency of P removal. Therefore, acidification of lakes does not significantly influence the uptake of P by sediments.</p> / Thesis / Master of Science (MSc)
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Lake Cycles and Sediments: Locality 80, Olduvai Gorge, TanzaniaBerry, Patricia A 07 August 2012 (has links)
Studies have shown that Bed I and Lower Bed II (1.92Ma- 1.76Ma) of Paleolake Olduvai at Locality 80 are primarily composed of the authigenic lacustrine clay minerals illite, smectite, and interlayered illite-smectite. X-ray fluorescence analysis and the sedimentation rates of Hay and Kyser (2001) were used to identify four apparent lake cycles beginning and ending with saline alkaline phases. Peaks in Al2O3/MgO ratios, and TiO2 and P2O5 abundances occur at approximately the same elevations within the stratigraphic section. Low values in these three parameters indicate saline alkaline conditions whereas high values represent fresh water conditions. Lake Cycles (LC) 1 and 4 completed in approximately 44,000 years and 42,000 years respectively, which is similar to the 41k.y. year cycle associated with Earth’s obliquity. Lake Cycles 2 and 3 span approximately 24,000 years and are similar to the 21k.y. precession cycle.
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An Analog for Large-Scale Lacustrine Deposits: 3D Characterization of a Pleistocene Lake Bonneville SpitLopez, Eli D. 07 September 2022 (has links)
Ultra-high-resolution subsurface stratigraphy mapped from 3D ground-penetrating radar (GPR) can provide insights into the fine-scale heterogeneity of reservoirs and other geologic features. Analog models derived from 3D GPR aid in understanding reservoir compartmentalization that may be sub-seismic but still affect fluid flow. We integrate 2D profiles and 3D GPR volumes with measured stratigraphic sections from outcrop exposure to characterize the fine-scale stratigraphy of an ancient Lake Bonneville shoreline deposit (locally, circa 20 ka based on carbon-14 dating) in the Great Basin (northwestern Utah). The heterogeneity of the deposit is expressed as multiple discordant patterns, separated by unconformities that likely were influenced by fluctuating lake levels on the lake margin. Although the study site is only ~8,000 square meters in area, the detailed stratigraphic relationships can be scaled up to inform the characterization of larger sedimentary deposits with economic reservoir potential. The sands, gravels, and marls composing the stratigraphy were deposited during the transgressive phase of the pluvial lake, which preserved shoreline features such as spits and barrier bars. We interpret our site as a spit that extended out into the Pleistocene lake, at times connecting to a nearby persistently subaerially exposed island to form a tombolo. The deposited strata are well-exposed in a fortuitously located gravel quarry. The site provides an excellent natural laboratory for detailed 3D imaging due to the mostly flat ground surface (the quarry floor), low-clay, low-salinity, and low-moisture content of the site. The GPR data were acquired with a 200-MHz antenna (for 2D profiles) and a 400-MHz antenna (for 3D volumes). For the latter, the line spacing was about 0.3 meters with a trace spacing of 2.5 cm. The GPR dataset offers high-resolution images of clinoform sequence stratigraphy down to about 3 meters below the surface of the quarry. The vertical resolution (Rayleigh criterion) of the data is about 6 cm (for 3D volumes) and 13 cm (for 2D profiles). Migration collapsed diffractions and re-positioned dipping reflectors correctly. Deconvolution suppressed multiple reflections and tightened the waveforms. Using petroleum industry mapping software, amplitudes were binned into voxels to create precise 3D volumes, which facilitated more accurate geometrical interpretation (e.g., true dip direction of reflectors). Facies associations from stratigraphic sections measured just above the GPR acquisition level (quarry floor) help to describe and reconstruct the depositional history of the spit. The lithologic interpretation of the GPR reflectors is constrained by the correlation (or extrapolation) of the measured sections to the subsurface data volumes. Reflectivity is controlled by variations in porosity and matrix content (e.g., quartz vs. clays vs. calcite). Our study furnishes a model of transgressive deposits in a lacustrine environment and an analog for clastic sediments deposited on a larger scale in such environments.
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Distribuição mineralógica dos sedimentos superficiais da lagoa do Caçó (MA)Mbengue, Abdoulaye 12 July 2017 (has links)
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Dissertaçãi final ultima.pdf: 1724559 bytes, checksum: fbd685dbe3586363bcfe625529593f18 (MD5) / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / A fração mineralógica é importante para a reconstrução de mudanças ambiental e
paleoambiental dos sedimentos lacustres. As frações inorgânicas alóctones e
autóctones fornecem informação sobre a evol
ução dos ecossistemas no ambiente de
sedimentação da lagoa e na ba
cia de sedimentação e s
obre também as condições
físico- químicas da coluna da água. Nós apr
esentamos resultados da distribuição
mineralógica dos sedimentos superficiais da
lagoa Caço. 59 amostras foram coletadas
por mergulhar ao longo dos transects tran
sversais e do transectlongitudinal nesta
lagoa. Cada perfil transversal começa pela
margem caracterizada por macrophytes,
atravessa a parte central e emerge na outr
a margem da lagoa. Todos os pontos da
amostragem foram -geo-referenciados e a pr
ofundidade da coluna da água foi medida.
A identificação da fração mineralógica
e sua quantificação foram feitas pela
difractometria de Raio-X e pela espectrom
etria no infravermelho. A distribuição da
fração mineralógica caracteriza as difer
entes zonas de prof
undidade da lagoa Caçó e
identifica os processos que controlam as
variações da sedimentação inorgânica. Os
minerais mais importantes identificados neste estudo forma quartzo, goethite, kaolinite e
sílica amorfo. Geralmente, ao longo de cada
transect, quartzo e sílica amorfa diminuem
da margem ao centro da lagoa. A goethite e
a kaolinite tendem a aumentar na parte
central da lagoa. A distribuição de mi
nerais detriticos parece ser controlada
principalmente pelo hidrodi
nâmico da lagoa, que é in
fluenciado fortemente pela
intensidade e a Constancia
dos ventos. Para os minerai
s autigenicos, os fatores
principais que controlam a distribuição minera
l devem ser: (1) para o sílica amorfo: a
ocupação da zona litoral pelos macrophytes, que
forneceram o substrato e os nutrientes
para a produção de diatomáceas, em maior
parte epiphytes ; (2) para o goethite: a
entrada hidrológica, pela superfície ou pelos
fluxos subsuperficiais, que contribuem com
a entrada de Fe(II), que será oxidada na água de superfície da lagoa, tendo por
resultado a precipitação do goethite. Assim, os
minerais detriticos (quartzo e kaolinite)
são bons marcadores potenciais da erosão na
bacia da drenagem da lagoa, quanto os
minerais autigenicos podem dar informação importante sobre as condições físico-
químicas do ambiente passado. / Mineralogical fraction is important to the reconstruction of environmental and
paleoenvironmental changes from lacustrine
sediments. Allochtonous and Autochtonous
inorganic fractions provide information about
the evolution of eco
systems in the lake
catchment and in the sedimentation basin
and about physical and chemical water
column conditions. We present results of rec
ent mineralogical distri
bution from surficial
sediments of Caço Lake. 59
samples were collected by
diving along transverse
transects and one longitudinal transect in this
lake. Each transverse profile stars from a
margin characterized by emergent macrophytes,
crosses the central part of the lake and
finishes in the other margin of the lake.
All sampling points were geo-referenced and the
water column depth was measured. The identif
ication of mineralogical fraction and its
quantification were d
one by x-ray diffractometry and by
infrared spectroscopy. The
distribution of the mineralogical fraction characterizes the different depth zones of the
Caço lake and identify the proce
sses that control variations
of inorganic sedi
mentation in
this lake. The most important
minerals identified in this
study were quartz, goethite,
kaolinite and amorphous si
lica. Generally, along each
transect quartz and amorphous
silica decrease from the margin to the center
of the lake. The goethite and kaolinite tend
to increase in the central part of the lake.
The distribution of detritic minerals appear to
be mainly controlled by lake hydrodynamics, wh
ich is strongly influenced for the intensity
and constancy of trade winds. Fo
r the authigenic minerals, the main factors controlling
the mineral distribution must be: (1) for amorphous silica: the occupation of the littoral
zone by macrophytes, which gave substrate and
nutrients to the production of diatom, in
larger part epiphytes; (2) for the goethite: hy
drological input, by surface or sub-surface
flows, which contribute with t
he entrance of Fe(II), which wil
l be oxidized in the lake
surface water, resulting in pr
ecipitation of goethite. Thus
, the detritic minerals (quartz
and kaolinite) are potentially go
od markers of erosion in the
lake drainage basin, while
authigenic minerals may give important
information about the past physicochemical
conditions of the environment.
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Environmentální dynamika svrchního pleistocénu ve střední Evropě: multidisciplinární výzkum spraší, paleopůd a jezerních sedimentů / Upper Pleistocene environmental dynamics in central Europe: multidisciplinary research of loess/paleosols sequences and lacustrine sedimentsHošek, Jan January 2017 (has links)
The principal goal of this thesis was to provide relevant information on the spatiotemporal dynamics of erosion-sedimentation and weathering processes in the last climatic cycle and to interpret the obtained data in the context of European paleoenvironmental development. Representative sequences of loess, paleosols and lacustrine sediments from the area of the Bohemian Massif, the Carpathian Foredeep, the the Vienna Basin and the northern edge of the Panno-nian Basin were investigated using a wide range of instru-mental tools and paleontological methods. A uniform analytical approach applied to these sedimentary facies has provided ample new information about the paleoclimatolog-ical and paleoenvironmental development of East-Central Europe - an important region in the transition zone from oceanic to continental macro-climatic settings. The individu-al studies included in this PhD thesis cover the complete period of the Upper Pleistocene (MIS 5-2; ~130-12.7 ky BP) and are presented as separate chapters in the order of the superposition of strata. Chapters III/1-3 deal with the results of research into six loess/paleosol sequences (LPSs) situated in the Central Bohemian Massif, throughout the Moravian Valleys, and at the northwest and north edge of the Pannonian Basin. A detailed paleoenvironmental...
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Korelace abiotických proxy v holocenních jezerních sedimentech peri-Atlantské Arktidy / Correlation of abiotic proxies in Holocene lacustrine sediments of Peri-Atlantic ArcticRoman, Matěj January 2017 (has links)
The peri-Atlantic Arctic, one of the most sensitive components of the Earth climate system, experienced pronounced climatic fluctuations during the Holocene. Several external forcings were considered responsible for these variations, including decline of insolation on the Northern Hemisphere, changes in distribution of land ice mass, explosive volcanism, or changes in atmospheric and oceanic circulation. In order to explore the driving mechanisms of the peri-Atlantic Arctic environmental variability, three sites located in different parts of the region were selected for palaeoenvironmental reconstructions with focus on extracting the climatic information. With this intention, sedimentary cores from i) Lake Garmaksla, Central Svalbard, ii) Jarfjorden, northeastern Norway, and iii) Kobbefjord area, southwestern Greenland, were retrieved and subjected to multi-proxy investigation. The absolute chronostratigraphic framework was established by comprehensive radiocarbon (14 C) and short-lived radioisotopes (210 Pb, 137 Cs) dating. Further analyses include measurements of magnetic susceptibility, grain size distribution, element composition by means of X-ray fluorescence (XRF), and elements bound to organic matter, i.e. organic carbon, nitrogen, sulphur and biogenic silica. The relationships between the...
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