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Fluvial and coastal depositional environments may have been quite different before the development of land plants in the late Silurian. Rapid drainage of terrestrial surfaces, flashy rivers with poorly stabilized banks, coarse sediment loads supplied to coasts from landscapes dominated by physical weathering, and the prevalence of epicontinental seas are expected to have altered depositional patterns and associated preserved Facies. Quarries in the Upper Cambrian Hickory Sandstone located in central Texas provide an exceptional opportunity to examine the sedimentology of deposits of this age in order to interpret sedimentary environments. During quarrying, vertical walls, one half-kilometer long and several tens of meters high, are blasted back a few tens of meters at a time and then the rubble excavated, exposing successive outcrops in walls that are perpendicular to the regional paleocurrent direction. The deposits are characterized by sheet-like bedsets dominated by unidirectional cross-stratified sandstones interpreted to have formed in coastal areas fed by bedload dominated rivers. Thinner heterolithic and clay beds locally separating cross-stratified bedsets are commonly bioturbated by marine organisms. Presence of tidal features, such as abundant mud drapes, concave-upward cross-stratification and sparse herringbone cross-stratification, also suggests marine influence during deposition. Detailed mapping of stratal geometry and Facies across these exposures shows a complex internal architecture that can be interpreted in terms of growth and superposition of bars within shallow fluvial channels and adjacent shallow marine areas along the coast. Detailed 3D reconstruction of bars and channels reveals a range of processes including growth, coalescence, and erosion of bars during channel migration, switching and filling of channel segments, and mouth bar growth as channelised flows decelerated seaward. Sedimentary Facies, stratal geometry and ichnofossils suggest that these deposits were formed in a braid-delta system fed by lowsinuosity bedload-dominated rivers. Basinal processes were controlled by the shallow epicontinental sea, dissipating wave action and strengthening tidal currents.

Waldsea, Deadmoose, and Lenore lakes are three saline lakes located in the Lenore Basin drainage complex north of the town of Humboldt in south-central Saskatchewan, Canada. Waldsea Lake and Deadmoose Lake are both meromictic, with anoxic, saline to hypersaline (~30-45 g L-1 TDS) Na-Mg-SO4 –rich monimolimnion waters underlying hyposaline to saline mixolimnions. Lenore Lake water shows similar ionic ratios but is less saline (~4 g L-1 TDS) and does not exhibit meromixis. Water levels in these closed-basin lakes have historically fluctuated dramatically. Present-day high levels in the basins have lead to considerable social, economic, and environmental disruptions and problems. Short sediment cores (~1 m length) were collected from deep-water offshore locations in each basin in order to study sedimentological and hydrological changes that have occurred over the past several millennia and to place the current high water levels into a longer-term perspective. The late Holocene stratigraphic sequences recovered from Waldsea and Deadmoose lakes are roughly similar: both comprise overall well-bedded, fine-grained, organic-rich sediment dominated by endogenic gypsum and detrital clay minerals, with associated quartz, plagioclase and carbonate minerals. They both contain laminae composed of endogenic aragonite. Two lithostratigraphic units are identified in each sequence on the basis of bedding, grain size, organic matter content, geochemistry, mineralogy, and δ18O and δ13C characteristics. Although chronostratigraphic control is limited, AMS 14C dating of plant remains in the cores indicate that the recovered sequence from Waldsea spans approximately 1500 years whereas the Deadmoose sequence covers about 3500 years. The recovered Lenore Lake sequence is mainly non-bedded and largely composed of fine to coarse-grained siliciclastics and detrital carbonate minerals. Like Waldsea and Deadmoose, two lithostratigraphic units are identified, however efforts to establish chronostratigraphic control for the section recovered from Lenore Lake were not successful. The short cores recovered from each of these basins show a clear change from shallow water deposition at the base to deep(er) water conditions further up the section. This change was likely a result of the development of a more positive hydrologic budget in each of the basins. The lack of chronological synchrony of the interpreted hydrologic changes, however, suggest that the effects of regional climatic fluctuations are masked by various intrinsic sedimentological, geochemical, and biological processes operating within each basin.

The balance of the physical processes that drive the morphodynamics of a complex inlet system is investigated in this work. For this purpose, an innovative technique using coupled video imaging and numerical modelling has been used to study the relative importance of the driving forces that control the sandbar dynamics at the Teignmouth inlet system. The sandbars that form the ebb tidal delta are highly dynamic, leading to a cyclic morphological behaviour. Application of the numerical model (MIKE21 HD, NSW, ST) served two separate functions. The hydrodynamic model has been used for the image processing and, combined with the sediment transport module, the full model has been used to understand the relative importance of the driving forces at the region. The iterative application of the hydrodynamic model and the video images, with the modelled water levels used as input to the image processing, provides the video-based intertidal morphology that is used in further modelling experiments. This loop is repeated several times during the three-year study period that covered a complete morphological cycle. This results in a quantitative assessment of the relative influence of the key processes that control the environment and in initial steps towards the prediction of its evolution. In order to assess the relative importance of the driving forces a series of modelling experiments were designed to include a variety of forcing conditions. These include the tidal range, wave conditions and river discharge values. The relative importance of each of the physical processes on the sediment transport and consequent morphodynamics varies across the region. The main inlet channel is dominated by tidal action that directs the sediment transport as a consequence of the varying tidal flow asymmetry, resulting in net offshore transport. Sediment transport over the shoals and secondary channels at both sides of the main channel is dominated by wave related processes, displacing sediment onshore. The interaction between waves and tide generated currents controls the transport over the submerged sandbar that defines the channel's seaward extent. High river discharge events are also proven to be important in this region as they can change sediment transport patterns across the area. Waves play a major role in the sandbar morphodynamics. Despite the relative low frequency of high wave energy events that reach the region they are responsible for large amounts of sediment displacement, catalysing some dramatic morphological changes. Therefore, the temporal distribution of storms defines the cyclic behaviour of such environments, making the system more dynamically active over the winter months. It is also during this period that river discharge values reach high peaks, increasing the capacity of the ebbing tidal flows and interacting with the opposing waves. The opposite occurs during summer periods, when less energetic conditions lead to slower morphological changes. The application of an initial sedimentation/erosion model proved to be useful in giving qualitative predictions of the morphological evolution of such a complex sandbar system, reflecting the initial morphological changes for different forcing conditions. Qualitative comparisons between the modelled sedimentation/erosion patterns and the video based observations of the changes at the dynamic offshore sandbar show that the model is able to reproduce its overall evolutionary tendency. The morphological adjustment of the system to the forcing conditions shows the progression towards the next morphological stage, allowing the initial steps towards predicting the evolution to be taken. The technique applied, coupling the numerical model with the video images, has been shown to be of great value in providing a better understanding of the processes that control the dynamics of inlet systems. At short time-scales, quantitative information about the acting processes and how they interact has been gained by the modelling experiments, and at medium time scales, the combined application resulted in qualitative predictions of the evolution of most regions of the system.

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No description available.

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No description available.