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Sedimentation
Published in Ronald C. Chaney, Marine Geology and Geotechnology of the South China Sea and Taiwan Strait, 2020
Figure 8.1 concentrates on sediments close to the People’s Republic of China coastline. A review of Figure 8.1 shows a narrow shelf bordered by a steep irregular slope along the east coast of Taiwan. In the Taiwan Strait, the sediment is largely relict sand. Continuing along the Chinese coast the shelf sediments as far south as Hong Kong are mainly considered predominately relict. South of Hong Kong, large rivers contribute recent muds, which form the sediment cover of the shelf except for narrow sand belts where the Kuroshio current has prevented deposition. Beyond this wide shelf that forms the Gulf of Tonkin, the shelf narrows and becomes very irregular along the coast of South Vietnam. South-west of Hainan, a large group of coral banks lie east of a deep basin, with depths of approximately 1500 m. The gentle continental slopes contrast greatly with the steep slopes that border the shelves farther south.
Introduction
Published in Dominic Reeve, Andrew Chadwick, Christopher Fleming, Coastal Engineering, 2018
Dominic Reeve, Andrew Chadwick, Christopher Fleming
At the local-scale, response of the geomorphological elements is key to the predictions of future coastal evolution. Understanding why the feature is where it is and its particular morphology is essential to understanding future behaviour. What are the key internal physical controls on the behaviour of the feature, for example, geology/composition, resistance to erosion, height, width, position, etc.?What are the key external physical controls on the behaviour of the feature, for example, is it a wind-created feature, wave-dominated feature, etc.?Does it depend on a sediment supply, and if so what are the key sources? Is the source of sediment contemporary or relict?What are its links with neighbouring geomorphic units, for example, does is depend upon another feature for its sediment supply or is it a source for other features?Does its evolution fit into a larger-scale pattern of change?
Metamorphic Rocks
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
The term fabric is used to denote the arrangement of mineral constituents and textural elements in a rock, in three dimensions. This is particularly useful in metamorphic rocks, as it enables the preferred orientation of minerals, when present, to be described with reference to broader structures. Thus, rocks are either isotropic, when there is no orderly arrangement of their components (as in hornfels); or anisotropic (as in schists) when there is parallel orientation of minerals, often well developed. Relict textures from an original sediment, such as banding due to variation in composition, may also be preserved in the fabric of the equivalent metamorphic rock (Fig. 7.1). In graded bedding (Figs. 2.1; 6.6) for example, the upper (clayey) part of a graded bed will show conspicuous crystals grown from the clays (e.g. andalusite), in contrast to the equigranular crystals of quartz, formed from the sandy base of the bed.
Geomorphic responses of uplifted mixed sand and gravel beaches: combining short-term observations from Kaikōura, New Zealand with longer-term evidence
Published in New Zealand Journal of Geology and Geophysics, 2023
Kate E. MacDonald, Deirdre E. Hart, Sebastian J. Pitman
Kirk (1980) proposed that there were four main morphological zones on a MSG beach. These zones are (1) backshore; (2) foreshore; (3) break point step and (4) nearshore. The backshore zone is the area landward of the storm berm, located at the edge of the active profile. It is commonly composed of relict sediment deposits (Dawe 1997), over-washed during storms (Kirk 1980), and some vegetation. The backshore is a good indicator of historical long-term change or events, as often there are paleo terraces present. These are abandoned berms in the backshore due to a change in environmental conditions, or an event with significant uplift (Orford et al. 1996). The foreshore comprises of multiple berms, usually one at the landward edge of the zone, the storm berm, which marks the highest elevation of contemporary storm wave runup. Further down the profile, subsequent smaller berms form with different wave energy and sediment supply (Pontee et al. 2004). There is no set number of berms a MSG profile will have, nor is there a set elevation the berms will commonly appear at, as they usually form at the limit of wave runup, which varies on different beaches depending on factors including slope and wave energy (Jennings and Shulmeister 2002).
The interplay of structure and metamorphism at Broken Hill, NSW, Australia
Published in Australian Journal of Earth Sciences, 2022
The Mt Robe–East Eldee Structure is a complex interference fold structure with a more or less figure-of-eight outline (Figure 6). The core of the structure mainly comprises Thackaringa Group, Broken Hill Group, and intrusive pegmatite, and is surrounded by Sundown Group metasediments. Sundown Group metasediments along the eastern side of the structure are andalusite-bearing, and Glen (1978), Stevens et al. (1994) and Thomson (1976) all placed the andalusite–sillimanite isograd at approximately the Broken Hill Group–Sundown Group boundary, confirmed by Fitzherbert (2015). On the Lakes Creek 1:25 000 sheet to the south, Stevens and Bradley (1993) placed the isograd at a slightly higher stratigraphic level in the Sundown Group. To the west of the Mt Robe Structure, the Sundown Group displays sillimanite-grade metamorphism, but relict andalusite is common (Fitzherbert, 2015). The core of the structure is at sillimanite grade, and metasediments in the core show considerable partial melting. However, partial melting is virtually absent in the Sundown Group metasediments that enclose the Mt Robe–East Eldee Structure.
Late Devonian contact metamorphism and a possible upper age to gold mineralisation in the northernmost portion of the Reefton Goldfield
Published in New Zealand Journal of Geology and Geophysics, 2019
Bryce A. Robinson, James M. Scott
The hornfelsic rocks within ∼1300 m of the granite-Greenland Group contact (Figure 2) are distinctly browner than either the albite-epidote hornfels facies or greenschist facies rocks. Relict detrital quartz grains are present but the metamorphic mineralogy consists of muscovite, quartz, oligoclase (confirmed by EDS), chlorite and biotite (Figure 4C). In some cases, oligoclase contains relict albite cores. Biotite is abundant, is randomly oriented around quartz grains and imparts the overall brown colour to the rock. Ilmenite, rutile, apatite, K-feldspar, pyrite, titanite, zircon and monazite occur in minor quantities (<1%). Spotted hornfels textures occur in some meta-argillite rocks. The spots are typically composed of fine-grained muscovite after what may have been cordierite.