China
Africa
Explore chapters and articles related to this topic
Stratigraphy
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
The stratigraphy and formations of the Grand Staircase and Grand Canyon are typical of continental regions where relatively flat-lying sedimentary rocks are found. If a sedimentary layer or formation extends over a large area, outcrops made of identical kinds of rocks can be correlated (matched with rock units of the same age but in different places), even if a valley or other erosional feature separates them. The areal extent, thickness, and compositions of different kinds of beds, and their relationships with beds above and below them, allow geologists to reconstruct geological histories. So, studying stratigraphy is important for the wealth of information it provides about Earth’s evolution, the evolution of life, and the history of civilization. It is also important because it can guide coal, oil, gas, and mineral exploration.
Distribution of rocks at and below the surface
Published in A.C. McLean, C. D. Gribble, Geology for Civil Engineers, 2017
Original layering in sediments is called stratification or bedding. (Different terms are used for the layering produced by other igneous and metamorphic processes.) Each layer is referred to as a stratum (plural, strata) or bed, though the latter term is normally applied only to sedimentary rocks and volcanic ash layers. It is never applied to the layer formed by a basaltic or rhyolitic lava flow. The interfaces between beds are called bedding planes. The outcrops of major bedding planes that separate thick beds of different rock type are depicted on geological maps. Bedding planes may also occur within a thick layer of sandstone, where minor changes of composition or texture, or even a break in deposition, are present. These are planes of weakness, or potential planes of failure, and their presence produces a change of mechanical properties of the rock with the direction in which they are measured (that is, the bulk properties of the rock are anisotropic). Minor bedding planes are abundant in micaceous shale, because mica flakes lie in the bedding direction as they grow in the rock or settle in water. Rocks that are devoid of bedding and other planes of weakness such as joints (see Section 4.4.4) are said to be massive.
Design tools
Published in G.J.C.M. Hoffmans, H.J. Verheij, Scour Manual, 2021
G.J.C.M. Hoffmans, H.J. Verheij
Overall degradation at, for example, a bridge site lowers the bed level and may thereby increase the risk of failure of the foundations. Aggradation, on the contrary, will cause higher water levels and may reduce the risk from scour. Degradation processes already in progress have to be considered, as well as the possibility of inducing degradation processes in the future (e.g. seasonal degradation). Overall degradation can affect a long reach of the river, extending over tens to hundreds of kilometres and over periods of decades to centuries (de Vries, 1975). Examples are the Bovenrijn and Waal branches of the river Rhine in the Netherlands which experience general bed degradation due to enhanced sediment transport capacity and reduced sediment supply from upstream.
Mapping a coastal transition in braided systems: an example from the Precipice Sandstone, Surat Basin
Published in Australian Journal of Earth Sciences, 2018
V. Bianchi, F. Zhou, D. Pistellato, M. Martin, S. Boccardo, J. Esterle
The outcrops were chosen by combining the Queensland State Geological Map (1:1 M) with field information from various works (Green et al., 1997; Martin, 1980; Mollan et al., 1972) and a slope analysis of the Queensland DEM made with ArcGIS. Facies analysis was undertaken on vertical stratigraphic sections (i.e. lithologs) and field photographs produced from each outcrop observation. Measured sections recorded grainsize, primary sedimentary structures, as well as fossil and trace fossil content in beds and bedsets. Measured sections were tied to photomosaics of the outcrop to highlight depositional architecture and stratal relationships. More than 70 paleocurrent measurements were collected from planar tabular and trough cross-beds exposed in outcrop. Other paleoflow indicators included imbricated clasts. These observations were used to subdivide the Precipice Sandstone into allounits (defined in the discussion).
The short-lived but successful tri-radial body plan: a view from the Ediacaran of Australia
Published in Australian Journal of Earth Sciences, 2020
C. M. S. Hall, M. L. Droser, E. C. Clites, J. G. Gehling
The Ediacara Member of the Rawnsley Quartzite crops out throughout the Flinders Ranges area and is the uppermost Ediacaran unit in the Neoproterozoic–middle Cambrian succession of South Australia (Gehling, 2000). It is uniquely characterised by dense and exceptionally preserved fossil assemblages of the Ediacara fossils of the White Sea assemblage (cf. Waggoner, 2003). The Ediacara Member consists of a siliciclastic, sandstone-dominated sequence interpreted to have been deposited across a range of shallow marine and deltaic settings. Fossils typically occur as hyporelief external and internal moulds on the base of sandstone beds.