Geology, Morphology, and Sedimentology of Estuaries and Coasts

摘要: The sedimentary rocks exposed at the surface of Earth today consist primarily volcaniclastics (∼17.6%), graywackes (∼2.6%), arkoses (∼5.3%), quartz sandstones (∼7.5%), mudrocks (∼60%), limestones and dolomites (∼6.0%), evaporites (∼1.0%). Together with weathering products igneous rocks, they form source sediments supplied to coasts world by river glacier discharge. It is estimated that between 20 70 × 10 9 t sediment are delivered coast every year. While majority beaches gravels sand, including various proportions bioclastic material, some remain muddy because wave action unable remove large amounts fine-grained rivers. morphodynamic behavior finely tuned local grain size climate, beach slope generally increasing size, but decreasing higher energy so for any given high-energy tend be flatter than low-energy beaches. Estuaries show a marked tripartite longitudinal zonation independent tidal range. Both lower upper estuaries sandy and/or gravely, material being restricted part. Middle estuaries, contrast, formed flocculation processes in mixing zone saltwater freshwater. Aggregates predominately particles smaller about 8 µm main components fluid muds found many estuaries. Muds have water contents hence bulk densities sands 50:50 sand–mud mixtures contain more mud per unit volume 100% pure mud.