SEDIMENTARY ROCKS FORMATION OF SEDIMENTARY ROCKS • Sedimentary rocks are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. • The formation takes place by 4 methods. Formation Weathering Transportation Deposition Consolidation WEATHERING: • Weathering means “erosion of existing rocks”. • This weathering takes place in 2 ways. WEATHERING MECHANICAL WEATHERING CHEMICAL WEATHERING TRANSPORTATION OF ERODED SEDIMENT: • After the erosion process (weathering) the products are transported . • This transportation is mostly done by running waters. DEPOSITION OF THE ERODED SEDIMENT: • This transportation continues till the velocity of transporting medium id unchecked. • When it reaches big waters like oceans the deposition process takes place. LITHIFICATION: • The transformation of a loosely deposited sediment into a rock is called as lithification. • This is done in 2 ways. Lithification By Compaction (or) Consolidation By Cementation CLASSIFICATION OF SEDIMENTARY ROCKS • Based on the processes responsible for their formation, sedimentary rocks can be subdivided mainly into two groups: 1.Clastic Rocks 2.Non-Clastic Rocks • The non-clastic rocks are again classified into two types. • They are: 1.Chemical 2.Organic • CLASTIC ROCKS: • Clastic sedimentary rocks are composed of silicate minerals and rock fragments that were transported by moving fluids (as bed load, suspended load, or by sediment gravity flows) and were deposited when these fluids came to rest. Clastic rocks are composed largely of quartz, feldspar, rock (lithic) fragments, clay minerals, and mica; numerous other minerals may be present as accessories and may be important locally. SANDSTONE: CONGLOMERATE: CHEMICALLY FORMED ROCKS: • Chemical sedimentary rock forms when mineral constituents in solution become supersaturated and inorganically precipitate. Common chemical sedimentary rocks include oolitic limestone and rocks composed of evaporite minerals such as halite (rock salt), sylvite, barite and gypsum. ROCK SALT: DOLOMITE: • ORGANICALLLY FORMED ROCKS: • Biochemical sedimentary rocks are created when organisms use materials dissolved in air or water to build their tissue. Examples include: • Most types of limestone are formed from the calcareous skeletons of organisms such as corals, mollusks, and foraminifera. • Coal which forms as plants remove carbon from the atmosphere and combine with other elements to build their tissue. • Deposits of chert formed from the accumulation of siliceous skeletons from microscopic organisms such as radiolaria and diatoms. COAL: OIL SHALE: TEXTURES • The size, form and orientation of clasts or minerals in a rock is called its texture. The texture is a small-scale property of a rock, but determined many of its large-scale properties, such as the density, porosity or permeability. • The form of a clast can be described by using four parameters: • Surface texture describes the amount of small-scale relief of the surface of a grain that is too small to influence the general shape. • Rounding describes the general smoothness of the shape of a grain. • 'Sphericity' describes the degree to which the grain approaches a sphere. • 'Grain form' describes the three dimensional shape of the grain. STRUCTURES OF SEDIMENTARY ROCKS • The term structure signifies some large scale features developed in the rock masses during the process of their formation. • Structure is of 3 types: STRUCTURE MECHANICAL CHEMICAL ORGANIC • MECHANICAL STRUCTURE: • These are developed due to physical processes operating at the time of deposition of the sediments. • The various types of mechanical structures are as follows: 1.Stratification 2.Lamination 3.Cross Bedding 4.Graded Bedding 5.Mud Cracks 6.Rain Prints 7.Ripple Marks CHEMICAL STRUCTURES: • Many sedimentary rocks are formed due to the chemical processes such as evaporation, precipitation and crystallization. • A few types of chemically formed rocks are: 1.Concretionary structure 2.Nodular structure 3.Geode structure ORGANIC STRUCTURES: • Some structures develop in the sedimentary rocks due to the manner in which the organic source material gets accumulated and compacted to form a rock. • They form 2 types of structures namely, fossilferrous and stromatolitic structures. SEDIMENTARY ROCKS Iron Ore Limestone Shale Flint Conglomerate Chert Coal Breccia ENGINEERING PROPERTIES OF SEDIMENTARY ROCKS: • Compressive strength and deformability of sandstone is influenced by its porosity, the amount and type of cement, and matrix material, grain contact and composition. • Shale mineral content influences geotechnical properties; most important is the quartz-clay mineral ratio. • Grain size and Cementation influence engineering properties of carbonate sediments.