Physical Characteristics of Sedimentary Rocks

Sedimentary rocks possess definite physical characteristics and display certain features that make them readily distinguishable from igneous or metamorphic rocks. Some of the most important sedimentary characteristics include the following  

Graded bedding—In a stream, as current velocity wanes, first the larger or denser particles are deposited followed by smaller particles. This results in bedding showing a decrease in grain size from the bottom of the bed to the top of the bed (fine sediment on top and coarse at the bottom). 

Ripple marks— These are characteristic of shallow water deposition and are caused by small waves or winds that leave ripples of sand on the surface of a beach or on the bottom of a stream. Ripples of this type have also been preserved in certain sedimentary rocks and may provide geologists with information about the conditions of deposition when the sediment was originally deposited. 

Concretions—These spherical or flattened masses of rock enclosed in some shales or limestones are generally harder than the rock enclosing them. Because concretions are usually harder than the enclosing rock, they are often left behind after the surrounding rock has been eroded away. 

Fossils—Fossils are the remains or evidence of once living organisms that have been preserved in the Earth s crust. Because life has evolved, fossils give clues to the relative age of the sediment and can be important indicators of past climates. 

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