3.2 – Sedimentary Rocks

Formation of Sedimentary Rocks sedimentary rock: rock made up of combinations of different types of sediment sediment: loose fragments of rock, minerals, and organic materials two main processes convert loose sediment into sedimentary rock - compaction and cementation

compaction: process where sediment is packed together tighter by the weight of overlying sediments cementation: process where minerals precipitate into pore spaces between sediment grains & glue the sediments together

Classes of Sedimentary Rocks classify sedimentary rocks by the processes that form the rocks and by the composition of the rocks three main classes of sedimentary rocks - chemical, organic, and clastic

Chemical Sedimentary Rocks chemical sedimentary rock: forms when minerals precipitate (separate) from a water solution when water evaporates or boils off, the minerals that were dissolved in the water are left behind

gypsum, rock salt (halite), and chemical limestone (oolitic gypsum, rock salt (halite), and chemical limestone (oolitic!) are common chemical sedimentary rocks

geodes are common chemical sedimentary rocks, too!

Organic Sedimentary Rocks organic sedimentary rock: forms from the remains of plants or animals coal and organic limestones are examples of organic sedimentary rocks

Clastic Sedimentary Rocks clastic sedimentary rock: sedimentary rock that forms when fragments of sediment are compacted or cemented together clastic sedimentary rocks are classified by the size of the sediments they contain

conglomerate: contains large, rounded pieces sandstone: contains sand-sized grains

shale: contains clay-sized particles

Features of Sedimentary Rocks unique features in sedimentary rocks can give clues to their origin sediments are moved by four main agents: water, ice, wind, and the effects of gravity as sediment is transported from its source to where it is deposited, the particles collide with each other &with other objects in their path

these collisions cause the particles to change size and shape in general, the farther sediment travels from its source, the finer and smoother the particles of sediment become

in well-sorted sediments, all of the grains are roughly the same size and shape in poorly sorted sediments, grains are many different sizes

look for mud cracks, ripple marks, and fossils as clues – oldest materials on the bottom!