Sedimentary Rocks

• Sedimentary rocks form when sediments harden into rocks

• 3 main kinds clastic, chemical and organic

• Most of Earth’s crust is covered by sedimentary rocks

Three Main Kinds of Sedimentary Rock

Clastic:cemented together fragments of other rocks

Chemical:mineral grains that are removed from a solution by evaporation or chemical action

Organic: remains of plants and animals

Clastic Rocks Clastic sedimentary rocks are made up of

weathered rocks that already exist Rocks are weathered and transported by

rivers, winds, waves, and glaciers Sediments are deposited when the

transport system loses energy ie: stream Ocean water, lake water, and groundwater

contain natural cements: silica(SiO2), calcite (CaCO3), and iron oxide(FeO)

These dissolved minerals settle into the spaces between the sand grains or pebbles, binding them together into rock

The pressure of overlying sediments can also make fine sediments stick together

Clastic Rocks: Conglomerate

• Coarse, large grains

• Deposited in high energy system (rough water)

• Cemented mixture of rounded pebbles and sand grains

• Pebbles can be any durable rock material

Clastic rocks: Sandstone

• Medium grained• Quartz grains (7 on

Moh’s scale of hardness)

• Porous (small holes)

• Permeable (water can pass through)

Clastic rocks: Shale

Fine grained clay minerals Impermeable Smooth, soft and easily broken Found in very low energy

environments

Sorting of Sediments

Chemical Sedimentary Rocks

Dissolved minerals fall out of solution Evaporation or the combining of dissolved

ions to form new minerals. The most common are limestone, rock

salt, and rock gypsum Limestones are formed from tiny grains of

calcite Rock salt is the natural form of table salt,

it is almost pure halite Rock gypsum occurs in layers and is

almost pure gypsum

Chemical Sedimentary Rocks

Rock Salt Limestone

Organic Sedimentary Rocks

Organic sediments come from the remains of plants and animals

The most common are shell limestone and coal

shell limestone is mostly calcite, shell producing animals die and their shells pile up and are cemented together

Sedimentary Features: Stratification Stratification is the arrangement of rocks in

visible layers When there is a change in the type of

sediments being laid down, new rock layers are formed

Change results from new source sediments or energy change

The layers are called beds and are separated by bedding planes

Sedimentary Features: Cross Bedding

Cross-bedding develops when beds are deposited at an angle:

wind on dunes, rivers on deltas or sandbars

Fossils in Sedimentary Rocks

Animals and plants that die and are buried, as sediments pile up= fossils

The hard parts may remain as fossils when the sediments turn to rock

Fossils are the remains, impressions, or any other evidence of plants and animals preserved in rock

Ripple Marks and Mud Cracks

Many sandstones show ripple marks that are formed by the action of winds, streams, waves or currents on sand.

Mud cracks develop when deposits of wet clay dry and contract

Mud cracks are later filled with different materials, and the clay becomes shale rock.

Nodules, Concretions, Geodes Nodules are lumps of fine-grained silica called

chert, solid replacement bodies Concretions are round masses of mineral

precipitation that form around some kind of nucleus A Geode is a hollow nodule of silica rock, filled with

crystals of quartz or calcite

Nodule

Geode