Sedimentary Rocks

Standards Classify matter in a variety of ways Describe the composition and structure of Earth’s materials, including: the major rock types (i.e., sedimentary, igneous, metamorphic) and their formation

Sedimentary Rocks Cover 75% of Earth’s surface Make up only 5% of the crust by volume Form by burial and lithification of sediments lithification = the process of turning sediments into sedimentary rock by compaction &/or cementation Compaction = grains squeezed together by overlying sediments Cementation = minerals precipitate around sediments and bind them together

Lithification of Sediments Loose Sediments Sedimentary Rock Photo: Windows to the Universe http://www.windows.ucar.edu/tour/ link=/earth/geology/sed_lithification.html

3 Types of Sedimentary Rocks Clastic Chemical Organic

Clastic Sedimentary Rocks Are formed from fragments of other rocks by the following process: Weathering breaks rocks into fragments Physical weathering occurs by: Water Wind (also called eolian) Gravity, or Freezing Chemical weathering occurs by: Chemical reactions

Clastic Sedimentary Rocks The rock fragments are eroded and transported to new locations by water or wind The rock fragments are deposited – called sedimentation

Clastic Sedimentary Rocks 4. The rock fragments are buried and turned into rock (lithification). Cementing agents are sometimes present and help turn the sediments into rock. Types of cementing agents are lime, iron and silica

Deposition of Sediments As sediments are transported from their source, the largest fragments get deposited first (i.e., closest to the source). This happens because the current that is carrying the sediments slows, and therefore can no longer carry the larger particles. This means that large sediments get deposited in high energy environments and small sediments get deposited in low energy environments. Examples: boulders are deposited in mountain streams, sand is deposited on beaches, and clay is deposited in the ocean

Naming Clastic Sedimentary Rocks Clastic sedimentary rocks are named according to the size of the fragments that make them. Fragment mm Fragments Rock Size Names Coarse 64 – 2 pebbles conglomerates gravel breccia Medium 2 – 1/16 sand sandstone Fine to 1/16 – 1/256 silt siltstone Very fine clay shale

Pebbles to Conglomerate Photo: Aradon, Australia http://www.aradon.com.au/Austgems.htm Photo: http://www.bluewatersbb.com/ images/pebbles.jpg Photo: USGS http://pubs.usgs.gov/of/2004/1007/ terraces.html

Sand to Sandstone Photo: http://www. mccullagh.org/db9/ 1ds-4/sahara-desert- sand-dune.jpg Photo: http:// www.photo- mark.com/cgi- bin/getpic.cgi? id=233 Photo: Zion National Park http://www.zionnationalpark.com/ zioninfo/photos/photos.htm

Clay to Shale Photo: http://www.saraarts. com/alaska/shale.html arikah.com/commons /en/2/2c/Clay-ss-2005 .jpg Photo: http://www.dannyburk.com/shale%20hills.htm

Grain Sorting The size of grains in a sedimentary rock will be either well-sorted (all near the same size) or poorly-sorted (lots of different sizes). Well-sorted sediments have been transported farther than poorly-sorted sediments. Wind-transported sediments are more well-sorted than water transported sediment. Poorly-sorted Well-sorted

Grain Rounding Grains in a sedimentary rock will be either rounded or angular, depending on how far they have been transported. Grains that have been transported further get abraded longer and are thus more rounded. Rounded Angular

Chemical Sedimentary Rocks Chemical sedimentary rocks are formed by: Precipitation out of a solution (a solid comes out of solution) Evaporation Chemical action

Names of Chemical Sedimentary Rocks Limestone – made of calcite &/or tiny sea creatures Rock salt (halite) – formed by evaporation Rock gypsum – formed by evaporation Silicates – microcrystalline (or cryptocrystalline) quartz exs: agate, chalcedony

Types of Chemical Sedimentary Rocks 5. Concretions – nodules (clumps) of silica in limestone with quartz or calcite crystals in center (geodes) Petrification – replacement of plant and animal remains by another mineral = fossil Ex: petrified wood: wood is replaced by microcrystalline quartz

Organic Sedimentary Rocks Organic sedimentary rocks are formed from plants and animals. Organic material dies, gets buried and turns into sedimentary rock.

Names of Organic Sedimentary Rocks Some limestone Coquina – made of shells and limestone 3. Coal – made of plants, peat 4. Chalk – made of microorganisms Photo: Chalk Cliffs, Dorset http://www.gsi.ie/everyone/europe/ uk/P005814_chalk_cliffs_dorset.jpg

Sedimentary Structures Sedimentary structures – features that are formed in sedimentary rocks when the sediments are deposited (i.e., before the sediments are turned into rock) They include: - bedding - cross-bedding - graded bedding - ripples - bioturbation structures

Bedding Also called stratification. Occurs when layers of different grain sizes or compositions are deposited on top of one another. Can be from millimeters to meters thick.

Cross-Bedding Sets of bedded material inclined at angles to each other. Occurs when sediments are deposited on steeper, downcurrent slopes of sand dunes or sandbars.

Cross-Bedding Photo: Zion National Park http://www.earth. northwestern.edu/grad/

Cross-Bedding Photo: Cross Beds in Jemez Red Rocks L. Brown 7-6-11

Graded Bedding Progression of a bedding layer from coarse-grained at the bottom to fine- grained at the top. Indicates a weakening of the current carrying the sediment.

Ripples Low narrow ridges. Symmetrical or asymmetrical.

Symmetrical Ripples Formed by back and forth motion of waves.

Asymmetrical Ripples Formed by currents moving in one direction.

Bioturbation Structures Tubes and other structures left by burrowing organisms

Sedimentary Rocks are Economically Important Coal is a major energy resource Limestone is used as building material, stone and an ingredient in cement Ores and native elements such as copper, lead, zinc, iron, gold & silver are all concentrated in sedimentary rock Fossils are found in sedimentary rocks