SEDIMENTARY ROCKS

Sedimentary Rocks 80 % of Earth’s surface is covered with sediments and Sedimentary Rocks

What is sediment???? Broken pieces of rocks called CLASTS Chemical precipitates ( dissolved solids come out of solution) Organic fragments – shells, decayed plant matter – this is called BIOCLASTIC

Source of Sediment When Igneous, Metamorphic Rocks, and Sedimentary Rocks are uncovered and exposed to the atmosphere and hydrosphere they start to break down Weathering is the general term for all actions that break down or wear away rock Erosion is the carrying away of the sediment

Sedimentary Rocks form when after weathering and erosion sediments/clasts are … Deposited in horizontal layers called beds or strata Buried Compacted – particles forced extremely close together because of the pressure of the overlying layers and water Cemented – glued together

Cementing Material (Glue) Minerals precipitate out of solution to cement particles together. Cementing material is often quartz, calcite, and hematite

Most Sedimentary Rocks form under large bodies of water, such as lakes, seas, and oceans

Horizontal layers deposited under water

Classification of Sedimentary Rocks We classify sedimentary rocks depending whether the sediments are LAND DERIVED CHEMICALLY - ORGANICALLY DERIVED

INORGANIC LAND DERIVED Main source of clasts are from pre-existing igneous, metamorphic or other sedimentary rocks that have been weathered.

CHEMICAL Sedimentary Rocks Sediment From Solution All liquid water contains dissolved minerals. These minerals precipitate (dissolved solids come out of solution/water) Usually happens because of evaporation

ORGANIC Sedimentary Rocks Bioclastic Sediment LIMESTONE AND CORALS Dissolved minerals taken out of solution by marine organisms for their hard parts (shells) can pile up on the seafloor when they die. These fossil remains accumulate into a thick enough layer to form an “organic” sedimentary rock Cement is commonly calcite ( bubbles with acid) COAL Decayed plant remains

Identifying Sedimentary Rocks To identify Sedimentary Rocks, we ask ourselves 2 questions: Where does it come from? Look at the composition Where was it put together? Look at the texture or grain size.

Composition of Inorganic Land-Derived Sedimentary Rocks Sediment is from pre-existing older rocks What type of minerals make up igneous and metamorphic rocks? Silicate minerals

Composition of Inorganic Land Derived Sedimentary Rocks Silicate Minerals Quartz – highly resistant (remember Moh’s scale) Feldspars Clay minerals (form when feldspars weather in water) HOW USEFUL IS COMPOSITION FOR CLASSIFYING THESE ROCKS?

WHERE WAS IT PUT TOGETHER??? Let’s see if 2nd question helps us. Texture or grain size What do you notice about grain size? Is there a range of sizes within each category?

Let’s look at Sand

Sand Composition Varies BLACK SAND HAWAII – BASALTIC MINERALS GREEN SAND – HAWAII – OLIVINE WHITE SAND – GYPSUM PINK SAND - CORALS

HOW DO WE KNOW THE SEDIMENT IS SAND?? To be considered sand the range of grain sizes is from 0.2 cms. to 0.006 cms. COMPOSITION MAY VARY – BUT ALL SAND CONTAINS SILICATE MINERALS

NAMING INORGANIC LAND DERIVED SEDIMENTARY ROCKS WE CANNOT NAME INORGANIC LAND-DERIVED SEDIMENTARY ROCKS BY THEIR COMPOSITION BECAUSE ALL CONTAIN SILICATE MINERALS WE CAN NAME BY THEIR GRAIN SIZE

Sediments are pebbles, cobbles, and boulders rounded Breccia angular

Silt (0.006 to 0.0004 cms. SILTSTONE Sand (0.2 to 0.006 cms.) SANDSTONE Clay (less than 0.0004 cms.) SHALE

IDENTIFYING CHEMICALLY AND/OR ORGANICALLY FORMED SEDIMENTARY ROCKS WE ASK SAME 2 QUESTIONS: Where was it put together? Look at the texture or grain size. Where does it come from? Look at the composition

2 TYPES OF TEXTURE CRYSTALLINE FOR CHEMICALLY FORMED SEDIMENTARY ROCKS BIOCLASTIC FOR ORGANICALLY FORMED SEDIMENTARY ROCKS HOW USEFUL IS GRAIN SIZE????

WHERE DOES IT COME FROM –COMPOSITION??? Comments ROCK NAME Halite Crystalline Rock Salt Gypsum Rock Gypsum Dolomite Dolostone Calcite Cemented shells or precipitates Limestone Carbon Plant remains Coal

ROCK SALT Intergrown crystals of just 1 mineral DOLOSTONE ROCK GYPSUM

Characteristics of Chemically Formed Sedimentary Rocks They are monominerallic – consisting of intergrown crystals of just 1 mineral. Uniform color Form in shallow seas

CHEMICALLY PRECIPITATED LIMESTONE BIOCLASTIC LIMESTONE COAL

Summary Inorganic Land-Derived Sedimentary Rocks are identified by Texture or Grain Size Chemically and/or Organically Formed Sedimentary Rocks are identified by Composition

ENVIRONMENT OF FORMATION How does the natural environment affect the formation of Sedimentary Rocks???? What conditions control which Sedimentary Rock is formed????? Why are certain rocks formed at different locations???

THE SIZE OF THE GRAIN IS DETERMINED BY THE ENVIRONMENT OF FORMATION HIGH ENERGY ENVIRONMENT Large particles Fast moving water – rivers, ocean waves LOW ENERGY ENVIRONMENT Small particles Slow moving water – lake, bay, swamp

DETERMINE THE STREAM VELOCITY NEEDED TO TRANSPORT A 1. 0 CM DETERMINE THE STREAM VELOCITY NEEDED TO TRANSPORT A 1.0 CM. SIZE PEBBLE

SEDIMENTARY ROCK WHERE IT WAS PUT TOGETHER CONGLOMERATE BRECCIA HIGH ENERGY SANDSTONE MEDIUM ENERGY SILSTONE LOW ENERGY SHALE VERY LOW ENERGY

HIGH ENERGY LOW ENERGY

Environment of Formation Ocean Derived Sedimentary Rocks help us understand our past geologic history There is evidence of climate change as well as lost species of plants and animals in

During the Cretaceous Period (about 120 mya) a shallow inland sea split North America. We know this by the Sedimentary Rocks deposited in the former shallow sea KANSAS AND KENTUCKY HAVE A GREAT DEAL OF CHALK – TELLS ME ONCE UNDERWATER WHITE CLIFFS OF DOVER – ENGLAND UNDER WATER DURING CRETACEOUS PERIOD 120 MYA, LATIN FOR CHALK – A GREAT DEAL OF CHALK WAS FORMED DURING THIS PERIOD. CLIMATE WAS VERY MILD, ICE FREE POLAR REGIONS 1/3 OF NORTH AMERICA WAS FLOODED – NO MODERN GULF OF MEXICO

Cretaceous Limestone Deposits in Kansas

New York's salt deposits occur layered with shale, dolomite, and anhydrite in the lower part of the Silurian-aged Salina group. The Salina group outcrops in an east-west band from near Buffalo and Rochester through Syracuse to Herkimer County. At the southern edge of the state the salt is 3,000 feet deep.

SALT AND GYPSUM EVAPORATION Bedrock of Salt and Gypsum around Buffalo What type of environment would cause salt and/or gypsum to evaporate? Ocean environment with hot temperatures KANSAS AND KENTUCKY HAVE A GREAT DEAL OF CHALK – TELLS ME ONCE UNDERWATER WHITE CLIFFS OF DOVER – ENGLAND UNDER WATER DURING CRETACEOUS PERIOD 120 MYA, LATIN FOR CHALK – A GREAT DEAL OF CHALK WAS FORMED DURING THIS PERIOD. CLIMATE WAS VERY MILD, ICE FREE POLAR REGIONS 1/3 OF NORTH AMERICA WAS FLOODED – NO MODERN GULF OF MEXICO

CHARACTERISTICS OF SEDIMENTARY ROCKS Horizontal layers called beds or strata Clasts are rounded and sorted because they have been moved by water Ripple Marks Mud Cracks Fossils Interconnected mineral crystals of 1 mineral (monominerallic)

HORIZONTAL LAYERS

A. SHALLOW WATER B. LOW ENERGY C. DIRECTION OF FLOW

MUDCRACKS ALTERNATING WET AND DRY CONDITIONS

Limestone - FOSSILS