WHAT HAPPENS TO THE PRODUCTS OF ROCK WEATHERING

Weathering Transport Deposition

II. Sedimentary Rocks

WHY STUDY SEDIMENTARY ROCKS?1) Cover over 70% of Earth’s Land Surface These are the rocks you see most often.2) Economically Important!! Contain all oil & gas deposits

Important source of mineral resources like iron, salt, aluminum; of agricultural fertilizer; of construction materials like gypsum for drywall.

Sedimentary rocks form important aquifers – sources of fresh drinking water.

WHY STUDY SEDIMENTARY ROCKS?

3) They retain information about how and where they formed. Important clues to Earth’s ancient environments!

4) They contain fossils. Important information on the history and evolution of life!!

WHY STUDY SEDIMENTARY ROCKS?They can be incredibly beautiful!!

II. Sedimentary Rocks: Two Typesa) Clastic: Rocks that form from the lithification

(compaction and cementation) of the weathered and eroded products of pre-existing rocks.

b) Chemical: Rocks that form from the crystallization of minerals out of water (usually sea water).

Clastic Sedimentary RocksRock names are based on the size of the particles that form the rock.

Siltstone

Shale

or Breccia

CONGLOMERATE

SANDSTONE

SHALE

Chemical Sedimentary RocksCan be chemical or biochemical precipitates

1) Limestone (CaCO3) – Composed of the mineral calcite. Several different varieties.a) Fossiliferous limestoneb) Lithographic limestonec) Oolitic Limestoned) Coquinae) Travertine

2) Dolostone (CaMg(CO3)2) – Compsed of the mineral dolomite.

Fossiliferous Limestone Travertine Deposits

Coquina – Fossil Hash Chert Nodules in Limestone

Chemical Sedimentary Rocks

3) Chert – microcrystalline quartz.4) Evaporites – halite, gypsum, annhydrite

Devil’s Golf Course – Salt Crystals, Death Valley, CA

INTERPRETING SEDIMENTARY ENVIRONMENTS:

Rocks contain a complex and beautiful story about the Earth’s history. To unravel this story we must learn to read the language of geology.

Clues To Interpreting Sedimentary Rocks1) Transport History

Clues To Interpreting Sedimentary Rocks2) Sedimentary Structures A) Ripple Marks – modern beach

Ripple Marks in Sandstone – Rock was formed on an ancient beach

2) Sedimentary Structures B) Cross Beds – the inside of Ripple Marks

Checkerboard Mesa – Zion National Park, Utah

2) Sedimentary Structures C) Mud Cracks – Environment that periodically dries out

2) Sedimentary Structures D) Graded Bedding – Which way is up?

Kissing Camels – Garden of the Gods, Colorado