Sedimentary Rocks - are one of the three main rock types

Transcription

1 Today s Objective: What Makes Sedimentary Rocks Special? Sedimentary Rocks - are one of the three main rock types

2 A sedimentary rock can form one of three ways: 1. by the deposition of the weathered remains of other rocks 2. by the deposition of the results of biologic activity 3. by precipitation from solution.

3 Weathering - is a process in which rocks are physically and chemically broken down by water, air, and living things. Erosion - involves weathering and the removal of rock. Deposition - when an agent of erosion water, wind, ice, or gravity lose energy, it drops the sediments.

4 Compaction is a process that squeezes, or compacts, sediments. Cementation glue - takes place when dissolved minerals are deposited in the tiny spaces among sediments.

5 Classification of Sedimentary Rocks Can be classified into two main groups according to the way they form.

6 Inorganic Land Derived (AKA) Clastic Sedimentary Rock - composed of weathered bits of rocks and minerals. These rocks are classified by particle size.

7 EXAMPLES of Inorganic Land Derived Conglomerate Shale with Plant Fossils Large grain size Small grain size

8 Chemical Sedimentary Rocks Forms when dissolved minerals precipitate from water solutions. (water usually evaporates or boils) Ex: Limestone & rock salt. Salt Flat

9 Organically Formed Sedimentary Rocks Forms when shell fragments are cemented together or when plant remains are compacted into rock. Ex: Fossiliferious Limestone & Bituminous Coal

10 Features only found in Sedimentary Rocks 1. The Law of Superpositioning - In undisturbed rocks, the oldest layers are found on the bottom and the youngest at the top.

11 2. Ripple Marks rock formed along the beach or stream bed. 3. Mud Cracks - formed when wet mud or clay dried and shrank, leaving a rock record of a dry environment. 4. Fossils traces of remains of ancient life. Trilobite

12 Where is the oldest layer located on this picture?

13

14 How can sedimentary layers help us understand the age of fossils? As sedimentary rocks are deposited, they form horizontal layers Scientists know that the layers on top (and the fossils in the top layer) are YOUNGER than the fossils in lower layers.

15 3 Types of Sedimentary Rocks: Clastic (also called Detrial) made of broken pieces of other rocks. Formed when rock fragments are squeezed together.

16 Clastic-Sedimentary Rocks Shale: Formed from tiny particles of clay compacted together. Sandstone: Forms from the compaction and cementation of small particles of sand.

17 Clastic-Sedimentary Rocks Conglomerate: Formed from fragments of various sizes of rocks and pebbles. Fragments are rounded because they have been worn along riverbeds. Breccia: Fragments are jagged with sharp edges. Formed from various size of rocks and pebbles.

18 3 Types of Sedimentary Rocks: Organic remains of plants and animals are deposited in thick layers Organic refers to substances that once were part of living things or were made by living things which contain calcite or calcium carbonate. (Can be tested by using acid)

19 Organic-Sedimentary Rocks Coal: Remains of swamp plants buried in water or by volcanic ash. Limestone: Formed by hard shells of once living things such as coral, clams, oysters, and snails. When they die their shells pile up and are covered by other sediments compacting and cementing them.

20 Types of Limestone Chalk-can be naturally occurring and in rock form. Coquina-made of large fragments of shells.

21 3 Types of Sedimentary Rocks: Chemical minerals dissolved in lakes, seas, or underground water. Can occur when lakes evaporate.

22 Chemical-Sedimentary Rocks Rock Salt: Made of the mineral halite. Gypsum: Formed by evaporation in dry climates.