rocas sedimentarias.wmv

Types of Sedimentary Rocks

Overview of Sedimentary Rocks

• Sedimentary rocks form at the Earth's surface and are categorized into three types: detrital, chemical, and organic.

Detrital Sedimentary Rocks

• Detrital rocks originate from erosion processes that transport mineral grains or rock fragments (clasts) from elevated areas to sedimentation basins through air, ice, or water action.

• Water is the primary agent in forming these rocks; it can carry clasts of varying sizes. The energy of water decreases as it moves from steep slopes to lower areas.

• In sedimentation basins, larger sediments settle closer to the continent forming conglomerates, while medium-sized sediments create sandstones and smaller particles like clay form shales.

Organic Sedimentary Rocks

• Organic sedimentary rocks can also form in deep zones where marine organisms like plankton accumulate on the seafloor. Their remains mix with clay sediments and transform under pressure over time into petroleum.

Chemical Sedimentary Rocks

• Chemical sedimentary rocks result from precipitation of dissolved chemicals in water rather than erosion. They form directly in their sedimentation basin.

• Gypsum forms when stagnant water evaporates, concentrating calcium sulfate which precipitates crystals that accumulate over time.

Common Types of Chemical Sediments

• Limestone is a prevalent chemical sediment formed from calcium carbonate often derived from shell and organism dissolution. Its formation involves microscopic crystal precipitation influenced by changes in physical and chemical conditions such as temperature and salinity.

Examples of Sedimentary Rock Formations

Observing Detrital Rocks

• At Altea's coast, conglomerates are observed formed by coarse gravel compacted together due to insufficient energy for further transport by waves.

Characteristics of Sandstone

• At Cabo de las Huertas, medium-grained detrital rocks (sandstones) show tightly packed small grains cemented together during consolidation processes involving mineral formation within pore spaces.

Fine-Grained Detrital Rocks

• Shales consist of very fine clay minerals that are not visible without powerful microscopes; they resemble modeling clay used in schools.

Chemical Rock Formations

Abundance of Limestones

• In Rodiles cliffs (Asturias), rhythmic layers of limestone display alternating colors due to variations in organic material content affecting their appearance.

Fossilized Shells in Limestone

Characteristics of the Rock Formation

• The rock exhibits a dark appearance with white elements visible within, indicating the presence of fossilized shells.

• These figures are sections of fossilized shells that are integral to the limestone composition.

• The fossils were trapped in the limestone while it was still unconsolidated at the bottom of the sea.

• This observation highlights how geological processes can preserve biological remnants over time.

• The discussion emphasizes the significance of fossils in understanding past marine environments and sedimentary processes.