Sedimentary Basins: Formation, Types, and Economic Importance
Sedimentary Basins: Formation and Processes
What is a Sedimentary Basin?
A sedimentary basin is a depression in the Earth’s relief, often bounded by mountains of varying sizes. At its bottom, vast quantities of sediment (such as gravel, sand, and mud) accumulate. These sediments are transported by rivers flowing into oceans or lakes, or by winds carrying dust from continents, which then settle on the basin floor.
Weathering and Erosion
Weathering is the breakdown or disintegration of rocks on the Earth’s surface. Erosion, in addition to weathering, involves the transport of these materials to areas of accumulation. The primary agents of weathering and erosion acting on rocks are climate, temperature, water, ice, and wind.
These processes are driven by both external and internal mechanical forces, including pressure release (wedge shots) and tectonic movements. The most important mechanical weathering processes include:
- Thermoclasty: Rock breakdown due to heat fluctuations.
- Gelifraction: Rock fracture caused by freezing and thawing of water (frost wedging).
- Hydroclasty: Disintegration of rocks by water action.
- Aeoloclasty: Rock breakdown by wind action.
- Corrosion: Chemical dissolution of rocks.
Chemical Weathering
Chemical weathering is a form of rock disintegration and rupture that occurs through chemical reactions. This process primarily involves dissolution and alteration.
Biological Weathering
Biological weathering (or organic weathering) is produced by the activity of animals and plants, such as root growth or burrowing.
Sediment Transport Agents
There are three major transport agents in the world: running water (rivers), glaciers, and wind.
Morphogenetic Systems
The collective set of processes that shape the Earth’s relief is called a morphogenetic system (from ‘morph’ meaning shape, and ‘genetic’ meaning origin – thus, the origin of forms). The combination of climate and a morphogenetic system is known as a morfoclimático domain, which are ultimately the true creators of relief features.
Classifications of Sedimentary Basins
Basin Types by Tectonic Setting
Sedimentary basins can be classified based on their tectonic setting:
Foreland Basins
A foreland basin is an accumulation of sediment derived from an orogenic (mountain-building) belt, deposited in a relatively small, adjacent region deformed by tectonic forces.
Marginal Sedimentary Basins
These basins form along the margins of continents, often in front of the mouths of major rivers.
Extensional Sedimentary Basins
Formed in areas where the Earth’s crust has been stretched and thinned.
Pull-Apart Basins
These sedimentary basins are formed in areas of tectonic tear or strike-slip faulting.
Carbonate Sedimentary Basins
Formed by the accumulation of calcium carbonate, often of biogenic origin.
Basin Types by Drainage and Economic Significance
Other classifications exist, considering characteristics like mineral deposits (metals, coal, etc.) and different nomenclature. For Petroleum Engineers, those of sedimentary origin are of particular interest:
- Arheic Basin: A basin whose water does not drain into lakes or seas, but instead evaporates.
- Endorheic Basin: A basin where the main river channel flows into lakes, ponds, or other small bodies of water without reaching the sea.
- Exorheic Basin: A basin that discharges its water into the sea.
- Cuenca (Mineralogy): An area where a specific mineral deposit is found.
- Ocean Basin: A large depression in the seabed.
- Petroleum Basin: Sedimentary basins where hydrocarbons, primarily asphalt, oil, and natural gas, have accumulated.
Importance of Sedimentary Basins
Social and Scientific Significance
The main social importance of sedimentary basins is that they provide ideal conditions for hydrocarbon maturation. From a scientific standpoint, the structure and age of sedimentary basin fill offer the best record of tectonic deformation events and other geological processes.
These basins are structural depressions or cavities located in favorable areas for the existence of hydrocarbon deposits.
Geological History and Hydrocarbon Potential
During the Cenozoic or Tertiary Era, specifically in the Neogene Period and Miocene Epoch (approximately 26 to 7 million years ago), a series of global events significantly impacted regions like the Andean highlands. These geological stages, including intermediate folding, are crucial for understanding basin development.
Economic Geology Applications
The most relevant geological-economic aspect is the potential for hydrocarbons stored in Jurassic and Cretaceous formations. For instance, while portions of a province like Tabasco may have limited extension, their formations are often extensions of structures projecting from areas like Chiapas and Guatemala, underlying Tertiary sediments in the Coastal Plain.
Another important aspect of economic geology is the use of certain limestones. These are valuable for the manufacture of hydrated lime, as ornamental stone, and as materials for various industrial applications.
