Marshes and mangrove swamps

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Marshes and mangrove swamps

Tidal marshes and mangrove swamps represent transitional regions between marine/brackish water and terrestrial environments. Tidl marshes occur in temperate areas, whereas the mangrove swamp is characteristic for tropics

Murray (1972) lists the following characteristics of these environments :

1. It is developed in the upper part of the intertidal zone
2. During much of each tidal cycle it is exposed to the atmosphere
3. It spends a smaller part of the tidal cycle submerged beneath sea or estuarine water
4. It is subject to the more dramatic fluctuations in temperature of the atmosphere
5. Fresh water is periodically introduced from rain showers
6. There is usually high organic productivity by the marsh plants and microflora
7. The fauna comprises few permanent indigenous species although migratory terrestrial animals are sometimes common

Tidal marshes can be subdivided in three groups according to salinity;

1. Hyposalina marshes
2. Normal marine marshes
3. Hypersaline marshes

Species diversity is highest in hyposaline marshes, although the general diversity is low.

The hyposaline marshes are characterized by the predominance of arenaceous species (Miliammina sp., Ammotium sp., Trochammina inflate) and rotaliids ( Elphidium spp.) and the absence of miliolids

Normal marine marshes are inhabited by dominantly arenaceous species with minor miliolieds and rotaliids.

In hypersaline marshes the percentage of arenaceous species, miliolids and rotaliids is about equal.

Typical cosmopolitan marsh species are:

- Ammotium salsum

- Arenoparrella Mexicana

- Miliammina fusca

- Taclammina macrescens

Interpreting an ancient marsh environment may be difficult. Due to reducing conditions calcareous test are easily destroyed after death. After complete solution of calcareous species, it is impossible to distinguish between the various marsh environments. Only the low diversity and an assemblage consisting of small arenaceous species such as Trochammina sp.. Haplophragmoides sp., Ammobaculites sp. points to a marsh origin. If Miliammina sp is present in this assemblage, a hyposaline lagoon could also be indicated.

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Introduction Tectonics

Tectonics

From Wikipedia, the free encyclopedia

Tectonics, (from the Greek for "builder", tekton), is a field of study within geology concerned generally with the structures within the crust of the Earth (or other planets) and particularly with the forces and movements that have operated in a region to create these structures.

Tectonics is concerned with the orogenies and tectonic development of cratons and tectonic terranes as well as the earthquake and volcanic belts which directly affect much of the global population. Tectonic studies are also important for understanding erosion patterns in geomorphology and as guides for the economic geologist searching for petroleum and metallic ores.

A subfield of tectonics that deals with tectonic phenomena in the geologically recent period is called neotectonics

Tectonic studies have application to lunar and planetary studies, whether or not those bodies have active tectonic plate systems.

Since the 1960s, plate tectonics has become by far the dominant theory to explain the origin and forces responsible for the tectonic features of the continents and ocean basins.

There are three main types of tectonic regime

• Extensional tectonics
• Thrust (Contractional) tectonics
• Strike-slip tectonics

Extensional tectonics is concerned with the structures formed, and the tectonic processes associated with, the stretching of the crust or lithosphere.

Areas of extensional tectonics are typically associated with:

• The development of continental rifts, with or without the effects of mantle upwelling
• The gravitational spreading of zones of thickened crust formed during continent-continent collision
• Tensional flexures along strike-slip faults
• On passive margins where an effective basal detachment layer is present at the upper end of a linked system

Extensional structures

The main structures formed in areas of extensional tectonics are normal faults and graben structures.

Prominent examples include:

• The East African Rift, a major continental rift system
• The Basin and Range province of western North America
• The global mid-ocean ridge system
• The Dead Sea basin formed at a releasing bend along a continental transform boundary

Thrust tectonics is concerned with the structures formed, and the tectonic processes associated with, the shortening of the crust or lithosphere.

Areas of thrust tectonics are typically associated with:

• The collision of two continents or a continent and an island arc at a destructive plate boundary
• Restraining bends on strike-slip faults
• On passive margins, balancing up-dip extension, where an effective detachment layer is present

Strike-slip tectonics is concerned with the structures formed by, and the tectonic processes associated with, zones of lateral displacement within the crust or lithosphere.

Areas of strike-slip tectonics are associated with

• Continental transform (conservative) plate boundaries
• Lateral ramps in areas of extensional or contractional tectonics accommodating lateral offsets between major extensional or thrust faults
• Zones of oblique continent-continent collision
• The deforming foreland of a zone of continent-continent collision, a process sometimes known as escape tectonics

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Introduction geology

From Wikipedia, the free encyclopedia

Geology (from Greek: γη, gê, "earth"; and λόγος, logos, "speech" lit. to talk about the earth) is the science and study of the solid matter that constitutes the Earth. Encompassing such things as rocks, soil, and gemstones, geology studies the composition, structure, physical properties, history, and the processes that shape Earth's components. It is one of the Earth sciences. Geologists have established the age of the Earth at about 4.6 billion (4.6x10⁹) years, and have determined that the Earth's lithosphere, which includes the crust, is fragmented into tectonic plates that move over a rheic upper mantle (asthenosphere) via processes that are collectively referred to as plate tectonics. Geologists help locate and manage the Earth's natural resources, such as petroleum and coal, as well as metals such as iron, copper, and uranium. Additional economic interests include gemstones and many minerals such as asbestos, perlite, mica, phosphates, zeolites, clay, pumice, quartz, and silica, as well as elements such as sulfur, chlorine, and helium. Geology is also of great importance in the applied fields of civil engineering, soil mechanics, hydrology, environmental engineering and geohazards.

Planetary geology (sometimes known as Astrogeology) refers to the application of geologic principles to other bodies of the solar system. Specialised terms such as selenology (studies of the moon), areology (of Mars), etc., are also in use. Colloquially, geology is most often used with another noun when indicating extra-Earth bodies (e.g. "the geology of Mars").

The word "geology" was first used by Jean-André Deluc in the year 1778 and introduced as a fixed term by Horace-Bénédict de Saussure in the year 1779. The science was not included in Encyclopædia Britannica's third edition completed in 1797, but had a lengthy entry in the fourth edition completed by 1809.An older meaning of the word was first used by Richard de Bury to distinguish between earthly and theological jurisprudence.

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