Benthic Carbonate Factories of the Phanerozoic - Research Paper Example

4) What is the carbonate factory? How does abiotic carbonate differ from biotic carbonate? How is the carbonate factory affected by depth and temperature? How do you think the tropical carbonate factory differs from the cool water carbonate factory? You may use figures to illustrate your point. (10 points) Schlager (2005) defines carbonate factory as the shallow and illuminated seafloor. On the seafloor, sediments are generated through crystallization of skeletal remains in the sea water and out of the sea water by precipitation. The carbonate factory is considered to be the hub of carbonate deposition in throughout the entire world. Since sea water is saturated with carbonates, at times, calcium carbonate precipitates at low pressure and high temperatures. The precipitation can either be abiotic or biotic. Biotic carbonates are formed in the presence of organisms such as corals, which use carbonates dissolved in water, to build their skeletons. However, abiotic carbonates involve minimal or no biological and organism influence. The carbonate factory is affected by depth and temperature of water. The Goldilocks theory supports this; it states that the physical constraints of depth and temperature have to be just right. The water should neither be too deep or shallow, nor too war or too cold. Tropical carbonate factory occurs in warm, sunlit waters of 20 degree Celsius and above, with low nutrients and high oxygen levels. It is built by organisms such as green algae, corals, and mollusks. On the other hand, cool water carbonate factories occur in higher latitudes and cooler waters with higher amounts of nutrients than tropical factories. In addition, precipitation is controlled by organisms such as red algae (Schlager 2003). 5) There are many different environments in which siliciclastic rocks are deposited. Discuss two of the environments in which siliciclastic deposit can be found and the types of deposits we may find in them. Your answer should include information about the grain size of that material, how the method of deposition affects the material deposited, is it rounded? Or angular? What types of sedimentary structures do we find in association with these deposits? (10 points) Siliciclastic deposits can be found in Northern Estonia and in the Lower Antelope Canyon. The type of siliciclastic deposit found in Lower Antelope canyon is sandstone while in Estonia is shale. Sandstones differ in abundance of quartz, lithic framework grains, muddy matrix between bigger grains, and feldspar content. Quartz, feldspar, and lithic framework are the chief components of sandstones. Sandstone exists in any shape depending on the transporting agent. Shale is sedimentary rock with fine grains formed by a combination of silt, clay and other minerals, which form into thin and impermeable layers. Shale has large amounts of organic matter thus is a rich source of hydrocarbon. In addition, its lack of permeability and fine grain size allows it to form an excellent trap for hydrocarbon. Siliciclastic sedimentary rocks are formed when sediment is deposited by gravity, air, water, wind, or ice. The particles are transported from the source to the deposition area. The nature of siliciclastic deposits in the two areas stated above depend not only on the nature of sediments carried from the source, but also on the nature of those found in the deposition area. 6) Passive margins are very important to the formation of petroleum. What is a passive margin? How is it different to an active margin? What types of deposit would you expect to find in a passive margin? Why are they good places for the formation of petroleum? What type of sedimentary structure would you expect to find in these passive margin environments? (10 points) A passive margin is a margin of an ocean and a continent that does not coincide with the boundary of a lithospheric plate, and along which collision in not occurring. It is formed by sedimentation on top of an ancient rift, during the transition between continental and oceanic crust (Margin structure, n.d.). Its characteristics are rifted and rotated blocks of thick sediments e.g. Atlantic margins of North America and Gulf of Mexico. In differentiating passive and active margins, it is crucial to understand that the earth’s crust is divided in to two sections; the oceanic and continental plates. Active continental margins are found on the edge where the continent crashes with the oceanic plate while passive margins are found where there is no collision taking place. The type of deposits found in passive margins includes methyl hydrates, mineral resources, thick undisturbed sedimentary, and hydrocarbons. Passive margins are excellent places for the formation of petroleum because of the presence of complex mixtures of hydrocarbons beneath the surface of the earth. The hydrocarbons are an essential component of petroleum. Passive margin environments are characterized by several structures. These include beddings, symmetric and asymmetric ripple marks, and large volumes of sedimentary debris eroded from the continental surface 7) There are two main types of weathering. What are they? How do they affect the types of deposit that we find? How do Stalactites and stalagmites (speleothems) form? What is a column? What types of process contribute to their formation? You may illustrate this using a figure. (10 points) The two major types of weathering are mechanical and chemical. Mechanical weathering involves the breakdown of soil and rock into smaller fragments. Chemical weathering involves complete transformation of original material into a substance with entirely different physical characteristics and composition. The deposits they form are different because mechanical weathering involves direct contact of rock and soil with atmospheric conditions such as water, heat, pressure, and ice. On the other hand, chemical weathering entails direct effect of biological chemicals in the fragmentation of minerals, soil, and rocks (Waugh, 2009). Stalactites and stalagmites are found in caves. A stalactite is formed when carbon dioxide dissolves in rain water and attacks the cave limestone rock, which contains calcite or calcium carbonate. This leads to calcium hydrogen carbonate formation, which is a water soluble compound. The bicarbonate water is filtered on the cave roof as it passes through cracks and carbon dioxide escapes. The resulting calcium carbonate precipitates forming concretions or stalactites at the falling point on the upper surface of the cave. The upper deposit forms a calcite deposit on the caves floor; thus creating the stalagmite. A column is an arrangement or sequence of rock layers of a region or area, showing the relationship between the various subdivisions. It is a vertical cross section of the earth’s crust, which contains the most recently deposited rocks at the surface and oldest rocks at the bottom. From the uniformitarian view point, the layers of sedimentary rocks are formed over millions of years, while from the catastrophic point of view, the layers form quickly. 8) Climate has a great impact on the type of deposits we find. Using two examples discuss how climate affects sediment deposits. What type of deposits do we find in the climate regime you selected? Why does this climate result in this type of sediment? ( 10 points) Climate changes include diverse weather seasons and changes in sea level; they affect sediment deposits. Different weather seasons create cyclic sediments in which occur in alternating bands of silt and clay known as verves. For example, sediments are deposited in glacial regions in lakes. The sediments get trapped in the ice and are released when it melts during summer. This creates paler and coarser silt bands in the lake deposits. During winter, melting is at its lowest, this means that only fine material is delivered to the lake, this causes thin clay layers. This leads to the formation of deposits known as autocycles. Changes in sea level lead to the creation of cyclic sediments such as coals, lime stones, and shale. In order for them to form, the environment first changes from marine to deltaic, then to the lagoon, and finally to continental environment. Retreat or advance of continental glaciers is the main cause of sea level change. Tectonic movements also change water depth thus affecting the environment of deposition. This leads to the formation of deposits known as allocycles. The duration over which autocyclic deposits form is usually less than that of allocyclic deposits. Changes in climate alter the amount and sediment type deposited resulting into different sedimentary rock types. REFERENCES. Margin Structure: Passive Margins. (n.d.). Retrieved October 30, from http://geology.uprm.edu/Morelock/margstruct.htm Schlager, Wolfgang. (2005). Sedimentology and Sequence Stratigraphy. Society for Sedimentary Geology. Schlager, Wolfgang. (2003). Benthic Carbonate Factories of the Phanerozoic. International Journal of Earth Sciences, 92(4), 445-464. Waugh, David. (2009). Geography: An Integrated Approach. (4th ed.). Nelson Thornes. Read More