Chronostratigraphy

Chronostratigraphy is the branch of stratigraphy that studies the ages of rock strata in relation to time. The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of the Earth. The standard stratigraphic nomenclature is a chronostratigraphic system based on palaeontological intervals of time defined by recognised fossil assemblages (biostratigraphy). The aim of chronostratigraphy is to give a meaningful age date to these fossil assemblage intervals and interfaces. Chronostratigraphy relies heavily upon isotope geology and geochronology to derive hard dating of known and well defined rock units which contain the specific fossil assemblages defined by the stratigraphic system. In practice, as it is very difficult to isotopically date most fossils and sedimentary rocks directly, inferences must be made in order to arrive at an age date which reflects the beginning of the interval. The methodology used is derived from the law of superposition and the principles of cross-cutting relationships. Because igneous rocks occur at specific intervals in time and are essentially instantaneous on a geologic time scale, and because they contain mineral assemblages which may be dated more accurately and precisely by isotopic methods, the construction of a chronostratigraphic column relies heavily upon intrusive and extrusive igneous rocks. Metamorphism, often associated with faulting, may also be used to bracket depositional intervals in a chronostratigraphic column. Metamorphic rocks can occasionally be dated, and this may give some limits to the age at which a bed could have been laid down. For example, if a bed containing graptolites overlies crystalline basement at some point, dating the crystalline basement will give a maximum age of that fossil assemblage. This process requires a considerable degree of effort and checking of field relationships and age dates.

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Magnetostratigraphy

Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their characteristic remanent magnetization (ChRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. This is possible because volcanic flows acquire a thermoremanent magnetization and sediments acquire a depositional remanent magnetization, both of which reflect the direction of the Earth's field at the time of formation.

Lithostratigraphy

Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneous or sedimentary relating to how the rock was formed. Sedimentary layers are laid down by deposition of sediment associated with weathering processes, decaying organic matter (biogenic) or through chemical precipitation.

Biostratigraphy

Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. The primary objective of biostratigraphy is correlation, demonstrating that a particular horizon in one geological section represents the same period of time as another horizon at a different section. Fossils within these strata are useful because sediments of the same age can look completely different, due to local variations in the sedimentary environment.

Geologic carbon storage is unlikely to trigger large earthquakes and reactivate faults through which CO2 could leak

Victor Vilarrasa Riano

Zoback and Gorelick [(2012) Proc Natl Acad Sci USA 109(26): 10164-10168] have claimed that geologic carbon storage in deep saline formations is very likely to trigger large induced seismicity, which may damage the caprock and ruin the objective of keeping ...

Natl Acad Sciences2015

Calculation of geological uncertainties associated with 3-D geological models

Ian Pomian-Srzednicki

3-D geological models are built with data collected in the field such as boreholes, geophysical measurements, pilot shafts or geological mapping. Unfortunately, these data are always limited in number. It implies that geological information is sparse and s ...

EPFL2002

Typologie des aquifères du cristallin

This hydrogeological study of the crystalline aquifers of the Mont-Blanc and the Aiguilles Rouges massifs is part of the AQUITYP project, which has been carried out at the Geology Laboratory of the Swiss Federal Institute of Technology, Lausanne (GEOLEP). ...

EPFL1992