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Stratigraphy
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Figure 9.29 shows how geologists use fossils to correlate rocks in different places. Studies of fossil shells and other preserved animal parts and plant remains tell us that species have changed greatly over time. In a normal stack of sedimentary rocks, like those shown in this figure, the oldest rocks are on the bottom and the youngest on top (law of superposition). So, fossil plants and animals vary vertically, with the oldest fossils normally in the lowest strata and the youngest in upper strata. The sequence from bottom to top reflects the order in which new species evolved and old species became extinct. Thus, geologists can match fossils to correlate rocks of similar ages even if they are found in different places. The lines from the column on the left to the column on the right show how fossils match. Note that there is one biostratigraphic unit that exists only in the column on the right (shown by converging dashed lines). Either that unit was not deposited in the location on the left, or after deposition, it was removed by erosion.
Introduction
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
The pioneers responsible for laying the foundation of sedimentology were not geologists by profession. The basic principles of stratigraphy and sedimentation developed out of studies by naturalists belonging to different disciplines. In the mid-17th century, a Danish physician-cum-clergyman, Nicolaus Steno (1638–1687), noticed that layers of sediments are always laid down in water in a sequence in which the oldest one lies at the bottom and the youngest one on top. This observation led to the formulation of a very fundamental rule known as the Law of Superposition. Steno’s second law, called the Law of Original Horizontality, states that the primary bedding of the layers of sediments laid down in water always parallels the surface of the earth. His third law, the Law of Original Continuity, states that all water-laid strata, must continue laterally. A corollary to this law, which came to be recognised by the eighteenth century, states that a truncation of an original sedimentary layer implies removal of the original sediments, either by erosion or due to faulting.
Data-driven subsurface modelling using a Markov random field model
Published in Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, 2023
Takayuki Shuku, Kok-Kwang Phoon
The proposed method in this study uses only site-specific boreholes for subsurface modelling. In practice, however, geological prior information such as geological cross-sections interpreted by geologists and fundamental principles of geology (e.g. the law of superposition, principle of original horizontality, principle of lateral continuity, etc) are often available and should be utilised them for better subsurface modelling especially when the number of site-specific boreholes is very limited. One possible way to quantitatively utilise geological prior knowledge in the proposed method is to use some virtual boreholes extracted from geologist-interpreted cross-sections as site-specific boreholes. The virtual boreholes should not be treated as deterministic because they are not actual data. Another possible approach is to introduce some mathematical models formulating geological knowledges and process into subsurface modelling (e.g. Diens 1974; Burns 1975; Diens and Mann 1977; Shiono and Wadatsumi 1991). Although inductive models (or interpolations) are commonly used in subsurface modelling, these mathematical models are deductive models and can play an important role in extrapolating data. A methodological framework to quantitatively utilise prior geological knowledge is left for future study.