These relationships may be based on rock type, called lithostratigraphy, on age, as in chronostratigraphy, on fossil content, label biostratigraphy, or on magnetic properties, named magnetostratigraphy. It is the study of the spatial relationships between bodies of sedimentary rocks. Stratigraphy is the science of describing the vertical and lateral relationships of rocks. He believed that while eustatic hypotheses apply worldwide, tectonic hypotheses do not and vary from region to region. He recognized that all these causes may be partially applicable, and are not mutually incompatible. Fairbridge summarized the main mechanisms of sea level change: tectono-eustasy, controlled by deformation of the ocean basin sedimento-eustasy, controlled by addition of sediments to basins, causing sea level rise glacio-eustasy, controlled by climate, lowering sea level during glaciation and raising it during deglaciation. However, Suess was not able to refute evidence presented by opponents of this theory-in many locations there were discrepancies between rock types found and types predicted by sea level variation. This view was challenged in 1906 when Eduard Suess hypothesized that changes in shoreline position were related to sea level changes and occurred on a global scale he called the phenomenon eustasy. At the turn of the century, shoreline movement was attributed to tectonic activity-the rising and falling of continents. By 1900, most layers had relative ages, and rock types had been associated with certain positions of the shoreline, which was known to move with time. By 1950, most of the major geologic time units had been named. For over 300 years after Steno, stratigraphers worked at unraveling the history of the earth, correlating fossils from one continent to another, assigning names, ages, and eventually physical mechanisms to the creation of rock layers. He thus developed three principles that form the basis of all stratigraphy-younger layers lie on top of older layers, layers are initially horizontal, and layers continue until they run into a barrier. He also recognized that some strata contain remnants of other strata, and so must be younger. In 1669, Nicholas Steno, a Darnish geologist working in Italy recognized that strata are formed as heavy particles settle out of a fluid. Stratigraphy in one form or another has been around since the 1600s. It can therefore provide a predictive tool for determining the likely presence of source rocks, and the distribution of reservoirs and seals. An explanation of strata in terms of relative sea-level fluctuations and a combination of eustatic sea-level change and tectonic subsidence allows an understanding of why sediment packages develop where they do. The implications of sequence stratigraphy are profound. It was clear that the stratal patterns in these areas of low tectonic activity were the signatures of sea-level rise and fall. The stratal patterns were as distinctive as the biostratigraphic correlations. Moreover, it was recognized from the circum-Atlantic passive margins that the stratal pattern in one area could be correlated with others that were far distant. It was founded on the same principle as used in seismic stratigraphy, that seismic reflectors are time surfaces and that unconformites are bounding surfaces that separate strata into time-coherent packages. Sequence stratigraphy was developed from seismic stratigraphy in the 1970s, by workers in the Exxon research facility. ![]() See sequence, sequence boundary, and Haq chart. The study of rock relationships within a chronostratigraphic framework of genetically related strata bounded by surfaces of erosion or nondeposition or their correlative conformities (Van Wagoner, 1995). Dictionary entry for Sequence stratigraphy ( edit)
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