STRATIGRAPHY: HISTORY, WHAT IT STUDIES, PRINCIPLES, METHODS - GEOGRAFÍA - 2025

The stratigraphy is a branch of geology that is responsible for studying and interpreting sedimentary rocks, metamorphic and volcanic stratified. It also seeks to identify, describe and establish their vertical and horizontal sequence.

This discipline is also concerned with determining the order of events in a specific geological time. Additionally, it establishes the correlation and mapping of the different rock units.

Statigraphy is the science that deals with the description of stratified rocks Source: Pixabay

Experts in the area describe two different approaches to stratigraphy, which are also complementary: the scientific and the applied. The first has the purpose of temporal ordering and genetic interpretation of materials. The second has the objective of locating exploitable natural resources and contributing to environmental conservation planning.

The term stratigraphy comes from the Latin stratum and the Greek graphia, which in its etymological sense means the "science that deals with the description of stratified rocks."

History

origins

The origins of geological knowledge go back to the seventeenth century, when there is a sudden change in the belief that was maintained since the Middle Ages, when the Earth was considered to be only a few thousand years old.

Nicolaus Steno (1638-1686) was the first to define a "stratum" as the unit of deposition time, which is limited by horizontal surfaces with lateral continuity.

This scientist developed two other fundamental ideas for stratigraphic science: the first, which indicates that the strata are originally deposited as horizontal; the second, which indicates that the bedding surfaces will always be laterally continuous.

Development

From then on, the most significant development of geology was recorded from the 19th century, but in the case of stratigraphy it did not change until the following century. The first treatise on stratigraphy was published by Amadeus Grabau in 1913, the year in which geology is considered to branch out to give rise to a science with its own entity.

Starting in 1917, with the application of radiometric techniques and, later, during the two world wars, with the development of oil exploration, a remarkable advance was made.

Towards the middle of the 20th century, a double approach to science was generated. The French school with a purely historical tendency, and the North American one focused on analyzing facies and interpreting sedimentary bodies. It was this second trend that ended up outlining the stratigraphy towards what it has become.

The emission between the years 60 and 70 of the global tectonic theory, produced a great revolution in the sciences that emerge from geology. Thanks to this, great attention began to be paid to the mobility of sedimentary basins and how they evolved over time.

The advancement of stratigraphy in recent years has generated subdivision into several branches with separate entities, among which it is worth highlighting: lithostratigraphy, biostratigraphy, chronostratigraphy, magnetostratigraphy, chemostratigraphy, sequential stratigraphy, and basin analysis.

What does stratigraphy study?

Its main method of study is stratigraphic survey. Source: Pixabay

Stratigraphy seeks to understand the genesis of rocks for scientific or applied purposes, so it requires knowing in detail their properties, as well as their lithology, geometry and three-dimensional arrangement.

The fundamental materials of stratigraphy are sedimentary rocks. The expert in the area, known as a stratigrapher, works with sedimentary processes and paleontology.

Among the objectives of stratigraphy can be mentioned the identification of materials, the ordering of stratigraphic units, the analysis of basins, the genetic interpretation of the units, the delimitation of stratigraphic units, the survey of stratigraphic sections and the correlation and allocation of time.

In general, stratigraphy aims to record, analyze, recognize and reconstruct all the geological events that have happened, sequentially and that have impacted the rocks. To achieve this, some eight specialized areas have been developed and interrelated with neighboring sciences.

Principles of stratigraphy

Principle of horizontality and lateral continuity

This principle establishes that a priori a stratum has the same age throughout its entire horizontal extension, regardless of interruptions due to events such as erosion.

Principle of original horizontality.

It indicates that the geometry of the strata is arranged parallel to the deposition surfaces, horizontally or sub-horizontally and successively, overlapping each other.

Principle of layer superposition.

It means that the upper layers will always be more recent than the lower ones, except if postdepositional processes (erosion, deformation by dissolution and collapses) or by tectonics are detected.

Principle of uniformism or actualism.

This principle supposes that during the history of the Earth, all the processes have been uniform and similar to the present ones, reason why the same effects always take place.

Principle of faunal succession or correlation

It indicates that each chronological interval recorded on Earth and represented by different strata, contains different fossils in accordance with the geological epochs in which they were formed.

Principle of the sequence of events

It assumes that each event and geological event that affects the rocks is subsequent to it, that is, an earthquake, volcanic explosion or fault is subsequent to the rock and stratum where it occurs.

Methods

The essential method of this branch of geology is the stratigraphic survey, which consists of the chronological and sequential recording and documentation of sedimentary events. These studies can be local, regional or global in nature, which may vary the method for data collection.

The idea is to achieve digital analysis in CAD, GIS or BD environments. What is generated is a triangulation mesh from which metric calculations will be made and units mapped to make cuts or sections.

Recognized elements can also be vectorized or combined with extracted data. This can be done with samples of various scales or of different origin.

In the case of surface materials, normally the recognition and data collection is carried out through field work. It is also achieved from aerial photos, satellite photos, orthophotos, photogrammetry, 3D laser scanner, total station and decimeter GPS.

In the case of the subsoil, data collection and identification can be carried out through geological-archaeological surveys, geophysical surveys and diagraphs.

For local and applied analysis, the development of new techniques and technological advances have been fundamental for archaeo-stratigraphic surveys. Photogrammetry, 3D laser scanner, decimetric GPS for large scales, satellite photos for small scales or for total station, are some of them.

References

1. Stratigraphy. (2019, November 05). Wikipedia, The Encyclopedia. Recovered from wikipedia.org
2. Mexican Geological Service. (2017, March 22). Stratigraphy. Recovered from sgm.gob.mx
3. Carreton, A. (sf) What is stratigraphy? Recovered from com
4. Wikipedia contributors. (2019, November 15). In Wikipedia, The Free Encyclopedia. Recovered from en.wikipedia.org
5. Portillo, G. (2019, November 5) What is stratigraphy. Recovered from meteorologiaenred.com
6. Ortiz, R. and Reguant, S. International stratigraphic guide (abridged version). Journal of the Geological Society of Spain, ISSN 0214-2708, Vol. 14, No. 3-4, 2001, p. 269