The fundamental principles of stratigraphy were highlighted by Nicolás Steno in the 19th century. In the following century, the Wernerian geognosts Abraham Gottlob Werner, followers of Neptunism, focused their efforts on the study of the layers but focused their attention on their order and relative age, at the expense of their arrangement which remained inexplicable in the century. The study of sedimentary formations, which emerge in the Tertiary basins (London and Paris basins), represented the establishment of the foundations of modern stratigraphy thanks to the work of Alcide d'Orbigny, father of biostratigraphy and the concepts of soil and stratotype (1852-1854), and Charles Lyell, who established the principle of James Hutton's uniformitarianism. (1830-1833).[18]​.

1. • Principle of original horizontality. Proposed by Nicolás Steno (1666-1669), Danish geologist and anatomist.[19] This is an axiom that establishes that sediment layers are originally deposited horizontally under the action of gravity. It is applied as a relative dating technique.

2. • Principle of superposition of strata. Proposed by Nicolás Steno. It is a key axiom based on observations that establishes that sediment layers are deposited in a temporal sequence, in which the oldest ones are inferior to the most recent ones. It is applied as a relative dating technique.

3. • Principle of lateral continuity of strata. Proposed by Nicolás Steno. It is an axiom of stratigraphy that indicates that the same layer continues laterally even if it is interrupted by topographic accidents due to the erosion of part of these layers. It is applied as a relative dating technique.

4. • Principle of shear and inclusion relations: Originally proposed by Nicolás Steno and published by Charles Lyell in his book Principles of Geology. It establishes that every geological feature that is cut by another is always older than the feature that cuts it and that every rock that contains elements of another is always more modern than the element it contains. Thus a fault or a dike is posterior to the affected rock. In the case of an inclusion in a rock, the inclusion is older than the rock in which it is found, because it needed to have existed before the rock in which it was included formed. It is applied as a relative dating technique.

5. • Principle of uniformitarianism or uniformitarianism, also referred to as actualism in English: actualism"). Initially proposed by the Scottish geologist and naturalist James Hutton (1726-1797) with his famous phrase "the present is the key to the past." Principle later published by the British geologist Charles Lyell in his book Principles of geology. The meaning of this principle, today, is that the physical and chemical laws that currently govern geological processes, have been the same in the past of Earth's history.

6. • Principle of faunal succession or correlation. Proposed by the English geologist William Smith "William Smith (geologist)") in 1815 with the publication of the first geological map (1815), for which he applied this principle. It establishes that the fossil content of sedimentary rocks varies vertically in a certain order and that each set can be identified laterally over considerable distances, due to the continuous and irreversible nature of biological evolution. Likewise, the layers that contain fossils belonging to the same taxa, even if they are of different lithology, will be of the same age. It is applied as a relative dating technique.

• - Stratification is the arrangement in layers, more or less parallel, of some sedimentary, igneous and metamorphic rocks.

• - Stratum is each of the layers that make up a stratified rock formation.

• - Roof of the stratum is its upper surface.

• - Wall or base of the stratum is its lower surface.

• - Stratum power is the thickness between the roof and the wall.

• - Stratigraphic sequence is a succession of strata.

• - Stratigraphic series is a succession of strata with continuity in time and separated from other series by a stratigraphic discontinuity.

• - Stratigraphic gap is the absence of materials that can be due to erosion or the absence of sedimentation records.

• - Direction of the stratum is the angle with respect to magnetic North that forms the line defined by the intersection of the stratum with the horizontal.

• - Dip of the stratum is the angle of depression, with respect to the horizontal, that the stratum forms, measured perpendicular to its direction.

Relative

Arrange the strata and events in a sequence according to their age.

Absolute

It allows you to find the age of a specific geological stratum or event, by the methods:.

• - Biological: they analyze biological rhythms that follow regular time intervals in their development (tree rings and coral striations).

• - Sedimentological: They analyze sediment deposits that follow regular time intervals. Example: glacial varves are sediments at the bottom of glacial lakes. In winter, a thin, dark sediment is deposited; and in summer, a thick and clear one. Thus, each pair of layers corresponds to a year.

• - Radiometric: they are based on the half-life of radioactive elements; During this period, they transform half of their mass into non-radioactive elements. Thus, once the half-life of a radioactive element contained in a stratum is known and the percentage of the radioactive element that has decayed, the age of the material can be determined.

Stratigraphic inversion

Stratigraphic inversion consists of the formation of an inclined fold to such a point that, in some part of the stratigraphic cut, the oldest strata are arranged above the most modern ones.

Stratigraphic unconformity

The discordance is the separation between two stratigraphic series, due to the existence of a stratigraphic gap. There are several types:

• - Angular discordance: the ancient series is folded, so that it forms an angle with the modern series.

This involves a folding stage after the deposit of the oldest materials, an erosion stage, and finally the sedimentation of the modern materials.

• - Erosive unconformity or unconformity: the ancient series is eroded in its upper part, and the modern series has been deposited on it. The strata remain parallel, but their contact surface shows the scar produced by erosion, which may be irregular.

• - Unconformity: The stratigraphic series is deposited on a non-stratified material (metamorphic or igneous rocks).

• - Paraconformity: the separation between the two stratigraphic series is horizontal and, therefore, not distinguishable from the normal separation between two strata.

• - Stratotype.

• - Relative dating.

• - Guide fossil.

• - Chronostratigraphy.

• - Layer (geology) "Layer (geology)").

• - Matrix Harris.

• - International Commission on Stratigraphy.

• - Paleomagnetism.

• - Boggs, S. Jr. (2016). Principles of Sedimentology and Stratigraphy. Prentice Hall, New Jersey. 560 pp. ISBN 978-1-292-02128-7 ISBN 1-292-02128-4.

• - Dabrio González, C.J. and Hernándo Costa, S. (2003). Stratigraphy. Madrid. Faculty of Geological Sciences, Geosciences Collection. 382 pp. ISBN 84-600-9887-7.

• - Fernández Martínez, V. (1989). Theory and method of archeology. Madrid. Editorial Síntesis, Universal History Series, Prehistory, 1. 280 pp. ISBN 84-7738-076-7.

• - Montenari, M. (2016). Stratigraphy and Timescales. Academic Press (Elsevier), Amsterdam. 506 pp. ISBN 978-0-12-811549-7.

• - Montenari, M. (2017). Advances in Sequence Stratigraphy. Academic Press (Elsevier), Amsterdam. 436 pp. ISBN 978-0-12-813077-3.

• - Montenari, M. (2018). Cyclostratigraphy and Astrochronology. Academic Press (Elsevier), Amsterdam. 384 pp. ISBN 978-0-12-815098-6.

• - Montenari, M. (2019). Case Studies in Isotope Stratigraphy. Academic Press (Elsevier), Amsterdam. 227 pp. ISBN 978-0-12-817552-1.

• - Montenari, M. (2020). Carbon Isotope Stratigraphy. Academic Press (Elsevier), Amsterdam. 755 pp. ISBN 978-0-12-820991-2.

• - Montenari, M. (2021). Calcareous Nannofossil Biostratigraphy. Academic Press (Elsevier), Amsterdam. 469 pp. ISBN 978-0-12-824624-5.

• - Montenari, M. (2022). Integrated Quaternary Stratigraphy. Academic Press (Elsevier), Amsterdam. 308 pp. ISBN 978-0-323-98913-8.

• - Montenari, M. (2023). Stratigraphy of Geo- and Biodynamic Processes. Academic Press (Elsevier), Amsterdam. 435 pp. ISBN 978-0-323-99242-8.

• - Prothero, D.R. and Schwab, F. (2014). Sedimentary Geology. W.H. Freeman and Company, 593 pp. ISBN 978-1-4292-3155-8.

• - Nichols, G. (2009). Sedimentology and Stratigraphy. Blackwell Science, Oxford., 419 pp. ISBN 978-1-4051-3592-4.

• - Vera Torres, J. A. (1994). Stratigraphy. Principles and methods. Madrid. Rueda Editorial. 806 pp. ISBN 84-7207-074-3.

The fundamental principles of stratigraphy were highlighted by Nicolás Steno in the 19th century. In the following century, the Wernerian geognosts Abraham Gottlob Werner, followers of Neptunism, focused their efforts on the study of the layers but focused their attention on their order and relative age, at the expense of their arrangement which remained inexplicable in the century. The study of sedimentary formations, which emerge in the Tertiary basins (London and Paris basins), represented the establishment of the foundations of modern stratigraphy thanks to the work of Alcide d'Orbigny, father of biostratigraphy and the concepts of soil and stratotype (1852-1854), and Charles Lyell, who established the principle of James Hutton's uniformitarianism. (1830-1833).[18]​.

1. • Principle of original horizontality. Proposed by Nicolás Steno (1666-1669), Danish geologist and anatomist.[19] This is an axiom that establishes that sediment layers are originally deposited horizontally under the action of gravity. It is applied as a relative dating technique.

2. • Principle of superposition of strata. Proposed by Nicolás Steno. It is a key axiom based on observations that establishes that sediment layers are deposited in a temporal sequence, in which the oldest ones are inferior to the most recent ones. It is applied as a relative dating technique.

3. • Principle of lateral continuity of strata. Proposed by Nicolás Steno. It is an axiom of stratigraphy that indicates that the same layer continues laterally even if it is interrupted by topographic accidents due to the erosion of part of these layers. It is applied as a relative dating technique.

4. • Principle of shear and inclusion relations: Originally proposed by Nicolás Steno and published by Charles Lyell in his book Principles of Geology. It establishes that every geological feature that is cut by another is always older than the feature that cuts it and that every rock that contains elements of another is always more modern than the element it contains. Thus a fault or a dike is posterior to the affected rock. In the case of an inclusion in a rock, the inclusion is older than the rock in which it is found, because it needed to have existed before the rock in which it was included formed. It is applied as a relative dating technique.

5. • Principle of uniformitarianism or uniformitarianism, also referred to as actualism in English: actualism"). Initially proposed by the Scottish geologist and naturalist James Hutton (1726-1797) with his famous phrase "the present is the key to the past." Principle later published by the British geologist Charles Lyell in his book Principles of geology. The meaning of this principle, today, is that the physical and chemical laws that currently govern geological processes, have been the same in the past of Earth's history.

6. • Principle of faunal succession or correlation. Proposed by the English geologist William Smith "William Smith (geologist)") in 1815 with the publication of the first geological map (1815), for which he applied this principle. It establishes that the fossil content of sedimentary rocks varies vertically in a certain order and that each set can be identified laterally over considerable distances, due to the continuous and irreversible nature of biological evolution. Likewise, the layers that contain fossils belonging to the same taxa, even if they are of different lithology, will be of the same age. It is applied as a relative dating technique.

• - Stratification is the arrangement in layers, more or less parallel, of some sedimentary, igneous and metamorphic rocks.

• - Stratum is each of the layers that make up a stratified rock formation.

• - Roof of the stratum is its upper surface.

• - Wall or base of the stratum is its lower surface.

• - Stratum power is the thickness between the roof and the wall.

• - Stratigraphic sequence is a succession of strata.

• - Stratigraphic series is a succession of strata with continuity in time and separated from other series by a stratigraphic discontinuity.

• - Stratigraphic gap is the absence of materials that can be due to erosion or the absence of sedimentation records.

• - Direction of the stratum is the angle with respect to magnetic North that forms the line defined by the intersection of the stratum with the horizontal.

• - Dip of the stratum is the angle of depression, with respect to the horizontal, that the stratum forms, measured perpendicular to its direction.

Relative

Arrange the strata and events in a sequence according to their age.

Absolute

It allows you to find the age of a specific geological stratum or event, by the methods:.

• - Biological: they analyze biological rhythms that follow regular time intervals in their development (tree rings and coral striations).

• - Sedimentological: They analyze sediment deposits that follow regular time intervals. Example: glacial varves are sediments at the bottom of glacial lakes. In winter, a thin, dark sediment is deposited; and in summer, a thick and clear one. Thus, each pair of layers corresponds to a year.

• - Radiometric: they are based on the half-life of radioactive elements; During this period, they transform half of their mass into non-radioactive elements. Thus, once the half-life of a radioactive element contained in a stratum is known and the percentage of the radioactive element that has decayed, the age of the material can be determined.

Stratigraphic inversion

Stratigraphic inversion consists of the formation of an inclined fold to such a point that, in some part of the stratigraphic cut, the oldest strata are arranged above the most modern ones.

Stratigraphic unconformity

The discordance is the separation between two stratigraphic series, due to the existence of a stratigraphic gap. There are several types:

• - Angular discordance: the ancient series is folded, so that it forms an angle with the modern series.

This involves a folding stage after the deposit of the oldest materials, an erosion stage, and finally the sedimentation of the modern materials.

• - Erosive unconformity or unconformity: the ancient series is eroded in its upper part, and the modern series has been deposited on it. The strata remain parallel, but their contact surface shows the scar produced by erosion, which may be irregular.

• - Unconformity: The stratigraphic series is deposited on a non-stratified material (metamorphic or igneous rocks).

• - Paraconformity: the separation between the two stratigraphic series is horizontal and, therefore, not distinguishable from the normal separation between two strata.

• - Stratotype.

• - Relative dating.

• - Guide fossil.

• - Chronostratigraphy.

• - Layer (geology) "Layer (geology)").

• - Matrix Harris.

• - International Commission on Stratigraphy.

• - Paleomagnetism.

• - Boggs, S. Jr. (2016). Principles of Sedimentology and Stratigraphy. Prentice Hall, New Jersey. 560 pp. ISBN 978-1-292-02128-7 ISBN 1-292-02128-4.

• - Dabrio González, C.J. and Hernándo Costa, S. (2003). Stratigraphy. Madrid. Faculty of Geological Sciences, Geosciences Collection. 382 pp. ISBN 84-600-9887-7.

• - Fernández Martínez, V. (1989). Theory and method of archeology. Madrid. Editorial Síntesis, Universal History Series, Prehistory, 1. 280 pp. ISBN 84-7738-076-7.

• - Montenari, M. (2016). Stratigraphy and Timescales. Academic Press (Elsevier), Amsterdam. 506 pp. ISBN 978-0-12-811549-7.

• - Montenari, M. (2017). Advances in Sequence Stratigraphy. Academic Press (Elsevier), Amsterdam. 436 pp. ISBN 978-0-12-813077-3.

• - Montenari, M. (2018). Cyclostratigraphy and Astrochronology. Academic Press (Elsevier), Amsterdam. 384 pp. ISBN 978-0-12-815098-6.

• - Montenari, M. (2019). Case Studies in Isotope Stratigraphy. Academic Press (Elsevier), Amsterdam. 227 pp. ISBN 978-0-12-817552-1.

• - Montenari, M. (2020). Carbon Isotope Stratigraphy. Academic Press (Elsevier), Amsterdam. 755 pp. ISBN 978-0-12-820991-2.

• - Montenari, M. (2021). Calcareous Nannofossil Biostratigraphy. Academic Press (Elsevier), Amsterdam. 469 pp. ISBN 978-0-12-824624-5.

• - Montenari, M. (2022). Integrated Quaternary Stratigraphy. Academic Press (Elsevier), Amsterdam. 308 pp. ISBN 978-0-323-98913-8.

• - Montenari, M. (2023). Stratigraphy of Geo- and Biodynamic Processes. Academic Press (Elsevier), Amsterdam. 435 pp. ISBN 978-0-323-99242-8.

• - Prothero, D.R. and Schwab, F. (2014). Sedimentary Geology. W.H. Freeman and Company, 593 pp. ISBN 978-1-4292-3155-8.

• - Nichols, G. (2009). Sedimentology and Stratigraphy. Blackwell Science, Oxford., 419 pp. ISBN 978-1-4051-3592-4.

• - Vera Torres, J. A. (1994). Stratigraphy. Principles and methods. Madrid. Rueda Editorial. 806 pp. ISBN 84-7207-074-3.