PRINICIPLES OF STRATIGRAPHY

STRATIGRAPHY

Introduction

• Stratigraphy is a core discipline of geology that focusses on the examination of rock strata and the analysis of Earth's evolution as documented in these strata.
• Geodetic analysis is an essential instrument for comprehending the chronological and geographical correlations of geological phenomena, including sedimentation, deformation, and the development of landscapes.
• Geological science is guided by numerous fundamental concepts that direct the interpretation of strata and the reconstruction of the geological history.

1. The Concept of Original Horizontality

• This theory asserts that sedimentary strata are first laid down horizontally due to the force of gravity.
• In due course, tectonic forces may induce the tilting or folding of these strata, although the original deposition often occurs on a level plane.
• Interpreting the orientation of strata and recreating the ancient contexts in which they developed is crucially dependent on this idea.

2. The Concept of Superposition

• Undisturbed strata are characterised by the oldest layers positioned at the bottom and the youngest layers positioned at the top. This concept enables geologists to determine a comparative age correlation among successive rock strata.
• When one rock layer is located above another, it is often presumed to be of a younger age, unless there is documented evidence of a subsequent disruption such as folding or faulting.

3. The Concept of Cross-Cutting Relationships

• When an igneous or sedimentary rock body penetrates other rock strata at an angle, it suggests that the intruding rock body is of a younger age than the rocks it crosses.
• This concept is valuable for ascertaining the comparative geological ages of intrusions, faults, and other geological phenomena that disturb the initial horizontal strata.

4. The Inclusion Principle

• Any inclusion, whether it be a rock fragment or a fossil, that is discovered inside a rock layer is considered to be older than the layer of rock that encompasses it.
• This paradigm is used to comprehend the origin of the inclusion and the circumstances under which it was integrated into the adjacent rock.

5. The Uniformitarianism Principle

• The theory of uniformitarianism asserts that the geological processes now seen have consistently and uniformly worked throughout the whole history of the Earth.
• This theory posits that the present-day natural laws and processes have been in operation in the past, enabling geologists to deduce the circumstances and occurrences that gave rise to the rock strata seen today.

6. The Fossil Succession Principle

• Fossils are preserved remnants or traces of ancient species that provide crucial evidence for determining the relative ages of rock strata.
• This concept asserts that some fossils are distinctive of certain historical eras and that these species are consistently found in a systematic sequence in the geological record.
• Through the analysis of fossil distribution in various strata, scientists are able to establish correlations between rock layers across extensive geographical areas.

7. The Lateral Continuity Principle

• The aforementioned concept suggests that sedimentary strata undergo lateral extension unless there is observable indication of a change in depositional circumstances or an intervening unconformity.
• The underlying premise is that sediments are deposited in a consistent and homogeneous fashion throughout a vast expanse, enabling the identification and comparison of layers at various spatial locations.

8. The Hypothesis of Faunal and Floral Succession

• This paradigm asserts that unique collections of fossils define various geological epochs.
• The temporal variations in the fossil record are indicative of the processes of species evolution and extinction, along with changes in the global environment.
• This notion is essential for biostratigraphy, the scientific investigation of the arrangement of fossils inside rock layers in order to determine the comparative ages of the deposits.

9. The Stratigraphic Correlation Principle

• Stratigraphic correlation refers to the procedure of establishing a correspondence between rock strata of same age in various geographical areas.
• This is accomplished by selecting prominent marker beds or index fossils that are both abundant and representative of a certain time period.
• This idea is crucial for formulating a thorough and logical representation of Earth's past.

10. The Fundamental Concept of Walther's Law

• Walther's Law asserts that the various sediment types included in a series of rocks correspond to the evolving circumstances under which the sediments were laid down.
• More precisely, it indicates that a sedimentary basin would gradually fill with a consistent succession of sediment types, ranging from coarse in close proximity to the source to fine in the middle of the basin.
• This pattern may be used to deduce the circumstances of the ancient environment and the mechanisms of sediment movement.

IMAGE SOURCE (THUMBNAIL)