Geologic Time Lecture: Stratigraphy and Sedimentary Layers

Geologic Time Lecture: Stratigraphy and Sedimentary Layers

Overview of Geological Units

• Kaibab Limestone

• Toroweap Formation

• Coconino Sandstone

• Hermit Shale

• Younger sedimentary units

• Supai Group

Principles of Stratigraphy

• Horizontal Deposition

  • Sedimentary rocks and some volcanic rocks are deposited horizontally under the influence of gravity.

  • This principle of horizontal deposition helps in understanding the layering of rocks in the geologic record.

Important Clarification

• The principle of horizontal deposition does not apply to igneous intrusions.

  • Igneous Intrusions:

  • Definition: Formed from liquid magma that cuts across pre-existing rock layers.

  • These intrusions disrupt the originally horizontal sedimentary layers, illustrating different geological processes at work.

Stratigraphic Nomenclature

• Naming of Geological Units

  • Each unit like Kaibab Limestone or Coconino Sandstone represents distinct geological formations with specific characteristics.

Conclusion

• Understanding the principles of geology, especially sedimentary processes, is crucial for interpreting the Earth’s history and the formation of its features.