Comment reconnaître les structures géologiques sur une carte (par Mme Ruault-Djerrab)

Introduction

This tutorial aims to help students and anyone interested in geology recognize geological structures on geological maps. We will explore the three main types of geological structures—tabular, monocline, and folded—and how to identify them using simplified geological maps and profiles.

Step 1: Recognizing Tabular Structures

Tabular structures are flat and horizontal layers of rock. Here’s how to identify them:

• Look for Layering: Check for distinct, parallel lines on the map indicating horizontal rock layers.
• Consistent Thickness: Tabular structures typically have a consistent thickness across large areas.
• Use of Color: Different colors on the geological map usually represent various rock types or ages.

Practical Tip: When analyzing a tabular structure, visualize how these layers would appear in a cross-section. This can help in understanding their extent and relation to other structures.

Step 2: Identifying Monoclinal Structures

Monoclinal structures appear as a single, steeply inclined layer of rock. To identify them:

• Check for a Slope: Look for a noticeable tilt in the rock layers on the map, which may appear as a staircase-like pattern.
• Observe Neighboring Layers: Ensure that the adjacent layers are horizontal or have different inclinations to confirm it’s a monocline.
• Cross-Sections: Use geological cross-sections to visualize how the monocline rises from the horizontal layers below.

Common Pitfall: Don’t confuse monoclines with other structures that may appear tilted. Always compare with nearby layers for accurate identification.

Step 3: Understanding Folded Structures

Folded structures are formed by the bending of rock layers. Here’s how to identify them:

• Look for Curves: Identify areas on the map where rock layers appear to be curved or wavy.
• Recognize Anticlines and Synclines:
  • Anticlines: Upward-arching folds.
  • Synclines: Downward-arching folds.
• Utilize Cross-Sections: Geological profiles can help visualize the folding and determine the type of fold.

Practical Tip: Familiarize yourself with the terminology of folds (e.g., axial planes, limbs) to enhance your understanding of folded structures.

Conclusion

In this tutorial, we covered how to identify tabular, monocline, and folded geological structures on geological maps. Understanding these concepts is crucial for geological studies and can enhance your ability to interpret geological data.

For further learning, consider exploring additional resources on sedimentary geology or practicing with more geological maps and cross-sections. Happy studying!