A-B-C-D-C-B-A
What is the most likely interpretation?
Rock Sequence Traverse Interpretation
A traverse across the strike direction reveals the rock sequence A-B-C-D-C-B-A. Understanding this pattern is key to interpreting the underlying geology.
Observed Rock Sequence Details
The sequence is noted as: A-B-C-D-C-B-A.
Pattern Analysis Across Strike
- The traverse progresses across strike, encountering rock units A, then B, then C, and finally D.
- Subsequently, the sequence reverses, encountering C, then B, and finally A.
- This symmetrical repetition (encountering the same units in reverse order) is the critical observation.
Geological Structure: Folding
This specific pattern of encountering units in reverse order while traversing across strike is a classic indicator of folded rock strata. It implies the traverse crossed a fold, such as an anticline or syncline, where rock layers are bent, causing repetition.
Evaluating Other Possibilities
- Faulting: Faults can cause repetition or omission, but the symmetrical reversal observed here strongly points away from typical faulting scenarios.
- Unconformity: Represents a gap in the geological record (erosion or non-deposition) and does not explain this type of sequential repetition.
- Jointing: Refers to fractures in rocks and does not influence the sequence of rock units encountered across strike.
Based on the evidence, the most likely interpretation is that the rock sequence results from folding.
Important Questions from Folds
The following figure shows the lower hemisphere, equal area plots of the poles to bedding surfaces. Which one of the following is the correct interpretation?
- The intersection of bedding surface with upright slaty cleavage surface occurs as horizontal lineation. Which one of the following is the most likely interpretation? The bedding surfaces are folded into
Figures A and B show two cross-sections of a folded sandstone bed.
Which one of the following is the correct interpretation of the Figs. A and B?
Match the outcrop patterns of folds with corresponding types.
Outcrop Patterns Fold A. 
P. Plunging antiform B. 
Q. Plunging synform C. 
R. Reclined D. 
S. Recumbent - Which one of the following is the correct angle between the hinge line and the strike line of the axial plane in a reclined fold?
