Question

The given section with uniform lithology and sedimentation rate records two ash layers dated at 77 Ma and 76 Ma, respectively. An index fossil species present in the lower part of the section becomes extinct at a horizon 7 m above the base. The estimated age of the extinction event is _________ Ma. (Answer in integer.) 

Hint:

For constant sedimentation, use linear interpolation between dated layers: Age = Lower Age – (Height × Sedimentation Interval / Total Thickness).

Answer 1

Correct Answer: 74

Step 1: Understanding the data.
Total vertical distance between the dated horizons = 10 m – 0 m = 10 m. Time difference between 77 Ma and 76 Ma = 1 Ma.
Step 2: Calculating sedimentation rate.
Sedimentation rate = 10 m per 1 Ma = 10 m/Ma.
Step 3: Calculating age at 7 m height.
From the base (77 Ma) to 7 m height: Time elapsed = 7 m ÷ 10 m/Ma = 0.7 Ma.
Therefore, age = 77 – 0.7 = 76.3 Ma.
Step 4: Conclusion.
The extinction event occurred at approximately 76.3 Ma.