Question

A marine organic-rich, black shale with tiny pyrite crystals shows complete absence of body or trace fossils. Which of the following statement(s) is/are TRUE?

• A. The sediments were deposited in low-energy conditions.
• B. The deposition took place in dysoxic to anoxic conditions.
• C. The rate of sedimentation was high.
• D. The environment was stressful for survival of living organisms.

Hint:

Black shale = low energy + anoxic + high organic matter preservation.

Answer 1

The Correct Option is A, B, D

Step 1: Interpreting environmental indicators.
Black shales are fine-grained, organic-rich sediments deposited under low-energy and oxygen-poor marine conditions. The presence of pyrite (FeS\textsubscript{2}) indicates reducing (anoxic) environments. Absence of fossils implies conditions unfavorable for benthic life.
Step 2: Evaluating options.
(A) True — Black shales form in quiet, low-energy basins.
(B) True — Pyrite and organic matter indicate anoxic conditions.
(C) False — High sedimentation rates reduce organic preservation; black shales form under slow deposition.
(D) True — Anoxic, sulfide-rich environments are stressful for organisms.
Step 3: Conclusion.
Hence, statements (A), (B), and (D) are correct.