Previous Year Question
Which one of the following pairs (Deccan Trap–Peculiarity) is not correctly matched?
Depth of middle trap — 1200 metres approximately
Intertrappean beds — Fossils of sea plants and animals
Depth of lower trap — 150 metres approximately
Depth of upper trap — 450 metres approximately
Correct Answer: B
Detailed Solution
The Deccan Trap was formed mainly by repeated outpourings of enormous basaltic lava flows deposited one above another. The term ‘Trap’ is associated with its characteristic step-like topography. During quiet intervals between successive volcanic eruptions, sediments accumulated between the lava flows; these are known as Intertrappean beds.
These intertrappean beds are mainly associated with freshwater sedimentation. They contain sediments such as limestone, clay and shale along with fossil remains of freshwater and terrestrial organisms. Therefore, associating them with fossils of sea plants and animals is not correct. Maharashtra GSDA also describes intertrappean sediments as freshwater sediments.
The Deccan Trap is conventionally divided into Lower, Middle and Upper divisions. In the question, their approximate thicknesses are given as 150 m, 1200 m and 450 m, respectively, and these are treated as correctly matched in the UPPSC context.
It is useful to remember that the thickness of the Deccan Trap is not uniform throughout the region. An official geological account of the Botanical Survey of India gives approximate thicknesses of 500 m, 1330 m and 160 m for the Upper, Middle and Lower flows respectively. Therefore, the figures in the question should be understood as approximate conventional values, not as universal exact thicknesses.