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Ocean Deposits – UPSC Geography Notes
Overview: The ocean floor is covered with layers of loose sediment known as ocean deposits. These deposits come from land, marine organisms, volcanic eruptions, and chemical processes. They help us understand past climates, ocean circulation, and marine ecosystem evolution — making this topic important for UPSC Geography.
Table of Contents
- 1. Introduction
- 2. Sources of Ocean Deposits
- 3. Types of Ocean Deposits
- 4. Distribution of Ocean Deposits
- 5. Economic Importance of Ocean Deposits
- 6. UPSC Quick Revision Notes
- 7. Previous Year Question
1. Introduction
Ocean deposits are sediments accumulated on the ocean floor. These sediments vary in size, thickness, and composition depending on the depth of water, distance from the coast, and biological activity.
The study of ocean deposits is known as Marine Sedimentology.
2. Sources of Ocean Deposits
Ocean sediments come from multiple sources:
- Terrigenous material: Soil, sand, and rock particles carried by rivers, winds, glaciers, and coastal erosion.
- Biogenous material: Remains of marine organisms (shells, bones, skeletons).
- Hydrogenous material: Minerals precipitated from seawater (e.g., manganese nodules).
- Volcanic material: Ash and lava fragments from underwater or island volcanoes.
- Cosmogenous particles: Microscopic debris from outer space (rare).
3. Types of Ocean Deposits
Ocean deposits are broadly classified into two major categories:
(A) Terrigenous Deposits
Also called lithogenous deposits.
- Derived from land through rivers, winds, glaciers, and coastal erosion.
- Common near continental margins.
- Examples: sand, silt, clay, mud.
(B) Biogenous Deposits
Composed of shells, skeletons, and remains of marine organisms.
- Calcareous Ooze: Formed from calcium carbonate shells of foraminifera, coccolithophores.
- Siliceous Ooze: Formed from silica-rich remains of diatoms and radiolarians.
Ooze: A deposit with more than 30% biological (organic) material.
(C) Hydrogenous (Authigenic) Deposits
Formed by precipitation from seawater.
- Manganese nodules
- Phosphorite deposits
- Metallic oxides (iron, copper)
(D) Volcanic Deposits
- Derived from volcanic eruptions (ash, lava fragments).
- Common near mid-ocean ridges and island arcs.
(E) Cosmogenous Deposits
- Microscopic particles of cosmic origin.
- Very rare; found mixed with other sediments.
4. Distribution of Ocean Deposits
(1) Continental Shelf
- Covered by terrigenous sands, gravels, and mud.
- Thicker deposits near river mouths (e.g., Ganga-Brahmaputra delta).
(2) Continental Slope & Rise
- Mixture of terrigenous and biogenous deposits.
- Turbidity currents carry sediments down the slope.
(3) Deep Sea Plains (Abyssal Plains)
- Dominated by biogenous oozes (calcareous or siliceous).
- Slow sedimentation rate: 1 cm every 1,000 years.
(4) Mid-Ocean Ridge Areas
- Thin sediments.
- Volcanic deposits and hydrogenous nodules.
5. Economic Importance of Ocean Deposits
- Manganese nodules contain valuable metals (nickel, cobalt, copper).
- Phosphorite deposits are used for fertilizers.
- Sand, gravel, and shells used in construction and industry.
- Oil and gas found in sedimentary deposits on continental shelves.
- Marine fossils help understand Earth’s past climate and evolution.
6. UPSC Quick Revision Notes
Sources → Terrigenous, Biogenous, Hydrogenous, Volcanic, Cosmogenous.
Biogenous oozes → Calcareous (CaCO₃) & Siliceous (SiO₂).
Calcareous ooze → warm waters; Siliceous ooze → cold waters.
Terrigenous → near coasts; Biogenous → deep ocean.
Hydrogenous → manganese nodules, metal oxides.
Continental shelf = thick sediments; Abyssal plains = fine oozes.
Economic value → manganese nodules, phosphates, hydrocarbons.
7. Previous Year Question
Q. Which one of the following ocean deposits is rich in manganese and other metals?
(a) Terrigenous deposits
(b) Hydrogenous deposits
(c) Calcareous ooze
(d) Siliceous ooze
Answer: (b) Hydrogenous deposits
Related Keywords
Ocean Deposits UPSC Notes, Marine Sediments, Calcareous Ooze, Siliceous Ooze, Manganese Nodules, Oceanography UPSC, Physical Geography Notes.
Sources: NCERT Class XI – Fundamentals of Physical Geography, Goh Cheng Leong, NOAA Ocean Sediments (simplified for UPSC preparation).
Next Topic → Ocean Currents and Tides – UPSC Geography Notes
