Give an account of stratigraphy of the Aravalli Supergroup.

Stratigraphy of the Aravalli Supergroup

The Aravalli Supergroup is broadly divided into two main groups: the Older Metamorphic Group and the Younger Metamorphic Group, with the Delhi Supergroup overlying the latter. The stratigraphic succession, from oldest to youngest, is as follows:

1. Older Metamorphic Group (Pre-Aravalli Basin Formation)

• Age: Archean to Early Proterozoic (older than 1.8 Ga)
• Lithology: Predominantly gneisses, schists, and granites. These represent the basement rocks over which the Aravalli sediments were deposited.
• Significance: Provides the crystalline basement for the Aravalli Supergroup.

2. Aravalli Group (Main Aravalli Basin Fill)

This is the core of the Aravalli Supergroup and is further subdivided into several formations:

• Delwara Formation:
  • Age: ~1.75-1.65 Ga
  • Lithology: Quartzite, conglomerate, shale, and minor limestone. Represents the oldest sedimentary unit of the Aravalli Group.
  • Depositional Environment: Shallow marine to fluvial.
• Sambhar Formation:
  • Age: ~1.65-1.58 Ga
  • Lithology: Massive quartzites, shales, and dolomites. Characterized by thick quartzite ridges.
  • Depositional Environment: Tidal flat and shallow marine.
• Jodhpur Formation:
  • Age: ~1.58-1.50 Ga
  • Lithology: Sandstones, shales, and conglomerates. Contains phosphorites and stromatolites.
  • Depositional Environment: Shallow marine and deltaic.
• Bundi Formation:
  • Age: ~1.50-1.45 Ga
  • Lithology: Red sandstones, shales, and conglomerates. Indicates oxidizing conditions.
  • Depositional Environment: Fluvial and terrestrial.
• Losari Formation:
  • Age: ~1.45-1.40 Ga
  • Lithology: Phyllites, schists, and quartzites. Represents a period of tectonic activity and metamorphism.
  • Depositional Environment: Deep marine.

3. Raoli Group (Transitional Phase)

Represents a transition between the Aravalli and Delhi Supergroups.

• Age: ~1.40-1.30 Ga
• Lithology: Phyllites, schists, and quartzites with intercalations of volcanic rocks.
• Significance: Indicates the onset of Delhi Supergroup sedimentation.

4. Delhi Supergroup (Overlying Sequence)

The Delhi Supergroup overlies the Aravalli Supergroup and is divided into several formations, including the Alwar, Ajgarh, and Mahendragarh groups. These formations are characterized by sedimentary and volcanic rocks, representing a period of extensive rifting and sedimentation.

Formation	Age (Ga)	Lithology	Depositional Environment
Delwara	~1.75-1.65	Quartzite, Shale, Conglomerate	Shallow Marine/Fluvial
Sambhar	~1.65-1.58	Quartzite, Shale, Dolomite	Tidal Flat/Shallow Marine
Jodhpur	~1.58-1.50	Sandstone, Shale, Conglomerate	Shallow Marine/Deltaic
Bundi	~1.50-1.45	Red Sandstone, Shale, Conglomerate	Fluvial/Terrestrial

Structural Features: The Aravalli Supergroup has undergone multiple phases of deformation, including folding, faulting, and metamorphism. The major structures include the Delhi-Aravalli Fold Belt and several regional faults. These structures have played a significant role in the geological evolution of the region and have influenced the distribution of mineral resources.