Paleozoic of Spiti - opengeology.in

The Continuous Paleozoic succession is beautifully exposed in the area of Spiti valley. A rich collection of fossils reported from the region has made Spiti valley a standard sections for correlation of Phanerozoic rocks of Indian and adjoining regions of the sub-continent.

The succession is overlies the Vaikrita Group of higher Himalaya that is made up of Schists, Gneisses and quartzites and is separated by an unconformity.

The succession starts with the Haimanta Group that can be correlated with the Dogra Slates of he Kashmir Basin. Haimanta Group is further divided into two formations –
- The lower Batal formation and upper kunzam-La formation (parahio formation). The lower Batal formation is unfossiliferous but later on every group and formation is fossiliferous.

The Batal formation is predominantly argillaceous and Kunjam-La formation begins with change in facies to arenaceous with upper fossiliferous sequences. The dolomitic bands in the sequence contains algal structures.

There are three more groups naming Sanugba Group, Kanawar Group and Kuling Group.

The Cambrian sequence is overlain by the Sanugba Group.
- The lower “Thangpo Formation“, it is poor in fossils. The upper and lower age limit of the of the Formation is fixed on the basis of trilobites of upper Cambrian and middle to upper Ordovician in the overlying beds.
- The upper “Takche Formation“ is of Silurian age on the basis of fossil record. The Ordovician-Silurian boundary is marked by the presence of fossils in the basal part of the formation.
  - There are reefs of Rugose and Tabulate corals building up during early and middle Silurian related to the marine transgression started in the Ordovicia.
  - A regressive phase set in Late Silurian that led to shallowing of basin and termination of reef building.

The Takche Formation is overlies by Kanawar Group, that is divided into Muth, Lipak, Po and Ganmachidam Formations.
- The “Muth Formation (Quartzite)” is formed due to gradational changes of limestone of Takche formation into calcareous quartzite. It is snow white and light green quartzite with dirty white thickly bedded sandstone. The age is assigned to be early Devonian.
The The time span between the Muth Formation and Lipak Formation is a phase of non deposition for greater part of Devonian period.
- The “Lipak Formation” is aged from Late Devonian to Early Carboniferous. It contains fossils of Ostrocods and Carbonifeorus Brachiopods.
- The “Po Formation” that overlies Lipak Formation is made up of shales and quartzite. Lower part is Thabo member contains Rhacopteris flora of Early Carboniferous.
- The upper part of the Kanawar Group is Ganmachidam Formation that is unfossiliferous.

The upper most Group is Kuling Group with two subunits – Gechang Formation & Gungri Formation.
- This Group marks the end of Paleozoic Era.

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