This document summarizes a seminar on the Precambrian period covering its evolution on Earth, important fossils and terrains in India, paleogeography and the breakup of a late Proterozoic supercontinent, stratigraphy of basins in India, and the Precambrian-Cambrian boundary. Key points include: Earth's atmosphere formed via outgassing; stromatolites and microplankton are common Precambrian fossils; a late Proterozoic supercontinent broke up during the period; and the Precambrian-Cambrian boundary marks major biotic changes in Earth's history.

1. Seminar on

2. Introduction
Evolution Of Earth During Precambrian
Precambrian Terrains Of India
The Important Fossils In The Krol Formation
Paleogeography A Break-Up of the Late Proterozoic supercontinent
Stratigraphy of the Birmania Basin,Rajasthan, India: Implications
for the Vendian-Cambrian Transition
Precambrian Cambrian Boundary
Conclusion
References

3.  The Precambrian is an informal name for the span of time
before the current Phanerozoic Eon, and is divided into several
eons of the geologic time scale.
 It spans from the formation of Earth around 4600 Ma (million
years ago) to the beginning of the Cambrian Period, when
macroscopic hard-shelled animals first appeared in abundance
about 542 Ma.
 The Precambrian is so named because it precedes the
Cambrian, the first period of the Phanerozoic Eon, which is
named after the Roman name for Wales, Cambrian, where rocks
from this age were first studied.
 In the Indian shield area precambrian rocks are widely
distributed in Assam, Karnataka, Bihar, Madhya Pradesh,
Rajasthan, Orissa, Andhra Pradesh, Tamil Nadu, Kerala and
Central Himalayan terrain.

4. Shortly after accretion, Earth was
a rapidly rotating, hot, barren, waterless planet
bombarded by comets and meteorites
with no continents, intense cosmic radiation
and widespread volcanism
• about 4.6 billion years ago

5.  Pre cambrain – cambrian boundary starts at (600ma) –(540ma).
 During the Archean time,micro continents collided with one
another throughout the proterozoic and formed the cores of the
continents.
 By the end of the proterozoic the first supercontinent, Pangea,
had formed.
 Earth’s early atmosphere and the oceans formed mainly by the
process of outgassing.
 Nearly all the Oxygen in the atmosphere is a result of
photosynthesis.
 Certain minerals oxidize,or rust in the presence of free oxygen.
 Proterozoic ‘red beds’are sedimentary rock deposits that
contain oxidized iron.
 They are the evidence that there was free Oxygen in the
atmosphere during the Proterozoic.

6. GEOLOGIC TIME SCALE

7. Stromatolites & planktons occur widely in the fossil record of
the Precambrian.
Kottah & karavli basin(Rajasthan) had abundance of
microplanktons.

8.  Archaean to Early proterozoic :
 Dharwar Craton
 Singhbhum Craton
 Rajasthan – bundelkhand region
 Bastar Craton
 Eastern Ghats Mobile Belts
 Satpura orogenic belt
 Proterozoic Sedimentary Basins :
 Cuddapah Basin
 Chattisgarh and Indravati/Bastar basins
 Pakhal basin

9. The following ediacaran fossils are recorded from the
upper part in the Lesser Himalaya in Uttarakhand.
 Beltaneliformis
 Pterinidium
 Ichnogenus
The change from the smooth and unprocessed and
spinate forms in Tal Formation coincides with the
appearance of the earliest skeletal fossils of Early
Cambrian age.

10.  Precambrian-cambrian transition is marked by major biotic
changes.
 Emergence of soft bodied Ediacaran fauna and their subsequent
extinction.
 Emergence of fauna with hard parts or chemical
changes,particularly variation in the C and Sr isotopic composition
of the carbonates.
 All of this provide significant stratigraphic information,which
may be used for the correlation of terminal proterozoic and early
cambrian strata to solve stratigraphic problems.

11. Ediacara community including a fixed and mobile tiered
benthos.

12. • Most continental plates formed a giant supercontinent
• This Late Proterozoic Supercontinent is occasionally
referred to as "Pangea I“.
• This was, most likely, the second supercontinent in the
history of the Earth (Rodinia was first.)
• The supercontinent began to rift apart in the latest
Proterozoic (evidence: rift basins, basalts, and
sedimentary sequences on paleocontinental margins).
• The drift continued throughout the Paleozoic until the
next supercontinent (Pangea) formed.
• The exact paleogeography of the supercontinent and its
subsequent break up is not known exactly.

13. Climate -From the Varangian Glaciation into a
Greenhouse Earth
• "Varangian" glaciation - probably the most severe ice age in the
Earth's history.
• Glacial deposits (deposited about 600 million years ago) are
found on almost all continents.
• Ice sheets must have extended to near the equator (unique in
the Earth's history).
• A further decrease in CO2 in the atmosphere - eukaryotic algae
diversify in the late Proterozoic (= increased use of CO2 for
photosynthesis).
• A supercontinent in the tropics could change atmospheric
patterns and cause global cooling.
• Changes in astronomical parameters of the Earth.

14.  The Birmania Basin is an oval-shaped, isolated remnant of the
Marwar Basin(Neoproterozoic-Early Palaeozoic) located in
the heart of the Thar Desert of western Rajasthan, India.
 The Birmania Basin comprises a 900-metre- thick
sedimentary sequence of siliciclastic, carbonate and
phosphorite facies.
 Global Neoproterozoic glacial activity in western Rajasthan is
represented by the Pokaran Boulder Bed, a few kms away from
study area.
 The Pokaran Boulder Bed overlies the Malani Igneous Suite
and mainly consists of boulders and angular fragments of
igneous rocks belonging to the Malani Suite.

15. The Precambrian-Cambrian boundary problem is studied in an
areno-argillaceous sequence in the Kashmir and Spiti Valley, Northwest
Himalaya.
In Kashmir, a rich and diversified microbiota-cryptarchs and algae of
the Late Precambrian, and Lower Cambrian trace fossils are recorded.
In the Spiti Valley, the yield of microbiota is poor and the trace fossils
are late Lower Cambrian.
Lahaul-Ladakh
A detailed outline of the geology of this region was described by
Lydekker(1883)
The crystalline and metamorphic rocks of this region consist of
granites,gneisses and schists

16. Kashmir-Ladakh
The stratigraphic successions from Precambrian to Lower Palaeozoic are
exposed in the Northwestern and Southwestern parts of the kashmir valley.
According to Wadia(1934) the rock of the Salkhala super group are the oldest and
consist of slates and crystalline limestone,flaggy quartzite,phyllites schists.
These are overlain conformably by the Dogra slates and fossiliferous lower
palaeozoics
Lahaul-Spiti
According to Gupta and Kumar the precambrian rocks are widely distributed in
different parts of Lahaul and Spiti
These are overlain by the unfossiliferous and fossiliferous strata of cambrian age
has been recorded near Kunzam pass,Pin river and Prahio river section.
The deposits in Spiti are known as Haimanta system and they consist of Slates,
micaceous quartzite and dolomitic limestones.

17.  Very little is known about the Precambrian, despite it making up
roughly seven-eighths of the Earth's history, and what little is known
has largely been discovered in the past fifty years.
 The Precambrian fossil record is poor, and those fossils present
(e.g. stromatolites) are of limited biostratigraphic use.
 Many Precambrian rocks are heavily metamorphosed, obscuring
their origins, while others have either been destroyed by erosion, or
remain deeply buried beneath Phanerozoic strata.
 A considerable area of peninsular India, the Indian Shield, consists
of Archean gneisses and schists which are the oldest rocks found in
India.
 The Precambrian rocks of India have been classified into two
systems, namely the Dharwar system and the Archaean system.

18.  K.C. Condie (1994). Archean crustal evolution. Elsevier.
Page No: 420-440.
 C.S. Pichamuthu (1985). Archean geology. Oxford&IBH
Publishing&Co,New Delhi. Page No: 43-75,151-340.
 A.M. Goodwin (1996). Principles of Precambrian geology,
Academic Press, London. Page No: 327-350.
 B.P.Radhakrishna & R.Vaidhyanadhan(1997). Geology Of
Karnataka. Geological Society Of India,Bangalore. Page No:
01-205.
 http://gondwanaresearch.com/hp/jaes.pdf
 http://www.portal.gsi.gov.in/portal/page?_pageid=127,68764
3&_dad=portal&_schema=PORTAL
 www.google/geology of india.com