Seminar on

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

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.

Shortly after accretion, Earth was a rapidly rotating, hot, barren, waterless planetbombarded by comets and meteoriteswith no continents, intense cosmic radiation and widespread volcanism

• about 4.6 billion years ago

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.

GEOLOGIC TIME SCALE

Stromatolites & planktons occur widely in the fossil record of

the Precambrian.

Kottah & karavli basin(Rajasthan) had abundance of

microplanktons.

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

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.

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.

Ediacara community including a fixed and mobile tiered benthos.

• 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.

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.

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.

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

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.

Very little is known about the Precambrian, despite it making uproughly seven-eighths of the Earth's history, and what little is knownhas 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, obscuringtheir origins, while others have either been destroyed by erosion, orremain deeply buried beneath Phanerozoic strata.

A considerable area of peninsular India, the Indian Shield, consistsof Archean gneisses and schists which are the oldest rocks found inIndia.

The Precambrian rocks of India have been classified into twosystems, namely the Dharwar system and the Archaean system.

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=127,687643&_dad=portal&_schema=PORTAL

www.google/geology of india.com