Precambrian (ediacara) cambrian stratigraphic boundary

2. CONTENTS
• Stratigraphic Boundary
• Introduction
• Trace Fossils
• PC/C stratigraphic boundary in India
• Conclusion
• Reference

3. Earth During Past
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

4. Geological Time Clock
• 88% of geologic time
Time Span
Cenozoic=1.4%
Mesozoic=4%
Paleozoic=6.3%
Proterozoic=42.5%
Archean =45.6%
Boundary Between
Palaeozoic----- Cambrian
------------------ ---------------
Proterozoic - Ediacarn
Precambrian

6. Stratigraphic Boundary
• Archean – Proterozoic (Eparchean)
•Precambrain –Cambrian
• Permian – Triassic
• Cretaceous – Tertiary (Famous K-T Bondary)

7. INTRODUCTION
 Precambrian-cambrian transition is marked by major
biotic changes,viz.
 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 corbonates.
 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.

8.  Explosion of life at PC/C boundary saw varieties of
animals emerging as builders,binders and encrusters
in various build-ups.
 During the early cambrian period there was an
evolutionary explosion,referred by palaeontologists
as the cambrian ‘Big Bang’.
 The most severe glaciation known in the geologic
record occurred during the Cryogenian, when ice
sheets reached the equator and formed a possible "
Snowball Earth".
 The earliest fossils of multicellular life are found in
the Ediacaran, including the earliest animals.

9. Stratigraphic distribution of the Ediacara biota. Solid triangles,
glaciations; C, calcified metazoans; (Based on Narbonne 2005.)

10. TRACE FOSSILS
 Trace fossils studies have begun to play an increasing
role in understanding of the nature of early metazoan
life and also as stratigraphic indicators
 The studies related to labenspurren (sedimentary
structure left by living organism)are of immense use in
interpreting the palaeoenvironment.

11. Charles Walcott (early 1900s) described structures
from the Paleoproterozoic Gunflint Iron Formation of Ontario,
Canada that he proposed represented reefs constructed by Algae
Oldest known fossil organisms
Now call
Stromatolites
not until 1954 were
they shown
to be products of
organic activity
Oldest Fossil Algae:
Stromatolites
Stromatolites (Shark Bay, Australia)

12. Putative trace fossils from the Precambrian of Australia, showing
Myxomitodes, a presumed trail of a mucus-producing multicellular
organism about 1.8–2 billion years old from Stirling Range, Western
Australia. (Photo is approximately 65 mm wide.) (Courtesy of Stefan
Bengtson.)

13.  An examination of all the recent worldwide studies on
ichnology(study of trace fossils,especially the study of
fossil tracks)seems to result in the following
generalised stratigraphic sequence from proterozoic
to lower palaeozoic.
 L.palaeozoic-
a)Rocks with trilobite,brachiopoda,archaeocyathids
and abundant trace fossils
b)Trilobites with other trace fossils
c)Soft-bodied metazoans(Ediacaran and alike fauna)
 Proterozoic-
d)Rare trace fossils with stomatolites.

14. Ediacara community including a fixed and mobile tiered benthos.
TYPICAL EDIACARA (UPPER MOST PRECAMBRIAN)
FAUNAL EVIDENCES IN FIXING PC-C BOUNDARY

15. Some typical Ediacara fossils: (a) the Radiata, which have been associated with
the cnidarians, and (b) the Bilateria, which may be related to the annelids and
arthropods. Ediacaria (×0.3), Charnia (×0.3), Rangea (×0.3), Cyclomedusa (×0.3),
Medusinites (×0.3), Dickinsonia (×0.6), Spriggina (×1.25), Tribrachidium (×0.9) and
Praecambridium (×0.6). (Redrawn from various sources by Anne Hastrup Ross.)

16. Precambrian & Cambrian Stratigraphy
(Stewart & Suczec, 1977)

17. PRECAMBRIAN – CAMBRIAN STRATIGRAPHIC
BOUNDARY IN INDIA
 Tethys Himalayan Zone
1. KASHMIR - LADAKH
2. LAHAUL - SPITI
3. KUMAUN
Lesser Himalayan Zone

18. IN INDIA PRECAMBRIAN-CAMBRIAN BOUNDARY
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.

19. 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

20.  The Dogra slates and the associated rock formations
exposed in different parts of the northwestern
Kashmir constitute one of the best section for
demarcating the boundary between the PC/C rocks.
 The find of Redlichia in the uppermost horizons of
the Lolab formation of lower cambrian from 8km SE
of Kupwarain the Barmula Dist.
Lahaul-Ladakh
 Adetailed 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

21. 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.

22. GEOLOGICAL MAP OF HIMALAYA

23. Significance of the diverse worm-like animals at the Precambrian–
Cambrian boundary and the postulated origins of some major Clades.
(Based on Dzik, J. & Krumbiegel, G. 1989. Lethaia 22.)
CAMBRAIN
VENDIAN

24. Conclusion
• Information on Precambrian-Lower Palaeozoic rocks of the Lesser
Himalaya zone is not yet sufficient to permit a detailed
reconstruction of the geologic history during that period.
• Detailed petrographic work supplemented by age determinations
of the rocks is needed to work out precisely the boundary between
the Algonkian and Palaeozoics.
• Presence of fossils of brachiopods and trilobites has been recorded
from lower to upper cambrian rocks of the Tethys belt of the
Himalaya.
• These fossils have been recorded from the micaceous quartzite and
limestone .
• Precambrian-cambrian transition is marked by major biotic changes
• Explosion of life at PC/C boundary saw varieties of animals
emerging as builders and binders .

25. Reference
• 2008,R.Vaidyanadhan & M.Ramakrishnan
Geology of India volume-2
Geological Society of India, Bangalore . pp:571-585
• 1977, V.J.Gupta Indian Precambrian Stratigraphy
Hindustan Publishing Corporation, Delhi. pp:140-148
• 1991, Alan M Goodwin, Precambrian Geology
Academic Press London, pp:555-567
• 1990,Memoir 16,Stratigraphic Boundary Problem in India
Geological Society of India. Pp:19-32
• Precambrian Cambrian boundary.Wikipedia.co/in
• http://www.geological survey India map.com
• www.geology.info.in

26. QUESTIONS?
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