This document discusses acritarchs, which are microscopic fossilized organic-walled cysts of unicellular protists. It provides an overview of acritarchs including their origins, morphology, classification schemes, stratigraphic distribution, paleoenvironmental indications, and applications in biostratigraphy. Acritarchs show diversity in the Neoproterozoic and Paleozoic and can be used to interpret age and depositional environment in Proterozoic-early Paleozoic sediments where other fossils are scarce. Their distributions reflect environmental conditions like depth, salinity, and nutrient levels.

1. Nurturing
talent through
mentoring
KDMIPE
Geology Group

2. Acritarchs and its application in Proterozoic-
early Paleozoic sedimentary basins of India
India’s Energy Enchor
Geology Group
KDMIPE, ONGC, Dehradun
Asher Ramson, GM (Palynology)

3. Introduction
 Acritarchs are microscopic & fossilized organic-
walled cysts of unicellular protist (one-celled organism) that
can not be assigned to the known groups of
organisms
 It is the resting cysts of marine phytoplankton and
is found from Proterozoic to Recent
 But, most common in Neoproterozoic & Paleozoic
sediments

4.  “Acritarchs” was coined by Evitt in 1963, which means "of
uncertain origin”
 It includes any small (04-350µm ), organic-walled microfossils
of algal affinity which cannot be assigned to a natural group.
 Characterised by varied sculptures, some are spiny and others
smooth.
 Good biostratigraphic tool for Mesoproterozoic,
Neoproterozoic & early Paleozoic where other fossils are not
available
Introduction

5. Introduction
 Acritarchs are marine, so they are useful for palaeo-environment
interpretation.
 Known from Paleoproterozoic & achieved considerable diversity in early
Mesoproterozoic (ca1600Ma).
 Diversity crashed during the Sturtian-Varanger glacial event around 700Ma.
 Again, increased during Ediacaran (ca 630Ma).
 Diversity declined at the end of Proterozoic (ca 542Ma).
 Shows greatest diversity during Cambrian, Ordovician, Silurian & Devonian
(ca 542 to 359.2Ma: Paleozoic)
 98% taxa become extinct during late Devonian
 Helps in assessing TOM and maturity

6. 6
Classification
a. Purpose of biological classification is to follow natural order & facilitate
phyllogenic communication
b. Most widely accepted acritarch classification is the Artificial Scheme
introduced by Downie, Evitt and Serjeant in 1963.
c. They established 9 subgroups upon vesicle shape & process topography.
d. However, Peat & Diver (1979) erected Nematomorphs and
Synaplomorhs in addition
e. The following is the summary of acritarch subgroups based on the
Downie et. al. scheme.
(1) Biological & (2) Artificial

7. 7
Classification
1. Acanthomorphs have spherical bodies with
spines which usually open into the body.
2. Polygonomorphs have a body-shape defined
by the number and position of spines, they are
often triangular or square in outline.
3. Netromorphs have a fusiform body with one or
more spines.
4. Diacromorphs have spherical to ellipsoidal
bodies with ornament confined to the poles.
5. Prismatomorphs have prismatic to polygonal
bodies the edges of which form a flange or
crest which may be serrated.

8. 6. Oomorphs have an egg shaped body with
ornament confined to one pole.
7. Herkomorphs have a roughly spherical body
divided into polygonal fields like honey
comb
8. Pteromorphs have a roughly spherical
central zone often compressed, surrounded
by a flange or wing lamella which may be
sustained by radial folds or processes.
9. Sphaeromorphs have simple spherical
morphology.
Classification

9. Sphaeromorphs

10. 10
Acanthomorphs

11. 11
Netromorphs

12. 1
2
Pteromorphs

13. 1
Polygonomorphs
Prismatomorphs

14. 1
Herkomorphs

15. 15
Synaplomorphs
Nematomorphs

16. 16
Steps in Biostratigraphic interpretation
 Identification of various taxa
 Stratigraphic distribution of key taxa
 Recognition of LADS and FADS of
marker taxa
 Deliniation of assemblage zones and
their comparisons
 Interpretation of age & depositional
environment
 Correlation
 Identification of Unconformity & span
if any

17. Biostratigraphy
1. Acritarchs have great value in
biostratigraphic applications
particularly Proterozoic and early
Paleozoic.

18. Range of acritarch groups
Geological ranges of Proterozoic acritarchs
1. It has evolutionary history of appearance and extinction
during their widespread distribution in time and space.
2. So they are useful in determining age, zonation,
interpretation of paleoenvironment etc. of Proterozoic
and early Paleozoic sediments.

19. Paleoproterozoic (2500- 1600Ma)
 Acritarchs are present in the late Paleoproterozoic; but they
are rare and consist of morphologically simple spheres
(spharomorphic acritarchs) Javaux et al. (2004).
 It was reported from shales of 1900-1600Ma old in the
former Soviet Union (Timofeev, 1969).
 Latter on Zang (1986) reported large leiosphaerids along
with filamentous and disc-shape acritarch from
Chuanlinggguo Formation (1900-1700 Ma) in China.
 Tyler (2007) discovered spinose acritarchs in the Harris
Greenstone Domain in South Australia and dated ~2500 Ma.
Sphaeromorphs
Fillamentus algae

20. Mesoproterozoic
 The stratigraphically more significant acritarchs are recorded in the
Mesoproterozoic
• Abundant occurrence of species like,
Tappania plana, T. tubata,
Spiromorpha segmentata,
Shuiyousphaeridium, Satka spp.,
Valeria lophostriata, etc. along with
filamentous sheaths marks the
Mesoproterozoic era.
Tappania
Spiromorpha
(1600 - 1000Ma)

21. Early Neoproterozoic
Melanocyrillium
Trachysphaeridium
(1000 - 635Ma)
Budding leiosphaerids
Vandalosphaeridium
• The significant diversification of
acritarchs begins near the base of
Neoproterozoic.
• Some of the important taxa such as,
budding leiosphaerids,
Trachysphaeridium laminaritum sp.,
Melanocyrilium spp.,
Vandalosphaeridium reticulatum,
Cymatiosphaera kullungi
characterize early Neoproterozoic.

22. Late Neoproterozoic (635 - 542Ma)
• Late Neoproterozoic (Ediacaran)
is marked by the abundant
occurrence of Cavaspina,
Appendisphaera,
Gyalosphaeridium, Obruchevella
valdaica, O. parva, O. delicata,
Bavlinela faveolata,
Germinosphaera unipinosa,
Cristalinium sp. Dictyodidium sp.,
etc.
Obruchevella
Germinosphaera
Cavaspina
Appendisphaera
Gyalosphaeridium

23. Cambrian (542-488.8Ma) PLATE 1
PLATE 2
Striatotheca
• The acritarch biostratigraphy of Paleozoic is
well established.
• The beginning of Cambrian marks the
appearance of species such as Asteridium
tornatum, Comaspharidium velvetum etc.
• Early Cambrian is characterized by Asteridium
tornatum, A. lanatum, Lophosphaeridium
tentativum, Comaspharidium velvetum and
Baltisphaeridium dubium.
• Late Cambrian is characterized by
Striatotheca sp, Dorsidinium sp. etc.
Dorsenidium
Baltisphaeridium Asteridium
Lophosphaeridium Skiagia cilosa

24. 542
550
560
570
580
590
635
(Ma
)
??
Marinoan/
Varanger
Glaciation
??
I
I
I
V
IV
II
I
Acritarch zones
SiO2
Sponge
Specule
s
SSFs
CaCO2
Micro-
fossils
Diverse
Ediacaran
fossils
-10 0 +10 .707
0
.708
5
87Sr / 86Sr
δ13C (%
PDB)
Moelv/
Biskop Gl. III

25. Paleoenvironment
• It is generally agreed that acritarchs are marine planktonic algae
(Downie 1973, Tappan 1980).
• Smith & Saunders (1970) stated that acritarch do not occur in fluvial
deposit and it is abundant in open marine facies whereas, marginal
marine facies contain very few or no acritarchs.
• Leiosphaeridia-dominated assemblage indicates nearshore (shallow
water) environment
• Dicommapalla assemblage is deposited in shoal environments and
• Deeper waters are characterized by acanthomorphs and
polygonomorphs

26. • Al-Ameri defined five palynofacies with sphaeromorhs dominated
acritarchs interpreted as near shore, and more diverse assemblage
as offshore.
• While considering the paleoecology of acritachs, it must be
remembered that several factors controlled acritarch distribution,
including nutrient availability, turbidity, temperature, salinity, light,
depth, bioturbation etc.
• The effects of some of these factors are difficult to determine.
Paleoenvironment

27. TOM, MATURATION & SOURCE POTENTIAL
FM DEPTH (m) OM TYPE & NATURE OM FACIES TOM (%) TAI SOURCE POT.
1839-1842 Algal amorphous: fluffy & spongy sapropelic mod.-poor (25)
2.00
1840-1845 Algal amorphous: fluffy & spongy sapropelic poor (<20) 2.00
1902-1905 poor (<20)
1948-1951 Algal amorphous: thallus & fluffy sapropelic poor (<20) 2.00
1988-1991.5 Algal amorphous: thallus & fluffy sapropelic poor (<20) 2.00
1992-1995 Algal amorphous: thallus & fluffy sapropelic poor (<20) 2.00
2001.5-2001.9 Algal amorphous: thallus sapropelic poor (<20) 2.00
2001.9 Algal amorphous: thallus sapropelic poor (<20) 2.00
2129-2135 Algal amorphous: thallus & fluffy sapropelic mod. (30) 2.00
2156-2162 poor (<20)
2186-2189 Algal amorphous: thallus & fluffy sapropelic poor (<20) 2.25
2220-2223 Algal amorphous: thallus & fluffy sapropelic poor (<20) 2.25
2241-2244 Algal amorphous: thallus sapropelic poor (<20) 2.25
2259-2262 Algal amorphous: thallus sapropelic poor (<20) 2.25
2280-2283 Algal amorphous: thallus sapropelic poor (<20) 2.25
2301-2304 Algal amorphous: FOM & fluffy sapropelic mod. (30) 2.25
2319-2322 Algal amorphous: thallus sapropelic poor (<20) 2.25
2334-2337 Algal amorphous: fluffy sapropelic poor (<20) 2.25
2337-2340
Algal amorphous: fluffy, spongy,
filaments
sapropelic rich (50) 2.25+
2385-2388 Algal amorphous: filaments sapropelic poor (<20) 2.25+
2400-2403 Algal amorphous: thallus & fluffy sapropelic mod. (30) 2.25+
2430-2435 Algal amorphous: fluffy sapropelic poor (<20) 2.25+
2448-2450 poor (<20)
2453-2456 Algal amorph.: thallus & filaments sapropelic rich (60) 2.25+
2480-2483 Algal amorph.: thallus & filaments sapropelic rich (50) 2.25+
2490-2493.2 Algal amorphous: thallus sapropelic poor (<10) 2.25+
2504-2507 Algal amorphous: fluffy sapropelic poor (<10) 2.25+
2528-2530 Algal amorphous: thallus & fluffy sapropelic rich (50) 2.25+
2531 Algal amorphous: thallus & fluffy sapropelic rich (50) 2.50
2549-2552 Algal amorph.: thallus & filaments sapropelic rich (65) 2.50
2659-2662 Algal amorphous: thallus sapropelic rich (50) 2.50
2683.4-2685.6 Algal amorphous: fluffy(rounded) sapropelic rich (55) 2.50
2685.6-2686.1 Algal amorphous: fluffy sapropelic rich (50) 2.50
2686.1-2692.5 Algal amorphous: fluffy sapropelic rich (50) 2.50
2731-2734 Algal amorphous: fluffy sapropelic mod. (40) 2.50
2767-2770 Algal amorphous: fluffy sapropelic mod. (40) 2.50
2803-2806 Algal amorphous: filaments sapropelic mod. (40) 2.50
2839-2842 Algal amorphous: thallus sapropelic poor (<10) 2.50
2887-2890 Algal amorphous: fluffy sapropelic poor (<20) 2.50
2932-2938
2971-2974 Algal amorphous: fungal sapropelic poor (<10) 2.50
3011-3013.9
3052-3055 Algal amorphous: FOM sapropelic poor (<5) 2.75
3076-3079
Algal amorphous: fluffy, thallus,
filaments
sapropelic mod. (35) 2.75
3100-3103 Algal amorph.: thallus & filaments sapropelic rich (55) 2.75
3160-3163 Algal amorphous: fluffy sapropelic poor (<25) 2.75
3251.5 Algal amorphous: fluffy sapropelic poor (<10) 2.75
3291-3294 Algal amorphous: fluffy sapropelic poor (<25) 2.75
3312-3315 Algal amorphous: fluffy sapropelic poor (<25) 2.75
FIG. 5: ORGANIC MATTER FACIES, TOTAL ORGANIC MATTER, MATURATION AND SOURCE
POTENTIAL IN SPN-A
KARNAPUR
T
I
L
H
A
R
U
J
H
A
N
I
SPN:Algal amorph. oxidized;
UJN & KDM:Algal amorphous
fluffy
sapropelic
3349-3351.85
A
V
A
D
H
MODERATE
MODERATE
mod.-rich
(30-50)
2.75+
MOD-GOOD
SOURCE POT.
GOOD
SOURCE
POT.
POOR
SOURCE
POTENTIAL
MAINLY
DUE
TO
IMMATURITY
POOR
SARDA
P o o r o r g a n i c m a t t e r
P o o r o r g a n i c m a t t e r
P o o r o r g a n i c m a t t e r
P o o r o r g a n i c m a t t e r
P o o r o r g a n i c m a t t e r
POOR
2531m
2731m
2839m
3055m
3315m
3103m
3351+m
STAPLIN'S
SCALE
RUSSIAN
SCALE
1
1.5
2.25
2.5
3.0
3.5
5.0
1
2
3
4
5
6
7

28. Application in Proterozoic-early Paleozoic basins of India
 Among these, ONGC/other E&P
companies involves in exploration in
Vindhyan, Ganga & Bikaner-Nagaur
basins
 Indian Craton includes 8 Proterozoic
basins,
 These are Vindhyan, Ganga,
Bikaner-Nagaur, Bhima, Kaladagi,
Cuddapah, Bastar, Chattisgarh

29. Pre-Tertiary Sequence of Ganga Basin
 Age of this sequence remained
disputed since the drilling of 1st well,
the UJN-D-1 in 1962
• Sequence occurring below
Tertiary (Siwaliks) in subsurface
referred as Pre-Tertiary Sequence

30. Ganga Basin: Diverse views on its age
• Mesozoic = Mathur & Evans (1964)
• Palaeozoic = (Metre, 1968)
• Cambrian- Carboniferous = Sastri & Venkatachala (1968)
• Pre-Ordovician = Venkatachala & Rawat (1972)
• Precambrian to = Salujha et al. (1967)
Silurian Salujha (1973)
• Late Riphean to Cambrian = Saxena 1992
• Precambrian to = Fuloria (1996)
Late Cretaceous Raiverman (1998)

31. Late Neoproterozoic –early Paleozoic
(Unmetamorphosed succession)
Unconformity (ca 900Ma)
Mesoproterozoic
(Metamorphosed succession)
Pre-Tertiary
Sequence
Age on the basis of acritarchs
Still, the age of Pre-Tertiary Sequence debatable
• Equated with Vindhyans, considering its northern continuation in Ganga
Basin
• Although, the age of Vindhyans appear different (ca.1600-570Ma)

32. Some acritarchs record from Ganga Basin
1
4
9
2
3
10
6
13
8
7
5
11
12
15
12
14
16

33. 1
5
2 3
4
8
7
6
9
12
11
13
15 16
18
14
1
4
2
9
3
5
6
7
8
12
13
18
Some acritarchs record from Ganga Basin

34. 3
Vindhyan Basin: Diverse views on its age
 ACRITARCHS : Early Mesoproterozoic (ca. 1550Ma)
to Ediacaran (ca 545Ma)
 MAGAFOSSILS : Riphean – Vendian (Meso-Neoproterozoic)
 STROMATOLITES : Early to Late Riphean
(Late Paleoproterozoic – Neoproterozoic)
 RADIOMETRIC : ca 1750-550 Ma
(Late Paleoproterozoic - Ediacaran)
 C δ13 VALUE : Precambrian-Cambrian Boundary In Sirbu Shale
(Bhander Group)
 SS MICROFOSSILS : Late Neoproterozoic-Early Paleozoic (Cambrian)

35. 3
VINDHYAN BASIN: AVAILABLE DIVERSE RADIOMETRIC AGE DATA
1. Late Paleoproterozoic-
Early Mesoproterozoic
2. Late Mesoproterozoic-
Late Neoproterozoic
3. Late Neoproterozoic
(Ediacaran)-Early
Paleozoic (Cambrian)

36. 36
Acritarch and other
organic-walled
microfossil evidences
suggest that the
Vindhyan Supergroup
spans from late
Paleoproterozoic (ca
1750Ma) to late
Neoproterozoic
(Ediacaran; 542Ma)-?
Early Cambrian
Vindhyans of Son Valley

37. 37
Some acritarchs record from Son Valley Vindhyans

38. Vindhyans of Chambal Valley
 Chambal Valley covers western parts of
Vindhyan Basin
 Separated from the Son Valley by
Bundhelkhand Granitic Complex (BGC)
and a Subsurface High
KOTA

39. Vindhyans of Chambal Valley
Chechat-1
 In Chambal Valley,
Lower Vindhyans
thin (700-1800m); Up.
Vindhyan very thick
(2500-3000m)
 In Son Valley Lower
Vindhyan very thick
(3000-4000m); Upper
Vindhyan very thin
(400-600m)
 Correlation problem
due to variation in
lithology and
Biostratigraphy in
corresponding units

40. Vindhyans of Chambal Valley: Biostratigraphy
 Acritarchs evidenses suggest Ediacaran (late
Neoproterozoic) age for Lower Vindhyans
 Early Cambrian for Upper Vindhyan
 Appears representing Infra-Cambrian Sequence
Palaita-1

41. 4
3
1 2
6
7 9
8
5
10
1
4
2
3 9
10
5
6
7 8
Some acritarchs record from Chambal Valley Vindhyans

42. Some acritarchs record from Chambal Valley Vindhyans
9
8
7
4
3
1 2
6
5
1
8 9
10
2
4 7
3
6
1
2
13 14 15
11
5

43. Acritarch based
biostratigraphic studies
suggest Late
Neoproterozoic-
(Ediacaran) to Middle
Cambrian age
 Pc/C Boundary marked
within Bilara Limestone on
the basis of acritarchs
which was later
coroborated by Sr/Sr.
isotope incursion
Biostratigraphy: Marwar Supergroup

44. Some acritarchs record of Marwar Supergroup

45. Thank You