Organic Acritarch's & Dinoflagellates

1. 12/9/2020 1

2. AAMIR ALI
AIZAZ KHAN
QAZI ABDULLAH
MUHAMMAD USMAN
PresenTATiOn On
OrgAnic AcriTArch's &
DinOflAgellATes
by
. 2

3. ORGANIC ACRITARCH'S
Contents
• Introduction
• Morphology
• Paleoecology
• Evolutionary History
3

4. INTRODUCTION:
Acritarchs are hollow, organic-walled microfossils. They
are believed to represent the cyst stages in the life cycles
of planktic algae similar to a modern group,
dinoflagellates, because both groups produce a
characteristic molecule, dinosterane. They are one of the
oldest groups of fossils and underwent a major radiation
in the late Precambrian.
4

5. • Organic walled microfossils
• Unicellular
• Mode of Nutrition: Autotrophic
• One of the oldest group of fossils
• Thought to be abandoned organic
envelops of protistan planktons.
• Were main phytoplankton in
Precambrian, Paleozoic and early
Cenozoic.
5

6. • During Mesozoic and Cenozoic, they
occur with dinoflagellates cysts.
• Recorded in near offshore, offshore
and deep basinal marine sequences.
• Widely used in hydrocarbon
exploration for biostratigraphy,
paleoenvironmental interpretation and
thermal history of sedimentary basins. 6

7. MORPHOLOGY:
 Most acritarch vesicles range between 50 and 100
µm in size and are usually preserved as compressed
films in black shales.
 Acritarchs are generally spheroidal but their shape is
very variable. Vesicle walls may be single or double
layered and most central chambers have an opening
considered to be for the release of the motile stage.
7

8.  Externally, acritarchs may be smooth or
granulated and most have processes
projecting from the vesicle surface.
 Some processes are branched or have
elaborate distal structures, supported by stiff
buttresses, while others are more simple and
flexible .
 Acritarchs are classified on the basis of :
 Shape
 Wall structure
 Thickness
 Structure of opening
 Ornamentation and form of the
processes.
8

9. 9

10. BASIC SHAPES OF ACRITARCHS:
10

11. PALEOECOLOGY:
 Acritarchs mainly occur in marine sediments, often in
association with other marine fossils.
 They have a worldwide distribution and occur in large
numbers, consistent with being primary producers rather
than consumers.
 Such evidence strongly suggests that they were members
of the phytoplankton.But some claim benthic mode of life.
 More diverse in offshores than near shore facies.
11

12. EVOLUTIONARY HISTORY:
 Acritarchs are amongst the oldest documented fossils Known
from chemical fossils from 2.7 billion years ago.
 They first became abundant 1 billion years ago and are
arguably the most complex Precambrian microfossils.
 Most forms are large for single cells (between 50 and 100
µm), and include species with a double-walled structure and
ornate processes. Such diversity may represent an increase
in marine productivity in the late Precambrian.
12

13.  Cambrian forms are smaller than Precambrian
forms.
 Effected by end Ordovician extinction event but
are recorded in Silurian with highest diversity.
 The diversity then reduced.
 A few specialized forms appeared in the Permian
but dinoflagellate cysts, spores, and pollen are the
dominant organic walled microfossils of the
Mesozoic and Cenozoic.
Rarely occurs in modern sediments.
13

14. 14

15. CONTENTS
• Introduction
• Morphology
• Paleoecology
• Evolutionary history
15

16. INTRODUCTION
• Protists
• Organic Walled
• Unicellular
• Autotrophic, Heterotrophic, Symbionts
• Mostly Marine, do occur in brackish and fresh water.
• Bioluminescent
16
Fig : dinoflagellates

17. 17
Fig : Bioluminescent dinoflagellates
Fig : Noctiluca

18. DINOFLAGELLATES
• 90% of all dinoflagellates are marine plankton.
• 1,200 species .
• Microscopic, largest are about 2mm diameter e.g. Noctiluca
• They reproduce asexually .
• Both sessile and motile exist
Distribution is limited by Temperature and nutrients .
18
Fig : Noctiluca

19. NOT RELATED TO DINOSAURS
• The prefix Dino means
whirling flagella. The
Dinoflagellates are said to
of out dated the Dinosaur
19
Fig : Ceratium

20. GOOD BUT BAD
• The Dinoflagellates
• oxygen
• Red Tides
Pfiesteria
Gonyanulax
20
Fig : Pfiesteria
Fig. Gonyanulax

21. 21
Fig. Red Tides and its effect on marine life (dead fishes

22. MORPHOLOGY
• size : 5 to 150µm
• 2 stages of life:
• Motile stage (rarely fossilize)
• Benthic Cyst stage (resistant organic material)
• Cell contains a nucleus, an endoplasmic reticulum, a Golgi
apparatus and mitochondria.
22

23. • Surface ornamentation
smooth, granulated, or have raised crests and spines.
• Motile Wall (Theca) is made of cellulose or
polysaccharides.
• The pattern of arrangement of the plates is called the
Tabulation .
23

24. • The encysted dinoflagellates, due
to their resistant surfaces, are preserved as fossils.
• Cyst forms have wall called Phragma,
made of organic material called
Dinosporin.
• Morphology of dinoflagellate cyst is
entirely or largely a reflection of internal
morphology of motile dinoflagellates
24

25. ANATOMY
• This is the anatomy of a
Dinoflagellate.
25

26. PALEOECOLOGY
• Most living dinoflagellate species are photosynthetic and
marine.
• the main primary producers in the open sea .
• Ancient specie’s paleoecology is difficult to determine due to
absence of cyst producing species.
26

27. • Cysts are easily transported by oceanic currents
• indicators of paleotemperature
Are found in shallow as well as deep marine settings.
•
27

28. EVOLUTIONARY HISTORY
• Late Silurian species “Arpylorus antiquus” is oldest known.
• No fossil record is present for the next 200million years.
• Dinoflagellate cysts were first found in late Triassic rocks
“Rhaetogonyaulax ”
• Diverse and abundant cysts increase in Early . Jurassic till
Cretaceous .
•
•
28

29. • Diversity peaks in Cretaceous and early Eocene. But declined
afterwards.
• Freshwater dinoflagellates are only known from Cenozoic and
rarely fossilize.
29
Late Jurassic cyst
Systematophora
penicillata
Stephanelytron
redcliffense a
Late
Jurassic
dinoflagellate
cyst

30. CONCLUSION:
• Distribution is limited by Temperature and nutrients
however they can tolerate variable salinities.
• some fossil forms act as indicators of paleotemperature .
• hydrocarbon exploration for biostratigraphy .
30

31. REFERENCE
• Fossils at a glance / Clare Milsom and Sue Rigby. – 2nd ed.
• Armstrong, Howard, 1957–Microfossils. – 2nd ed./Howard A.
Armstrong and Martin D. Brasier.
• Micropaleontology
Principles and Applications by Pratul Kumar Saraswati • M.S.
Srinivasan
31

32. THANK YOU FOR YOUR ATTIONS
32
ThAnk yOu