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Palynomorphs-Applications in Geology.pptx
- 1. Dr Husain Shabbar Independent Consultant Geoscientist
- 2. Microfossils Microfossils are the tiny remains of bacteria, protists, fungi, animals, and plants. Size generally ranges between 1 µm to 1 mm. Microfossils are common feature of geological records from the Archaean to present On basis of composition, they can be divided into four groups. I. Calcareous microfossils II. Phosphatic microfossils III. Siliceous microfossils IV. Organic-walled microfossils /Palynomorphs
- 3. Organic-walled Microfossils/Palynomorphs Organic-walled microfossils are composed of entirely mineralized proteinaceous material. Ranges in size 5 to 500 µm. Types of organic-walled microfossils: 1. Chitinozoa 2. Acritarchs 3. Spores and Pollen 4. Dinoflagellates 5. Scolecodont
- 5. Acritarchs They are defined as small, organic-walled microfossils of unknown biological affinity. They are characterised by varied sculpture, some being spiny and others smooth. The group includes any small (20-150 microns ), organic- walled microfossil. Many acritarchs are marine and can include a wide range of organisms, such as metazoan egg cases, copepod eggs, planktonic eukaryotic algae, and cryptospores. Acritarchs are found in sedimentary rocks from the present back into the Archean.
- 6. Morphology of Acritarch Acritarch morphology forms the basis of their classification. Body shape ranges from spherical through fusiform (grain of rice shaped), stellate to prismatic. Processes may be simple or complex, solid or hollow, opening into the body or separated from it. Ornament may occur on the body and/or the processes. The form of opening called a pylome ranges from a distinctive opening in a defined area, a random split anywhere on the body or complete disintegration.
- 7. Classification of Acritarchs Acanthomorphs have spherical bodies with spines which usually open into the body. Polygonomorphs have a body-shape defined by the number and position of spines, they are often triangular or square in outline. Netromorphs have a fusiform body with one or more spines. Diacromorphs have spherical to ellipsoidal bodies with ornament confined to the poles. Prismatomorphs have prismatic to polygonal bodies the edges of which form a flange or crest which may be serrated.
- 8. Oomorphs have an egg shaped body with ornament confined to one pole. Herkomorphs have a roughly spherical body divided into polygonal fields, rather like a football. 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, they resemble under the light microscope a fried egg! Sphaeromorphs have simple spherical morphology.
- 10. Chitinozoa Chitinozoa are marine, flask-shaped palynomorphs which appear dark, almost opaque when viewed using a light microscope. Chitinozoa range in length from about 50 to 2000µm. The biological affinities of Chitinozoa are poorly understood, but they may be eggs of marine metazoans. Walls of Chitinozoa are usually resistant to oxidation, thermal alteration, tectonism, and recrystallization of CaCO3 matrix. They first appeared in the Early Ordovician (Tremadoc Stage), abundant and diverse until Silurian, but majority became extinct at the end of Devonian and disappeared in the Earliest Carboniferous.
- 12. Classification of Chitinozoa Classification within Chitinozoa is based largely upon the gross morphology of the Test. The Order Operculatifera containing one family the Desmochitina (simple spherical forms often found in chains). And the Order Prosomatifera containing two families the Conochitinidae (with little differentiation between flask and neck) and the Lagenochitinidae (with clearly distinct flask and neck). The most Tests have to some extent been distorted by compression during compaction of sediments, so original shape of a Chitinozoa test requires a careful interpretation.
- 14. Distribution and Paleoecology Chitinozoa are known only from marine sediments. Acritarchs are thought to be marine (Pre-Triassic). Chitinozoa are common in rocks deposited under well aerated shallow water conditions, especially in shale and siltstone but they are also found in limestone, dolomites, graptolitic shales, slates and cherts. Acritarchs are typically isolated from siliciclastic sedimentary rocks but are occasionally extracted from carbonate-rich rocks. Both were planktonic, dead vesicles would have settled on the ocean floor, where they were covered in sediment.
- 15. Applications They are important Palaeozoic microfossils as stratigraphic markers. Acritarchs are extremely valuable for stratigraphic correlation of rocks of Proterozoic and Palaeozoic age, primarily because they are the only microfossils commonly preserved. Chitinozoa are similarly utilised in studies of Palaeozoic strata especially during Ordovician, Silurian and Devonian periods. Both groups are also used in palaeoenvironmental reconstructions, providing useful evidence on environmental conditions where few other fossils exist. Occurrence of Chitinozoa in less metamorphosed sedimentary rocks may allow an approximation of the depositional environment. Both have potential as the Thermal Maturity Indices.