Fossil Algae and Their Importance

Fossil algae are considered rock-builders that also serve as environmental indicators. They are useful as true fossils that are used for correlation and dating of sedimentary sequences. The presence of algal fossils indicates the presence of hydrocarbons since they originate from the accumulation of algal residues and plankton. 

Classification and Stratigraphy of Fossil Algae

All algal fossils are grouped under Protista by Haeckel (1866), which contains unicellular organisms without a definite cellular arrangement. These fossils are found in sedimentary rocks, sand, and limestones dating from the Proterozoic to the Holocene Periods. All types of fossil algae except those from Cryptophyta have been recorded. 

Algal Fossils from Different Periods

Keewatin Period (Ca, 2500-4000 million years ago)

• Primitive prokaryotes: Cyanophycean algae such as Archaeospheroids- 3200m yrs ago.
• Eubacterial types: Microfossils of Eubacterium.

Pre-Cambrian- 2800 million years ago

Thread-like fossils of members of Oscillatoriaceae. These autotrophic organisms originated from the lower Proterozoic era, a period that marked the Earth’s early history as an oxygen-rich environment. 

Laurentian Period (Ca, 1700-2500 million years ago)

• Algae of great diversity and complexity, such as the members of Cyanophycean families, such as Hurioniospora, Siphonophycus, Gunfinita, etc.
• Oxygen-producing algae were dominant in this period, which initiated the transition from an anoxic environment to an oxygenic atmosphere.

Huronian Period (Ca., 600-1700 million years ago)

Common fossils of this period include coccoid forms of Paleoanacystis and Glenobostridion. 

• Filamentous forms of Archeonima, Anabeanidium and Causiculophycus.
• Spherical meokaryotic dinoflagellates like Glocoidinopsis and Zosterosphaera.
• Spheroid form of Caryosphaeroides.
• It is estimated that Dinophyta, Chrysophyta, and Bacillariophyta were from the Late Huronian Period.
• Bacillariophyta were significant from the Cretaceous period.
• Phaeophyta originated in the early Huronian period from Dinophyta.
• Bangiophyceae might have originated from Cyanophyta.
• Florideophyceae were developed before the Ordovician Period and dominated the offshore flora by the Triassic Period.
• Green Algae with thallus were produced during the Cambrian Period.
• Highly specialized Charophyta were developed during the Devonian Period.
  Euglenophyta were evident in the upper Cretaceous Period.

Importance of Fossil Algae

Fossil algae are useful in several ways, as mentioned below.

As Indicators of Hydrocarbon Deposits

The marine sediments from the Proterozoic to the Holocene period showed the presence of various cysts of dinoflagellates and other algae. Coccolithophorids and other microbes are important in identifying the petroleum-bearing strata. 

As Indicators for Different Environment

• Algal limestones in the dune are an indication of the desert environment.
• Lime-secreting algae indicate a cave environment.
• Charophytes and freshwater diatoms indicate fluvial or stream and lacustrine or lake environments, respectively.
• Marine diatoms indicate neritic (Sea depth up to 400), bathyal (depth 400-6000).
• Reef-building algae are in the neritic environment.

As Indicators of Organic Population

Only a very small fraction of algae have undergone calcification, which is assumed to be the same in other geological periods. So fossil algae represent the organic population of an environment. 

As Indicators of Oil Deposits

Fossil algae such as Coccolithophorids help locate petroleum-bearing oil rocks. Diatom cells have 11% oil.

Reference

• https://edscl.in/pluginfile.php/4071/mod_resource/content/1/Scan%2015%20Feb%2022%20%C2%B7%2010%C2%B714%C2%B717.pdf