Crustose red algae in deep time environments: Palaeoecological insights from northeastern India and Türkiye (Turkey)

Crustose red calcareous algae are key organisms in benthic ecosystems worldwide with critical functions like reef-building and substrate stabilization. Coralline algae thrived as major carbonate producers, with corals and/or larger benthic foraminifera (LBF) in numerous shallow-marine Tethyan carbonate platforms from the early Palaeogene to the Neogene. The Palaeocene–Eocene limestone successions in the Jaintia and Khasi Hills, Meghalaya, northeastern India, encompass two principal community types — algal-foraminiferal and coralline algal, with no associated colonial corals, while the Oligocene–Miocene carbonates from the Sivas basin and Siirt province in Türkiye are characterized by an algal-foraminifera assemblage with bryozoans, corals, and molluscs as other noteworthy components pertinent to the carbonate platform environment. We found that the diversity and ecology of these algal communities were influenced by systematic structure of the algal assemblage, sediment input, substrate stability, water depth, and hydrodynamic energy. The algal assemblages from different epochs and varying localities diverge based on the sedimentary regime, environmental settings, and the predominant taxa. The climatic transition from the Palaeocene–Eocene greenhouse to the Oligocene–Miocene icehouse corresponded to a shift from crustose algal assemblages dominated by Sporolithales to assemblages dominated by Hapalidiales.