Non-calcified warm-water marine macroalgae from the Ordovician strata of Spiti, Tethys Himalaya, India

The calcareous siltstones within the Ordovician section of the Takche Formation near Takche, Spiti region of Tethyan Himalaya, India, contain numerous specimens of non-calcified marine macroalgae in association with brachiopods, gastropods, tentaculitoids, and few trace fossils. The algal remains, representing five genera, are preserved as black or dark brown carbonaceous compression fossils, interpreted as warm-water marine macroalgae, namely, Inocladus sp., Callisphenus? sp., Algites sp. (siphonous algae), Fisherites sp., and Mastopora sp. (non-siphonous). Callisphenus is characterised by a radially symmetrical short pyriform thallus, with a central axis surrounded by short laterals whereas Inocladus sp. is characterised by an unsegmented simple thallus with internal parallel medullary siphons and cortical tubes. These algal remains, probably transported from a more near-shore living niche, co-occur with Cyclocrinitids, Tentaculitoids tube worms, trace fossils and brachiopods, suggesting that deposition of the studied units took place in low energy hydrodynamic conditions influenced by intermittent storm events. The study represents the first diversified macroalgal records from the Ordovician strata in the Tethyan realm of Indian subcontinent.