Invertebrate macrofossils in the early to middle Miocene sedimentary sequence of Aruwakkalu, Northwestern Sri Lanka: Biostratigraphic and paleoenvironmental implications

This study presents a detailed analysis of late Miocene invertebrate fossil assemblages from the Aruwakkalu area of the North western coastal region in Sri Lanka, focusing on biostratigraphy and paleoenvironmental reconstruction. This investigation reveals diverse fossil taxa, such as bryozoans, corals, bivalves, and gastropods, providing insights into marine ecosystems.  Bryozoans belonging to the class Gymnolaemata were identified in impure limestone layers, displaying sustained features such as sorus and autozooid structures. Coral fossils from the order Scleractinia were abundant in sandstone layers, highlighting the presence of colonial organisms indicative of coral   reef environments. Bivalve fossils, predominantly from the families of Veneridae, Ostreidae, and Pectinidae, were found in various limestone layers, indicating a diverse marine habitat. Gastropod fossils, representing families such as Strombidae, Drilliidae, and Conidae, provided further evidence of a thriving marine environment. The paleoenvironmental reconstruction suggests clear and warm and shallow waters with nutrient-rich conditions, supporting diverse ecosystems and intricate ecological interactions. The biostratigraphic classification reveals three distinct layers at upper middle and lower horizons characterized by coral, oyster, and gastropod dominance, respectively, offering a timeline of environmental changes during the late Miocene. Preservation modes, including casts, molds, and mineral recrystallization, indicate favorable conditions for fossil retention. These findings enhance our understanding of the paleoenvironmental history of the Aruwakkalu region in Sri Lanka and provide a basis for future research in paleontology and evolutionary biology.