Benthic Foraminiferal recovery following a massive Submarine Landslide in the Laxmi Basin, Arabian Sea (IODP U1457)

Submarine mass transport deposits (MTDs) are sedimentary deposits formed by transporting large amounts of sediment downslope, usually in a marine setting. Evidence of such deposits was found in the Laxmi Basin, Arabian Sea, during the International Ocean Discovery Program (IODP) Expedition 355. The MTDs of the Laxmi Basin include matrix-supported carbonate breccia, reworked Indus-derived sediment, material from western Indian rivers, and some from the Deccan Traps. It is estimated to have occurred during the Late Miocene period (∼11 to 9 Ma). The diverse sediment sources suggest that the region had undergone significant sedimentary loading, contributing to instability. In this study, we conducted foraminiferal analysis to examine the benthic foraminiferal groups within MTDs to gain insights into the environmental conditions during deposition and subsequent reworking. Benthic foraminiferal communities in MTDs show reduced diversity and altered abundance compared to undisturbed sediments in the region, reflecting the stress and rapid deposition associated with mass transport events. The specific group of species belonging to Cibicidoides, Epistominella, Gavelinopsis, and Oridorsalis taxa struggled to exist due to changes in sediment texture, which further primed variation in the organic matter affecting the foraminiferal food sources. The benthic foraminifera, which were considered as oxygen minimum zone (OMZ) taxa were buried, leaving behind broken fragments during the event and affecting the region's abundance, diversity, and community structure. The bottom water oxygen estimated in these sediments was less than 0.7 mL/L, revealing the dysoxic conditions that altered the sediment nutrient distribution during deposition. The diversity index shows a significant decrease during MTD, indicating that the benthic foraminiferal community is experiencing gradual recovery or shifts in species composition over time. This process is characterized by succession, where pioneer species colonize the new sediments before a more stable community establishes itself. Despite the challenges, the foraminiferal and geochemical proxies demonstrate the importance of understanding the paleoenvironmental impacts associated with MTD.