Cyprinid fishes from Eocene molasse deposits (Liyan Formation), India-Asia collision zone, Eastern Ladakh, NW Himalaya, India: implications for non-marine aquatic connections between India and Mainland Asia

摘要

The molasse deposits in the Indus Basin of India-Asia collision zone (Indus Suture Zone) of Ladakh, NW Himalaya, preserve a record of orogenic sedimentation associated with uplift and erosion of the southern margin of Asia in the course of ongoing India-Eurasia collision. Fossils from these continental deposits are scarce but hold important clues to the early history of India-Asia collision. Here we describe a small collection of dental remains of cyprinids, a family of freshwater fishes, from the Late Eocene Liyan Formation exposed in a high altitude (>5000 m) locality in the Indus Suture Zone of Eastern Ladakh. The find assumes significance since, unlike the Liyan Formation, most other molassic deposits of Ladakh rest unconformably over the Ladakh Batholith and are much younger (Late Oligocene/Early Miocene). The Liyan cyprinids, which represent the oldest record of Cyprinidae in India, suggest fluvial connections with contemporary Eocene ecosystems in Mainland Asia where this family originated in the middle Eocene or earlier. Dispersal of cyprinids from the Mainland Asia into the Indus Suture Zone of Ladakh took place from Tibet via alluvial drainage of the paleo-Indus river during floods or high runoff following the India-Asia collision.