Freshwater Molluscan Fauna of the Miocene-Pliocene Churia (Siwalik) Group of Nepal and Their Palaeoecological Implication

摘要

Freshwater molluscan fossils occur abundantly in the Churia Group, in West-central Nepal. Study to evaluate their faunal composition and stratigraphical distribution shows some interesting trends. The molluscan fossils are found to occur most abundantly between ca. 10.5Ma and ca. 3.5Ma, before and after which they are rare. Relative abundance of localities as well as diversity increases toward the upper part with the fossil localities concentrated along four horizons. The faunal composition shows two phases of change, around 7 Ma and 4 Ma, with disappearance and appearance of taxa.