LATEST TRIASSIC–EARLIEST JURASSIC BIVALVES OF THE GERMIG FORMATION FROM LANONGLA (TIBET, CHINA)

Abstract

The Germig Formation of the Tethyan Himalaya of southern Tibet contains an exceptionally abundant bivalve fauna which has been found in association with choristoceratid and psiloceratid ammonoids and spans the Triassic/Jurassic boundary. The bivalve fauna consists of 25 species, including four new species: Newaagia lanonglaensis, Persia hallami, Liostrea tibetica, and Ctenostreon newelli. The fauna comprises three biostratigraphically controlled bivalve assemblages: 1) an upper Rhaetian Palaeocardita–Krumbeckiella Assemblage including seven species; 2) a high diversity transitional Rhaetian-Hettangian Persia–Plagiostoma Assemblage with many as 19 species; and 3) a low diversity lower Hettangian Liostrea–Chlamys Assemblage containing three species. The transitional Rhaetian-Hettangian Assemblage is dominated by cementing species and exhibits a high degree of endemism. A large proportion of lower latitude and cementing taxa from the lower two levels may indicate that they inhabited shallow subtidal tropic or subtropic paleoenvironments.