Temporal and spatial distribution patterns of the marine–brackish-water bivalve Waagenoperna in China and its implications for climate and palaeogeography through the Triassic–Jurassic transition

Abstract

Waagenoperna was a genus of epi-byssate, marine to brackish-water/littoral bivalves. It used to be regarded as Late Permian–Late Triassic in age. However, a review of the genus reveals that it did not occur until the Late Triassic, and in the Early Jurassic some species of Waagenoperna (i.e. W. lilingensis, W. mytiloides and W. cf. lilingensis) had a wide distribution in the areas southwest of the Shanghai–Altay Mountain Range, including parts of southern China. The sediments hosting these bivalves are intercalated with non-marine strata including coal. The geographic and stratigraphic distribution patterns of Waagenoperna can not only aid in the correlation of the non-marine coal-bearing strata, spanning the Triassic–Jurassic transition, and constrain their age, but also particularly demonstrate a history of transgressions, flooding the areas southwest of Shanghai–Altay during the Sinemurian. These extensive transgressions influenced the climate and changed the palaeo-topography of southwestern Shanghai–Altay: they ensured a humid climate and resulted in the formation of marsh and even paralic swamp environments. These environments allowed the flora and fauna to thrive and led to the accumulation of large quantities of organic matter that eventually formed coal and probably oil as well.