NEW DATA ON THE FOLIOMENA FAUNA (BRACHIOPODA) FROM THE UPPER ORDOVICIAN OF SOUTH CHINA

Abstract

A newly discovered Late Ordovician (early Ashgill) brachiopod assemblage from the Linhsiang Formation in the middle part of the Yangtze Platform, South China, bridges the paleobiogeographical gap between the early Ashgill Foliomena-bearing associations known previously from the upper and the lower parts of the Yangtze Platform. Characterized by minute shells in calcareous to siliciclastic mudstones, the fauna contains 13 brachiopod genera, of which two plectambonitoids are new: Hadroskolos and Jingshanella. Cluster and principal component analyses, based on 29 global occurrences of the Foliomena fauna in Laurentia, Avalonia, Kazakhstan, Baltica, Sardinia, Bohemia, Sibumasu, North China, and South China, revealed broad trends of spatial and temporal faunal differentiation in terms of taxonomic compositions. The analyses demonstrate for the first time that early Foliomena-bearing associations of Caradoc age occupied primarily deepwater (distal shelf) environments with a siliciclastic or calcareous mud substrate. The fauna attained its widest paleogeographical distribution and paleoecological range (midshelf to shelf margin settings) during the early Ashgill.