Chitinozoans from the Telychian (Llandovery, Silurian) Shenxuanyi Member, upper Ningqiang Formation of the northwestern Yangtze Platform, China

Abstract

Silurian strata are well-developed in the northwest margin of Yangtze Platform. A total of 117 densely spaced argillaceous samples were taken from the Shenxuanyi Member, upper Ningqiang Formation to the lowermost Chejiaba Formation of the Majia section in northern Sichuan Province. The main aim of this study is to obtain chitinozoans to test whether Wenlock deposits are preserved here. A highly diverse and abundant chitinozoan assemblage is documented, including 21 species from six genera. This assemblage was then compared to contemporaneous chitinozoan assemblages reported from adjacent areas. This study proposes that Eisenackitina venusta (corresponds to the Pterospathodus celloni conodont Biozone) is of chronostratigraphical significance for discussing the Telychian of the Yangtze region. It is suggested that the Silurian upper red bed (lower part of the Shenxuanyi Member) in the study area is younger than the Xiushan Formation and can be correlated with the Huixingshao Formation of the Central Yangtze Platform. There are no index chitinozoan species near the Llandovery–Wenlock boundary that have been found in the upper part of the Shenxuanyi Member, and the updated chronostratigraphic framework suggests that it is Telychian-aged deposits.