Integrated biochronology for Triassic marine vertebrate faunas of Guizhou Province, South China

Abstract

The Middle and Upper Triassic marine deposits of Guizhou Province, which yielded exceptionally well-preserved vertebrate faunas, are further investigated. New age-diagnostic conodonts and ammonoids from six measured sections, together with already published data, allow us to construct an integrated biochronology straddling strata from the upper Guanling Formation (Anisian, Middle Triassic) to the basal Xiaowa Formation (Carnian, Upper Triassic). Age constrains for those fossil Lagerstätten are now dated to the substage and zone levels: the Panxian Fauna, within the conodont Nicoraella kockeli Zone and broadly coexisted with the ammonoid ‘Schreyerites’ binodosus, is suggested as latest Pelsonian (middle Anisian) in age; the Xingyi Fauna is assumed to be not younger than the middle Longobardian (Late Ladinian) because the conodont Paragondolella inclinata with free-blade and the ammonoid Haoceras xingyiensis are recorded from slightly younger strata; the conodont Paragondolella auriformis and the ammonoid Trachyceras multituberculatum and Austrotrachyceras triadicum clearly indicate that the Guanling Fauna is not older than Julian (early Carnian) in age (time interval between Aon Zone or Aonoides Zone). With the new biostratigraphic data, a relative sequence and correlation of the Middle Triassic vertebrate faunas from Guizhou (South China) and Monte San Giorgio (Southern Alps, Switzerland/Italy) is proposed.