中国科学院南京地质古生物研究所机构知识库

The Global boundary Stratotype Section and Point (GSSP) for the base of the Drumian Stage (Cambrian Series 3) is defined at the base of a limestone (calcisiltite) layer 62 in above the base of the Wheeler Formation in the Stratotype Ridge section, Drum Mountains, Utah, USA. The GSSP level contains the lowest occurrence of the cosmopolitan agnostoid trilobite Ptychagnostus atavus (base of the P. atavus Zone). Secondary global markers near the base of the stage include the DICE negative delta C-13 excursion, the onset of a long monotonic Sr-87/Sr-86 isotopic shift, and the transgressive phase of a eustatic event. Faunal turnovers close to the base of the Drumian Stage are recognized as the base of the Bolaspidella Zone (polymerid trilobites) in Laurentia, the historic base of the Floran Stage in Australia, the base of the Dorypyge richthofeni Zone (polymerid trilobites) in South China, and the base of the Gapparodus bisulcatus-Westergaardodina brevidens Assemblage-zone (conodonts) in Baltica and South China. The last occurrence of the cosmopolitan trilobite Ptychagnostus gibibus occurs in the lower part of the Drumian Stage, and the base of the Hydrocephalus hicksii Zone (polymerid trilobites) as used in Siberia and Baltica occurs near the base of the stage.