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 m above the base of the Wheeler Formati...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 m 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 δ^13C excursion, the onset of a long monotonic ^87Sr/^86Sr 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 gibbus 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.展开更多
基金We would like to thank all the people, including members of the ISCS, involved in the process of defining the base of the Drumian for stimulating discussion and scientific support. J.G. 0gg thoroughly reviewed the final GSSP proposal. A.M. English and L.A. Ford assisted with assembly of the final illustrations. This work was supported in part by a grant from the U.S. National Science Foundation （EAR-0106883） to Babcock.
文摘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 m 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 δ^13C excursion, the onset of a long monotonic ^87Sr/^86Sr 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 gibbus 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.
