| Summary: | The Global boundary Stratotype Section and Point (GSSP) for the base of the Guzhangian Stage (Cambrian Series 3) is defined at the base of a limestone (calcisiltite) layer 121.3 in above the base of the Huagiao Formation in the Louyixi section along the Youshui River (Fengtan Reservoir), about 4 km northwest of Luoyixi (4 km southeast of Wangcun), in northwestern Hunan, China. The GSSP is exposed in a road cut at a position of 28 degrees 43.20' N and 109 degrees 57.88' E. The GSSP level contains the lowest occurrence of the cosmopolitan agnostoid trilobite Lejopyge laevigata (base of the L. laevigata Zone). Secondary global markers near the base of the stage include the appearance of either L. calva or L. armata just below the base of the stage, the appearance of conodonts associated with the base of the Laiwugnathus laiwuensis Zone, and the transgressive phase of a small eustatic event. Faunal turnovers close to the base of the Guzhangian Stage are recognized as near the base of the Boomerangian Stage in Australia, the base of the Aldanaspis Zone (polymerid trilobites) in Siberia, and the base of the Paradoxides forchhammeri Zone in western Avalonia. The horizon corresponding to the first appearance of L. laevigata is near the peak of a rather long negative delta C-13 excursion of up to 0.58 parts per thousand.
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