State;
Key;
Laboratory;
of;
Environmental;
Geochemistry,;
Institute;
of;
Geochemistry,;
Chinese;
Academy;
of;
Sciences,;
Guiyang;
550002,;
China;
Guizhou;
University;
of;
Technology,;
Guiyang;
550003,;
China;
Guizhou;
University;
of;
Technology,;
Guiyang;
550003,;
China;
State;
Key;
Laboratory;
of;
Environmental;
Geochemistry,;
Institute;
of;
Geochemistry,;
Chinese;
Academy;
of;
Sciences,;
Guiyang;
550002,;
China;
negative; carbon; isotopic; excursion,; extinction,; Lower/Middle; Cambrian; boundary,; Guizhou; Province.;