The base is defined as the first appearance of the trilobite Ptychagnostus atavus around 504.5 million years ago.
The top is defined as the first appearance of another trilobite Lejopyge laevigata around 500.5 million years ago.
The GSSP is defined in the Drumian section (39°30′42″N 112°59′29″W / 39.5117°N 112.9915°W / 39.5117; -112.9915) in the Drum Mountains, Millard County, Utah, United States.
[5] The Cambrian Drumian carbon isotope excursion (DICE) event is associated with the beginning of this age.
DICE hampered the recovery of reef ecosystems already affected by the early–middle Cambrian mass extinctions.