==Reference standard==The standard established for carbon-13 work was the Pee Dee Belemnite (PDB) and was based on a Cretaceous marine fossil, "Belemnitella americana", which was from the Pee Dee Formation in South Carolina.
Стандартным образцом для оценки δ13C является «Pee Dee Belemnite» (PDB) из морских окаменелостей мелового периода "Belemnitella americana" формации Pee Dee в Южной Каролине.