| Group/formation name | Group/formation name |
|---|
| Adu Asa - Asa Koma, - Ethiopia | Agitkan - Russian Federation |
| Advance - Lower, Upper, - Canada | Agnevo - Russian Federation |
| Adventdalen/Agardfjellet - Lardyfjellet, Lardyfjellet-Oppdalsata, Oppdalen-Lardyfjellet, Oppdalsata-Slottsmoya, - Svalbard and Jan Mayen | Agoudim - IV, - Morocco |
| Adventdalen/Carolinefjellet - Svalbard and Jan Mayen | Agoudim Marls - Morocco |
| Adventdalen/Helvetiafjellet - Ullaberget, - Svalbard and Jan Mayen | Agrio - Agrio, Agua de la Mula, Lower, Lower Agrio, Pilmatué, Upper, - Argentina |
| Adventdalen/Rurikfjellet - Ullaberget, - Svalbard and Jan Mayen | Aground Ouadar - Morocco |
| Adz'va - Russian Federation | Agua Blanca - Psefitico Inferior, - Argentina |
| Adze - Sweden | Agua Caliente - Peru |
| Aerado - Brazil | Agua Clara - Cauderalito, - Venezuela |
| Aertashi - China | Agua de la Peña/Chañares - Lower, - Argentina |
| Afon Ffinnant - United Kingdom | Agua de la Peña/Ischigualasto - Valle de la Luna, - Argentina |
| Afyon - Türkiye | Agua de la Peña/Los Colorados - Argentina |
| AG4 - New Zealand | Agua de la Peña/Los Rastros - Argentina |
| Agabyt - Russian Federation | Agua de la Piedra - Argentina |
| Agadez/Assaous - Niger | Agua de la Zorra - Argentina |
| Agadez/Téloua - Niger | Agua de Lucho - Argentina |
| Agalatas - Upper, - Kazakhstan | Agua de Madeiros - Portugal |
| Aganane - Morocco | Agua del Jaguel - Argentina |
| Agardhfjellet - Slottsmøya, - Norway, Svalbard and Jan Mayen | Agua Doce - Caete, Mandacaru, - Brazil |
| Agatdal - Abraham, Sonja, Turritellakloft, Turritellakløft, - Greenland | Agua Fria - Honduras |
| Agate Creek Volcanics - Australia | Agua Negra - Venezuela |
| Agawam/Boonton - United States | Agua Negra/Pauji - Venezuela |
| Agawam/Portland - United States | Agua Nueva - Upper, Vallecillo, Vallecillo Platy Limestone, - Mexico |
| Agenais Limestone - France | Agua Salada - Mexico |
| Ageptinskaya - Russian Federation | Agua Salada/Pozón - Policarpo, - Venezuela |
| Ager - Spain | Agua Salda - Venezuela |
| Agglomeratic Slate - India | Aguada de la Perdiz - Chile |
| Agha Jari - Iraq | Aguada Limestone - Puerto Rico |
| Aghdarband/Sina - Shale, - Iran | Agueguexquite - Mexico |
| Agidyl - Russian Federation | Agui-Ula - Mongolia |