| Group/formation name | Group/formation name |
|---|
| Aguilar - Santa María la Real, - Spain | Aitym - A1, Meshekli, - Uzbekistan |
| Aguille - Gabon | Aix-en-Provence - France |
| Aguion - Spain | Ajabgarh/Kushalgarh - India |
| Aguja - Abajo Shale, Alto Shale, Rattlesnake Canyon, Rattlesnake Mountain, - Mexico, United States | Ajax Limestone - Australia |
| Agulak Suite - Russian Federation | Ajax limestone - Australia |
| Agwu Shale - Nigeria | Ajax Limestone - Australia |
| Agé/Kameyama - Japan | Ajima - Japan |
| Ahbach - Hallert, Olifant, - Germany | Ajiri - Japan |
| Aheimer - Egypt | Ajka Coal - Hungary |
| Ahlen - Beckum, Stromberg, Vorhelm, Vorhelmer schichten, - Germany | Ajlun - Jordan |
| Ahmadi - Kuwait | Ajlun/Fuheis - Jordan |
| Ahrdorf - Bildstock, Flesten, Köll, Wassen, - Germany | Ajlun/Hummar - Jordan |
| Aidarly - Kazakhstan | Ajlun/Na’ur - Jordan |
| Aiduna - Indonesia | Ajlun/Shuayb - Jordan |
| Aifat - Indonesia | Ajlun/Shueib - Jordan |
| Aigu - Estonia | Aka Aiteputh - Kenya |
| Aigyrzhal'skaya Suite - Kazakhstan | Aka Aithputh - Kenya |
| Aimau - Indonesia | Akabira - Japan |
| Ain ed Dick Limestone - Morocco | Akachan - Russian Federation |
| Ain Maqfi Limestone - Egypt | Akaishi - Japan |
| Ain Ouarka - First, Second, - Algeria | Akan - Japan |
| Ain Targa - Kalkmergel, - Morocco | Akansaiskaya - Kazakhstan |
| Aina Dal - Greenland | Akasaka - Japan |
| Ainonai - Japan | Akasaka - Japan |
| Aisemont - Belgium | Akasaka - Middle, - Japan |
| Aisol - Lower section, Middle Section, - Argentina | Akasaka Limestone - Upper, - Japan |
| Aisčiai - Russian Federation | Akasaki - Japan |
| Ait Ouarhitane - Morocco | Akatievo - Russian Federation |
| Aitamir - Iran | Akatuevskaya - Russian Federation |
| Aitutu - Indonesia | Akaura - Nanao, - Japan |