In the geologic timescale, the Aeronian is an age of the Llandovery Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon that began 440.8 ± 1.2 Ma and ended 438.5 ± 1.1 Ma (million years ago).
[8] During the Aeronian the Sedgwickii Event occurred in which graptolite diversity was greatly reduced.
[9] This event has been attested in locations such as today's Canada, Libya as well as in La Chilca Formation in Argentina (then part of Gondwana).
[9] The GSSP is located in the Trefawr Track section, 500m north of Cwm-coed-Aeron Farm, Wales, UK.
[10] The GSSP lies within the gently-dipping blocky mudstones of the Trefawr Formation, which principally yield abundant and diverse shelly faunas, but also contain enough graptolites to allow recognition of several biozones.