52°02′32″N 3°41′42″W / 52.0422°N 3.695°W / 52.0422; -3.695 Trefawr Track , a forestry road north of Cwm-coed-Aeron Farm, Llandovery , Wales , is the location of the Global Boundary Stratotype Section and Point (GSSP) which marks the boundary between the Rhuddanian and Aeronian stages of the Silurian period on the geologic time scale . The GSSP was ratified in 1984.
4-513: The boundary is defined as the first appearance of the graptolite Monograptus austerus sequens (the base of the Monograptus triangulatus biozone). The section is primarily mudstone , which yields an abundance of shelly faunas . The graptolite Diplograptus elongatus occurs immediately below the boundary. This Carmarthenshire location article is a stub . You can help Misplaced Pages by expanding it . This paleontological site article
8-405: Is a stub . You can help Misplaced Pages by expanding it . First appearance datum First appearance datum (FAD) is a term used by geologists and paleontologists to designate the first appearance of a species in the geologic record. FADs are determined by identifying the geologically oldest fossil discovered, to date, of a particular species. A related term is last appearance datum (LAD),
12-559: The last appearance of a species in the geologic record. FADs are frequently used to designate segments in the geologic time scale . A given FAD can be used to define a Global Boundary Stratotype Section and Point (GSSP). For example, the beginning of the Tremadocian Stage of the Ordovician Period is marked by the first appearance of the conodont Iapetognathus fluctivagus in the geologic record. This occurs in bed 23 of
16-537: The rock formation known as the Green Point section, located in western Newfoundland , as well as in geologically correlated strata in many parts of the world. However, diachronous FADs can be problematic for correlating chronostratigraphic units, particularly over longer distances. Use of other data, such as radiometric data , may be ultimately necessary in order to establish more reliable correlations of chronostratigraphic units. This paleontology article
#354645