A re‐examination of the type Arenig Series

Abstract

The stratotypc of the Arenig Series (Ordovician System) and its boundaries are critically re‐examined. The lithostratigraphy and biostratigraphy of the Tremadoc, Arenig, and Llanvirn age rocks at Arenig Fawr, North Wales that were constructed by Feamsides in 1905 are amended. The Arenig Series at Arenig is represented by the Camedd Iago Formation which was established by Lynas (1973) in the Migneint area. Examination of the sparse graptolite faunas indicates that the type Arenig Series is incomplete, only the extensus Zone having been recognized with certainty. There is a possible unconformity at the base and a probable unconformity at the top, and on present knowledge the succession cannot be correlated precisely with what are considered to be Arenig sequences elsewhere. It therefore may prove necessary to redefine the Arenig Series at a more useful type section. It is suggested that the Carmarthen district may provide a suitable stratotype.

An Ordovician variation on Burgess Shale-type biotas

“…3g–i, l–o ) of the Afon Gam Biota is typical of Tremadocian marine mudstones, comprising mostly trilobites, lingulate brachiopods, tergomyans and hyolithids. Trilobites are the most diverse group, with 15 species known from the formation, including those from previous work 20 21 ; these species are typical of the shallower parts of the Welsh Basin at this time. The other groups are represented by at least three species each.…”

“…The biota has been collected from several sections in the Dol-cyn-Afon Formation (early late Tremadocian, Conophrys salopiensis Trilobite Biozone 19 ) around the mountain Arenig Fawr, near Bala, North Wales 20 21 ( Fig. 1 ).…”

Middle Cambrian sponges from the Drum Mountains and House Range in western Utah

“…Material was collected from several locations within the Ceunant-y-garreg-ddu natural stream section on the southwest slopes of Arenig Fawr (Fearnsides 1905;Zalasiewicz 1984, grid reference for base of section National Grid SH 82103600). There are numerous extensive exposures along this stream, but placing beds onto an accurate measured section is impossible due to complex faulting and local deformation; approximate stratigraphic positions based on the left bank exposures are possible for the lower part of the section.…”

“…The stage was originally defined to include what is now the entire Floian, Dapingian, and Darriwilian, but this was eventually reduced (Williams et al 1972), before being replaced by globally recognised units. The succession exposed in the Arenig Fawr area was described in detail by Fearnsides (1905), and revised by Zalasiewicz (1984), who recognised the Tremadoc succession as correlated with the upper part of the Afon Gam Formation of Lynas (1973), defined in the nearby Migneint area. This formation corresponded to the Niobe Beds, Dictyonema Band, Nant-ddu (or Bellerophon) Beds, Tai-Herion Flags and Amnodd Shales of Fearnsides (1905), which together constitute the lower part of the Tremadoc (Rushton and Fortey 2000).…”

“…2), with discrete bedding surfaces weathering out at typically 10-50 cm intervals. The fauna from these beds has been previously described as dominated by trilobites (Zalasiewicz 1984) few other skeletal fossils, notably brachiopods, tergomyans, hyoliths, and the cystoid Macrocystella (Fearnsides 1905;Zalasiewicz 1984). Following reports of articulated sponges from Richard.…”