In its small size the new species is similar to Diorthelasma in the Caradocian
(Sandbian to Katian) of North America (Cooper 1956) but differs from the latter in more circular outline and a short hinge line, and in a narrow anteriorly elongate notothyrial platform.
174), that "Two spectacular bursts in diversity took place [in the broad Ordovician context], one in the late Arenig and the other in the late Llanvirnian to early Caradocian
New data on the mineralogy of some Estonian Lower Caradocian
The corresponding event is known as the Middle Caradocian
Facies and Faunal Turnover (Ainsaar et al.
The oldest rocks in the area are middle to late Ordovician are-related mafic volcanic rocks and Caradocian
slates and cherts of the Balmoral Group (Fig.
and Ashgillian Chitinozoa from the subsurface of Gotland.
As interpreted from rubble, the one metre of tuff is faulted on the southeast against Caradocian
dark grey slate-chert and is underlain by nearly 2 metres of weakly cleaved, massive and weakly laminated slate, light green-grey to light grey, to the end of the trench in till.
Limestone associated with quartzose sandstone in the lower part of the Goss Point Formation contains a conodont assemblage dated as Late Ordovician (late Caradocian
to Ashgillian) (Nowlan et al.
Conodonts from the limestone and brachiopods from associated calcareous siltstone, together with U-Pb dating of the crystal tuff, indicate that the Nepisiguit Falls Formation is late Arenigian in age; graptolites from black shale of the Little River Formation are late Caradocian
brachiopod faunas of the Bala District, Merionethshire.
The Popelogan Inlier consists largely of mafic volcanic rocks of the Goulette Brook Formation, which underlies a thin unit of black chert (Popelogan Formation) containing early Caradocian
(N gracilis zone) graptolites.