Survival of Burgess Shale-type animals in a Middle Ordovician deep-water setting

Exceptional preservation of non-biomineralized arthropods, sponges and vermiform taxa occurs in the Darriwilian (Middle Ordovician) Llanfallteg Formation of South Wales, UK. The assemblage contains elements typical of Ordovician communities juxtaposed with those more commonly associated with Cambrian Konservat–Lagerstätten. This assemblage is preserved in rocks of a deep-marine succession dominated by fine-grained siliciclastic and volcaniclastic density-current deposits. Non-biomineralized taxa of Cambrian aspect are preserved as pyritized carbonaceous compressions on the spectrum of Burgess Shale-type preservation. Trilobites with phosphatized digestive structures have also been recovered. The assemblage of the Llanfallteg Formation Konservat–Lagerstätte demonstrates that some Burgess Shale-type faunal elements survived into the Middle Ordovician within cool, deep-water refugia in the Welsh Basin, offshore from communities dominated by typical Ordovician taxa.