A solution to Darwin's dilemma of 1859: exceptional preservation in Salter's material from the late Ediacaran Longmyndian Supergroup, England

Abstract

Study of historical and fresh collections from the Longmyndian Supergroup sheds new light on Ediacaran microbial communities and taphonomy. First reported by Salter in 1856, and noted by Darwin in the Origin of Species in 1859, a range of macroscopic bedding plane markings are already well known from the Longmyndian supergroup. Here we report filamentous and sphaeromorph microfossils, variously preserved as carbonaceous films, by aluminosilicate permineralization and as bedding plane impressions. This supports a long-suspected link between wrinkle markings and microbes, and draws further attention to our hypothesis for a taphonomic bias towards high-quality soft tissue preservation in the Ediacaran Period.

Remarkable preservation of microbial mats in Neoproterozoic siliciclastic settings: Implications for Ediacaran taphonomic models

“…Petrographic thin sections through carbonaceous siltstones of the Lightspout Formation (see McIlroy et al, 2005 and references therein) reveal abundant carbonized microbial filaments, <20μm in diameter (Callow & Brasier, 2009), similar to those described by Peat (1984), which show no evidence for branching and are non-septate and untapered. They are commonly found in parallel to sub-parallel orientations and form interwoven mat laminae (Fig.…”

“…These microfossils can be preserved in a number of taphonomic modes, including as carbonaceous sheaths and films and as pyritized remains (e.g. Fedonkin & Waggoner, 1997;Noffke et al, 2003;Noffke et al, 2006a, b;Grazhdankin & Gerdes, 2007;Callow & Brasier, 2009). Importantly they can be found preserved in preservational styles that are similar to those of Ediacaran macrofossils (i.e.…”

“…They are commonly found in parallel to sub-parallel orientations and form interwoven mat laminae (Fig. 4A, Callow & Brasier, 2009). Associated wrinkle structures on the base of the filament-bearing horizons are also interpreted as microbial in origin (cf.…”

“…Salter's historic material (see Salter, 1856;1857) has revealed a variety of exceptionally preserved, filamentous and discoidal microbial fossils from siltstone bedding planes (Fig. 4-5, Callow & Brasier, 2009). The most common structures are long, thin (c. 20μm), non-septate, untapered threads, which can show unequivocal branching structures.…”

“…4B-C), which Energy Dispersive X-ray (EDX) spectrometry has shown to be an iron and potassium aluminosilicate. Although the exact mineralogy remains uncertain, a phyllosilicate seems likely (Callow & Brasier, 2009; see also Cohen et al, 2009). The replication of unmineralized tissues by aluminosilicate minerals is otherwise unusual in the Phanerozoic (e.g.…”