Revisiting the phosphorite deposit of Fontanarejo (central Spain): new window into the early Cambrian evolution of sponges and the microbial origin of phosphorites
Open Access
- 29 September 2021
- journal article
- research article
- Published by Cambridge University Press (CUP) in Geological Magazine
- Vol. 159 (7), 1220-1239
- https://doi.org/10.1017/s001675682100087x
Abstract
Fossils within early Cambrian phosphorites worldwide are often well preserved due to early diagenetic permineralization. Here, we examine the fossil record contained within phosphorites of the Lower Cambrian Pusa Formation (late Fortunian to Cambrian Stage 2) in Fontanarejo, central Spain. The sedimentology and age of these phosphorites have been controversial and are here reviewed and discussed, providing also an updated geological map. The Pusa Formation is composed of fine clastic sediments that are partly turbiditic, with channels of quartz-rich conglomerates and abundant phosphorites in the upper part of the succession. The microfacies and mineralogy of these channel deposits are studied here for the first time in detail, showing that they are mainly composed of subspherical apatite clasts, with minor mudstone intraclasts, quartzite and mica grains. Numerous sponge spicules, as well as entirely preserved hexactinellid sponges and demosponges, were collected within these phosphorites and likely represent stem groups. In addition to sponges, other fossils, such as small shelly fossils (SSF) of the mollusc Anabarella sp., were found. The phosphorites exhibit multiple evidence of intense microbial activity, including diverse fabrics (phosphatic oncoidal-like microbialites, thrombolites, stromatolites and cements) and abundant fossils of filamentous microbes that strongly resemble extant sulphur-oxidizing bacteria. Our findings strongly suggest that microbial processes mediated the rapid formation of most of the Fontanarejo apatite, probably accounting for the exceptional preservation of fragile fossils such as sponge skeletons. The apparent presence of taxonomically diverse hexactinellid and demosponge communities at the lowermost Cambrian further corroborates a Precambrian origin of the phylum Porifera.This publication has 115 references indexed in Scilit:
- Spicule structure and affinities of the Late Ordovician hexactinellid-like sponge Cyathophycus loydelli from the Llanfawr Mudstones Lagerstätte, WalesLethaia, 2013
- Ediacaran to Lower Ordovician age for rocks ascribed to the Schist–Graywacke Complex (Iberian Massif, Spain): Evidence from detrital zircon SHRIMP U–Pb geochronologyGondwana Research, 2012
- Deep Phylogeny and Evolution of Sponges (Phylum Porifera)Published by Elsevier BV ,2012
- The role of microbes in the formation of modern and ancient phosphatic mineral depositsFrontiers in Microbiology, 2012
- Occurrence of a Silicatein Gene in Glass Sponges (Hexactinellida: Porifera)Marine Biotechnology, 2010
- Sulfide induces phosphate release from polyphosphate in cultures of a marine Beggiatoa strainThe ISME Journal, 2010
- Age constraints from small shelly fossils on the early Cambrian terminal Cadomian Phase in IberiaGFF, 1999
- Neoproterozoic-early Cambrian geology and palaeontology of IberiaGeological Magazine, 1994
- The bearing of the new Late Cambrian monoplacophoran genus Knightoconus upon the origin of the CephalopodaLethaia, 1973
- Ontogeny and Systematics in SpongesSystematic Zoology, 1957