Abstract

The area of western Montes de Toledo to Guadalupe boasts a thick succession of mainly siliciclastic sediment spanning terminal Ediacaran to lower Cambrian strata as indicated by a relatively sparse but diverse palaeontological record. A terminal Ediacaran age is based on the occurrence of Cloudina in platform carbonates of the lower part of the Ibor group and in correlative levels of olistostromes at the base of the Río Huso group. Higher in the Río Huso group are found trace fossils which indicate a Cambrian age, notably Treptichnus bifurcus, which overlaps the local stratigraphic range of macroscopic carbonaceous disc-shaped fossils identified as Beltanelliformis. Strata underlying the Río Huso group contain treptichnids. The fossil record of the terminal Ediacaran–Lower Cambrian of this area is in part comparable to Cloudina-bearing sediments from other regions, in particular Namibia, where treptichnid trace fossils also overlap the range of Cloudina. The possibility of a wider biostratigraphic significance of this should be further tested, including its relation to the base of the Cambrian.