Wenlock–Ludlow graptolite biostratigraphy and extinction: a reassessment from the southwestern Iberian Peninsula (Spain and Portugal)

Abstract

A detailed reexamination of a key Wenlock–Ludlow transition section in the Valle syncline region, Spain, and the incorportation of data from a coeval section in the Barrancos area, Portugal, both within the Ossa Morena Zone, reveal seven biostratigraphic units. These are Monograptus belophorus? and Cyrtograptus lundgreni−Monograptus testis biozones, representing the upper Sheinwoodian and the preextinction, lower Homerian faunas, respectively; the Pristiograptus dubius "parvus" – Gothograptus "nassa" Concurrent Range Biozone, Colonograptus? praedeubeli – Colonograptus? deubeli Biozone, and Colonograptus? ludensis Biozone, representing the upper Homerian postextinction faunas; and the Ludlow Neodiversograptus nilssoni and Saetograptus fritschi linearis biozones. The extinction beds between the lower Homerian lundgreni−testis Biozone and the lowest upper Homerian dubius "parvus"−"nassa" Interval Biozone make up a several centimetre thick, soft, orange-weathered, almost barren, volcanic? bed.

Graptolite zonation in the Late Wenlock (Early Silurian), with a new graptolite-brachiopod fauna from New South Wales

“…4B, for the ventral thecal lip to grow more distally than ventrally-to change direction, in fact. Figure 4B conforms approximately to M. vulgaris Wood, 1900(which Holland et al [1969 placed in synonymy with M. ludensis) and Figs 4C-D approach the change to what has been described as M. gerhardi Kiihne (see Kiihne, 1955;Jaeger, 1991;Gutierrez-Marco et al, 1996). In short, the syntype series of M ludensis embraces several "species" increasingly being used to characterise subdivisions of the old M ludensis Biozone (see, for example, Koren', 1992;Rickards et al, 1995).…”

Early Silurian sea-level changes

“…In Bohemian and Iberian sections, the lundgreni-nassa biozone boundary is marked by a lithological change, but to volcanic and possibly volcanic deposits, respectively (Kříž et al 1993;Gutiérrez-Marco et al 1996). No sealevel changes can be inferred.…”

Graptolite faunas and monaxonid demosponges of theCyrtograptus lundgrenievent (late Wenlock, Silurian) interval from the Orange district, New South Wales

“…Colonograptus praedeubeli -Co. deubeli Biozone, Spring Creek; Co. ludensis Biozone s.l., Wallace Creek. Colonograptus ludensis is abundant and widespread during the late Homerian: found in Arctic Canada (Lenz 1995, Lenz & Kozłowska-Dawidziuk 2002, Nevada, USA (Berry & Murphy 1975), the Baltic region (Kaljo et al 1984), north Africa (Bohrmann & Fischer 1985, Corne´e et al 1987, Australia (Rickards et al 1995, Rickards & Wright 1997, Rickards & Sandford 1998, China , Ni 1997, Zhang & Lenz 1997), central Asia (Koren' 1991 and Europe (Gutierrez-Marco et al 1996, Zalasiewicz & Williams 1999.…”

“…Pristiograptus parvus is widely known from the P. parvus -G. nassa Biozone in Europe (e.g. Kaljo et al 1984, Gutierrez-Marco et al 1996, Kozłowska-Dawidziuk 1999.…”