caa a22 4500 386384525 CHVBK 20180307112054.0 cr unu---uuuuu 161130s1989 xx s 000 0 eng 10.1017/S0263593300014401 doi S0263593300014401 pii (NATIONALLICENCE)cambridge-10.1017/S0263593300014401 Ordovician graptolites from the northern Sierra de Cobachi, Sonora, Mexico [Elektronische Daten] Two Ordovician graptolite assemblages are recognised and described for the first time in the allochthonous siliceous assemblage or succession forming the Guayacan Group of central Sonora in northwestern Mexico. A Middle Ordovician assemblage referable to the Nemagraptus gracilis-Climacograptus wilsoni zonal interval occurs in the upper siliceous shale of unit 1 of the Guayacan Group and an Upper Ordovician assemblage representative of the Dicellograptus ornatus Zone of the Pacific faunal province has been collected from shaly partings in the bedded radiolarian chert constituting unit 2. The stratigraphical make-up of the siliceous assemblage bears a striking similarity to the better known—and correlative—Lower Palaeozoic siliceous succession of central and northern Nevada, giving credence to the hypothesis that the Palaeozoic siliceous assemblage in northwestern Mexico was originally the extension of the Nevadan assemblage into California, which has been transposed to its present position along a left-lateral megashear of the magnitude of at least 1000 km. A review of the proximal development of the spinose species remaining in the form genus Climacograptus Hall has led to the proposal to restrict the genus to Climacograptus bicornis (Hall), its type species, and to two other septate species of early Middle Ordovician age (Llandeilo-early Caradoc) with a primitive type of proximal-end development. The genus Euclimacograptus, with Climacograptus hastatus T. S. Hall as the type species, is proposed for spinose Upper Ordovician climacograptids with an advanced proximal-end development. The genus Ensigraptus, with Climacograptus caudatus Lapworth as the type species, is also proposed for species homeomorphic with those included in Normalograptus Legrand but with a less advanced proximal-end development. Five species are described. Copyright © Royal Society of Edinburgh 1989 Genus Climacograptus nationallicence Guayacan Group nationallicence megashear nationallicence Nevada nationallicence N America nationallicence Pacific faunal province nationallicence proximal development nationallicence siliceous assemblage nationallicence Riva John F. Department of Geology, Laval University, Ste-Foy, Quebec, Canada G1K7P4. Ketner Keith B. U.S. Geological Survey, Denver, Colorado 80225, U.S.A. Transactions of the Royal Society of Edinburgh: Earth Sciences Royal Society of Edinburgh Scotland Foundation 80/2(1989), 71-90 0263-5933 80:2<71 1989 80 TRE https://doi.org/10.1017/S0263593300014401 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1017/S0263593300014401 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Riva John F. Department of Geology, Laval University, Ste-Foy, Quebec, Canada G1K7P4 NATIONALLICENCE 700 1- Ketner Keith B. U.S. Geological Survey, Denver, Colorado 80225, U.S.A NATIONALLICENCE 773 0- Transactions of the Royal Society of Edinburgh: Earth Sciences Royal Society of Edinburgh Scotland Foundation 80/2(1989), 71-90 0263-5933 80:2<71 1989 80 TRE CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-cambridge