SHRIMP U-Pb age of the radiolarian-bearing Yoshiki Formation in Japan

Abstract

The dating of radiolarian biostratigraphic zones from the Silurian to Devonian is only partially understood. Dating the zircons in radiolarian-bearing tuffaceous rocks has enabled us to ascribe practical ages to the radiolarian zones. To extend knowledge in this area, radiometric dating of magmatic zircons within the radiolarian-bearing Yoshiki Formation, Japan, was undertaken. The Yoshiki Formation is mainly composed of alternating beds of tuffaceous sandstones, tuffaceous mudstones, and felsic tuff. The felsic tuff and tuffaceous mudstone yield well-preserved radiolarian fossils. Radiolarians and zircon grains were collected from 21 tuffaceous mudstone and 30 tuff horizons of the Yoshiki Formation. The following radiolarian species which can be ascribed to the <i>Zadrappolus yoshikiensis</i>-<i>Futobari solidus </i>assemblage were identified: <i>Oriundogutta</i>(?) <i>kingi, Oriundogutta</i>(?) <i>varispina</i>, <i>Zadrappolus yoshikiensis</i>, <i>Zadrappolus tenuis</i>, <i>Zadrappolus hitoeganensis</i>, <i>Zadrappolus lunaris</i>, <i>Zadrappolus</i>(?) <i>nudus</i>, <i>Zadrappolus</i>(?) sp., <i>Futobari solidus</i>, <i>Futobari morishitai</i>, <i>Rotasphaera</i>(?) sp., and <i>Ceratoikiscum armiger</i>. U-Pb SHRIMP ages of 420.5 ± 2.5 Ma and 421.0 ± 1.9 Ma were obtained from the zircon grains. Thus the lower limit of the <i>Zadrappolus yoshikiensis-Futobari solidus </i>assemblage, that has previously been assigned to an age from Přidolian to Pragian, is in reality before Ludlowian. The technique in this paper has the capability of refining and making more accurate the dating of many radiolarian zones worldwide, and potentially of changing the direction of the entire study of radiolarian biostratigraphy

Ambiguous biogeographical patterns mask a more complete understanding of the Ordovician to Devonian evolution of Japan

“…Early Devonian is Lochkovian to Emsian, Middle Devonian is Eifelian to Givetian, and Late Devonian is Frasnian to Famennian. Absolute dates are from Shibata and Ozawa (1992) for the metamorphic basement of the South Kitakami Terrane, Nakama et al (2010) for the Ordovician of the Hida-Gaien Terrane, and Aitchison et al (1996, Kurosegawa) and Manchuk et al (2013a, 2013b for the Siluro-Devonian. In the absence of detailed palaeontological control, we have represented the boundary between the lower conodont-bearing and upper trilobite-bearing parts of the 'Hitoegane Formation' as a questionable unconformity.…”

Chitinozoans and scolecodonts from the Silurian and Devonian of Japan

“…Chitinozoans are rare, with 137 specimens being recovered from eight out of 42 samples (Figures and ; Table ). Of these, a few samples from the upper member ( sensu Manchuk et al, ) of the Yoshiki Formation in the Ichinotani Valley, central Honshu (Figure ), contain age‐diagnostic species from an interval sampled for radiolarians and zircons (Manchuk, Horie, & Tsukada, op. cit., Figure , samples 8–23).…”

“…Suggested chitinozoan‐based correlation of the upper member of the Yoshiki formation (sensu Manchuk et al, ), with the chronostratigraphy of the Type Ludlow in the Welsh Borderland. (*) The range of A. elongata in the Eastern Baltic region is a compilation based on Loydell, Nestor, and Männik (), Nestor (, , , 2003, 2007, 2008, 2009, 2012), Nestor and Einasto ()…”

“…Zadroppolus tenuis is also recorded from west Junggar, China, whilst O .(?) kingi and Ceratoikiscum armiger are known from the southern Urals (Manchuk et al, ). Based on their geochronology, Manchuk et al () suggest that the F. solidus‐Z.…”

Editorial preface: IGCP 596, Mid-Paleozoic climate and biodiversity: Proceedings of the Opening Meeting in Graz, Austria (September 19–24, 2011)

“…In summary, the collection of 13 papers published in this issue of the Bulletin of Geosciences combine various topics related to geochemistry, palynology, ichnology and taxonomy (radiolarians, foraminifers, ostracods, bivalves and conodonts), having a strong focus on biostratigraphy, palaeoecology and the interpretation of palaeoenvironmental conditions. The first contribution by Manchuk et al (2013) concerns biostratigraphic ranges of late Silurian to early Devonian radiolarians paired with U-Pb SHRIMP data of magmatic zircons from tuffaceous rocks of the Fukuji area in Japan which allow an age-refinement of some radiolarian biozones. The manuscript shows that this technique might lead to a more precise radiolarian biostratigraphy, if applied in other radiolarian-bearing sequences globally.…”