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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 Zadrappolus yoshikiensis-Futobari solidus assemblage were identified: Oriundogutta(?) kingi, Oriundogutta(?) varispina, Zadrappolus yoshikiensis, Zadrappolus tenuis, Zadrappolus hitoeganensis, Zadrappolus lunaris, Zadrappolus(?) nudus, Zadrappolus(?) sp., Futobari solidus, Futobari morishitai, Rotasphaera(?) sp., and Ceratoikiscum armiger. 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 Zadrappolus yoshikiensis-Futobari solidus 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

We describe the mode of occurrence and geochemical characteristics of basalts, in the Khangai-Khentei belt in Mongolia, overlain by Middle Paleozoic radiolarian chert in an extensive accretionary complex. These basalts are greatly enriched in K, Ti, Fe, P, Rb, Ba, Th, and Nb in comparison to the composition of the mid-ocean ridge basalts, indicative of within-plate alkaline type. Ti/Y vs Nb/Y and MnO/TiO 2 /P 2 O 5 ratios of the basalts also suggest within-plate affinities. Considering the geochemical characteristics as well as the conformable relationship with the overlying radiolarian chert, the alkaline basalts were clearly not continental but formed a pelagic oceanic island. The mode of occurrence and geochemistry of the basalts show that the alkaline basaltic volcanic activity had taken place to form an oceanic island in the Paleozoic pelagic region sufficiently far from continents to allow radiolarian ooze accumulation.

This study conducted petrographic and geochemical analyses of chert artifacts from the Late Middle Paleolithic, the Initial Upper Paleolithic, the Early Upper Paleolithic, and the Epi-Paleolithic assemblages in the Jebel Qalkha area, southern Jordan, to examine their correlations with the visual attributes and diachronic variability. The results revealed two different aspects of the petrographic and geochemical signatures. The first aspect showed some correlations with the visual chert types that were characterized by the abundance/ preservation of fossils, the enrichment of several elements (i.e., Ca, Sr, and Ba), and the quartz crystallite size. The second aspect of geochemical signatures, such as Fe, Mn, Ni, Cr, and Co, showed no correlation with the visual types but was correlated with the chronocultural groups. Given the chert occurrences and variability in and around the study area, the first aspect of the chert variability likely represents the variations of different chert outcrops as well as the internal variations within the same sources. Whether the second aspect represents chrono-cultural changes in the use of chert sources needs to be clarified in future by our ongoing examination of geological chert samples in the study area.