Geochronology and geochemistry of the Huntington Formation, Olds Ferry terrane, Blue Mountains province, northern U.S. Cordillera: Implications for accreted terrane correlation and assembly

The Olds Ferry terrane is the more inboard of two accreted volcanic arc terranes in the late Paleozoic−early Mesozoic Blue Mountains province of the northern U.S. Cordillera. We present geologic, geochronologic, and geochemical data from the volcano-sedimentary Huntington Formation of the Olds Ferry arc that place the terrane within a firm temporal and tectonomagmatic context, and establish its identity as a fringing arc terrane along the Triassic to Early Jurassic Cordilleran margin. The Huntington Formation is divided into two unconformity-bounded informal members: a Norian (ca. 220 Ma) lower member comprising a sequence of mafic-intermediate volcanics, massive volcaniclastic breccias, and minor carbonates deposited unconformably onto the 237.7 Ma Brownlee pluton and intruded by the 210.0 Ma Iron Mountain pluton; and a Rhaetian through Pleinsbachian (<210−187.0 Ma) upper member composed of massive conglomerates, abundant rhyodacite to rhyolite effusive and pyroclastic flows, and interlayered sandstone turbidites, deposited with angular unconformity onto the lower member. An erosional hiatus and regional tilting produced an angular unconformity separating the Huntington Formation from the overlying basal conglomerates of the late Early to Middle Jurassic Weatherby Formation of the Izee forearc basin transgressive onlap sequence. Huntington Formation volcanic rocks are isotopically enriched relative to depleted mantle and coeval igneous rocks in the outboard Wallowa terrane. A temporal evolution to more radiogenic 87Sr/86Sr ratios (0.7036−0.7057) and εNd values (+5.4 to +3.1) in the upper member volcanics suggests increasing involvement of continental-derived material in their petrogenesis. Precambrian xenocrystic zircons in both lower and upper member volcaniclastic rocks strongly support a proximal location of the Olds Ferry terrane to cratonal North America during much of its history. The chronology and tectonostratigraphic architecture of the Olds Ferry terrane allows its robust correlation to other fringing-arc terranes along the U.S. and Canadian Cordillera.

Brachiopods from the Río del Peñón Formation. Río Blanco Basin, Upper Palaeozoic of Argentina.

This paper reviews the brachiopod fauna from the Ríoo de! Peñón Formation, Río Blanco Basin, Upper Palaeozoic of La Rioja province, Argentina. Traditionally, this unit was referred to the Carboniferous, however the braquiopod fauna here studied suggests a new biostratigraphical interpretation, indicating an age range from the latest Carboniferous to Early Permian. Three different brachiopod assemblages can be identified in the section: Assemblage I, from the lower member, includes Streptorhynchus? sp., Dyschrestia? sp., Costatumulus sp. A, Trigonotreta sp., Spiriferellina sp., Orbiculoidea sp., and unidentifiable productids and strophomenids.Assemblage II, from the middle member, includes Tivertonia jachalensis (Amos), Kochiproductus riojanus (Leanza), Costatumulus sp. B, Trigonotreta riojanensis (Lech and Acefiolaza) and Orbiculoidea sp. Assemblage III, from the highest part of the middle member, includes Neochonetes pegnonensis sp. nov., Costatumulus sp. C, Rhynchopora sp., Septosyringothyris jaguelensis Lech, and Orbiculoidea sp. These brachiopod assemblages demonstrate close affinities with faunas from the lower Permian of Western Australia and India. Affinities with faunas from Peru and Texas are less close.

Distribution and correlation of Sabellidites cambriensis (Annelida?) in the basal Cambrian on Baltica

Sabellidites cambriensis is a tubular non-mineralized metazoan that appears as compressed ribbon-shaped imprints with transverse wrinkling, thick walls and an even tube diameter of up to 3 mm. The distribution of Sabellidites is investigated in three Ediacaran–Cambrian sections on the Digermulen Peninsula in Arctic Norway, spanning the Manndrapselva Member of the Stáhpogieddi Formation and the lower member of the Breidvika Formation. Here, the Ediacaran–Cambrian boundary is located in the lower part of the upper parasequence (third cycle) of the Manndrapselva Member. Specimens of Sabellidites are rare but consistently present close to the lowest level of Treptichnus pedum and upsection, whereas the taxon is common and abundant in the lower part of the lower member of the Breidvika Formation, with an upper record at c. 55 m above the base. The range is comparable with that of the GSSP section in Newfoundland, Canada, establishing Sabellidites as an index fossil for the lowermost Cambrian. In the Manndrapselva Member, Sabellidites co-occurs with the acritarch Granomarginata, indicative of the lowermost Cambrian Granomarginata Zone, whereas in the Breidvika Formation it co-occurs with Asteridium. Sabellidites is widely distributed in Baltica, through the Rovnian and Lontovan regional stages but confined to the Fortunian global stage. In its lower range, Sabellidites is associated with a Treptichnus pedum trace fossil association and a depauperate leiosphaerid acritarch assemblage, followed by a Granomarginata assemblage. In its upper range, Sabellidites co-occurs with acritarchs of the Asteridium–Comasphaeridium Zone and the tubular foraminiferan Platysolenites. In Baltica, Sabellidites is a useful index fossil.

Industrial disability in the Japanese railways business: the activity of Testudō Kōsaikai, 1931–1955

The industrialization process generated many disabilities. However, the historical study of industrial disability has not progressed. This study examines disability welfare in the Japanese railroad industry. In particular, Testudō Kōsaikai, an organization of the Japanese National Railways (JNR) established in 1931, was uniquely devoted to welfare activities by linking a profit-making business and the provision of welfare. To cover welfare costs, such as providing workshops for disabled people, Kōsaikai conducted profit-making businesses, such as sales at station stalls. However, the welfare of disabled people in the JNR, including the activities of Kōsaikai, has not been previously examined. This study clarified the structure of disability welfare in the Japanese railroad industry until the early postwar period. People with a lower degree of disability, such as one upper or lower member amputation, were employed by the JNR, while some of these people were employed by Kōsaikai as sellers or officers, or accepted job training in Kōsaikai workshops. On the contrary, although few people with higher degrees of disability were employed by the JNR and Kōsaikai, the latter employed their family members to compensate them for their living costs.

Neoproterozoic-Cambrian stratigraphy of the Mackenzie Mountains, northwestern Canada, part IV: a stratigraphic reference section for the Ediacaran-Cambrian transition in NTS 95-M (Wrigley Lake map area)

A composite reference section for the upper Ediacaran and lower Cambrian is documented for a location near Moose Horn River in Wrigley Lake map area (NTS 95-M), Mackenzie Mountains, Northwest Territories. Four measured stratigraphic sections cover, in ascending order: the uppermost Sheepbed Formation; the informal Sheepbed carbonate; the lower, middle, and upper members of the Backbone Ranges Formation; the Sekwi Formation; and the lowermost beds of the Rockslide Formation. The uppermost Sheepbed Formation is dominated by dark-weathering shale and siltstone. The Sheepbed carbonate (440 m) lies conformably on the Sheepbed Formation and consists of limestone, dolostone, and dolomitic siltstone, including several horizons of rudstone with clasts up to boulder size. The upper surface of the Sheepbed carbonate has been eroded and the unit thins to a zero edge to the east. The lower member of the Backbone Ranges Formation (253 m) is heterolithic, including interbedded quartzose siltstone and quartzose sandstone, quartz arenite (locally with horizons of quartz pebbles), and dolostone to dolomitic sandstone. The middle member of the Backbone Ranges Formation (93 m) consists mainly of pink to grey-weathering limestone with red mudstone partings. The upper member (501.5 m) is dominated by quartz arenite, but also contains intervals of siltstone. Partway through the upper member there is a marker unit of dolostone to dolomitic sandstone that previous work suggests is a tongue of the Ediacaran Risky Formation. Based on regional correlations, the top of this marker may approximate the Ediacaran-Cambrian boundary in this section. The Sekwi Formation lies abruptly upon the Backbone Ranges Formation. The contact is unconformable at this locality and mapping in the area indicates eastward erosional removal of the upper member of the Backbone Ranges Formation beneath the Sekwi Formation. The Sekwi Formation here consists of variegated siltstone with lesser dolostone, limestone, and quartz sandstone. An abrupt contact with nodular limestone and grey shale of the overlying Rockslide Formation approximates the base of Cambrian Series 3.

Inverted South China: A novel configuration for Rodinia and its breakup

Disentangling records of Rodinia fragmentation and true polar wander remains a challenge for understanding late Tonian plate tectonics. The ca. 760 Ma lower member of the Liántuó Formation, South China, yields a primary paleomagnetic remanence that passes both the fold and reversal tests. This new result and recently reported ca. 800 Ma data from elsewhere in South China suggest a new interpretation of its apparent polar wander path, whereby pre–770 Ma poles have inverted absolute polarity relative to traditional interpretations. Based on this inversion, and an interpretation of several oscillations of true polar wander documented by global data during 810–760 Ma, we propose a novel reconstruction for Rodinia and its breakup. Our reconstruction places the South China, India, and Kalahari cratons to the southwest of Laurentia, with connections that might have been established as early as ca. 1000 Ma. Our model also suggests that initial rifting of Rodinia occurred at ca. 800 Ma via fast northward motion of the India craton and South China.

Calc-alkaline volcanic rocks and zircon ages of the late Tonian: early Cryogenian arc-related Big Naryn Complex in the Eastern Djetim-Too Range, Middle Tianshan block, Kyrgyzstan

The Big Naryn Complex (BNC) in the East Djetim-Too Range of the Kyrgyz Middle Tianshan block is a tectonized, at least 2 km thick sequence of predominantly felsic to intermediate volcanic rocks intruded by porphyric rhyolite sills. It overlies a basement of metamorphic rocks and is overlain by late Neoproterozoic Djetim-Too Formation sediments; these also occur as tectonic intercalations in the BNC. The up to ca. 1100 m thick Lower Member is composed of predominantly rhyolites-to-dacites and minor basalts, while the at least 900 m thick pyroclastic Upper Member is dominated by rhyolitic-to-dacitic ignimbrites. Porphyric rhyolite sills are concentrated at the top of the Lower Member. A Lower Member rhyolite and a sill sample have LA-ICP-MS U–Pb zircon crystallization ages of 726.1 ± 2.2 Ma and 720.3 ± 6.5 Ma, respectively, showing that most of the magmatism occurred within a short time span in the late Tonian–early Cryogenian. Inherited zircons in the sill sample have Neoarchean (2.63, 2.64 Ga), Paleo- (2.33–1.81 Ga), Meso- (1.55 Ga), and Neoproterozoic (ca. 815 Ma) ages, and were derived from a heterogeneous Kuilyu Complex basement. A 1751 ± 7 Ma 40Ar/39Ar age for amphibole from metagabbro is the age of cooling subsequent to Paleoproterozoic metamorphism of the Kuilyu Complex. The large amount of pyroclastic rocks, and their major and trace element compositions, the presence of Neoarchean to Neoproterozoic inherited zircons and a depositional basement of metamorphic rocks point to formation of the BNC in a continental magmatic arc setting.

Lithostratigraphy of the Siwalik Group along the Muksar Khola section, Siraha-Udayapur District, Eastern Nepal Himalaya

The Siwalik Group extending east to west co-linear to the main Himalayan range is well exposed along the Muksar Khola section, Siraha-Udayapur district, eastern Nepal Himalaya. Siwalik Group in the present study area is divided into the Lower, Middle, and Upper Siwaliks based on grain size and sandstone-mudstone proportion. The Lower Siwaliks is characterized by very fine- to fine-grained, light grey sandstone interbedded with dark grey to olive black mudstone. The Middle Siwaliks, is characterized by the domination of fine- to coarse-grained sandstone, and based on the lithology and bed thickness it is divided into two members. The lower member is dominated by fine- to medium-grained “salt and pepper” sandstone with dark greenish to olive-grey mudstone while, the upper member is dominated by light grey to white medium- to coarse-grained sandstone with grey, dark grey to black mudstone. Increase in the grain size and thickness of sandstone beds, increase in the proportion of mudstone, decrease in induration of sandstone and decrease in the proportion of biotite grain in sandstone makes upper member different from lower member of the Middle Siwaliks. The Upper Siwaliks is characterized by very thick beds of clast supported conglomerate associated with coarse- to very coarse-grained, very thick bedded sandstone and dull yellowish-grey to grey mudstone. The boundary between the Lower Siwaliks and the Middle Siwaliks, lower member and upper member of the Middle Siwaliks, and the Upper Siwaliks are 10.0 Ma, 5.7 Ma, and 3.5 Ma, respectively. The present study records the presence of a large succession of intra-formational conglomerate succession in the Lower Siwaliks.

Precise early Cambrian U–Pb zircon dates bracket the oldest trilobites and archaeocyaths in Moroccan West Gondwana

New U–Pb radioisotopic ages on early Cambrian volcanic zircons condition a high-resolution Bayesian age model that constrains the first occurrences and zonations of West Gondwanan archaeocyaths and trilobites in southern Morocco. The oldest archaeocyaths in the Tiout Member of the Igoudine Formation (519.71 + 0.26/− 0.35 Ma) are c. 6 Ma younger than the oldest Siberian archaeocyaths. The oldest Moroccan trilobite fragments, from the lower member of the Igoudine, are constrained to 519.95 + 0.43/− 0.40 Ma. The succeeding Issendalenian Stage (i.e. Hupetina antique – Eofallotaspis tioutensis – Fallotaspis plana – Choubertella – Daguinaspis trilobite zones) spans c. 1.5 Ma (519.78 + 0.26/− 0.37 Ma to 518.43 + 0.25/− 0.69 Ma). Identifiable Moroccan fallotaspidids and bigotinids, among Earth’s oldest trilobites, occur above a positive δ13C excursion dated with our age model at 520.27 + 0.59/− 0.57 Ma, and correlated with the IV excursion peak within the lower range of Siberian Atdabanian Stage trilobites (Repinaella Zone). This excursion is the best standard for a Cambrian Series 2 base. The oldest West Gondwana trilobite fragments are c. 1 Ma younger than those in Siberia and c. 0.5 Ma older than the oldest Avalonian trilobites (Callavia Zone). This diachrony means a trilobite first appearance datum is an inappropriate chronostratigraphic base for Cambrian Series 2. Taxonomic differences in the oldest trilobites between Cambrian palaeocontinents are in accordance with trace fossil evidence for the group’s appearance possibly as late as c. 530 Ma in the Cambrian Evolutionary Radiation. Coeval 519–517 Ma dates from Avalonia (cool-water siliciclastic shelf) and West Gondwana (tropical carbonate platform) sections with distinct macrofaunas emphasize these successions were latitudinally separate by the late Ediacaran Period.