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This study provides a taxonomic treatment and comparison of lower Gorstian (Silurian) radiolarians recovered from two sections of the Cape Phillips Formation in the Canadian Arctic that accumulated in two different paleoenvironmental settings. Twilight Creek is more basinal, located ~100 km from the paleo-shelf margin, whereas Snowblind Creek is located within 1 km of the paleo-shelf break, on Cornwallis Island. The fauna, like other material from the Cape Phillips Formation, is extremely well preserved and was recovered from four samples at two localities, all from the Lobograptus progenitor graptolite Zone, an interval that has few published studies regarding radiolarians. A total of 28 species are recognized, of which two are new and described herein (Fusalfanus bilateralis n. sp. and Pseudospongoprunumparvispina n. sp.), belonging to the Haplotaeniatidae, Inaniguttidae, 'Sponguridae', Ceratoikiscidae, Entactiniidae, Palaeoscenidiidae, and Secuicollactidae. Based on these new data, the stratigraphic ranges of some taxa are extended. The species concepts of several closely related inaniguttid species are re-evaluated. As a result, Inanihella tarangulica Nazarov and Ormiston, 1984 is transferred to the genus Fusalfanus Furutani, 1990 based on cortical shell structure, and Inanihella duroacus, Inanihella legiuncula, and Inanihella perarmata are synonymized under Fusalfanus tarangulica sensu lato. Aciferopylorum admirandum is transferred to Fusalfanus and considered a junior synonym of Fusalfanus osobudaniensis. The comparative analysis of taxonomic richness and composition reveals that the more distal sample from Bathurst Island exhibits a slight, but statistically significant, higher alpha diversity at the species rank than the more proximal basin/platform samples from Snowblind Creek. Biodiversity indices at the genus rank produced mixed results, indicating that differences between sites are at best slight. There is also a strong taxonomic separation between the fine and coarse size radiolarian fractions recovered during the sieving of each sample. The siliceous sponge spicule assemblages from these faunas show an inverse diversity relationship to the radiolarians in that Snowblind Creek contains greater alpha diversity than Twilight Creek. This study provides the first documentation of facies-controls in Silurian radiolarian diversity and is useful in evaluating the role of taxa used in biostratigraphy. L'etude presente le traitement taxonomique et la comparaison de radiolaires du Gorstien (Silurien) inferieur recuperes de deux sections de la Formation de Cape Phillips, dans l'Arctique canadien, accumulees dans deux contextes paleoenvironnementaux differents. Twilight Creek s'apparente plus a un milieu de bassin situe a ~100 km de la bordure de la paleoplateforme, alors que Snowblind Creek est situe a moins de 1 km de la bordure de cette derniere, dans l'ile Cornwallis. La faune, comme d'autre materiau de la Formation de Cape Phillips, est extremement bien preservee et a ete recuperee de quatre echantillons provenant de deux localites, tous de la zone a graptolite Lobograptus progenitor, un intervalle caracterise par peu d'etudes publiees sur les radiolaires. Un total de 28 especes sont reconnues, dont deux nouvelles decrites dans la presente etude (Fusalfanus bilateralis n. sp. et Pseudospongoprunum parvispina n. sp.), appartenant aux Haploteniatides, Inaniguttides, <>, Ceratoikiscides, Entactiniides, Paleoscenidiides et Secuicollactides. A la lumiere de ces nouvelles donnees, les repartitions stratigraphiques de certains taxons sont elargies. Le concept d'espece pour plusieurs especes d'inaniguttides etroitement reliees est reevalue et, en consequence, Inanihella tarangulica Nazarov and Ormiston, 1984 est transfere au genre Fusalfanus Furutani, 1990 a la lumiere de la structure corticale de sa coquille, et Inanihella duroacus, Inanihella legiuncula et Inanihella perarmata sont etablis comme des synonymes de Fusalfanus tarangulica sensu lato. Aciferopylorum admirandum est transfere a Fusalfanus et considere comme etant un synonyme junior de Fusalfanus osobudaniensis. L'analyse comparative de la richesse et de la composition taxonomiques revele que l'echantillon plus distal de l'ile Bathurst presente une diversite alpha legerement, bien que significativement, plus forte au rang de l'espece que les echantillons plus proximaux de bassin/plateforme de Snowblind Creek. Les indices de biodiversite au rang du genre produisent des resultats mitiges, indiquant que les differences entre localites sont, au mieux, minimes. Il y a egalement une separation taxonomique marquee entre les fractions fines et grossieres de radiolaires produites par le criblage de chacun des echantillons. Les assemblages de spicules d'eponges siliceux de ces faunes presentent une relation de diversite inverse a celle des radiolaires, en cela que l'assemblage de Snowblind Creek contient une plus grande diversite alpha que celui de Twilight Creek. Cette etude fournit la premiere documentation d'un controle de la diversite de radiolaires siluriens par le facies et est utile pour l'evaluation du role des taxons utilises en biostratigraphie. [Traduit par la Redaction], Introduction Since their appearance in the lower Cambrian (Pouille et al. 2011), Polycystine radiolarians diversified during the entire Phanerozoic (De Wever et al. 2001); they thus have the potential to [...]

Integrated sequence stratigraphic, biostratigraphic, and chemostratigraphic analyses of three stratigraphic sections in central Nevada indicate that Late Ordovician glaciation-induced sea-level fall produced diachronous, stepwise faunal turnover in graptolites, conodonts, chitinozoans, and radiolarians, and also triggered a strong, but transient, positive [[Delta].sup.13]C excursion. This pattern is very different from that described for most mass extinction events.

A regionally extensive Early Mississippian hiatus is recognized at the transition from preflysch to flysch rocks in the Ouachita system of the southern mid-continental United States. It is recognized only in sections where detailed biostratigraphic control exists, and it is coeval with a regional unconformity in the Ouachita foreland throughout parts of Texas, New Mexico, and Oklahoma. Widespread Early Mississippian erosion and nondeposition is attributed to a reconfiguration in basin geometry caused by the onset of Ouachita orogenic activity. Crustal flexure resulting from the impending collision would have initiated erosional processes throughout the foreland, while simultaneously altering bottom-current pathways in the basin and allowing for a prolonged period of sedimentary bypass. In the Late Mississippian, increased constriction may have eventually cut off transequatorial bottom-water circulation, allowing deposition to resume on the shelf and in the basin. An important tectonic implication of this study is that Ouachita deformation started in the Late Devonian to earliest Mississippian, at least 10 m.y. before the onset of flysch deposition.

An unusually fossiliferous sedimentary sequence is exposed near Scarborough, Tobago, West Indies. It occurs within the Tobago Volcanic Group above an undifferentiated sequence of volcaniclastic breccia and lava and includes volcanogenic sedimentary rocks at the base of the Bacolet Formation. An ammonite-radiolarian assemblage has been recovered from this sedimentary interval in the Tobago Volcanic Group. Ammonites from the Spring Gardens quarry are moderately evolute and have unbranched ribs; they are probably juveniles of Mojsisoviczia, of middle Albian age. Another ammonite from a stratigraphically higher locality (i.e., volcanogenic sedimentary rocks at the base of the Bacolet Formation) is identified as Manuaniceras decsernae Young, of early late Albian age. Radiolarian assemblages from intercalations of black siliceous argillite of the Tobago Volcanic Group are characterized by abundant Archaeospongoprunum spp. and the common occurrence of Pseudodictyomitra pentacolaensis, Dictyomitra montisserei, Thanarla brouweri, and Pantanellium ventosum. Also present in lesser abundances are other members of the family Archaeodictyomitridae, Xitus, Napora durhami, and Sciadiocapsa speciosa. This assemblage correlates with the Romanus subzone of O'Dogherty (1994) and Kozurium zingulai zone of Pessagno (1977), both of which are dated as early to middle Albian. These newly reported fossils indicate an Albian age for deposition of the Tobago Volcanic Group. Earlier published [sup.40]Ar/[sup.39]Ar radiometric ages from the group are consistent with the stratigraphic age assignment of the fossils and thereby suggest that volcanism associated with the Tobago Volcanic Group began ca. 105 Ma. Possible correlative, accreted fragments of the Mesozoic oceanic-arc of the southern Caribbean include the Curacao Lava Formation, the lower part of the Washikemba Formation (Bonaire), the Tiara Formation of north-central Venezuela, and possibly the subsurface Mejillones complex of the Carupano basin. The Mesozoic rocks of Tobago consist of two distinct, oceanic-arc rock sequences. The older North Coast Schist ([is greater than or equal to] 120 Ma) exhibits polyphase deformation and lower greenschist facies metamorphism. The structurally overlying Tobago Volcanic Group is not penetratively deformed or folded; it has undergone prehnite-pumpellyite facies metamorphic conditions and has been tilted to moderate dips by various brittle faults. We interpret the hiatus that separates these oceanic-arc rock sequences as representing a significant event in the evolution of the Great Arc of the Caribbean. Consequently, we propose that the commonly postulated reversal in subductionzone polarity of the Great Arc occurred prior to deposition of the Tobago Volcanic Group (ca. 105 Ma), and that older, more highly deformed and metamorphosed oceanic-arc sequences (e.g., North Coast Schist) served as a basement for younger sequences or as wall rock for intrusive elements of younger magmatic suites of the Great Arc. Keywords: Caribbean area, Tobago, Cretaceous, ammonites, radiolarians.

This study addresses the effects of climate, land-use, and atmospheric nitrogen (N) deposition on the Fallen Leaf Lake watershed, Lake Tahoe Basin, through diatom and geochemical analyses of sediment cores. Four diatom zones are recognized from a core taken at Fallen Leaf Lake (FLL), a site moderately impacted by human activities: (1) Pre-Little Ice Age Zone (840-1385), (2) Little Ice Age Zone (1385-1810) characterized by Stephanodiscus alpinus and Aulacoseira subarctica, (3) Transitional Zone (1810-1950) of warming and anthropogenic influence with increased Lindavia rossii- ocellata group and Discostella stelligera and decreased Pseudostaurosira brevistriata, and (4) Anthropogenic Zone (1950-2010) characterized by a rapid increase of mesotrophic diatoms of the Fragilaria tenera- nanana group, Tabellaria flocculosa strain IIIP, and Nitzschia gracilis. The Transitional Zone increases in elemental Co, Zn, and Sn that may be attributed to an increase in coal burning and smelting activities in California and Nevada. Beginning around 1910 and accelerating in the 1940s, increased building, land-use, and recreation around FLL caused an increase in terrestrial sedimentary input. Down core proxies for atmospheric N deposition in the FLL watershed are, at best, weakly expressed and appear to be overshadowed by stronger signals. Lack of support for N deposition includes the asynchrony in the appearance of the N-sensitive diatom Asterionella formosa in FLL and a lower impact site at Gilmore Lake, and an uninformative δN record. Asterionella formosa is a dominant component in the FLL water column today, but has been present in similar abundances for at least the last 1200 years. Asterionella formosa is present in the water column at Gilmore Lake and absent from the sediment, indicating a very recent appearance. The data collected show that the FLL record is sensitive to climatic cooling during the Little Ice Age and to anthropogenic activities commencing in the 1800s that increased throughout the latter half of the twentieth century; however the effects of anthropogenic N deposition in these lakes could not be substantiated. [ABSTRACT FROM AUTHOR]

Geochemical data from the Cape Phillips Formation, Arctic Canada, are examined in association with three Silurian biotic crises in the graptolite community; the early Wenlockian Ireviken, mid Wenlockian Cyrtograptus lundgreni, and end Wenlockian Colonograptus ludensis extinction events. Positive δ13Corg excursions are associated with the Ireviken and C. lundgreni events, but not the Co. ludensis Event. The Ireviken and C. lundgreni excursions are recognized worldwide and are herein interpreted to be the result of carbonate weathering in response to eustatic sea-level drop. The C. lundgreni excursion is of greater magnitude in the more proximal basin margin section at Abbott River, Cornwallis Island, and is explained by the amplification of a more strongly positive δ13C signature in shallower parts of an epeiric basin during increased exposure and weathering of the carbonate shelf. Excursion C5, within the C. praedeubeli – C. deubeli Zone, is also of regional significance, as it occurs in both the Abbott River section and Twilight Creek section on Bathurst Island, and is also recognized in Estonia, Poland, and England. Excursion C6 is recognized in the Gorstian Stage, yet its regional significance remains equivocal. There is a reasonable general agreement between the shape of the δ13Corg and δ13Ccarb curves, yet the δ13Ccarb curve is largely a record of detrital carbonate derived from the shelf. The δ13Corg curve represents extraction of dissolved inorganic carbon by plankton and thus is more indicative of ambient paleoceanographic conditions. These data are valuable in that they provide a detailed secular marine δ13C curve for the Wenlockian of Arctic Canada from relatively unaltered sections of varying facies whose ages are well constrained by graptolite biostratigraphy. [ABSTRACT FROM AUTHOR]

Presents a study which reviewed the geologic setting of Carlin-type gold deposits in the Jerritt Canyon mining district in the northern Independence Range, Elko County in Nevada. Description of stratigraphic and structured controls of the ore bodies; Methods used; Regional geologic setting; Geology of the Jerritt Canyon mining district; Mineral deposits in the district.

Blocks and tectonic slices within the Mersin Mélange (southern Turkey), which are of Northern Neotethyan origin (Izmir–Ankara–Erzincan Ocean (IAE)), were studied in detail by using radiolarian, conodont, and foraminiferal assemblages on six different stratigraphic sections with well‐preserved Permian succesions. The basal part of the Permian sequence, composed of alternating chert and mudstone with basic volcanics, is assigned to the late Asselian (Early Permian) based on radiolarians. The next basaltic interval in the sequence is dated as Kungurian. The highly alkaline basic volcanics in the sequence are extremely enriched, similar to kimberlitic/lamprophyric magmas generated at continental intraplate settings. Trace element systematics suggest that these lavas were generated in a continental margin involving a metasomatized subcontinental lithospheric mantle source (SCLM). The middle part of the Permian sequences, dated by benthic foraminifera and conodont assemblages, includes detrital limestones with chert interlayers and neptunian dykes of middle Wordian to earliest Wuchiapingian age. Higher in the sequence, detrital limestones are overlain by alternating chert and mudstone with intermittent microbrecciated beds of early Wuchiapingian to middle Changhsingian (Late Permian) age based on the radiolarians. A large negative shift at the base of the Lopingian at the upper part of section is correlated to negative shifts at the Guadalupian/Lopingian boundary associated with the end‐Guadalupian mass extinction event. All these findings indicate that a continental rift system associated with a possible mantle plume existed during the late Early to Late Permian period. This event was responsible for the rupturing of the northern Gondwanan margin related to the opening of the IAE Ocean. When the deep basinal features of the Early Permian volcano‐sedimentary sequence are considered, the proto IAE oceanic crust formed possibly before the end of the Permian. This, in turn, suggests that the opening of the IAE Ocean dates back to as early as the Permian. Blocks and tectonic slices within the Mersin Mélange (southern Turkey), which are of Northern Neotethyan origin (Izmir–Ankara–Erzincan Ocean), were studied in detail by using Radiolaria, Conodont, and Foraminiferal assemblages on six different stratigraphic sections with well‐preserved Permian succesions. The findings indicate that a continental rift system associated with a possible mantle plume existed during late Early to Late Permian period. This event was responsible for the rupturing of northern Gondwanan margin related to the opening of the Izmir–Ankara–Erzincan Ocean. [ABSTRACT FROM AUTHOR]

Data analysis of all published and well-dated Silurian radiolarian localities was conducted with the goal of revealing long-term patterns in Silurian radiolarian biological diversity. The chronostratigraphic distribution of 161 species was compiled from 25 publications, each selected because of their independent age control. The pattern and dynamics of changes in biodiversity are described using indices that allow for the assessment of changes in taxonomic richness through time. Following the Hirnantian (end-Ordivician) mass extinction, the Rhuddanian stage records very low levels of diversity, which then increase gradually throughout the Llandovery series and reach a maximum by the Sheinwoodian stage, before decreasing during the Homerian, and finally, rebounding during the Gorstian stage. The early Silurian (Llandovery) appears to be an interval during which few species went extinct, although the number of last occurrences increases progressively to reach a peak in the Ludfordian. At the same time first occurrences progressively decrease and are relatively low during the Silurian. Only the Gorstian is marked by a sudden increase in origination. The early Silurian is an interval of faunal recovery from the end-Ordovician mass extinction event. Similarly, the Gorstian stage is characterized by a recovery following the Homerian low in radiolarian diversity that may be correlated with the C. lundgreni extinction event, which affected a number of other pelagic groups (e.g. graptolites, acritarchs, conodonts, and chitinozoans), and with the Mulde event, which coincides with a 4.6‰ positive excursion of the δ 13 C curve. [ABSTRACT FROM AUTHOR]