Middle Ordovician Upwelling-Related Ironstone of North Wales: Coated Grains, Ocean Chemistry, and Biological Evolution

Middle Ordovician phosphatic ironstone of the Welsh Basin provides new insight into the paleoenvironmental significance of ironstone and Ordovician ocean chemistry. Deposition occurred in a back-arc basin along the southern margin of Avalonia as the Rheic Ocean opened to the south. Ironstone is interpreted to have accumulated as part of an aggradational parasequence on a storm-dominated shelf with coastal upwelling. This parasequence has a laminated pyritic mudstone base that grades upward into variably bioturbated mudstone and coated grain-rich, intraclastic ironstone, which is overlain in turn by cross-stratified grainstone composed entirely of coated Fe grains. A coarser clastic parasequence composed of more proximal lithofacies rests conformably above and suggests the contact between the two parasequences is a maximum flooding surface marking the onset of highstand conditions. Lithofacies associations suggest that sustained coastal upwelling created a wedge of nutrient-rich, ferruginous seawater on the middle shelf that stimulated high surface ocean productivities. Large, coated Fe grains (granule size) composed of discontinuous and concentric carbonate fluorapatite, hematite, and chamosite cortical layers record fluctuations in pore water Eh that are interpreted to have been related to changes in upwelling intensity and intermittent storm reworking of the seafloor. Results support an emerging model for Ordovician ironstone underpinned by the development of ferruginous bottom water that was periodically tapped by coastal upwelling. Expanding, semi-restricted seaways such as the Rheic Ocean were ideal locations for the ponding of this anoxic, hydrothermally enriched seawater, especially during the early Paleozoic when the deep ocean was variably and inconsistently oxygenated. The coincidence of ironstone depositional episodes with graptolite diversification events suggests that, in addition to Fe, the sustained supply of upwelling-related P may have driven the radiation of some planktonic ecosystems during the Great Ordovician Biodiversification Event. Concomitant minor extinctions of benthic trilobites occurred as these ferruginous waters impinged on the shelf

A 2200-year record of Andean Condor diet and nest site usage reflects natural and anthropogenic stressors

Understanding how animals respond to large-scale environmental changes is difficult to achieve because monitoring data are rarely available for more than the past few decades, if at all. Here, we demonstrate how a variety of palaeoecological proxies (e.g. isotopes, geochemistry and DNA) from an Andean Condor (Vultur gryphus) guano deposit from Argentina can be used to explore breeding site fidelity and the impacts of environmental changes on avian behaviour. We found that condors used the nesting site since at least approximately 2200 years ago, with an approximately 1000-year nesting frequency slowdown from ca 1650 to 650 years before the present (yr BP). We provide evidence that the nesting slowdown coincided with a period of increased volcanic activity in the nearby Southern Volcanic Zone, which resulted in decreased availability of carrion and deterred scavenging birds. After returning to the nest site ca 650 yr BP, condor diet shifted from the carrion of native species and beached marine animals to the carrion of livestock (e.g. sheep and cattle) and exotic herbivores (e.g. red deer and European hare) introduced by European settlers. Currently, Andean Condors have elevated lead concentrations in their guano compared to the past, which is associated with human persecution linked to the shift in diet.Fil: Duda, Matthew P.. Queen's University; CanadáFil: Grooms, Christopher. Queen's University; CanadáFil: Sympson, Lorenzo. Sociedad Naturalista Andino Patagonica; ArgentinaFil: Blais, Jules M.. University of Ottawa; CanadáFil: Dagodzo, Daniel. University of Ottawa; CanadáFil: Feng, Wenxi. Queen's University; CanadáFil: Hayward, Kristen M.. Queen's University; CanadáFil: Julius, Matthew L.. St. Cloud State University; Estados UnidosFil: Kimpe, Linda E.. University of Ottawa; CanadáFil: Lambertucci, Sergio Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Layton Matthews, Daniel. Queen's University; CanadáFil: Lougheed, Stephen. Queen's University; CanadáFil: Massaferro, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Michelutti, Neal. Queen's University; CanadáFil: Pufahl, Peir K.. Queen's University; CanadáFil: Vuletich, April. Queen's University; CanadáFil: Smol, John P.. Queen's University; Canad

Petrographic, cathodoluminescent, and compositional characters of organic dolomites from ODP Leg 175 holes

The main objective of Leg 175 was to reconstruct the Late Neogene paleoceanographic history of the Benguela Current and associated upwelling regimes along the southwest African margin between 5° and 32°S. This area is one of the great upwelling regions of the world and plays an important role in the global ocean-carbon cycle. It is characterized by organic-rich sediments that contain a high-resolution record of productivity history that is closely linked to changes in regional dynamics of circulation, mixing, and upwelling (Wefer et al., 1998, doi:10.2973/odp.proc.ir.175.1998). The Benguela Current region also provides an excellent setting to investigate the early diagenetic processes governing the formation of authigenic dolomite. Although unexpected, the discovery of widespread and pervasive dolomite horizons along the southwest African margin was one of the principal findings of Leg 175. Dolomite precipitation within upwelling regimes is stimulated by the effects of high productivity and occurs early within the uppermost tens to hundreds of meters of sediment (Garrison et al., 1984; Hay, Sibuet, et al., 1984, doi:10.2973/dsdp.proc.75.1984; Kastner et al., 1990, doi:10.2973/odp.proc.sr.112.144.1990; Kelts and McKenzie, 1982, doi:10.2973/dsdp.proc.64.110.1982; Kulm et al., 1984; Lyle, Koizumi, Richter, et al., 1997, doi:10.2973/odp.proc.ir.167.1997; Middelburg et al., 1990, doi:10.1130/0091-7613(1990)0182.3.CO;2; Pisciotto and Mahoney, 1981, doi:10.2973/dsdp.proc.63.118.1981; Suess et al., 1988, doi:10.1130/0091-7613(1988)0162.3.CO;2). Productivity must be sufficiently high to generate a favorable environment; the microbial respiration of sedimentary organic matter increases alkalinity and pH of pore waters and simultaneously alters Mg-Ca solution and crystal surface chemistries to promote dolomite precipitation (Baker and Burns, 1985; Baker and Kastner, 1981, doi:10.1126/science.213.4504.214; Compton and Siever, 1986; Compton, 1988, doi:10.1016/0016-7037(86)90057-8; Compton et al., 1994; Hardie, 1987; Mazzullo, 2000; Slaughter and Hill, 1990; Vasconcelos and McKenzie, 1997). These organogenic dolomites are distinguished from other types of authigenic carbonates by having a significant portion of their carbon derived from microbially degraded organic carbon (Froelich et al., 1979, doi:10.1016/0016-7037(79)90095-4) and are thus characterized by 13C values that deviate strongly from those of normal marine carbonates (Friedman and Murata, 1979, doi:10.1016/0016-7037(79)90126-1; Irwin et al., 1977, doi:10.1038/269209a0; Murata et al., 1972; Pisciotto and Mahoney, 1981, doi:10.2973/dsdp.proc.63.118.1981). Here, we report the occurrence of organogenic dolomite horizons within organic-rich Neogene and Quaternary hemipelagic sediments from the southwest African margin. The purpose of this paper is to document the mineralogical, compositional, textural, and cathodoluminescent (CL) properties of dolomite horizons. It is not within the scope of this report to discuss horizon formation in detail. Aspects of horizon development based on the interpretation of these properties will be the focus of a subsequent paper

Upper Cretaceous (Campanian) phosphorites in Jordan: Implications for the formation of a south Tethyan phosphorite giant: Sedimentary Geology, v

Abstract A record of sedimentary, authigenic, and biological processes are preserved within the Upper Cretaceous (Campanian) Alhisa Phosphorite Formation (AP) in central and northern Jordan. The AP formed near the eastern extremity of the south Tethyan Phosphorite Province (STPP), a carbonate-dominated Upper Cretaceous to Eocene ''phosphorite giant'' that extends from Colombia, North Africa to the Middle East. Multidisciplinary research of the AP and associated cherts, chalks, and oyster buildups indicate that phosphatic strata formed on a highly productive, storm-dominated, east -west trending epeiric platform along the south Tethyan margin. The onset of phosphogenesis and the accumulation of economic phosphorite coincided with a rise in relative sea level that onlapped peritidal carbonates of the Ajlun Group. Pristine phosphates are associated with well-developed micrite concretionary horizons and contain abundant non-keeled spiral planktic foraminifera and a low diversity benthic assemblage of Buliminacean foraminifera, suggesting that pristine phosphates are a condensed facies and phosphogenesis was stimulated by the effects of a highly productive surface ocean and the suboxic diagenesis of sedimentary organic matter. The bulk sediment composition and absence of Fe-bearing authigenic phases such as glauconite, pyrite (including pyrite molds), siderite, and goethite within pristine phosphates suggests that deposition and authigenesis occurred under conditions of detrital starvation and that ''iron-pumping'' played a minimal role in phosphogenesis. Authigenic precipitation of phosphate occurred in a broad array of sedimentary environments-herein termed a ''phosphorite nursery''-that spanned the entire platform. This is a non-uniformitarian phenomenon reflecting precipitation of sedimentary apatite across a wide depositional spectrum in a variety of depositional settings, wherever the conditions were suitable for phosphogenesis. Sedimentologic data indicate that pristine phosphates were concentrated into phosphatic grainstones through storm wave winnowing, and storm-generated, shelf-parallel geostrophic currents. Economic phosphorites formed through the amalgamation of storm-induced event beds. Stratigraphic packaging of phosphatic strata indicates that temporal variations in storm frequency were a prerequisite for the formation of economic phosphorite. Syndepositional phosphogenesis, reworking, and amalgamation to form phosphorites contrasts sharply with the principles of ''Baturin Cycling''. A transgressive systems tract coupled with high surface productivity created detritally starved settings favourable for phosphogenesis; storm reworking of pristine phosphate facies produced granular phosphorite; and amalgamation of storm-generated granular event beds formed economic phosphorite in a single systems tract.