Abstract Mantle plumes provide an attractive mechanism for generating short-duration, voluminous magmas in large igneous provinces (LIPs) while at the same time providing an explanation for the frequently associated break-up of supercontinents. This model has also been invoked for the Ferrar large igneous province (FLIP) in Antarctica, which zircon and baddeleyite U–Pb dating shows was emplaced over a short duration at 182.7 ± 0.5 Ma, contemporaneously with fragmentation of the supercontinent Gondwanaland. Here, we present platinum-group-element (PGE) and Os-isotopic data for the Basement Sill in the McMurdo Dry Valleys – a part of the FLIP – that challenge the plume interpretation. The Basement Sill samples studied are cumulate-textured gabbro to norite, and pyroxenite with minor ferro- or leuco-lithofacies with MgO ranging from 2 to 19 wt%. The 187Os/188Os values range from 0.1609 ± 0.003 (2σ) to 8.100 ± 1.600 (2σ); the minimum value overlaps with a previously published estimated initial 187Os/188Os ratio for Ferrar magmas of 0.145 ± 0.049 (2σ). The PGE abundance patterns for the Basement Sill define positive, convex-shaped slopes between the IPGE (Os, Ir and Ru) and PPGE (Pt, Pd and Rh). The most significant feature of the entire data set is the extreme sub-chondritic Os/Ir ratios (
The Cretaceous-Paleogene boundary ~65.5 million years ago marks one of the three largest mass extinctions in the past 500 million years. The extinction event coincided with a large asteroid impact at Chicxulub, Mexico, and occurred within the time of Deccan flood basalt volcanism in India. Here, we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction. Notably, a single ejecta-rich deposit compositionally linked to the Chicxulub impact is globally distributed at the Cretaceous-Paleogene boundary. The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction.
Research Article| April 01, 1996 Continental runoff of osmium into the Baltic Sea Bernhard Peucker Ehrenbrink; Bernhard Peucker Ehrenbrink 1Woods Hole Oceanographic Institution, Department of Marine Chemistry and Geochemistry and Department of Geology and Geophysics, Woods Hole, Massachusetts 02543-1541 Search for other works by this author on: GSW Google Scholar Greg Ravizza Greg Ravizza 1Woods Hole Oceanographic Institution, Department of Marine Chemistry and Geochemistry and Department of Geology and Geophysics, Woods Hole, Massachusetts 02543-1541 Search for other works by this author on: GSW Google Scholar Author and Article Information Bernhard Peucker Ehrenbrink 1Woods Hole Oceanographic Institution, Department of Marine Chemistry and Geochemistry and Department of Geology and Geophysics, Woods Hole, Massachusetts 02543-1541 Greg Ravizza 1Woods Hole Oceanographic Institution, Department of Marine Chemistry and Geochemistry and Department of Geology and Geophysics, Woods Hole, Massachusetts 02543-1541 Publisher: Geological Society of America First Online: 02 Jun 2017 Online Issn: 1943-2682 Print Issn: 0091-7613 Geological Society of America Geology (1996) 24 (4): 327–330. https://doi.org/10.1130/0091-7613(1996)024<0327:CROOIT>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Bernhard Peucker Ehrenbrink, Greg Ravizza; Continental runoff of osmium into the Baltic Sea. Geology 1996;; 24 (4): 327–330. doi: https://doi.org/10.1130/0091-7613(1996)024<0327:CROOIT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The isotopic composition of osmium (Os) in continental surface waters and shallow ground waters has been determined by analyzing fresh-water Fe-Mn nodules and bog ores. The isotopic composition of the continental runoff from the Precambrian Baltic shield is much more radiogenic (187Os/186Os = 31.2–65.4) than the runoff from the Phanerozoic sedimentary platform to the south of the Baltic Sea (187Os/186Os = 8.6–11.0). Fe-Mn nodules from the Baltic Sea have intermediate values (187Os/186Os = 12.4–21.2), indicating mixture of North Sea water and continental fresh water. Isotope mass-balance calculations indicate that the concentration of Os in the continental runoff is similar to the Os concentration in seawater. Extrapolating these data to infer the global runoff yields ∼48 kg/yr, comparable with previous estimates. The residence time of Os in seawater relative to continental runoff is calculated at ∼32 ka. The oceanic residence time of Os relative to the bulk input to seawater is ∼16 ka, if the mean 187Os/186Os of the continental runoff is 16. The Os isotopic composition of the continental runoff is much more variable than previously suggested, 187Os/186Os values >30 being characteristic of Precambrian shields. Glaciation of old cratonic shields might therefore modulate riverine supply of this very radiogenic cratonic Os, linking accelerated increase in the marine Os isotope record to glaciations of Precambrian shields. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
