High Iridium Research Articles

Iridium Abundances Across the Ordovician-Silurian Stratotype

Chemostratigraphic analyses in the Ordovician-Silurian boundary stratotype section, bracketing a major extinction event in the graptolitic shale section at Dob's Linn, Scotland, show persistently high iridium concentrations of 0.050 to 0.250 parts per billion. There is no iridiumn concentration spike in the boundary interval or elsewhere in the 13 graptolite zones examined encompassing about 20 million years. Iridium correlated with chromium, both elements showing a gradual decrease with time into the middle part of the Lower Silurian. The chromium-iridium ratio averages about 10(6). Paleogeographic and geologic reconstructions coupled with the occurrence of ophiolites and other deep crustal rocks in the source area suggest that the high iridium and chromium concentrations observed in the shales result from terrestrial erosion of exposed upper mantle ultramafic rocks rather than from a cataclysmic extraterrestrial event.

New method for the measurement of osmium isotopes applied to a New Zealand Cretaceous/Tertiary boundary shale

The determination of osmium content and isotopic abundances in geological materials has received increasing attention in recent years following the proposal of Alvarez et al.1 that mass extinctions at the end of the Cretaceous period were caused by the impact of a large (∼10km) meteorite which left anomalously high iridium levels as a geochemical signature in the boundary shales. Here we report a new and simple method for measuring osmium in geological materials, involving fusion of the sample with sodium peroxide, distillation of the osmium as the tetroxide using perchloric acid, extraction into chloroform, and absorption of the chloroform extract onto graphite powder before instrumental neutron activation analysis. In a variant of this technique, the chloroform extract is back-extracted into an aqueous phase and the osmium isotopes are determined by plasma-source mass spectrometry (ICPMS). We have used this method on the Woodside Creek (New Zealand) Cretaceous/Tertiary boundary clay and have obtained the first osmium content (6g ng g−1) for this material. The 187Os/186Os ratio is 1.12±0.16, showing a typical non-crustal signature. This combined distillation–extraction–ICPMS method will prove to be useful for measuring osmium isotopes in other geological materials.

Stratigraphic occurrences of iridium anomalies at four Cretaceous/Tertiary boundary sites in New Zealand

Research Article| September 01, 1986 Stratigraphic occurrences of iridium anomalies at four Cretaceous/Tertiary boundary sites in New Zealand Robert R. Brooks; Robert R. Brooks 1Department of Chemistry and Biochemistry, Massey University, Palmerston North, New Zealand Search for other works by this author on: GSW Google Scholar C. Percy Strong; C. Percy Strong 2New Zealand Geological Survey, P.O. Box 30368, Lower Hutt, New Zealand Search for other works by this author on: GSW Google Scholar Julian Lee; Julian Lee 3Applied Biochemistry Division, Department of Scientific and Industrial Research, Private Bag, Palmerston North, New Zealand Search for other works by this author on: GSW Google Scholar Charles J. Orth; Charles J. Orth 4Los Alamos National Laboratory, Los Alamos, New Mexico 87545 Search for other works by this author on: GSW Google Scholar James S. Gilmore; James S. Gilmore 4Los Alamos National Laboratory, Los Alamos, New Mexico 87545 Search for other works by this author on: GSW Google Scholar Douglas E. Ryan; Douglas E. Ryan 5Trace Analysis Research Centre, Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada Search for other works by this author on: GSW Google Scholar Jiri Holzbecher Jiri Holzbecher 5Trace Analysis Research Centre, Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information Robert R. Brooks 1Department of Chemistry and Biochemistry, Massey University, Palmerston North, New Zealand C. Percy Strong 2New Zealand Geological Survey, P.O. Box 30368, Lower Hutt, New Zealand Julian Lee 3Applied Biochemistry Division, Department of Scientific and Industrial Research, Private Bag, Palmerston North, New Zealand Charles J. Orth 4Los Alamos National Laboratory, Los Alamos, New Mexico 87545 James S. Gilmore 4Los Alamos National Laboratory, Los Alamos, New Mexico 87545 Douglas E. Ryan 5Trace Analysis Research Centre, Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada Jiri Holzbecher 5Trace Analysis Research Centre, Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1986) 14 (9): 727–729. https://doi.org/10.1130/0091-7613(1986)14<727:SOOIAA>2.0.CO;2 Article history First Online: 01 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 Robert R. Brooks, C. Percy Strong, Julian Lee, Charles J. Orth, James S. Gilmore, Douglas E. Ryan, Jiri Holzbecher; Stratigraphic occurrences of iridium anomalies at four Cretaceous/Tertiary boundary sites in New Zealand. Geology 1986;; 14 (9): 727–729. doi: https://doi.org/10.1130/0091-7613(1986)14<727:SOOIAA>2.0.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 Three new iridium anomaly sites have been discovered in Cretaceous/Tertiary boundary sequences in New Zealand. These are at Needles Point, Chancet Rocks, and Waipara, where integrated iridium deposition values were 165, 211, and 7 ng/cm2, respectively. In contrast to the previously reported Woodside Creek stratigraphic sequence that had an iridium anomaly of 187 ng/cm2, a ferruginous boundary clay is absent in the three new sites, though the base of the Tertiary is marked by limonite staining. The relatively weak anomaly at the Waipara section is probably due to extensive bioturbation coupled with a high sedimentation rate at the time of deposition. The discovery of these additional boundary rock sequences in New Zealand negates suggestions that the Woodside Creek iridium anomaly was a fortuitous occurrence caused by unusual weathering conditions. The integrated iridium deposition values at these three new sites of somewhat different geology support the previously reported high iridium level for Woodside Creek, which until now was the only iridium anomaly on land in the Southern Hemisphere. 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.

Preparation and characterization of very highly dispersed iridium on Al 2O 3 and SiO 2

To obtain highly dispersed alumina- and silica-supported iridium catalysts, two preparation methods, the incipient wetness method and the urea technique, were investigated. Hydrogen and carbon monoxide chemisorption clearly showed that on γ-Al 2O 3 the incipient wetness method resulted in catalysts with a very high iridium dispersion (H/Ir > 2.0 for loadings < 2.5 wt% Ir and H/Ir > 1.0 up to 6.8 wt% Ir), in contrast with the catalysts made by this technique on SiO 2 (H/Ir < 1.0 for Ir loadings between 0.4 and 7.0 wt% Ir). Temperature programmed reduction, desorption and oxidation studies supported this conclusion. The behaviour of these systems in oxygen at elevated temperature also demonstrates a stronger interaction between iridium and alumina. The difference between the alumina- and silica-supported systems is caused by diffences in adsorption processes during the impregnation. Using the urea technique, highly dispersed Ir/SiO 2 and Ir/Al 2O 3 catalysts were obtained (H/Ir = 1.6 for 1.5 wt% Ir/SiO 2 and H/Ir = 1.2 for 5.5 wt% Ir/SiO 2, H/Ir = 2.5 for 1.5 wt% Ir/Al 2O 3 and H/Ir = 1.6 for 5.7 wt% Ir/Al 2O 3). Thus, the incipient wetness method proved successful for Al 2O 3, whereas the urea technique resulted in highly dispersed iridium catalysts on both supports.

Iridium in sea-water

Iridium in sea-water has been measured (after isolation from the saline matrix by reduction with magnesium) by neutron bombardment, radiochemical purification and high-resolution γ-ray spectroscopy. The concentration obtained in a Pacific coastal water was 1.02 ± 0.26 × 10 −14 g per g of sea-water. At such extremely low concentrations, seawater is an extremely unlikely source for anomalously high iridium concentrations measured in the Cretaceous-Tertiary boundary layer of deep-sea sediments.

The Precursor of the Cretaceous-Tertiary Boundary Clays at Stevns Klint, Denmark, and DSDP Hole 465A

Results of detailed mineralogical, chemical, and oxygen isotope analyses of the clay minerals and zeolites from two Cretaceous-Tertiary (K/T) boundary regions, Stevns Klint, Denmark, and Deep Sea Drilling Project (DSDP) Hole 465A in the north central Pacific Ocean, are presented. In the central part of the Stevns Klint K/T boundary layer, the only clay mineral detected by x-ray diffraction is a pure smectite with > 95 percent expandable layers. No detrital clay minerals or quartz were observed in the clay size fraction in these beds, whereas the clay minerals above and below the boundary layer are illite and mixed-layer smectite-illite of detrital origin as well as quartz. The mineralogical purity of the clay fraction, the presence of smectite only at the boundary, and the delta(18)O value of the smectite (27.2 +/- 0.2 per mil) suggest that it formed in situ by alteration of glass. Formation from impact rather than from volcanic glass is supported by its major element chemistry. The high content of iridium and other siderophile elements is not due to the cessation of calcium carbonate deposition and resulting slow sedimentation rates. At DSDP Hole 465A, the principal clay mineral in the boundary zone (80 to 143 centimeters) is a mixed-layer smectite-illite with >/=90 percent expandable layers, accompanied by some detrital quartz and small amounts of a euhedral authigenic zeolite (clinoptilolite). The mixed-layer smectite-illite from the interval 118 to 120 centimeters in the zone of high iridium abundance has a very low rare earth element content; the negative cerium anomaly indicates formation in the marine environment. This conclusion is corroborated by the delta(18)O value of this clay mineral (27.1 +/- 0.2 per mil). Thus, this mixed-layer smectite-illite formed possibly from the same glass as the K/T boundary smectite at Stevns Klint, Denmark.

Stability of noble metal catalysts for the hydrogen-oxygen reaction

Stability of various supported noble metal catalysts for initiation of the hydrogen-oxygen reaction was tested by means of steam-hydrogen treatment at 1000–1200 °C followed by a simple activity test. Many catalysts were stable to 1100 °C, but all lost some activity at 1200 °C. The most active with very good stability was an iridium/alumina catalyst of high iridium content.