Iridium abundance measurements across bio-event horizons in the fossil record

Conference · Sun Jan 01 00:00:00 EST 1989

OSTI ID:5584069

Orth, C J; Attrep, M Jr; Quintana, L R ^[1]

---

1. Los Alamos National Lab., NM (USA)

Geochemical measurements have been performed on thousands of rock samples collected across bio-event horizons using Instrumental Neutron Activation Analysis (INAA) for about 40 common and trace elements and radiochemical isolation procedures for Ir. On selected samples, Os, Pt and Au were also radiochemically determined. These studies have encompassed the time interval from the Precambrian-Cambrian transition to the Late Eocene impact (microspherule) horizons. Our early work strengthened the Alvarez impact hypothesis by finding the Ir (PGE) anomaly at the K-T boundary in continental sedimentary sequences. In collaborations with paleontologists, weak to moderately string Ir anomalies have been discovered at the Frasnian-Famennian boundary in Australia, in the Early Mississippian of Oklahoma, at the Mississipian-Pennsylvanian boundary of Oklahoma and Texas, and in the Late Cenomanian throughout the western interior of North America and on the south coast of England to date. We have found no compelling evidence for an impact related cause for these anomalies although PGE impact signatures in the two Late Cenomanian anomalies could be masked by the strong terrestrial mafic to ultramafic overprint. Thus far, our evidence for extinction events older than the terminal Cretaceous does not support recent hypotheses which suggest that impacts from cyclic swarms of comets in the inner Solar system were responsible for the periodic mass extinctions. 50 refs., 7 figs., 3 tabs.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: DOE/ER; National Aeronautics and Space Administration (NASA)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 5584069
• Report Number(s): LA-UR-89-354; CONF-891065-2; ON: DE89007752
• Resource Relation: Conference: Snowbird conference on global catastrophies in earth history, Snowbird, UT (USA), 20-23 Oct 1989
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
BIOLOGICAL EXTINCTION
VALIDATION
IRIDIUM
DETECTION
ROCKS
GEOCHEMISTRY
CLIMATE MODELS
COLLISIONS
COMETS
ENVIRONMENTAL EFFECTS
GEOCHEMICAL SURVEYS
MODIFICATIONS
RADIOCHEMICAL ANALYSIS
SPECIES DIVERSITY
CHEMICAL ANALYSIS
CHEMISTRY
ELEMENTS
MATHEMATICAL MODELS
METALS
PLATINUM METALS
QUANTITATIVE CHEMICAL ANALYSIS
SURVEYS
TESTING
TRANSITION ELEMENTS
580100* - Geology & Hydrology- (-1989)