Iridium, sulfur isotopes and rare earth elements in the Cretaceous-Tertiary boundary clay at Stevns Klint, Denmark

Journal Article · Fri Jan 01 00:00:00 EST 1988 · Geochim. Cosmochim. Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(88)90072-5· OSTI ID:7252282

Schmitz, B; Andersson, P; Dahl, J

Microbial activity and redox-controlled precipitation have been of major importance in the process of metal accumulation in the strongly Ir-enriched Cretaceous-Tertiary (K-T) boundary clay, the Fish Clay, at Stevns Klint in Denmark. Two important findings support this view: (1) Kerogen, recovered by leaching the Fish Clay in HCl and HF, shows an Ir concentration of 1100 ppb; this represents about 50% of the Ir present in the bulk sample Fish clay. Strong organometallic complexes is the most probable carrier phase for this fraction of Ir. Kerogen separated from the K-T boundary clay at Caravaca, Spain, similarly exhibits enhanced Ir concentrations. (2) Sulfur isotope analyses of metal-rich pyrite spherules, which occur in extreme abundance (about 10% by weight) in the basal Fish Clay, give a delta/sup 34/S value of -32 per thousand. This very low value shows that sulfide formation by anaerobic bacteria was intensive in the Fish Clay during early diagenesis. Since the pyrite spherules are major carriers of elements such as Ni, Co, As, Sb and Zn, microbial activity may have played an important role for concentrating these elements. In the Fish Clay large amounts of rare earth elements have precipitated from sea water on fish scales. Analyses reveal that, compared with sea water, the Fish Clay is only about four times less enriched in sea-water derived lanthanides than in Ir. This shows that a sea-water origin is plausible for elements that are strongly enriched in the clay, but whose origin cannot be accounted for by a lithogenic precursor.

• Research Organization: Univ. of Stockholm (Sweden)
• OSTI ID: 7252282
• Journal Information: Geochim. Cosmochim. Acta; (United States), Vol. 52:1
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CLAYS
BIOCONVERSION
CHEMICAL COMPOSITION
DIAGENESIS
GEOCHEMISTRY
REDOX REACTIONS
CRETACEOUS PERIOD
DENMARK
IRIDIUM ISOTOPES
ISOTOPE RATIO
KEROGEN
ORIGIN
PYRITE
SULFUR ISOTOPES
TERTIARY PERIOD
BITUMINOUS MATERIALS
CARBONACEOUS MATERIALS
CENOZOIC ERA
CHALCOGENIDES
CHEMICAL REACTIONS
CHEMISTRY
EUROPE
GEOLOGIC AGES
IRON COMPOUNDS
IRON SULFIDES
ISOTOPES
MATERIALS
MESOZOIC ERA
MINERALS
ORGANIC MATTER
SCANDINAVIA
SULFIDE MINERALS
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
WESTERN EUROPE
580400* - Geochemistry- (-1989)