Strontium isotope dating of Upper Cenozoic marine deposits, northwestern Alaska

Conference · Tue May 01 00:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6645480

Kaufman, D S; Farmer, G L; Miller, G H ^[1]; Carter, L D ^[2]; Brigham-Grette, J ^[3]

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1. Univ. of Colorado, Boulder (USA)
2. Geological Survey, Anchorage, AK (USA)
3. Univ. of Massachusetts, Amherst (USA)

High-precision Sr isotope measurements were obtained for 24 late Cenozoic molluskan shells from northwestern Alaska to test whether such data can be used to date arctic marine deposits. At present, the ages of geologic and climatologic events recorded by circum-arctic deposits older than the range of radiocarbon dating (>30 k.y.) are poorly known. Improving the chronological control would elucidate the interrelations between late Cenozoic global climate evolution and environmental changes in the Arctic, such as the inception of northern hemispheric ice sheets and perennial Arctic Ocean sea ice. Samples for this study were chosen from emerged and offshore marine deposits at Skull Cliff, Nome, and the Colville River area, where depositional ages are relatively well constrained on the basis of paleontologic, paleomagnetic, and amino acid criteria. At Skull Cliff, {sup 87}Sr/{sup 86}Sr ratios were measured in molluskan shells from five upper Pliocene to upper Pleistocene stratigraphic units composed of nearshore and inner shelf sediments. The {Delta}Sr values ({Delta}Sr = {sup 87}Sr/{sup 86}Sr{sub (sample)} {sup {minus}87}Sr/{sup 86}Sr{sub (standard)} {times} 10{sup 5}) range from 0.0 to {minus}7.2, and, except for the oldest unit decrease with increasing age. Four shells of two general collected from a single stratigraphic horizon over a distance of 100 m have indistinguishable {Delta}Sr values, within the range of external reproducibility ({plus minus}1{Delta}Sr), confirming an absence of vital effects. Sample ages for the upper three units at Skull Cliff, based on the comparison of the measured {Delta}Sr with the Sr isotope evolution of seawater recorded in independently dated deep-sea cores, agree broadly with the expected ages. The agreement suggests that the Arctic Ocean was in Sr isotope equilibrium with the world ocean during at least the past 1 m.y.

• OSTI ID: 6645480
• Report Number(s): CONF-900605-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 74:5; Conference: Annual convention and exposition of the American Association of Petroleum Geologists, San Francisco, CA (USA), 3-6 Jun 1990; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ALASKA
STRATIGRAPHY
ISOTOPE RATIO
MOLLUSCS
STRONTIUM 86
STRONTIUM 87
ALKALINE EARTH ISOTOPES
ANIMALS
AQUATIC ORGANISMS
BETA DECAY RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FEDERAL REGION X
GEOLOGY
HOURS LIVING RADIOISOTOPES
INTERMEDIATE MASS NUCLEI
INVERTEBRATES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
NORTH AMERICA
NUCLEI
RADIOISOTOPES
STABLE ISOTOPES
STRONTIUM ISOTOPES
USA
580000* - Geosciences