Contribution No. 3401 from the Woods Hole Oceanographic Institution.
Relict magnesian calcite oolite and subsidence of the Amazon shelf
Article first published online: 14 JUN 2006
Volume 22, Issue 1, pages 137–145, February 1975
How to Cite
MILLIMAN, J. D. and BARRETTO, H. T. (1975), Relict magnesian calcite oolite and subsidence of the Amazon shelf. Sedimentology, 22: 137–145. doi: 10.1111/j.1365-3091.1975.tb00288.x
- Issue published online: 14 JUN 2006
- Article first published online: 14 JUN 2006
- Manuscript received 23 July 1974; revision received 16 September 1974
Oolitic sediments occur over large portions of the outer continental shelf off northernmost Brazil and southern French Guiana. Carbon-14 dates, stable isotope values and analogies with similar deposits from other areas in the world indicate that the ooids were formed in shallow water (possibly protected hypersaline environments) during low stands of sea level. In contrast to both modern ooids and other relict ooids, however, the Amazon shelf ooids are composed entirely of magnesian calcite (12 mol % MgCO3) and possess radial crystal microstructures.
A comparison of water depths and ages of the Amazon ooids with the generally accepted eustatic sea level curve indicates that the Amazon shelf subsided more than 100 m 16-21 thousand years ago. Prior to and subsequent to the subsidence, however, the outer shelf remained relatively stable.